Assessment of zinc solubilization potential of zinc-resistant Pseudomonas oleovorans strain ZSB13 isolated from contaminated soil

Abstract Zinc is an essential micronutrient that is required for optimum plant growth. It is present in soil in insoluble forms. Bacterial solubilization of soil unavailable form of Zn into available form, is an emerging approach to alleviate the Zn deficiency for plants and human beings. Zinc solubilizing bacteria (ZSB) could be a substitute for chemical Zn fertilizer. The present study aimed to isolate and characterize bacterial species from the contaminated soil and evaluate their Zn solubilizing potential. Zn resistant bacteria were isolated and evaluated for their MIC against Zn. Among the 13 isolated bacterial strains ZSB13 showed maximum MIC value upto 30mM/L. The bacterial strain with the highest resistance against Zn was selected for further analysis. Molecular characterization of ZSB13 was performed by 16S rRNA gene amplification which confirmed it as Pseudomonas oleovorans. Zn solubilization was determined through plate assay and broth medium. Four insoluble salts (zinc oxide (ZnO), zinc carbonate (ZnCO3), zinc sulphite (ZnS) and zinc phosphate (Zn3(PO4)2) were used for solubilization assay. Our results shows 11 mm clear halo zone on agar plates amended with ZnO. Likewise, ZSB13 showed significant release of Zn in broth amended with ZnCO3 (17 and 16.8 ppm) and ZnO (18.2 ppm). Furthermore, Zn resistance genes czcD was also enriched in ZSB13. In our study, bacterial strain comprising Zn solubilization potential has been isolated that could be further used for the growth enhancement of crops.

Resumo O zinco é um micronutriente essencial necessário para o crescimento ideal das plantas. Ele está presente no solo em formas insolúveis. A solubilização bacteriana da forma indisponível de Zn no solo para a forma disponível é uma abordagem emergente para aliviar a deficiência de Zn em plantas e seres humanos. Bactérias solubilizadoras de zinco (ZSB) podem ser um substituto para fertilizantes químicos de Zn. O presente estudo teve como objetivo isolar e caracterizar espécies bacterianas de solo contaminado e avaliar seu potencial de solubilização de Zn. Bactérias resistentes ao Zn foram isoladas e avaliadas quanto ao seu MIC contra o Zn. Entre as 13 cepas bacterianas isoladas, ZSB13 apresentou valor máximo de MIC de até 30 mM/L. A cepa bacteriana com maior resistência ao Zn foi selecionada para análise posterior. A caracterização molecular de ZSB13 foi realizada por amplificação do gene 16S rRNA que o confirmou como Pseudomonas oleovorans. A solubilização do Zn foi determinada através de ensaio em placa e meio caldo. Quatro sais insolúveis (óxido de zinco (ZnO), carbonato de zinco (ZnCO3), sulfito de zinco (ZnS) e fosfato de zinco (Zn3 (PO4) 2) foram usados para o ensaio de solubilização. Nossos resultados mostram uma zona de halo clara de 11 mm em placas de ágar corrigidas com ZnO. Da mesma forma, ZSB13 mostrou liberação significativa de Zn em caldo alterado com ZnCO3 (17 e 16,8 ppm) e ZnO (18,2 ppm). Além disso, os genes de resistência ao Zn czcD também foram enriquecidos em ZSB13. Em nosso estudo, a cepa bacteriana compreendendo potencial de solubilização de Zn foi isolada e poderia ser usada posteriormente para o aumento do crescimento de safras.

Assessment of zinc solubilization potential of zinc-resistant Pseudomonas oleovorans strain ZSB13 isolated from contaminated soil / Avaliação do potencial de solubilização do zinco da cepa ZSB13 de Pseudomonas oleovorans resistente ao zinco isolada de solo contaminado

Zinc is an essential micronutrient that is required for optimum plant growth. It is present in soil in insoluble forms. Bacterial solubilization of soil unavailable form of Zn into available form, is an emerging approach to alleviate the Zn deficiency for plants and human beings. Zinc solubilizing bacteria (ZSB) could be a substitute for chemical Zn fertilizer. The present study aimed to isolate and characterize bacterial species from the contaminated soil and evaluate their Zn solubilizing potential. Zn resistant bacteria were isolated and evaluated for their MIC against Zn. Among the 13 isolated bacterial strains ZSB13 showed maximum MIC value upto 30mM/L. The bacterial strain with the highest resistance against Zn was selected for further analysis. Molecular characterization of ZSB13 was performed by 16S rRNA gene amplification which confirmed it as Pseudomonas oleovorans. Zn solubilization was determined through plate assay and broth medium. Four insoluble salts (zinc oxide (ZnO), zinc carbonate (ZnCO3), zinc sulphite (ZnS) and zinc phosphate (Zn3(PO4)2) were used for solubilization assay. Our results shows 11 mm clear halo zone on agar plates amended with ZnO. Likewise, ZSB13 showed significant release of Zn in broth amended with ZnCO3 (17 and 16.8 ppm) and ZnO (18.2 ppm). Furthermore, Zn resistance genes czcD was also enriched in ZSB13. In our study, bacterial strain comprising Zn solubilization potential has been isolated that could be further used for the growth enhancement of crops.

O zinco é um micronutriente essencial necessário para o crescimento ideal das plantas. Ele está presente no solo em formas insolúveis. A solubilização bacteriana da forma indisponível de Zn no solo para a forma disponível é uma abordagem emergente para aliviar a deficiência de Zn em plantas e seres humanos. Bactérias solubilizadoras de zinco (ZSB) podem ser um substituto para fertilizantes químicos de Zn. O presente estudo teve como objetivo isolar e caracterizar espécies bacterianas de solo contaminado e avaliar seu potencial de solubilização de Zn. Bactérias resistentes ao Zn foram isoladas e avaliadas quanto ao seu MIC contra o Zn. Entre as 13 cepas bacterianas isoladas, ZSB13 apresentou valor máximo de MIC de até 30 mM/L. A cepa bacteriana com maior resistência ao Zn foi selecionada para análise posterior. A caracterização molecular de ZSB13 foi realizada por amplificação do gene 16S rRNA que o confirmou como Pseudomonas oleovorans. A solubilização do Zn foi determinada através de ensaio em placa e meio caldo. Quatro sais insolúveis (óxido de zinco (ZnO), carbonato de zinco (ZnCO3), sulfito de zinco (ZnS) e fosfato de zinco (Zn3 (PO4) 2) foram usados para o ensaio de solubilização. Nossos resultados mostram uma zona de halo clara de 11 mm em placas de ágar corrigidas com ZnO. Da mesma forma, ZSB13 mostrou liberação significativa de Zn em caldo alterado com ZnCO3 (17 e 16,8 ppm) e ZnO (18,2 ppm). Além disso, os genes de resistência ao Zn czcD também foram enriquecidos em ZSB13. Em nosso estudo, a cepa bacteriana compreendendo potencial de solubilização de Zn foi isolada e poderia ser usada posteriormente para o aumento do crescimento de safras.

