Methylobacterium spp. mitigation of UV stress in mung bean (Vigna radiata L.).

Methylotrophs are a diverse group of bacteria that abundantly colonize the phyllosphere and have great potential to withstand UV irradiation because of their pigmented nature and ability to promote plant growth through various mechanisms. The present study investigated the effects of UVB radiation on plant growth-promoting (PGP) properties of methylotrophic bacteria and the growth of Vigna radiata L. A total of 55 methylotrophic bacteria were isolated from desert plants, and 15 methylotrophs were resistant to UVB radiation for 4 h. All UVB-resistant methylotrophs possess a methyldehydrogenase gene. Identification based on 16S rRNA gene sequencing revealed that all 15 UVB-resistant methylotrophs belonged to the genera Methylorubrum (07), Methylobacterium (07), and Rhodococcus (01). Screening of methylotrophs for PGP activity in the presence and absence of UVB radiation revealed that all isolates showed ACC deaminase activity and growth on a nitrogen-free medium. Furthermore, the production of IAA-like substances ranged from 8.62 to 85.76 µg/mL, siderophore production increased from 3.47 to 65.75% compared to the control. Seed germination assay with V. radiata L. (mung bean) exposed to UVB radiation revealed that methylotrophs improved seed germination, root length, and shoot length compared to the control. The present findings revealed that the isolates SD3, SD2, KD1, KD5, UK1, and UK3 reduced the deleterious effects of UVB radiation on mung bean plants and can be used to protect seedlings from UVB radiation for sustainable agriculture.

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.

Encapsulation of Pseudomonas aeruginosa strain KBN12 decolourizes and bioremediates brilliant blue dye mediated toxicity in mung bean (Vigna radiata L.).

AIM: The aim of this study was to explore the decolourization and bioremediation ability of non-encapsulated and encapsulated Pseudomonas aeruginosa (strain KBN 12) against the azo dye brilliant blue (BB). METHODS AND RESULTS: Six efficient BB dye-decolourizing bacteria were isolated from textile dye effluent. The most efficient free cells of P. aeruginosa KBN 12 along with the optimized conditions such as carbon source (maltose: 5 g L-1), and nitrogen source (ammonium chloride: 4 g L-1) at pH 6 at 37°C decolourized 72.69% of BB dye aerobically after 9 days of incubation under static conditions. Encapsulated (calcium alginate) P. aeruginosa KBN 12 decolourized 87.67% of BB dye aerobically after 9 days of incubation under the same optimized conditions. Fourier-transform infrared spectroscopy (FTIR) and gas chromatography (GC) analysis of the chemical structure of BB dye after decolourization found changes in functional and chemical groups. Phytotoxicity and soil respiration enzyme assays revealed that the decolourized dye or dye products were less toxic than the pure BB dye. CONCLUSION: The encapsulation of P. aeruginosa KBN 12 proved to be an effective method for BB dye decolourization or remediation.

Complete genome sequencing of Bacillus subtilis (CWTS 5), a siderophore-producing bacterium triggers antagonistic potential against Ralstonia solanacearum.

AIM: The aims of this study were to explore the antagonistic potential of siderophore-producing Bacillus subtilis (CWTS 5) for the suppression of Ralstonia solanacearum and to explore the mechanisms of inhibition by FTIR, LC-MS, and whole genome analysis. METHODS AND RESULTS: A siderophore-producing B. subtilis (CWTS 5) possessing several plant growth-promoting properties such as IAA and ACC deaminase production, phosphate solubilization, and nitrogen fixation was assessed for its inhibitory effect against R. solanacearum, and its mechanisms were explored by in vitro and in vivo analyses. The active secondary metabolites in the siderophore extracts were identified as 2-deoxystreptamine, miserotoxin, fumitremorgin C, pipercide, pipernonaline, gingerone A, and deoxyvasicinone by LC-MS analysis. The Arnow's test and antiSMASH analysis confirmed the presence of catecholate siderophores, and the functional groups determined by FTIR spectroscopy confirmed the presence of secondary metabolites in the siderophore extract possessing antagonistic effect. The complete genome sequence of CWTS 5 revealed the gene clusters responsible for siderophore, antibiotics, secondary metabolite production, and antibacterial and antifungal metabolites. Furthermore, the evaluation of CWTS 5 against R. solanacearum in pot studies demonstrated 40.0% reduced disease severity index (DSI) by CWTS 5, methanolic extract (DSI-26.6%), ethyl acetate extract (DSI-20.0%), and increased plant growth such as root and shoot length, wet weight and dry weight of Solanum lycopersicum L. owing to its antagonistic potential. This genomic insight will support future studies on the application of B. subtilis as a plant growth promoter and biocontrol agent against R. solanacearum for bacterial wilt management. CONCLUSION: The results of this study revealed that B. subtilis (CWTS 5) possesses multiple mechanisms that control R. solanacearum, reduce disease incidence, and improve S. lycopersicum growth.

