Rejuvenating potato growth and yield in challenging semiarid and saline sandy Cholistan: harnessing PGPB-coated N and P application strategies.

BACKGROUND: Potato serves as a major non-cereal food crop and income source for small-scale growers in Punjab, Pakistan. Unfortunately, improper fertilization practices have led to low crop yields, worsened by challenging environmental conditions and poor groundwater quality in the Cholistan region. To address this, we conducted an experiment to assess the impact of two fertilizer application approaches on potato cv. Barna using plant growth-promoting bacteria (PGPB) coated biofertilizers. The first approach, termed conventional fertilizer application (CFA), involved four split applications of PGPB-coated fertilizers at a rate of 100:75 kg acre-1 (N and P). The second, modified fertilizer application (MFA), employed nine split applications at a rate of 80:40 kg acre-1. RESULTS: The MFA approach significantly improved various plant attributes compared to the CFA. This included increased plant height (28%), stem number (45%), leaf count (46%), leaf area index (36%), leaf thickness (three-folds), chlorophyll content (53%), quantum yield of photosystem II (45%), photosynthetically active radiations (56%), electrochromic shift (5.6%), proton flux (24.6%), proton conductivity (71%), linear electron flow (72%), photosynthetic rate (35%), water use efficiency (76%), and substomatal CO2 (two-folds), and lowered non-photochemical quenching (56%), non-regulatory energy dissipation (33%), transpiration rate (59%), and stomatal conductance (70%). Additionally, the MFA approach resulted in higher tuber production per plant (21%), average tuber weight (21.9%), tuber diameter (24.5%), total tuber yield (29.1%), marketable yield (22.7%), seed-grade yield (9%), specific gravity (9.6%), and soluble solids (7.1%). It also reduced undesirable factors like goli and downgrade yields by 57.6% and 98.8%, respectively. Furthermore, plants under the MFA approach exhibited enhanced nitrogen (27.8%) and phosphorus uptake (40.6%), with improved N (26.1%) and P uptake efficiency (43.7%) compared to the CFA approach. CONCLUSION: The use of PGPB-coated N and P fertilizers with a higher number of splits at a lower rate significantly boosts potato production in the alkaline sandy soils of Cholistan.

Novel melatonin-producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean.

Recently, microorganism and exogenous melatonin application has been recognized as an efficient biological tool for enhancing salt tolerance and heavy metal detoxification in agriculture crops. Thus, the goal of this study was to isolate and evaluate a novel melatonin-producing plant growth promoting bacterium. With high-throughput whole genome sequencing, phytohormone measurements, expression profiling, and biochemical analysis, we can identify a novel PGPB that produces melatonin and unravel how it promotes soybean growth and development and protects against salt and Cd stress. We identify the melatonin synthesis pathway (tryptophan→tryptamine→serotonin melatonin) of the halotolerant (NaCl > 800 mM) and heavy metal-resistant (Cd >3 mM) rhizobacterium Bacillus safensis EH143 and use it to treat soybean plants subjected to Cd and NaCl stresses. Results show that EH143 will highly bioaccumulate heavy metals and significantly improve P and Ca2+ uptake and the K+/Na+ (93%↑under salt stress) ratio while reducing Cd uptake (49% under Cd stress) in shoots. This activity was supported by the expression of the ion regulator HKT1, MYPB67, and the calcium sensors CDPK5 and CaMK1 which ultimately led to increased plant growth. EH143 significantly decreased ABA content in shoots by 13%, 20%, and 34% and increased SA biosynthesis in shoots by 14.8%, 31%, and 48.2% in control, salt, and Cd-treated plants, upregulating CYP707A1 and CYP707A2 and PAL1 and ICS, respectively. The melatonin content significantly decreased along with a reduced expression of ASMT3 following treatment with EH143; moreover, reduced expression of peroxidase (POD) and superoxide dismutase (SOD) by 134.5% and 39% under salt+Cd stress, respectively and increased level of total amino acids were observed. Whole-genome sequencing and annotation of EH143 revealed the presence of the melatonin precursor tryptophan synthase (trpA, trpB, trpS), metal and other ion regulators (Cd: cadA, potassium: KtrA and KtrB, phosphate: glpT, calcium: yloB, the sodium/glucose cotransporter: sgIT, and the magnesium transporter: mgtE), and enzyme activators (including the siderophore transport proteins yfiZ and yfhA, the SOD sodA, the catalase katA1, and the glutathione regulator KefG) that may be involved in programming the plant metabolic system. As a consequence, EH143 treatment significantly reduced the contents of lipid peroxidation (O2-, MDA, and H2O2) up to 69%, 46%, and 29% in plants under salt+Cd stress, respectively. These findings suggest that EH143 could be a potent biofertilizer to alleviate NaCl and Cd toxicity in crops and serve as an alternative substitute for exogenous melatonin application.