Assessment of zinc solubilization potential of zinc-resistant Pseudomonas oleovorans strain ZSB13 isolated from contaminated soil / Avaliação do potencial de solubilização do zinco da cepa ZSB13 de Pseudomonas oleovorans resistente ao zinco isolada de solo contaminado

Abstract Zinc is an essential micronutrient that is required for optimum plant growth. It is present in soil in insoluble forms. Bacterial solubilization of soil unavailable form of Zn into available form, is an emerging approach to alleviate the Zn deficiency for plants and human beings. Zinc solubilizing bacteria (ZSB) could be a substitute for chemical Zn fertilizer. The present study aimed to isolate and characterize bacterial species from the contaminated soil and evaluate their Zn solubilizing potential. Zn resistant bacteria were isolated and evaluated for their MIC against Zn. Among the 13 isolated bacterial strains ZSB13 showed maximum MIC value upto 30mM/L. The bacterial strain with the highest resistance against Zn was selected for further analysis. Molecular characterization of ZSB13 was performed by 16S rRNA gene amplification which confirmed it as Pseudomonas oleovorans. Zn solubilization was determined through plate assay and broth medium. Four insoluble salts (zinc oxide (ZnO), zinc carbonate (ZnCO3), zinc sulphite (ZnS) and zinc phosphate (Zn3(PO4)2) were used for solubilization assay. Our results shows 11 mm clear halo zone on agar plates amended with ZnO. Likewise, ZSB13 showed significant release of Zn in broth amended with ZnCO3 (17 and 16.8 ppm) and ZnO (18.2 ppm). Furthermore, Zn resistance genes czcD was also enriched in ZSB13. In our study, bacterial strain comprising Zn solubilization potential has been isolated that could be further used for the growth enhancement of crops.

Resumo O zinco é um micronutriente essencial necessário para o crescimento ideal das plantas. Ele está presente no solo em formas insolúveis. A solubilização bacteriana da forma indisponível de Zn no solo para a forma disponível é uma abordagem emergente para aliviar a deficiência de Zn em plantas e seres humanos. Bactérias solubilizadoras de zinco (ZSB) podem ser um substituto para fertilizantes químicos de Zn. O presente estudo teve como objetivo isolar e caracterizar espécies bacterianas de solo contaminado e avaliar seu potencial de solubilização de Zn. Bactérias resistentes ao Zn foram isoladas e avaliadas quanto ao seu MIC contra o Zn. Entre as 13 cepas bacterianas isoladas, ZSB13 apresentou valor máximo de MIC de até 30 mM/L. A cepa bacteriana com maior resistência ao Zn foi selecionada para análise posterior. A caracterização molecular de ZSB13 foi realizada por amplificação do gene 16S rRNA que o confirmou como Pseudomonas oleovorans. A solubilização do Zn foi determinada através de ensaio em placa e meio caldo. Quatro sais insolúveis (óxido de zinco (ZnO), carbonato de zinco (ZnCO3), sulfito de zinco (ZnS) e fosfato de zinco (Zn3 (PO4) 2) foram usados ​​para o ensaio de solubilização. Nossos resultados mostram uma zona de halo clara de 11 mm em placas de ágar corrigidas com ZnO. Da mesma forma, ZSB13 mostrou liberação significativa de Zn em caldo alterado com ZnCO3 (17 e 16,8 ppm) e ZnO (18,2 ppm). Além disso, os genes de resistência ao Zn czcD também foram enriquecidos em ZSB13. Em nosso estudo, a cepa bacteriana compreendendo potencial de solubilização de Zn foi isolada e poderia ser usada posteriormente para o aumento do crescimento de safras.

Assessment of zinc solubilization potential of zinc-resistant Pseudomonas oleovorans strain ZSB13 isolated from contaminated soil / Avaliação do potencial de solubilização do zinco da cepa ZSB13 de Pseudomonas oleovorans resistente ao zinco isolada de solo contaminado

Zinc is an essential micronutrient that is required for optimum plant growth. It is present in soil in insoluble forms. Bacterial solubilization of soil unavailable form of Zn into available form, is an emerging approach to alleviate the Zn deficiency for plants and human beings. Zinc solubilizing bacteria (ZSB) could be a substitute for chemical Zn fertilizer. The present study aimed to isolate and characterize bacterial species from the contaminated soil and evaluate their Zn solubilizing potential. Zn resistant bacteria were isolated and evaluated for their MIC against Zn. Among the 13 isolated bacterial strains ZSB13 showed maximum MIC value upto 30mM/L. The bacterial strain with the highest resistance against Zn was selected for further analysis. Molecular characterization of ZSB13 was performed by 16S rRNA gene amplification which confirmed it as Pseudomonas oleovorans. Zn solubilization was determined through plate assay and broth medium. Four insoluble salts (zinc oxide (ZnO), zinc carbonate (ZnCO3), zinc sulphite (ZnS) and zinc phosphate (Zn3(PO4)2) were used for solubilization assay. Our results shows 11 mm clear halo zone on agar plates amended with ZnO. Likewise, ZSB13 showed significant release of Zn in broth amended with ZnCO3 (17 and 16.8 ppm) and ZnO (18.2 ppm). Furthermore, Zn resistance genes czcD was also enriched in ZSB13. In our study, bacterial strain comprising Zn solubilization potential has been isolated that could be further used for the growth enhancement of crops.(AU)