Augmenting the bioavailability of iron in rice grains from field soils through the application of iron-solubilizing bacteria.

The biofortification approach has been widely used to enhance mineral nutrients in staple foods such as rice (Oryza sativa). In the present study, iron-solubilizing plant growth-promoting bacteria (PGPB) were evaluated for iron fortification of rice grains and NPK via field experiments. Inoculation of iron-solubilizing bacteria showed significant improvements in growth parameters, such as plant height, root and shoot dry weight, panicle length, grain yield, and nitrogen, potassium, phosphorus, and iron uptake. The mobilization of iron was ranged from 53.88% to 89.05% in rice grains compared to the uninoculated plants. The present study results revealed that application of PGPB strains is vital approach to combat the problem of iron deficiency in rice and subsequently in humans.

Zinc solubilizing Bacillus sp (SS9) and Enterobacter sp (SS7) promote mung bean (Vigna radiata L.) growth, nutrient uptake and physiological profiles.

Zinc (Zn) is a crucial micronutrient required for optimum plant growth. Zn-solubilizing bacteria (ZSB) are potential alternatives for Zn supplementation and convert applied inorganic Zn to available forms. In this study, ZSB were isolated from the root nodules of wild legumes. From a set of 17 bacteria, the isolates SS9 and SS7 were found to be efficient in tolerating 1 g (w/v) Zn. The isolates were identified as Bacillus sp (SS9, MW642183) and Enterobacter sp (SS7, MW624528) based on morphology and 16S rRNA gene sequencing. The screening of PGP bacterial properties revealed that both isolates possessed production of indole acetic acid (50.9 and 70.8 µgmL-1), siderophore (40.2% and 28.0%), and solubilization of phosphate and potassium. The pot study experiment in the presence and absence of Zn revealed that the Bacillus sp and Enterobacter sp inoculated plants showed enhanced mung bean plant growth (45.0% to 61.0% increment in shoot length and 26.9 to 30.9% in root length) and biomass compared to the control. The isolates also enhanced photosynthetic pigments such as total chlorophyll (1.5 to 6.0-fold) and carotenoids (0.5 to 3.0-fold) and 1-2-fold increase in Zn, phosphorous (P), and nitrogen (N) uptake compared to the Zn-stressed control. The present results indicated that the inoculation of Bacillus sp (SS9) and Enterobacter sp(SS7) reduced the toxicity of Zn and, in turn, enhanced the plant growth and mobilization of Zn, N, and P to the plant parts.

Assessment of copper (Cu) nanoparticle for their biocontrol activity against Xanthomonas oryzae pv. oryzae, growth promotion, and physiology of rice (Oryza sativa L.) plants.

Among the various biotic factors that disrupt crop yield, Xanthomonas oryzae pv oryzae (Xoo) is the most ruinous microbe of rice and causes bacterial leaf blight (BLB) disease. The present study focused on the utilization of copper nanoparticles (Cu-NPs) to control BLB. The copper nanosuspension (259.7 nm) prepared using Na-CMC, CuSO4·7H2O, and NaOH showed effectively inhibited Xoo (65.0 µg/ml). The performance of Cu-NPs in vivo showed enhanced plant attributes (127.9% root length and 53.9% shoot length) compared to the control and CuSO4 treated seedling. Furthermore, Cu-NPs treated seedlings showed 23.01% disease incidence (DI) compared to CuSO4 (85.71%) treated and control plants (91.83%). In addition to enhancing the growth parameters and reducing DI, seed priming with Cu-NPs improved the total chlorophyll content to 36.0% compared to the control. The assessment of antioxidant enzymes such as superoxide dismutase (1.9 U), polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase (two- to three-fold) in roots and shoots of rice plants revealed significant enhancement in Cu-NPs treated seedlings (P < 0.05). The present study suggests that Cu-NPs can be used to control Xoo and enhance rice growth.