Differential responses of bell pepper genotypes to indigenous Pseudomonas putida A32 treatment: implications for drought resilience.

AIMS: This study aimed to evaluate the potential of endophytic plant growth-promoting bacterium (PGPB), Pseudomonas putida A32, to mitigate drought stress in two bell pepper genotypes, Amfora 19 and Amfora 26, and to assess the genotype-specific responses to bacterial treatment. METHODS AND RESULTS: The isolate P. putida A32 was selected for its remarkable beneficial properties, exhibiting 13 out of 14 traits tested. Under drought conditions, Amfora 26 showed increased relative water content and decreased H2O2 and malondialdehyde following bacterial treatment, while Amfora 19 exhibited enhanced growth parameters but responded less to bacterial treatment regarding drought parameters. However, Amfora 19 displayed inherent drought tolerance mechanisms, as indicated by lower stress parameters compared to Amfora 26. CONCLUSIONS: The study emphasizes the importance of genotype-specific responses to PGPB treatment and the mechanisms of drought tolerance in peppers. Pseudomonas putida A32 effectively mitigated drought stress in both genotypes, with differential responses influenced by plant genotype. Our study confirmed our initial hypothesis that Amfora 19, as a genotype tolerant to biotic stress, is also more tolerant to abiotic stress. Understanding these interactions is crucial for the development of customized strategies to improve plant productivity and tolerance to drought.

Comparative genomics of plant growth promoting phosphobacteria isolated from acidic soils.

Despite being one of the most abundant elements in soil, phosphorus (P) often becomes a limiting macronutrient for plants due to its low bioavailability, primarily locked away in insoluble organic and inorganic forms. Phosphate solubilizing and mineralizing bacteria, also called phosphobacteria, isolated from P-deficient soils have emerged as a promising biofertilizer alternative, capable of converting these recalcitrant P forms into plant-available phosphates. Three such phosphobacteria strains-Serratia sp. RJAL6, Klebsiella sp. RCJ4, and Enterobacter sp. 198-previously demonstrated their particular strength as plant growth promoters for wheat, ryegrass, or avocado under abiotic stresses and P deficiency. Comparative genomic analysis of their draft genomes revealed several genes encoding key functionalities, including alkaline phosphatases, isonitrile secondary metabolites, enterobactin biosynthesis and genes associated to the production of indole-3-acetic acid (IAA) and gluconic acid. Moreover, overall genome relatedness indexes (OGRIs) revealed substantial divergence between Serratia sp. RJAL6 and its closest phylogenetic neighbours, Serratia nematodiphila and Serratia bockelmanii. This compelling evidence suggests that RJAL6 merits classification as a novel species. This in silico genomic analysis provides vital insights into the plant growth-promoting capabilities and provenance of these promising PSRB strains. Notably, it paves the way for further characterization and potential application of the newly identified Serratia species as a powerful bioinoculant in future agricultural settings.

Co-applied biochar and PGPB promote maize growth and reduce CO2 emission by modifying microbial communities in coal mining degraded soils.