O zinco é um micronutriente essencial necessário para o crescimento ideal das plantas. Ele está presente no solo em formas insolúveis. A solubilização bacteriana da forma indisponível de Zn no solo para a forma disponível é uma abordagem emergente para aliviar a deficiência de Zn em plantas e seres humanos. Bactérias solubilizadoras de zinco (ZSB) podem ser um substituto para fertilizantes químicos de Zn. O presente estudo teve como objetivo isolar e caracterizar espécies bacterianas de solo contaminado e avaliar seu potencial de solubilização de Zn. Bactérias resistentes ao Zn foram isoladas e avaliadas quanto ao seu MIC contra o Zn. Entre as 13 cepas bacterianas isoladas, ZSB13 apresentou valor máximo de MIC de até 30 mM/L. A cepa bacteriana com maior resistência ao Zn foi selecionada para análise posterior. A caracterização molecular de ZSB13 foi realizada por amplificação do gene 16S rRNA que o confirmou como Pseudomonas oleovorans. A solubilização do Zn foi determinada através de ensaio em placa e meio caldo. Quatro sais insolúveis (óxido de zinco (ZnO), carbonato de zinco (ZnCO3), sulfito de zinco (ZnS) e fosfato de zinco (Zn3 (PO4) 2) foram usados para o ensaio de solubilização. Nossos resultados mostram uma zona de halo clara de 11 mm em placas de ágar corrigidas com ZnO. Da mesma forma, ZSB13 mostrou liberação significativa de Zn em caldo alterado com ZnCO3 (17 e 16,8 ppm) e ZnO (18,2 ppm). Além disso, os genes de resistência ao Zn czcD também foram enriquecidos em ZSB13. Em nosso estudo, a cepa bacteriana compreendendo potencial de solubilização de Zn foi isolada e poderia ser usada posteriormente para o aumento do crescimento de safras.(AU)

Optimization of oxalic acid production by fungi for biotechnological solubilization of rock phosphate

This study describes a biotechnological strategy for producing and applying oxalic acid to solubilize phosphorus (P) from rock phosphate (RP). We evaluated six fungal species (Aspergillus niger FS1, Penicillium islandicum FS41, Pleurotus ostreatus PO1, Rhizoctonia solani Rhiz555, Sclerotium rolfsii Sr25, and Sclerotinia sclerotiorum Scl134) and three culture media (potato dextrose broth, Tsao and Strasser media) to maximize oxalic acid production. Among the fungal isolates tested and culture media, S. rolfsii Sr25 and Tsao medium showed efficient oxalic acid production. Tsao medium was optimized following a response surface methodology after initial screening of factors affecting RP solubilization. The optimized concentrations were 1 g L-1 NaNO3, 100 g L-1 glucose, 2 g L-1 KH2PO4, 4.5 g L-1 yeast extract, and 25 mg L-1 MgSO4·7H2O used for 20 days of incubation. Under these conditions, 71 mmol L-1 oxalic acid was obtained, representing a three-fold increase over production under non-optimized conditions (20 mmol L-1). Under optimized conditions, oxalic acid produced by S. rolfsii Sr25 reacted with low-solubility RP and solubilized 100 % of the P contained in ore. Thus, using S. rolfsii Sr25 to produce oxalic acid seems a promising biotechnological alternative for P solubilization from RP.(AU)

Endophytic bacteria Bacillus safensis and Pseudomonas hibiscicola and their ability to increase rice seedling growth

Endophytic bacteria Bacillus safensis RS95 and Pseudomonas hibiscicola RS121 were evaluated for their ability to promote the growth of rice seedlings and produce indole-acetic acid (IAA) and siderophores and to solubilize phosphates. 'Guri' rice seeds were immersed in bacterial endophyte cell suspensions (separated and two-strain mixed), as well as in Escherichia coli DH5α, phosphate-buffered saline (PBS) and water treatments (negative controls). Seeds were sown on agar-water in Petri plates placed vertically at an angle of 65°. The ability of plant growth-promoting endophytic bacteria (PGPEB) to produce IAA and siderophores was determined by Salkowski colorimetric and chrome azurol S (CAS) assays, respectively. Mineral phosphate solubilization activity was calculated by inoculating the endophytes onto medium containing insoluble phosphate. PGPEB showed a positive effect on the growth of rice seedlings, causing a mean growth of shoots and primary-roots of 60 and 67%, respectively. Bacterial strains also showed positive traits for IAA and siderophore production, as well as phosphate-solubilization activity

Isolation and characterization of Klebsiella oxytoca from the rhizosphere of Lotus corniculatus and its biostimulating features / Isolamento e caracterização de Klebsiella oxytoca da rizosfera de Lotus corniculatus e suas características bioestimulantes

Significant food resource shortages are occurring worldwide. Plant growth-promoting rhizobacteria (PGPR) represent an ecofriendly and efficient approach for increasing soil fertility and plant productivity. The current study explored biostimulating traits of PGPR from the rhizosphere of Lotus corniculatus growing in the Al-Ahsa region. A bacterial isolate (LCK121) was obtained, characterized for phenotypic, and identified by 16S rRNA gene sequencing. In addition, its growth-stimulating effects on barley were investigated. The strain identity was confirmed via comparative analysis of the 16S rDNA sequences with Klebsiella oxytoca (99.3% similarity level). LCK121 exhibited multiple plant growth-promoting features, including indole-3-acetic acid (IAA) production (16.34 µg mL-1), 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (1.35±0.02 µmol α-ketobutyrate mg−1 h−1), phosphate solubilization, and nitrogen fixation. Furthermore, in vitro inoculation of barley with LCK121 significantly increased the root and shoot dry weights. The results highlight the potential of LCK121 for developing green fertilizers for sustainable agriculture.

A escassez significativa de recursos alimentares está ocorrendo em todo o mundo. As rizobactérias promotoras de crescimento de plantas (PGPR) representam uma abordagem ecologicamente correta e eficiente para aumentar a fertilidade do solo e a produtividade das plantas. O presente estudo explorou características bioestimulantes de PGPR da rizosfera de Lotus corniculatus crescendo na região de Al-Ahsa. Um isolado bacteriano (LCK121) foi obtido, caracterizado quanto ao fenotípico, e identificado por sequenciamento do gene 16S rRNA. Além disso, seus efeitos estimulantes do crescimento na cevada foram investigados. A identidade da cepa foi confirmada por meio de análise comparativa das sequências de 16S rDNA com Klebsiella oxytoca (nível de similaridade de 99,3%). LCK121 exibiu várias características de promoção do crescimento de plantas, incluindo produção de ácido indol-3-acético (IAA) (16,34 µg mL-1), atividade de desaminase de ácido 1-aminociclopropano-1-carboxílico (ACC) (1,35±0,02 µmol α-cetobutirato mg −1 h−1), solubilização de fosfato e fixação de nitrogênio. Além disso, a inoculação in vitro da cevada com LCK121 aumentou significativamente os pesos secos da raiz e da parte aérea. Os resultados destacam o potencial do LCK121 para o desenvolvimento de fertilizantes verdes para a agricultura sustentável.