Salt-tolerant bacteria enhance the growth of mung bean (Vigna radiata L.) and uptake of nutrients, and mobilize sodium ions under salt stress condition.

Salinity is one of the significant abiotic stresses that exert harmful effects on plant growth and crop production. It has been reported that the harmfulness of salinity can be mitigated by the use of salt-tolerant plant growth-promoting (PGP) bacteria. In this study, four bacteria were selected from a total of 30 cultures, based on salt-tolerant and PGP properties. The isolates were found to produce indole acetic acid (8.49-19.42 µg/ml), siderophore (36.04-61.77%), and solubilize potassium and inorganic phosphate. Identification based on 16S rRNA gene sequencing revealed that the isolates belonged to Cronobacter (two isolates) and Enterobacter (two isolates). Inoculation of PGP bacteria under 2 and 10% salinity stress showed enhanced plant growth parameters in Vigna radiata compared to both salinity and non-salinity control plants. The rate of germination (113.32-206.64%), root length (128.79-525.31%), shoot length (34.09-50.32%), fresh weight, and dry weight were 3-fold higher in bacteria-treated seeds than control plants. The estimation of chlorophyll (1-5-fold), carotenoids (1-4-fold), and proline content (3.65-14.45%) was also higher compared to control plants. Further, the bacterized seeds showed enhanced nitrogen and phosphorous uptake and mobilized sodium ions from roots to leaves. Overall the strains SS4 and SS5 performed well in both 2 and 10% salt-amended soils. These strains could be formulated as a bioinoculant to mitigate the salinity stress in salinized soils.

Salinity severely affects the growth and productivity of Vigna radiate (mung bean) worldwide. Approximately 50 mM concentration of NaCl can cause >60% yield loss of mung bean. In this study, inoculation of salt-tolerant root nodule-associated plant growth-promoting bacteria showed 2­3-fold enhancements in mung bean plant growth, biomass, and physiology even at 2 and 10% salinity stress. Further, the inoculated mung bean plants showed an increment in the uptake of nitrogen and phosphorous in the salinized conditions and mobilized the Na⁺ ions from root to shoot to reduce the toxicity posed by Na⁺ ions. Therefore the strains identified in this study could be formulated to mitigate the salinity stress and improve the mung bean growth in salinized soils.

Bacteria isolated from e-waste soil enhance plant growth and mobilize trace metals in e-waste-amended soils.

Worldwide accumulation of e-waste poses a major threat to environmental health. However, printed circuit boards contain precious metals, such as gold, and silver, and also contain micronutrient metal elements, such as Fe, Cu, Zn, etc. Therefore, the present study investigated the effects of e-waste-tolerant bacteria (ETB) on promoting plant growth in e-waste-amended soils and mobilizing trace metals into the plants. For this, a total of 18 bacteria were isolated and screened for e-waste tolerance. Screening for plant growth-promoting properties revealed the production of indole-3-acetic acid-like compounds, siderophore production, and phosphate solubilization. Identification based on 16S rRNA gene sequencing revealed that all isolates belonged to the genus Bacillus. Pot experiment revealed that the treated seeds showed the enhancement of chili plants root growth ranging from 106.55 to 208.07% compared to control plants (e-waste) and 0.0 to 47.90% (without e-waste). A similar enhancement was also observed in the shoot length, and size of the leaf compared to e-waste amended control plants. Inoculation of ETB significantly (p < 0.05) mobilized Fe, Zn, Cu, and Ni into chili plants. The identified ETB could be used to mitigate the toxicity posed by the e-waste, enhancing plant growth and mobilization of micronutrients into plants from e-waste.

Bacillus species identified in this study are the potential e-tolerant (PCB) PGP bacteria. Inoculation of e-tolerant bacteria resulted in increased plant growth attributes and biomass index in e-waste amended soil. Bacterial inoculation also showed maximum uptake of Cu, Fe, Zn, and Ni from the e-waste amended soil. This study demonstrated that micronutrients can be fortified/mobilized from e-waste using PGP bacteria.