Coal mining is one of the human activities that has the greatest impact on the global carbon (C) cycle and biodiversity. Biochar and plant growth-promoting bacteria (PGPB) have been both used to improve coal mining degraded soils; however, it is uncertain whether the effects of biochar application on soil respiration and microbial communities are influenced by the presence or absence of PGPB and soil nitrogen (N) level in coal mining degraded soils. A pot experiment was carried out to examine whether the effects of biochar addition (0, 1, 2 and 4% of soil mass) on soil properties, soil respiration, maize growth, and microbial communities were altered by the presence or absence of PGPB (i.e. Sphingobium yanoikuyae BJ1) (0, 200 mL suspension (2 × 106 colony forming unit (CFU) mL-1)) and two soil N levels (N0 and N1 at 0 and 0.2 g kg-1 urea- N, respectively). The results showed the presence of BJ1 enhanced the maize biomass relative to the absence of BJ1, particularly in N1 soils, which was related to the discovery of Lysobacter and Nocardioides that favor plant growth in N1 soils. This indicates a conversion in soil microbial communities to beneficial ones. The application of biochar at a rate of 1% decreased the cumulative CO2 regardless of the presence or absence of BJ1; BJ1 increased the ß-glucosidase (BG) activities, and BG activities were also positively correlated with RB41 strain with high C turnover in N1 soils, which indicates that the presence of BJ1 improves the C utilization rates of RB41, decreasing soil C mineralization. Our results highlight that biochar addition provided environmental benefits in degraded coal mining soils, and the direction and magnitude of these effects are highly dependent on the presence of PGPB and the soil N level.

Enhancement of the germination and growth of Panicum miliaceum and Brassica juncea in Cd- and Zn-contaminated soil inoculated with heavy-metal-tolerant Leifsonia sp. ZP3.

The addition of plant-growth-promoting bacteria (PGPB) to heavy-metal-contaminated soils can significantly improve plant growth and productivity. This study isolated heavy-metal-tolerant bacteria with growth-promoting traits and investigated their inoculation effects on the germination rates and growth of millet (Panicum miliaceum) and mustard (Brassica juncea) in Cd- and Zn-contaminated soil. Leifsonia sp. ZP3, which is resistant to Cd (0.5 mM) and Zn (1 mM), was isolated from forest soil. The ZP3 strain exhibited plant-growth-promoting activity, including indole-3-acetic acid production, phosphate solubilization, catalase activity, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging. In soil contaminated with low concentrations of Cd (0.232 ± 0.006 mM) and Zn (6.376 ± 0.256 mM), ZP3 inoculation significantly increased the germination rates of millet and mustard 8.35- and 31.60-fold, respectively, compared to the non-inoculated control group, while the shoot and root lengths of millet increased 1.77- and 4.44-fold (p < 0.05). The chlorophyll content and seedling vigor index were also 4.40 and 18.78 times higher in the ZP3-treated group than in the control group (p < 0.05). The shoot length of mustard increased 1.89-fold, and the seedling vigor index improved 53.11-fold with the addition of ZP3 to the contaminated soil (p < 0.05). In soil contaminated with high concentrations of Cd and Zn (0.327 ± 0.016 and 8.448 ± 0.250 mM, respectively), ZP3 inoculation led to a 1.98-fold increase in the shoot length and a 2.07-fold improvement in the seedling vigor index compared to the control (p < 0.05). The heavy-metal-tolerant bacterium ZP3 isolated in this study thus represents a promising microbial resource for improving the efficiency of phytoremediation in Cd- and Zn-contaminated soil.

Conservation of beneficial microbes between the rhizosphere and the cyanosphere.

Biocrusts are phototroph-driven communities inhabiting arid soil surfaces. Like plants, most photoautotrophs (largely cyanobacteria) in biocrusts are thought to exchange fixed carbon for essential nutrients like nitrogen with cyanosphere bacteria. Here, we aim to compare beneficial interactions in rhizosphere and cyanosphere environments, including finding growth-promoting strains for hosts from both environments. To examine this, we performed a retrospective analysis of 16S rRNA gene sequencing datasets, host-microbe co-culture experiments between biocrust communities/biocrust isolates and a model grass (Brachypodium distachyon) or a dominant biocrust cyanobacterium (Microcoleus vaginatus), and metabolomic analysis. All 18 microbial phyla in the cyanosphere were also present in the rhizosphere, with additional 17 phyla uniquely found in the rhizosphere. The biocrust microbes promoted the growth of the model grass, and three biocrust isolates (Bosea sp._L1B56, Pseudarthrobacter sp._L1D14 and Pseudarthrobacter picheli_L1D33) significantly promoted the growth of both hosts. Moreover, pantothenic acid was produced by Pseudarthrobacter sp._L1D14 when grown on B. distachyon exudates, and supplementation of plant growth medium with this metabolite increased B. distachyon biomass by over 60%. These findings suggest that cyanobacteria and other diverse photoautotrophic hosts can be a source for new plant growth-promoting microbes and metabolites.