Screening of plant growth-promoting bacteria isolated from sugarcane / Seleção de bactérias promotoras de crescimento de plantas isoladas de cana-de-açúcar

Plant growth-promoting bacteria (PGPB) are known to establish positive relationships with plants. They act in favoring plant nutrition, production of phytohormones, control of pathogens and enhancement of stress tolerance. Thus, this study aimed to isolate bacteria from soil, rhizosphere, and root endosphere from sugarcane cultivated in the Southeastern of Brazil, to prospect strains with potential for plant growth promotion. The samples were plated in Nutrient Agar medium, and the morphologically distinct colonies were isolated and analyzed about indoleacetic acid production, phosphate solubilization and the growth control of the phytopathogenic fungus Fusarium verticillioides. A total of 219 isolates were obtained, of which 86 from soil, 67 from rhizosphere and 66 from sugarcane root endosphere. The strains that presented more than one mechanism of plant growth promotion were identified by the sequencing of 16S gene. Most species belonged to the genus Bacillus, which has strains already used in various biological products for the control of diseases in agriculture. Some Bacillus species isolated in our study have never been isolated from sugarcane, and others have been studied for the first time as plant growth promoters. The isolated strains constitute an important microbial bank to be explored to compose innovative products for agriculture.(AU)

Bactérias promotoras de crescimento de plantas são conhecidas por estabelecer relações positivas com as plantas. Atuam no favorecimento da nutrição das plantas, produção de fitohormônios, controle de patógenos e aumento da tolerância ao estresse. Desta forma, este estudo teve como objetivo isolar bactérias do solo, rizosfera e endosfera radicular de cana-de-açúcar, cultivada na região Sudeste do Brasil, para prospectar cepas com potencial para promoção de crescimento vegetal. As amostras foram semeadas em meio Ágar Nutriente, e as colônias morfologicamente distintas foram isoladas e analisadas quanto à produção de ácido indolacético, solubilização de fosfato e controle de crescimento do fungo fitopatogênico Fusarium verticillioides. Foram obtidos 219 isolados, sendo 86 do solo, 67 da rizosfera e 66 da endosfera da raiz da cana-de-açúcar. As cepas que apresentaram mais de um mecanismo de promoção do crescimento vegetal foram identificadas pelo sequenciamento do gene 16S. A maioria das espécies pertence ao gênero Bacillus, que possui linhagens utilizadas em diversos produtos biológicos para o controle de doenças na agricultura. Algumas espécies de Bacillus nunca foram isoladas da cana-deaçúcar e outras foram estudadas pela primeira vez como promotoras de crescimento de plantas. As cepas isoladas constituem um importante banco microbiano a ser explorado para a composição de produtos inovadores para a agricultura.(AU)

Response of Rhizobacterial strains and organic amendments on chickpea growth / Resposta de cepas de rizobactérias e alterações orgânicas no crescimento do grão-de-bico

Plant Growth Promoting Rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots and promote plant growth through a variety of mechanisms such as phosphate solubilization, phytohormones production, antifungal activity and also improve plant growth and yield. Field experiment was carried out to investigate the residual effect of organic amendments plus soil microbes along with integrated nutrient management. (PGPR) are important soil organism that promotes plant growth and yield root colonization is an example of a direct and indirect mechanism. The treatments included control, (inorganic fertilizer and no organic fertilization).Five bacterial strains were identified morphologically and biochemically screened from the rhizospheres of chickpea, lentil, barseem, mungbean, and sesame. The experiment was conducted at the Arid Zone Research Center in D.I.Khan (Pakistan). The majority of isolates resulted in significant increase in shoot length, root length, and dry matter production of Cicer arietinum seedlings' shoot and root. The experiment represented that isolates treated plots with rhizobium strain inoculation resulted in greater plant height (35.000 cm) and nodule count (38.00) No of pods per plant-1 (44.66) when compared to the control treatment, While (Mesorhizobium cicero) along with organic amendments showed significant response the greater root length (50 cm) was observed in T4 treatment. The Performance of rhizobial strains on chickpea germination in an arid environment was found to significantly increase crop germination percentage. This combination thus increases nitrogen and phosphorus uptake in inoculation treated plots. The study found that plots with inoculation treatments yielded significantly higher than non-treated plots Treatment with Mesorhizobium Cicero and compost resulted in a higher grain yield (8%) as compared to the control. The greater grain yield was observed in Treatment T4 (183.67).The result showed that use of PGPR have the potential to increase nutrient absorption from soil while improved growth of chickpea.(AU)