Current status and future prospect of managing lead (Pb) stress through microbes for sustainable agriculture.

Soil is an important residence under various biotic and abiotic conditions. Contamination of soil by various means has hazardous effects on both plants and humans. Soil contamination by heavy metals occurs due to various man-made activities, including improper industrial and agricultural practices. Among the heavy metals, after arsenic, lead (Pb) was found to be the second most toxic metal and potent pollutants that accumulate in sediments and soils. Pb is not considered an essential element for promoting plant growth but is readily absorbed and accumulated in different plant parts. Many parameters such as pH, root exudation, soil particle size, cation exchange capacity, and other physicochemical parameters are involved in Pb uptake in plants. Excess amounts of Pb pose a threat to plant growth and cause toxicity such as chlorosis, blackening of the root system, and stunted growth. Pb toxicity may inhibit photosynthesis, disturb water balance and mineral nutrition, and alter the hormonal status, structure, and membrane permeability of plants. Therefore, this review addresses the effects of Pb toxicity and its impact on plant growth, including the morphological, physiological, and biological effects of Pb toxicity, the mechanisms behind different strategies promoting plant growth, and in combating Pb-induced stress. The bioremediation strategy for Pb removal from Pb-contaminated soil also plays an important role in combating Pb toxicity using bacterial community. Pb-contaminated soil may be remediated using different technologies such as rhizofiltration and phytoremediation, which tend to have a great capacity to curb Pb-contamination within the soil.

Interference of bio-control Trichoderma to enhance physical and physiological strength of sugarcane during Pokkah boeng infection.

Tremendous benefits have been derived from the use of fungicides but excessive use of chemical fungicides not only posing threat to human and animal life but also contaminates the prevailing environment. Damage by pathogenic fungi alone causes significant damage to crops like maize, rice, wheat, soybeans, and potatoes. Therefore, it becomes imperative that these diseases are checked and controlled, for which chemical pesticides are being sprayed on plants extensively. Considering the devastating damage and toxicity, the global focus has taken a drift from synthetic chemicals to nature-friendly biological control agents. The present study focuses on the use of biological control agents particularly Trichoderma in sugarcane during Pokkah boeng infection. In the present experiment, twenty promising Trichoderma strains were evaluated for plant growth promotion, lytic enzymes, and physiological and biocontrol activity. Out of the twenty, four potential Trichoderma strains were assessed in the pot experiment viz. T. harzianum strain T28, T41 and T49 and T. aureoviride strain T38. The T. harzianum (T28) showed efficient plant growth-promoting traits as it produced IAA (20.67 µg/ml), phosphorus solubilization (18.57 µg/ml), and cell wall degrading enzymes such as chitinase (24.98 µg/ml) and ß-glucanase (29.98 µg/ml). The interference of biocontrol agent T. harzianum (T28) controlled the disease by 73.55%. Apart from this, the inoculation of Trichoderma (T28) enhanced growth attributes including germination percentage (26.61%), mean tiller number (8.28 tiller/pot), individual cane length (241.5 cm), single cane weight (1.13 kg) and the number of milleable canes (6.00 cane/pot). Improvements in physiological activities at different growth stages of the sugarcane crop were observed based on the photosynthetically active radiation (PAR) on the leaf surface, transpiration rate, stomatal conductance, and photosynthetic rate. Further, improvement in juice quality parameters was also observed as it recorded the highest 0brix, sucrose, and commercial cane sugar by 21.26%, 19.28%, and 13.50%, respectively, by applying T. harzianum strain T28. Thus, results proved that T. harzianum strain T28 may be an effective eco-friendly biocontrol tool for managing Pokkah boeng disease in sugarcane. This is the first report of the biocontrol potential of Trichoderma spp. against Fusarium proliferatum causing Pokkah boeng disease in sugarcane.

Evaluation of biocontrol Bacillus species on plant growth promotion and systemic-induced resistant potential against bacterial and fungal wilt-causing pathogens.