Biostimulation of Salicornia europaea L. crops with plant growth-promoting bacteria in laboratory and field conditions: effects on growth and metabolite profile.

AIM: The objective of the work was to assess the effect of biostimulation with selected plant growth-promoting bacteria on growth and metabolite profile of Salicornia europaea. METHODS AND RESULTS: Salicornia europaea seeds were inoculated with different combinations of plant growth-promoting bacteria Brevibacterium casei EB3, Pseudomonas oryzihabitans RL18, and Bacillus aryabhattai SP20. Plants germinated from inoculated seeds were grown either in laboratory conditions or in a saline crop field. Fresh and dry weight were determined at the end of the experiment, for biomass quantification. The microbiological quality of fresh shoots for human consumption as salad greens was assessed, and the persistence of the inoculated strains in the plant rhizosphere was confirmed by next-generation sequencing (Illumina) of the 16S rDNA gene. The primary metabolite profile of biostimulated plants was characterized by GC-TOF-MS.In laboratory conditions, inoculation with the two strains Br. casei EB3 and Ps. oryzihabitans RL18 caused the most significant increase in biomass production (fresh and dry weight), and caused a shift in the central metabolic pathways of inoculated plants toward amino acid biosynthesis. In the field experiment, no significant biostimulation effect was detected with any of the tested inoculants. Seed inoculation had no significant effect on the microbiological quality of the edible parts. The persistence of inoculants was confirmed in both experiments. CONCLUSIONS: Manipulation of the plant microbiome can trigger primary metabolic reconfiguration and modulate the plant metabolism while promoting plant growth.

Predation pressure regulates plant growth promoting (PGP) attributes of bacterial species.

AIM: The present study aimed to investigate the effect of bacterivorous soil protists on plant growth promoting (PGP) attributes of bacterial species and their co-inoculative impact on rice seedling growth. METHODS AND RESULTS: The effect of protists on the PGP attributes of bacteria was tested using standard protocols. The results revealed that the plant-beneficial properties of plant growth promoting bacteria (PGPB) were altered in the presence of various protist species. A significant increase in the production of siderophore units (86.66%), ammonia (34.80 µmol mL-1), and phosphate solubilization index (PSI) (5.6) was observed when Bacillus cereus (Bc) and Pseudomonas fluorescens (Ps) were co-inoculated with unidentified species belonging to the family Kreyellidae (C5). In the case of Enterobacter cloacae co-inoculated with C5 (Kreyellidae), a higher amount of siderophore (51.33%), ammonia (25.18 µmol mL-1), and indole-3-acetic acid (IAA)-like substance (28.59 µg mL-1) production were observed. The biofilm-forming ability of B. cereus is enhanced in the presence of Tetrahymena sp. (C2Bc), unidentified Kreyellidae (C5Bc), and Colpoda elliotti (C12Bc), whereas E. cloacae showed higher biofilm formation in the presence of Tetrahymena sp. alone Although IAA production decreased under predation pressure, a significant increase in shoot length (64.24%) and primary root length (98.18%) in co-inoculative treatments (C12Bc and C5Bc) compared to bacteria alone (25% and 61.50% for shoots and roots, respectively) was observed. The results of enhanced PGP attributes and rice seedlings growth under predation pressure correlated with the enhanced bacterial activity under predation pressure and protist involvement in plant growth development. CONCLUSIONS: Protists may act as regulators of the bacterial activities involved in plant growth promotion and thus enhance plant growth.

Synthetic algocyanobacterial consortium as an alternative to chemical fertilizers.