As rizobactérias promotoras de crescimento de plantas (PGPR) são bactérias benéficas que colonizam as raízes das plantas e promovem o crescimento das plantas através de uma variedade de mecanismos, como solubilização de fosfato, produção de fito-hormônios, atividade antifúngica e também melhoram o crescimento e o rendimento das plantas. O experimento de campo foi realizado para investigar o efeito residual de corretivos orgânicos mais micróbios do solo, juntamente com o manejo integrado de nutrientes. PGPR são importantes organismos do solo que promovem o crescimento das plantas e produzem a colonização de raízes, que é um exemplo de mecanismo direto e indireto. Os tratamentos incluíram controle (fertilizante inorgânico e sem adubação orgânica). Cinco cepas bacterianas foram identificadas morfologicamente e bioquimicamente selecionadas das rizosferas de grão-de-bico, lentilha, barseem, feijão-mungo e gergelim. O experimento foi conduzido no Arid Zone Research Center em D.I.Khan (Paquistão). A maioria dos isolados resultou em aumento significativo no comprimento da parte aérea, comprimento da raiz e produção de matéria seca da parte aérea e raiz das plântulas de Cicer arietinum. O experimento demonstrou que isolados de parcelas tratadas com inoculação de cepa de rizóbio resultaram em maior altura de planta (35.000 cm) e contagem de nódulos (38,00) n.º de vagens por planta-1 (44,66), quando comparado ao tratamento controle, enquanto (Mesorhizobium cicero), juntamente com as alterações orgânicas, apresentaram resposta significativa quanto maior o comprimento da raiz (50 cm) observado no Tratamento T4. O desempenho de linhagens de rizóbios na germinação do grão-de-bico em ambiente árido aumentou significativamente a porcentagem de germinação da cultura. Esta combinação aumenta assim a absorção de nitrogênio e fósforo nas parcelas tratadas com inoculação. O estudo constatou que as parcelas com tratamentos de inoculação produziram significativamente mais do que as parcelas não tratadas. O tratamento com Mesorhizobium cicero e composto resultou em maior produtividade de grãos (8%) em comparação com o controle. A maior produtividade de grãos foi observada no Tratamento T4 (183,67). O resultado mostrou que o uso de PGPR tem potencial para aumentar a absorção de nutrientes do solo enquanto melhora o crescimento do grão-de-bico.(AU)

Phosphate-solubilizing fungi co-inoculated with Bradyrhizobium promote cowpea growth under varying N and P fertilization conditions

We evaluated the compatibility between two nitrogen-fixing Bradyrhizobium inoculant strains and phosphate-solubilizing fungal strains and the effect of co-inoculation of these bacterial and fungal strains on cowpea growth under different N and P conditions. First, the compatibility between Bradyrhizobium strains UFLA03-84 and INPA03-11B and fungi Haematonectria ipomoeae FSA381, Eleutherascus lectardii FSA257a, Pochonia chlamydosporia var. catenulata FSA109, and Acremonium polychromum FSA115 was tested in both solid and liquid media. Cowpea growth and nodulation promotion under two mineral N doses and two P conditions (a low dose of soluble P plus a high dose of Ca3(PO4)2 and another condition with a high dose of soluble P) were tested with two N2 fixing Bradyrhizobium strains co-inoculated with each of the P-solubilizing fungal strains FSA109, FSA115, and FSA381. There was compatibility between each fungal strain and the two Bradyrhizobium strains, except for FSA257a with either of the bacterial strains in liquid medium. When both mineral N and P were limiting, plants were able to grow and accumulate N and P based on biological N2 fixation and solubilization of calcium phosphate in the same amount as the mineral N and soluble phosphate. Even when both nutrients were fully available, the type of co-inoculation promoted plant growth and nutrient accumulation. The responses varied in accordance with the co-inoculated strains, the N source, and the P source, reflecting the enormous complexity of the biological interactions between plants and microorganisms, and the nutrient conditions provided by the environment.

Ornamental plant Pachystachys lutea as a source of promising endophytes for plant growth and phytoprotective activity

Endophytes are growth-promoting agents capable of synthesizing phytohormones, uptaking nutrients, and controlling pathogens. There is a strong potential to exploit them in the agriculture field like biofertilizers and biocontrol agents. In this work, we aimed to evaluate endophytic fungi isolated from Pachystachys lutea for their potential to solubilize phosphate, synthesise indole acetic acid (IAA), antagonize phytopathogens, and promote plant growth under greenhouse conditions. The phosphate solubilization efficiency was assessed on Pikovskaya’s agar medium. For analysis of IAA production, mycelia plugs of endophytes were cultured in Potato Dextrose Broth medium supplemented with L-tryptophan, with Salkowski Reagent, and the absorbance of the culture was measured. The antagonism evaluation of strain Alternaria sp. PL75 against phytopathogens was performed using the paired-culture technique. The promotion of plant growth provided by Alternaria sp. PL75 was evaluated in tomato plants. All strains evaluated were able to solubilize phosphate; however, the strain Alternaria sp. PL75 was the most effective (4.29). Two strains, Nemania sp. PL27 and Alternaria sp. PL75, produced 1.86 and 1.73 & 956;g mL-1 of IAA, respectively. In the antagonism assay, the endophyte Alternaria sp. PL75 and its fungal extract showed the best results against the pathogen Moniliophthora perniciosa. The greenhouse experiment result showed the endophyte Alternaria sp. PL75 increased the plantlets emergency speed index and the percentage of germination from 60 to 81.63%. It was also observed a statistical significance in the shoot length of the treated plants with the endophyte suspension (55.38 cm) compared to the control (41.67 cm).

Ornamental plant Pachystachys lutea as a source of promising endophytes for plant growth and phytoprotective activity

Endophytes are growth-promoting agents capable of synthesizing phytohormones, uptaking nutrients, and controlling pathogens. There is a strong potential to exploit them in the agriculture field like biofertilizers and biocontrol agents. In this work, we aimed to evaluate endophytic fungi isolated from Pachystachys lutea for their potential to solubilize phosphate, synthesise indole acetic acid (IAA), antagonize phytopathogens, and promote plant growth under greenhouse conditions. The phosphate solubilization efficiency was assessed on Pikovskayas agar medium. For analysis of IAA production, mycelia plugs of endophytes were cultured in Potato Dextrose Broth medium supplemented with L-tryptophan, with Salkowski Reagent, and the absorbance of the culture was measured. The antagonism evaluation of strain Alternaria sp. PL75 against phytopathogens was performed using the paired-culture technique. The promotion of plant growth provided by Alternaria sp. PL75 was evaluated in tomato plants. All strains evaluated were able to solubilize phosphate; however, the strain Alternaria sp. PL75 was the most effective (4.29). Two strains, Nemania sp. PL27 and Alternaria sp. PL75, produced 1.86 and 1.73 & 956;g mL-1 of IAA, respectively. In the antagonism assay, the endophyte Alternaria sp. PL75 and its fungal extract showed the best results against the pathogen Moniliophthora perniciosa. The greenhouse experiment result showed the endophyte Alternaria sp. PL75 increased the plantlets emergency speed index and the percentage of germination from 60 to 81.63%. It was also observed a statistical significance in the shoot length of the treated plants with the endophyte suspension (55.38 cm) compared to the control (41.67 cm).(AU)