Bacillus spp. have a wide range of activities in the biocontrol potential against various phytopathogens. This study focuses on the biocontrol potential of two species belonging to the same genera, as Bacillus subtilis (SSR2I) and Bacillus flexus (AIKDL) have contrasting activity under in vivo and in vitro conditions. In this study, two medicinal plants-associated bacteria showing antagonistic activity against wilt-causing pathogens were selected and identified as B. subtilis (SSR2I) and B. flexus (AIKDL) based on 16S rRNA gene sequencing. Crude extracts of these bacteria showed that chloroform extracts of AIKDL, and ethyl acetate extraction of SSR2I showed effective potential inhibition of both the wilt-causing pathogens in the well-diffusion method. PCR-based detection of antimicrobial peptide genes revealed the presence of five genes in B. subtilis and none in B. flexus. On the basis of in vivo analysis, the isolate SSR2I showed reduced disease incidence and enhanced biocontrol efficiency against Ralstonia solanacearum and Fusarium oxysporum compared with AIKDL and control plants. Further, the isolates SSR2I also enhanced the induced systemic resistance (ISR) against both the pathogens compared to the control. However, the isolate AIKDL showed enhanced ISR against F. oxysporum-treated plants, but not against R. solanacearum-treated plants. The results indicated that even though the isolates had strong antagonistic potential under in vitro conditions, their biocontrol efficiency differed in in vivo condition. On the basis of the overall performance, the isolate SSR2I could be formulated as biocontrol agents against both the wilt-causing pathogens tested in this study.

Amelioration effect of chromium-tolerant bacteria on growth, physiological properties and chromium mobilization in chickpea (Cicer arietinum) under chromium stress.

In this study, chromium (Cr)-tolerant bacteria were test for their efficiency in alleviating Cr stress in Cicer arietinum plants. On the basis of 16S rRNA gene analysis, the isolates were identified belonging to genus Stenotrophomonas maltophilia, Bacillus thuringiensis B. cereus, and B. subtilis. The strains produced a considerable amount of indole-3-acetic acid in a medium supplemented with tryptophan. The strains also showed siderophore production (S2VWR5 and S3VKR17), phosphorus production (S1VKR11, S3VKR2, S3VKR16, and S2VWR5), and potassium solubilization (S3VKR2, S2VWR5, and S3VKR17). Furthermore, the strains were evaluated in pot experiments to assess the growth promotion of C. arietinum in the presence of chromium salts. Bacterization improved higher root and shoot length considerably to 6.25%-60.41% and 11.3%-59.6% over the control. The plants also showed increase in their fresh weight and dry weight in response to inoculation with Cr-tolerant strains. The accumulation of Cr was higher in roots compared to shoots in both control and inoculated plants, indicating phytostabilization of Cr by C. arietinum. However, phytostabilization was found to be improved manifold in inoculated plants. Apart from the plant attributes, the amendment of soil with Cr and Cr-tolerant bacteria significantly increased the content of total chlorophyll and carotenoids, suggesting the inoculant's role in protecting plants from deleterious effects. This work suggests that the combined activity of Cr-tolerant and plant growth-promoting (PGP) properties of the tested strains could be exploited for bioremediation of Cr and to enhance the C. arietinum cultivation in Cr-contaminated soils.

Amelioration effect of salt-tolerant plant growth-promoting bacteria on growth and physiological properties of rice (Oryza sativa) under salt-stressed conditions.

For sustainable agriculture in saline soil, extensive exploitation of salt-tolerant plant growth-promoting (PGP) bacteria and other symbiotic bacteria is required. This study was carried out to evaluate the efficiency of native salt-tolerant rice rhizobacteria for plant growth promotion under salt stress. A total of 188 bacteria were screened for assessing salt-tolerant capacity and nine isolates tolerating 12% NaCl (w/v) concentration were selected. Biochemical and molecular identification revealed that the salt-tolerant bacteria belonged to Bacillus sp, Exiguobacterium sp, Enterobacter sp, Lysinibacillus sp, Stenotrophomonas sp, Microbacterium sp, and Achromobacter sp. The increase in NaCl concentration from 2 to 4% decreases the PGP activities such as IAA production, P solubilization, K solubilization, and nitrate reduction. The effects of inoculation of salt-tolerant bacteria on the growth and different physiological properties of rice (Oryza sativa) were studied. It was found that the salinity affected the root and shoot length of the control plants; however, bacterial inoculant were found to effectively promote the growth of paddy under salinity stress. Further, bacterial inoculants substantially enhanced total chlorophyll, proline, total phenol, and oxidative damage such as electrolyte leakage and membrane stability index under salt stress. This study suggests that salt-tolerant PGP bacteria may be used for cultivation of O. sativa in salinized agricultural lands.