The use of unregulated pesticides and chemical fertilizers can have detrimental effects on biodiversity and human health. This problem is exacerbated by the growing demand for agricultural products. To address these global challenges and promote food and biological security, a new form of agriculture is needed that aligns with the principles of sustainable development and the circular economy. This entails developing the biotechnology market and maximizing the use of renewable and eco-friendly resources, including organic fertilizers and biofertilizers. Phototrophic microorganisms capable of oxygenic photosynthesis and assimilation of molecular nitrogen play a crucial role in soil microbiota, interacting with diverse microflora. This suggests the potential for creating artificial consortia based on them. Microbial consortia offer advantages over individual organisms as they can perform complex functions and adapt to variable conditions, making them a frontier in synthetic biology. Multifunctional consortia overcome the limitations of monocultures and produce biological products with a wide range of enzymatic activities. Biofertilizers based on such consortia present a viable alternative to chemical fertilizers, addressing the issues associated with their usage. The described capabilities of phototrophic and heterotrophic microbial consortia enable effective and environmentally safe restoration and preservation of soil properties, fertility of disturbed lands, and promotion of plant growth. Hence, the utilization of algo-cyano-bacterial consortia biomass can serve as a sustainable and practical substitute for chemical fertilizers, pesticides, and growth promoters. Furthermore, employing these bio-based organisms is a significant stride towards enhancing agricultural productivity, which is an essential requirement to meet the escalating food demands of the growing global population. Utilizing domestic and livestock wastewater, as well as CO2 flue gases, for cultivating this consortium not only helps reduce agricultural waste but also enables the creation of a novel bioproduct within a closed production cycle.

Deciphering the role of non-Frankia nodular endophytes in alder through in vitro and genomic characterization.

Endophytic bacterial populations are well-positioned to provide benefits to their host plants such as nutrient acquisition and plant hormone level manipulation. Actinorhizal plants such as alders are well known for their microbial symbioses that allow them to colonize harsh environments whether natural or anthropized. Although the nitrogen-fixing actinobacterium Frankia sp. is the main endophyte found in alder root nodules, other bacterial genera, whose roles remain poorly defined, inhabit this niche. In this study, we isolated a diverse panel of non-Frankia nodular endophytes (NFNE). Some NFNE were isolated from alders grown from surface-sterilized seeds and maintained in sterile conditions, suggesting these may have been seed-borne. In vitro testing of 24 NFNE revealed some possessed putative plant growth promotion traits. Their genomes were also sequenced to identify genes related to plant growth promotion traits. This study highlights the complexity of the alder nodular microbial community. It paves the way for further understanding of the biology of nodules and could help improve land reclamation practices that involve alders.

Effects of co-applied biochar and plant growth-promoting bacteria on soil carbon mineralization and nutrient availability under two nitrogen addition rates.

In the background of climate warming, the demand for improving soil quality and carbon (C) sequestration is increasing. The application of biochar to soil has been considered as a method for mitigating climate change and enhancing soil fertility. However, it is uncertain whether the effects of biochar application on C-mineralization and N transformation are influenced by the presence or absence of plant growth-promoting bacteria (PGPB) and soil nitrogen (N) level. An incubation study was conducted to investigate whether the effects of biochar application (0 %, 1 %, 2 % and 4 % of soil mass) on soil respiration, N status, and microbial attributes were altered by the presence or absence of PGPB (i.e., Sphingobium yanoikuyae BJ1) under two soil N levels (N0 and N1 soils as created by the addition of 0 and 0.2 g kg-1 urea- N, respectively). The results showed that biochar, BJ1 strain and their interactive effects on cumulative CO2 emissions were not significant in N0 soils, while the effects of biochar on the cumulative CO2 emissions were dependent on the presence or absence of BJ1 in N1 soils. In N1 soils, applying biochar at 2 % and 4 % increased the cumulative CO2 emissions by 141.0 % and 166.9 %, respectively, when BJ1 was absent. However, applying biochar did not affect CO2 emissions when BJ1 was present. In addition, the presence of BJ1 generally increased ammonium contents in N0 soils, but decreased nitrate contents in N1 soils relative to the absence of BJ1, which indicates that the combination of biochar and BJ1 is beneficial to play the N fixation function of BJ1 in N0 soils. Our results highlight that biochar addition influences not only soil C mineralization but also soil available N, and the direction and magnitude of these effects are highly dependent on the presence of PGPB and the soil N level.