Characterization of Pseudomonas bacteria of Piper tuberculatum regarding the production of potentially bio-stimulating compounds for plant growth / Caracterização de bactérias Pseudomonas de Piper tuberculatum quanto à produção de compostos potencialmente bioestimulantes para o crescimento de plantas

Despite advances in the identification and characterization of endophytic bacteria in various plant species worldwide, little is known about such microorganisms in plants from the Amazon region. Previous studies reported that Piper tuberculatum endophytic Pseudomonas (isolates Pt12 and Pt13, identified as Pseudomonas putida and Pseudomonas sp., respectively) were able to inhibit the in vitro growth of Fusarium solani f. sp. piperis, which causes root rot in black pepper (Piper nigrum), and that Pt13 promoted the growth of P. nigrum. Therefore, the aim here was to characterize these bacteria regarding their ability to produce plant growth-promoting substances [siderophores, indol acetic acid (IAA) and soluble phosphate]. Chrome azurol S assays were performed for the detection of siderophores. For qualitative and quantitative assays of IAA production and phosphate solubilization, Salkowski´s reagent and NBRIP medium with molybdenum blue reagent, respectively, were used. Results revealed that Pt12 and Pt13 were able to synthesize IAA, mainly under a high concentration of L-tryptophan, indicating that they are IAA-producing bacteria, probably through a tryptophan-dependent biosynthesis pathway. The presence of P. nigrum extract positively influenced the IAA production by Pt12 and Pt13, with highest values of 125 and 90 µg mL-1, respectively. In addition, Pt12 was positive for the production of siderophores and produced 56.56 µg mL-1 of soluble phosphate. In contrast, Pt13 showed no ability to produce siderophores or to solubilize phosphate. Besides their potential in controlling plant diseases, Pt12 and Pt13 have potential as biofertilizers, favoring sustainable agriculture.(AU)

Apesar dos avanços na identificação e caracterização de bactérias endofíticas em espécies vegetais em todo o mundo, pouco se sabe sobre esses microrganismos em plantas da região amazônica. Estudos anteriores mostraram que Pseudomonas de Piper tuberculatum (isolados Pt12 e Pt13, identificados como Pseudomonas putida e Pseudomonas sp., respectivamente) são capazes de inibir Fusarium solani f. sp. piperis, que causa a podridão das raízes da pimenteira-do-reino (Piper nigrum), e que Pt13 promoveu o crescimento de P. nigrum. Portanto, o objetivo do presente trabalho foi caracterizar essas bactérias quanto à capacidade de produzir substâncias potencialmente bioestimulantes para o crescimento vegetal [sideróforos, ácido indol acético (AIA) e fosfato solúvel]. Ensaios de Cromo Azurol S foram realizados para detecção de sideróforos. Para os ensaios qualitativos e quantitativos de produção de AIA e solubilização de fosfato, foram utilizados o reagente de Salkowski e o meio NBRIP com azul de molibdênio, respectivamente. Os resultados revelaram que Pt12 e Pt13 sintetizaram AIA, principalmente sob alta concentração de L-triptofano, indicando que provavelmente utilizam uma via de biossíntese dependente deste aminoácido. A presença do extrato de P. nigrum influenciou positivamente a produção de AIA por Pt12 e Pt13, com valores máximos de 125 e 90 µg mL-1, respectivamente. Além disso, Pt12 foi positiva para produção de sideróforos e produziu 56.56 µg.mL-1 de fosfato solúvel. Em contraste, Pt13 não produziu sideróforos, nem solubilizou fosfato. Além do potencial de controle de doenças de plantas, Pt12 e Pt13 têm potencial como biofertilizantes, favorecendo a agricultura sustentável.(AU)

Selection of microorganisms and preparation of inoculants with potential applications in the remediation of soil contaminated with hexazinone / Seleção de microrganismos e preparo de inoculantes com potencial de aplicação na remediação de solo contaminado com hexazinona

The excessive use of agrochemicals negatively impacts the environment, making the development of sustainable technologies for the reduction of contaminants in soil necessary. Hexazinone is the herbicide most used for sugarcane crops and persists in the environment. Moreover, its main route of degradation in the soil is through microorganisms. Therefore, six microorganisms were selected that presented growth in the presence of the herbicide; SCR1 - Microbacterium arborescens; SCR2 - Bacillus pumilus; SCM3 - Stenotrophomonas maltophilia; SCM4 - Bacillus cereus; SCM5A - M. arborescens; and SCM5B - B. safensis. A test was performed to evaluate the ability of each lineage in phosphate solubilization. For the Ca3(PO4)2 solubilization test, the strains that showed the best results were B. pumilus and S. maltophilia. Subsequently, the inoculants were prepared and the concentrations after plating were 2.71 × 109 CFU mL-1 for B. pumilus, 1.02 × 109 CFU mL-1 for S. maltophilia, and 1.14 × 1010 CFU mL-1 for a combination of the two strains. These were satisfactory values for use as inoculants.(AU)

O uso de agroquímicos resulta em impactos ambientais e torna-se necessário o emprego de tecnologias sustentáveis para diminuição de contaminantes no solo. O hexazinona é o herbicida mais utilizado para a cultura da cana-de-açúcar, e apresenta persistência no ambiente. A principal via de degradação no solo é por meio de microrganismos. Com isso, selecionou-se seis microrganismos que apresentaram crescimento na presença do herbicida: SCR1 - Microbacterium arborescens; SCR2 - Bacillus pumilus; SCM3 - Stenotrophomonas maltophilia; SCM4 - Bacillus cereus; SCM5A - M. arborescens; SCM5B - Bacillus safensis. Foi realizado um teste para avaliar a habilidade de cada linhagem na solubilização de fosfatos, e no caso da solubilização de Ca3(PO4)2, as linhagens que apresentaram melhores resultados foram B. pumilus e S. maltophilia. Posteriormente, os inoculantes foram preparados e a concentração após plaqueamento de 2,71x109 UFC mL-1 para B. pumilus, 1,02x109 UFC mL-1 para S. maltophilia e consórcio com as duas linhagens 1,14x1010 UFC mL-1 apresentaram valores satisfatórios para utilização como inoculantes.(AU)

Diversity of bacterial strains in biochar-enhanced Amazon soil and their potential for growth promotion and biological disease control in tomato / Diversidade de isolados bacterianos em solo amazônico enriquecido com biocarvão e seu potencial para a promoção de crescimento e controle biológico de doenças em tomate

The use of bacteria in growth promotion and biological control of plant diseases can minimize environmental contamination caused by the indiscriminate use of pesticides and chemical fertilizers. We aimed to evaluate growth promotion and biological control of Corynespora cassiicola in tomato seedlings mediated by beneficial bacteria isolated from a non-rhizospheric Amazon soil containing different amounts of biochar, and to identify to which groups of bacteria the strains belong. We obtained 200 strains of bacteria from experimental plots containing biochar doses of 0, 40, 80 and 120 t ha-1. Of these, 53 strains were selected by root colonization tests. Based on growth promotion parameters, 25 strains were screened, identified by molecular characterization and evaluated for indoleacetic acid (IAA) production, phosphate solubilization and biological control. The best dose of biochar for colony formation was 40 t ha-1, and a regression model indicated 34 t ha-1 as the optimal dose. The production of IAA was observed in 18 (75%) strains, and two (8%) strains were able to solubilize phosphate. The efficiency in root growth promotion was up to 125%, and the percentage of plant protection ranged from 50 to 59%. Molecular characterization showed that the bacteria used in this study belong to the genera Bacillus and Lysinibacillus.(AU)

O uso de bactérias na promoção do crescimento e no controle biológico de doenças em plantas pode minimizar a contaminação ambiental causada pela aplicação indiscriminada de pesticidas e fertilizantes químicos. Objetivamos avaliar a promoção do crescimento e o controle biológico de Corynespora cassiicola em mudas de tomate mediadas por bactérias benéficas isoladas de solo amazônico não-rizosférico contendo diferentes dosagens de biocarvão, e identificar a quais grupos de bactérias os isolados pertencem. Obtivemos 200 isolados de parcelas experimentais contendo doses de biocarvão de 0, 40, 80 e 120 t ha-1. Destes, 53 foram selecionados por testes de colonização radicular. Com base nos parâmetros de promoção do crescimento, 25 isolados foram selecionados, identificados através de análise molecular e avaliados para produção de ácido indolacético (AIA), solubilização de fosfato e controle biológico. A melhor dose de biocarvão para a formação de colônias foi 40 t ha-1, e um modelo de regressão indicou 34 t ha-1como dose ótima. A produção de AIA foi observada em 18 (75%) isolados e dois (8%) isolados foram capazes de solubilizar fosfato. A eficiência na promoção do crescimento das raízes foi de até 125%, e a porcentagem de proteção das plantas variou de 50,3 a 59,0%. A caracterização molecular indicou que as bactérias utilizadas nesse estudo pertencem aos gêneros Bacillus e Lysinibacillus.(AU)

Characterization of bacterial endophytes from the roots of native and cultivated Brazil nut trees (Bertholletia excelsa) / Caracterização de bactérias endofíticas de raízes de castanha-do-Brasil (Bertholletia excelsa) em habitats nativos e cultivados

Brazil nut is a very important nontimber forest product in the Amazon region. Propagation of this tree still represents a challenge due to slow and uneven seed germination. In this context, plant growth-promoting bacteria can facilitate the process of propagation. The aims of this study were to isolate and characterize endophytic bacteria from the roots of Brazil nut trees in native terra firme forest and cultivation areas in northern Brazil, and to identify mechanisms by which bacteria act in plant growth promotion. Overall, 90 bacterial isolates were obtained from the roots of Brazil nut trees in monoculture, agroforestry and native forest areas by using different semisolid media. The isolates were characterized by sequencing the 16S rRNA gene. Plant growth-promoting characteristics were evaluated by the presence of the nifH gene, aluminum phosphate solubilization and the production of indole compounds. The isolates were affiliated with 18 genera belonging to 5 different classes (α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Bacilli and Actinobacteria). The genus Bacillus was predominant in the forest and monoculture areas. Fourteen isolates presented the nifH gene. Most of the bacteria were able to solubilize aluminum phosphate and synthetize indole compounds. The results indicated high diversity of endophytic bacteria present among the roots of Brazil nut trees, mainly in the agroforestry area, which could be related to soil attributes. Among the 90 isolates, the 22 that presented the best results regarding plant growth promotion traits were good candidates for testing in seedling production of Brazil nut trees.(AU)

A castanha-do-brasil é um produto florestal não madeireiro muito importante na região amazônica. A propagação desta árvore ainda representa um desafio, devido ao lento e irregular processo de germinação das sementes. Neste contexto, bactérias promotoras do crescimento vegetal podem facilitar o processo de propagação. O objetivo deste estudo foi isolar e caracterizar bactérias endofíticas em raízes de castanha-do-Brasil em floresta de terra firme e em áreas cultivadas no norte do Brasil, e identificar alguns mecanismos de promoção do crescimento vegetal executados por essas bactérias. No total, 90 isolados bacterianos foram obtidos de raízes de castanha-do-Brasil em monocultura, agrofloresta e floresta nativa, usando diferentes meios de cultivo semi-sólidos. Os isolados foram caracterizados pelo sequenciamento do gene 16S rRNA. As características de promoção do crescimento vegetal foram avaliadas através da presença do gene nifH, solubilização de fosfato de alumínio e produção de compostos indólicos. Os isolados foram afiliados a 18 gêneros, pertencentes a cinco diferentes classes (α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Bacilli e Actinobacteria). O gênero Bacillus foi predominante, principalmente nas áreas de floresta e monocultura. Quatorze isolados apresentaram o gene nifH. A maioria dos isolados foi capaz de solubilizar fosfato de alumínio e sintetizar compostos indólicos. Os resultados indicam uma elevada diversidade de bactérias endofíticas presente em raízes de castanha-do-Brasil, principalmente em área de agrofloresta, que pode estar relacionado aos atributos do solo. Entre os 90 isolados, 22 apresentaram os melhores resultados relacionados às características de promoção do crescimento vegetal, e são bons candidatos para testes em produção de mudas de castanha-do-Brasil.(AU)

Functional diversity of bacteria isolated from rhizosphere and non-rhizosphere soils under maize cultivation / Diversidade funcional de bactérias isoladas de solos rizosférico e não rizosférico em cultura de milho