Reconnoitering the capabilities of nodule endophytic Pantoea dispersa for improved nodulation and grain yield of chickpea (Cicer arietinum L.).

Microorganisms belonging to root and soil provide a wide range of services and benefits to the plant by promoting plant growth and controlling phytopathogens. This study aimed to isolate endophytic bacteria from the root nodules of chickpea (Cicer arietinum L.) and determine their potential in improving plant growth. A total of nineteen different bacterial morphotypes were isolated from root nodules of chickpea and characterized in vitro for plant growth promotion abilities. All bacterial isolates were able to produce indole acetic acid at varying levels, out of which MCA19 was screened as the most efficient indole acetic acid producer (10.25 µg mL-1). MCA8, MCA9, MCA10, MCA11, MCA16, MCA17 and MCA19 were positive for phosphate solubilization, out of which MCA9 was best phosphate solubilizer (18.8 µg mL-1). All bacterial strains showed varying ability to grow on nitrogen-free media. Hydrogen cyanide, pectinase, and cellulase production ability were also observed in isolates, in which MCA9, MCA12, MCA17 and MCA19 were found best. Based on in vitro testing, five isolates MCA2, MCA9, MCA11, MCA17 and MCA19 were selected for further studies. Bacterial isolates MCA9, MCA11, MCA17 and MCA19 were identified by 16S rRNA gene sequence analysis as Pantoea dispersa while MCA2 as Rhizobium pusense. This is the first report on the existence of Pantoea dispersa in the root nodules of chickpea. In pot experiment, a maximum increase of 30% was recorded in plant dry weight upon the application of MCA19. Under field conditions, bacterial isolates, MCA2, MCA11 and MCA19 significantly enhanced nodulation and yield parameters of chickpea, compared to control. Pantoea dispersa MCA19 displayed the highest plant growth-promoting potential by increasing 38% grain yield. Our results indicate that Pantoea dispersa MCA19 is a promising biofertilizer for future applications.

Analysis of the Physiological Response and Reactive Oxygen Species in Castor Oil Plant (Ricinus Communis) in the Phytoremediation Processes with Plant Growth Promoter Bacteria (PGPB).

In the phytoremediation processes of mine tailings with Ricinus communis inoculated with PGPB, it was found that the Serratia K120 bacterium favors the translocation of Al, As, Cu, Pb, Cr, Cd, and Mn to the aerial part of the plant, with a significant difference (p < 0.05) concerning for the control. The bioaccumulation factor (BF) was > 1 in Al with all the bacteria, Pb, Serratia K120, Fe, Pantoea 113, Cu, Pb, Cd, Mn in Serratia MC119 and Serratia K120, Fe and As in Serratia K120 and Pantoea 134, indicating that Ricinus communis inoculated with PGPB functions as a hyper accumulating plant. The PGPB help to reduce the stress in the plants generated by the heavy metals, decreasing the H2O2, and increasing the activity of the enzymes SOD, CAT, APX, POX, and GR, for which the bacteria Serratia K120 and Pantoea 113 can be used as bioinoculants to favor phytoremediation processes.

Co-inoculation with tropical strains of Azospirillum and Bacillus is more efficient than single inoculation for improving plant growth and nutrient uptake in maize.

Usage of Bacillus and Azospirillum as new eco-friendly microbial consortium inoculants is a promising strategy to increase plant growth and crop yield by improving nutrient availability in agricultural sustainable systems. In this study, we designed a multispecies inoculum containing B. thuringiensis (strain B116), B. subtillis (strain B2084) and Azospirillum sp. (strains A1626 and A2142) to investigate their individual or co-inoculated ability to solubilize and mineralize phosphate, produce indole acetic acid (IAA) and their effect on maize growth promotion in hydroponics and in a non-sterile soil. All strains showed significant IAA production, P mineralization (sodium phytate) and Ca-P, Fe-P (tricalcium phosphate and iron phosphate, respectively) solubilization. In hydroponics, co-inoculation with A1626 x A2142, B2084 x A2142, B2084 x A1626 resulted in higher root total length, total surface area, and surface area of roots with diameter between 0 and 1 mm than other treatments with single inoculant, except B2084. In a greenhouse experiment, maize inoculated with the two Azospirillum strains exhibited enhanced shoot dry weight, shoot P and K content, root dry weight, root N and K content and acid and alkaline phosphatase activities than the other treatments. There was a significant correlation between soil P and P shoot, alkaline phosphatase and P shoot and between acid phosphatase and root dry weight. It may be concluded that co-inoculations are most effective than single inoculants strains, mainly between two selected Azospirillum strains. Thus, they could have synergistic interactions during maize growth, and be useful in the formulation of new inoculants to improve the tropical cropping systems sustainability.

Microorganisms in biological control strategies to manage microbial plant pathogens: a review.

Chemical fertilizers and pesticides are an integral part of modern agriculture and are often associated with numerous environmental problems. Biological agents such as microorganisms can largely replace chemical fertilizers and pesticides. The proper use of selected microorganisms such as bacteria, fungi and viruses have several benefits for agriculture. These include a healthy soil microbiota, biological production of important compounds that promote plant health, and to be used as biocontrol agents (BCAs) that provide protection from plant pathogenic microorganisms. Scientists have found that several bacterial genera including Bacillus and Pseudomonas have antimicrobial activity against numerous pathogenic bacterial and fungal plant pathogens. Trichoderma, Aspergillus, and Penicillium are among the most common fungal genera used as BCAs against both bacterial and fungal plant pathogens. Several bacteriophages and mycoviruses are also found effective as BCAs against selective plant pathogens. Fusarium oxysporum is a commonly found microbial plant pathogen causing wilts and rots in plants. Overall, it can be concluded that the use of microbial BCAs is an effective practice against microbial plant pathogens.

Six novel Micromonospora species associated with the phyllosphere and roots of leguminous plants: Micromonospora alfalfae sp. nov., Micromonospora cabrerizensis sp. nov., Micromonospora foliorum sp. nov., Micromonospora hortensis sp. nov., Micromonospora salmantinae sp. nov., and Micromonospora trifolii sp. nov.

Six actinobacterial strains isolated from diverse legume tissues collected in various locations in Spain were characterized to determine their taxonomic status. Using 16S rRNA gene sequencing, the strains were primarily identified as members of the genus Micromonospora with more than 99 % similarity. Digital DNA-DNA hybridization values and average nucleotide identities between the six strains and the nearest type strains confirmed that each strain represented a novel species. Genome sequences were analysed to infer their metabolic profiles, their potential to produce secondary metabolites and plant growth promoting features. Chemotaxonomic and physiological studies were carried out to complete the phenotypic characterization and to distinguish the new Micromonospora species. The genomic and phenotypic characterization of the Micromonospora strains strongly support their classification as representatives of new species with the following names: Micromonospora alfalfae sp. nov., Micromonospora cabrerizensis sp. nov., Micromonospora foliorum sp. nov., Micromonospora hortensis sp. nov., Micromonospora salmantinae sp. nov. and Micromonospora trifolii sp. nov., with the type strains MED01T, LAH09T, PSH25T, NIE111T, PSH03T and NIE79T, respectively.

Shifts in the Rhizosphere and Endosphere Colonizing Bacterial Communities Under Drought and Salinity Stress as Affected by a Biofertilizer Consortium.