This study evaluated the hydrolytic and phosphate-solubilizing potentials of soil bacteria isolated from a red latosol (oxisol) under maize cultivation. Rhizosphere soil (SR) and non-rhizosphere soil (NR) were collected and, subsequently, distinct bacterial colonies were isolated in pure cultures. Solid culture media were employed to evaluate production of hydrolases and phosphate solubilization by the isolates. From SR and NR, 30 and 19 distinct colonial types were isolated, respectively. From 29 SR isolates, 68.9%, 65.5%, 20.7% and 24.1% displayed proteolytic, cellulolytic, amylolytic, and phosphate-solubilizing activities, respectively. From the NR isolates, 57.9% produced cellulase, 42.1% protease, 57.9% amylase and 21.0% solubilized phosphate; however, 31.6% of these isolates did not display any activity. Diverse bacteria presented combined activities, representing about 58% of the SR and NR isolates. In addition to environmental and agricultural relevance, the microbial ability to secrete enzymes related to carbon and nitrogen cycles and phosphate solubilization might be important from a biotechnological perspective.

Este estudo avaliou os potenciais hidrolítico e de solubilização de fosfato de bactérias isoladas de Latossolo Vermelho cultivado com milho. A coleta de solo rizosférico (SR) e solo não rizosférico (NR) foi realizada, sendo procedido o isolamento de colônias bacterianas em culturas puras. Meios de cultura sólidos foram utilizados na avaliação da produção de hidrolases e solubilização de fosfato pelos isolados. A partir de SR e NR foram isolados 30 e 19 tipos coloniais distintos, respectivamente. De 29 isolados de SR, 68,9%, 65,5%, 20,7% e 24,1% apresentaram atividade proteolítica, celulolítica, amilolítica e solubilização de fosfato, respectivamente. Dos isolados de NR, 57,9% produziram celulase, 42,1% protease, 57,9% amilase e 21,0% solubilizaram fosfato; contudo, 31,6% destes isolados não demonstraram qualquer atividade. Diversas bactérias apresentaram atividades combinadas, representado aproximadamente 58% dos isolados de SR e NR. Além da relevância ambiental e agrícola, a habilidade microbiana em secretar enzimas relacionadas ao ciclo do carbono e nitrogênio e a solubilização de fosfato podem ser importantes na perspectiva biotecnológica.

Functional diversity of bacteria isolated from rhizosphere and non-rhizosphere soils under maize cultivation / Diversidade funcional de bactérias isoladas de solos rizosférico e não rizosférico em cultura de milho

This study evaluated the hydrolytic and phosphate-solubilizing potentials of soil bacteria isolated from a red latosol (oxisol) under maize cultivation. Rhizosphere soil (SR) and non-rhizosphere soil (NR) were collected and, subsequently, distinct bacterial colonies were isolated in pure cultures. Solid culture media were employed to evaluate production of hydrolases and phosphate solubilization by the isolates. From SR and NR, 30 and 19 distinct colonial types were isolated, respectively. From 29 SR isolates, 68.9%, 65.5%, 20.7% and 24.1% displayed proteolytic, cellulolytic, amylolytic, and phosphate-solubilizing activities, respectively. From the NR isolates, 57.9% produced cellulase, 42.1% protease, 57.9% amylase and 21.0% solubilized phosphate; however, 31.6% of these isolates did not display any activity. Diverse bacteria presented combined activities, representing about 58% of the SR and NR isolates. In addition to environmental and agricultural relevance, the microbial ability to secrete enzymes related to carbon and nitrogen cycles and phosphate solubilization might be important from a biotechnological perspective.(AU)

Este estudo avaliou os potenciais hidrolítico e de solubilização de fosfato de bactérias isoladas de Latossolo Vermelho cultivado com milho. A coleta de solo rizosférico (SR) e solo não rizosférico (NR) foi realizada, sendo procedido o isolamento de colônias bacterianas em culturas puras. Meios de cultura sólidos foram utilizados na avaliação da produção de hidrolases e solubilização de fosfato pelos isolados. A partir de SR e NR foram isolados 30 e 19 tipos coloniais distintos, respectivamente. De 29 isolados de SR, 68,9%, 65,5%, 20,7% e 24,1% apresentaram atividade proteolítica, celulolítica, amilolítica e solubilização de fosfato, respectivamente. Dos isolados de NR, 57,9% produziram celulase, 42,1% protease, 57,9% amilase e 21,0% solubilizaram fosfato; contudo, 31,6% destes isolados não demonstraram qualquer atividade. Diversas bactérias apresentaram atividades combinadas, representado aproximadamente 58% dos isolados de SR e NR. Além da relevância ambiental e agrícola, a habilidade microbiana em secretar enzimas relacionadas ao ciclo do carbono e nitrogênio e a solubilização de fosfato podem ser importantes na perspectiva biotecnológica.(AU)

Polyphasic characterization of bacteria obtained from upland rice cultivated in Cerrado soil

This work aimed to characterize 20 isolates obtained from upland rice plants, based on phenotypic (morphology, enzymatic activity, inorganic phosphate solubilization, carbon source use, antagonism), genotypic assays (16S rRNA sequencing) and plant growth promotion. Results showed a great morphological, metabolic and genetic variability among bacterial isolates. All isolates showed positive activity for catalase and protease enzymes and, 90% of the isolates showed positive activity for amylase, catalase and, nitrogenase. All isolates were able to metabolize sucrose and malic acid in contrast with mannitol, which was metabolized only by one isolate. For the other carbon sources, we observed a great variability in its use by the isolates. Most isolates showed antibiosis against Rhizoctonia solani (75%) and Sclerotinia sclerotiorum (55%) and, 50% of them showed antibiosis against both pathogens. Six isolates showed simultaneous ability of antibiosis, inorganic phosphate solubilization and protease activity. Based on phylogenetic analysis of the 16S rRNA gene all the isolates belong to Bacillus genus. Under greenhouse conditions, two isolates (S4 and S22) improved to about 24%, 25%, 30% and 31% the Total N, leaf area, shoot dry weight and root dry weight, respectively, of rice plants, indicating that they should be tested for this ability under field conditions.(AU)

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest

Erythrina velutina ("mulungu") is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of "mulungu" rhizobia are poorly understood. The aim of this study was to characterize "mulungu" rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L-1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.(AU)