The present research asks how plant growth-promoting bacterial (PGPB) inoculants and chemical fertilizers change rhizosphere and root endophytic bacterial communities in durum wheat, and its dependence on environmental stress. A greenhouse experiment was carried out under drought (at 40% field capacity), or salinity (150 mM NaCl) conditions to investigate the effects of a chemical fertilizer (containing nitrogen, phosphorus, potassium and zinc) or a biofertilizer (a bacterial consortium of four PGPBs). High-throughput amplicon sequencing of the 16S rRNA of the rhizosphere, non-sterilized, or surface-sterilized roots, showed shifts in bacterial communities in response to stress treatments, which were greater for salinity than for drought and tended to show increased oligotrophs relative abundances compared to non-stress controls. The results also showed that Proteobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes, Thaumarchaeota, Firmicutes, and Verrucomicrobia had a higher relative abundance in the rhizosphere, while Actinobacteria were more abundant on roots, while Candidatus_Saccharibacteria and Planctomycetes inside roots. The results indicated that the root endophytic bacterial communities were more affected by (bio-) fertilization treatments than those in the rhizosphere, particularly as affected by PGPB inoculation. This greater susceptibility of endophytes to (bio-) fertilizers was associated with increased abundance of the 16S rRNA and acdS genes in plant roots, especially under stress conditions. These changes in root endophytes, which coincided with an improvement in grain yield and photosynthetic capacity of plants, may be considered as one of the mechanisms by which PGPB affect plants.

Bacteria isolated from Triticum monococcum ssp. monococcum roots can improve wheat hologenome in agriculture.

BACKGROUND: Triticum monococcum ssp. monococcum is an ancestral wheat species originated from Karacadag Mountain of Turkey more than ten thousand years ago. Because of environmental and anthropogenic effects, food supply and demand are not balanced. Agricultural activities such as breeding, and fertilization are important to sustain the balance. Conventional breeding and fertilization applications usually neglect contribution of plant related hologenomes in agricultural yield. The disruption of plant growth promoting microorganisms results in intensive usage of chemical fertilizers. The harmony between plant and plant-associated microorganisms is important for sustainability. In this study, isolation, biochemical characterization, and impact on plant growth parameters of natural bacteria associated with Triticum monococcum ssp. monococcum hologenome were aimed. METHODS AND RESULTS: The collection of root samples and isolations of the root-associated bacterial species were carried out from local wheat lands. According to interpretation of three identification methods (MALDI-TOF, 16S rDNA, 16S-23S rDNA) eight isolates are Arthrobacter spp. ESU164, Arthrobacter spp. ESU193, Pseudomonas spp. ESU131, Pseudomonas spp. ESU141, Pseudomonas poae strain ESU182, Pseudomonas thivervalensis strain ESU192, Pseudomonas spp. ESU1531, Bacillus subtilis strain ESU181. For each isolate we investigated biochemical properties especially nitrogen fixation, phosphate solubilization, and indole-3-acetic acid production abilities. The results show that all isolates are nitrogen fixers and the best phosphate solubilizer have been reported as Pseudomonas spp. ESU131 with 2.805 ± 0.439. CONCLUSIONS: All isolates are indole-3-acetic acid productors. 2 isolates affected the coleoptile lengths, 7 bacterial isolates showed statistically positive effect on root number, and 5 isolates promote the root lengths and the root fresh weights.

Identification of a plant endophytic growth-promoting bacteria capable of inhibiting cadmium uptake in rice.

AIMS: The study aims to identify a novel plant growth-promoting bacteria (PGPB), which contributes to promoting growth and reducing cadmium (Cd) concentration in rice under Cd-contaminated conditions. METHODS AND RESULTS: Nine bacterial strains were isolated from plants grown in Cd-contaminated soil. These bacteria were tolerant to 1000 µmol/L CdCl2 , capable of producing indole-3-acetic acid, fixing nitrogen and solubilizing phosphate. The result of hydroponic experiment showed that under the control and Cd stress conditions, the dry weight of the Tm02-inoculated rice seedlings increased significantly. Furthermore, under Cd stress, the concentration of Cd in the shoot of the Tm02-inoculated seedlings decreased significantly, while there was no significant difference in Cd concentration between treatment with other eight strains and noninoculated seedlings. The same results were observed in the pot experiment as well, where there was a significantly reduced Cd concentration in rice grains of the Tm02-inoculated rice plants. Tm02 was classified as Pantoea agglomerans through 16S rDNA sequencing. CONCLUSIONS: A novel PGPB strain Tm02 was identified and confirmed that it has the function of promoting rice growth and reducing Cd concentration in rice grain under Cd-contaminated conditions. This strain has the potential to improve rice yield in Cd-contaminated paddy fields. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides a new example of using PGPB to improve the tolerance of rice to Cd pollution.