Characterisation of antagonistic Bacillus paralicheniformis (strain EAL) by LC-MS, antimicrobial peptide genes, and ISR determinants.

Plants have their own defense mechanisms such as induced systemic resistance (ISR) and systemic-acquired resistance. Bacillus spp. are familiar biocontrol agents that trigger ISR against various phytopathogens by eliciting various metabolites and producing defense enzyme in the host plant. In this study, B. paralicheniformis (strain EAL) was isolated from the medicinal plant Enicostema axillare. Butanol extract of B. paralicheniformis showed potential antagonism against Fusarium oxysporum compared to control well (sterile distilled water) A liquid chromatography mass spectrometry analysis showed 80 different compounds. Among the 80 compounds, we selected citrulline, carnitine, and indole-3-ethanol based on mass-to-charge ratio, database difference, and resolution of mass spectrum. The synthetic form of the above compounds showed biocontrol activity against F. oxysporum under in vitro condition in combination, not as individual compounds. However, the PCR amplification of 11 antimicrobial peptide genes showed that none of the genes amplified in the strain. B. paralicheniformis inoculation challenged with F. oxysporum on tomato plants enhanced production of defense enzymes such as peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and proline compared to control plants (without inoculation of B. paralicheniformis) at significant level (p < 0.005). Stem of tomato plants expressed higher POD (2.2-fold), SOD (2.2-fold), PPO (1.9-fold), and PAL (1.3-fold) contents followed by the leaf and root. Elevated proline accumulation was observed in the leaf (1.8-fold) of tomato plants. Thus, results clearly showed potentiality of B. paralicheniformis (EAL) in activation of antioxidant defense enzyme against F. oxysporum-infected tomato plants and prevention of oxidative damage though hydroxyl radicals scavenging activities that suppress the occurrence of wilt diseases.

Effect of copper-resistant Stenotrophomonas maltophilia on maize (Zea mays) growth, physiological properties, and copper accumulation: potential for phytoremediation into biofortification.

In this study, Cu-tolerant PGP bacteria were isolated from the contaminated soils of Tapi (Surat, Gujarat, India). From a set of 118 bacteria isolated from the contaminated soil, the isolate RBTS7 was found to be efficient in tolerating 0.3 g (w/v) Cu. The isolate was identified as Stenotrophomonas maltophilia, based on biochemical and 16S rRNA gene sequencing. Further, the isolate was also found to produce indole acetic acid (140 µg/ml) and siderophore, and solubilize potassium. Inoculation study was carried out in the presence and absence of Cu in the greenhouse. The results revealed that S. maltophilia enhanced plant growth and biomasses compared to control. In addition to plant growth attributes, the isolate also enhanced chlorophyll a and b (434.1 and 496.7%) contents and antioxidant properties such as proline (168.2%), total phenolic compounds (33.5%), and ascorbic acid oxidase (62.3%) compared to control with Cu and without Cu. Inoculation of S. maltophilia + Cu enhanced the uptake of Cu in maize root (77.4%) and stem (112.0%) compared to Cu-stressed control. The results clearly indicated the inoculation of S. maltophilia reduced the toxicity of Cu and in turn enhanced the plant growth and mobilization of Cu to the plant parts.

Biocontrol and plant growth-promoting ability of plant-associated bacteria from tomato (Lycopersicum esculentum) under field condition.

Forty-five bacterial isolates recovered from surface-sterilized root, stem and leaf tissues of tomato were studied for their antifungal activity against phytopathogens, and plant growth-promoting (PGP) and biocontrol traits. Six plant-associated bacteria suppressed all the pathogens tested under in vitro plate assay and also shown PGP and biocontrol traits. The six isolates showing PGP and biocontrol properties were identified as Bacillus spp., based on the microbial identification system (Biolog) and partial sequence analysis of 16S rDNA. Two independent field trials were conducted with biocontrol bacteria along with chemical control (Thiram+Fytolan) and control (Without treatment). The averaged results of two field trails revealed that tomato plants inoculated with BETS11 (11.73 t/ha) and BETR11 (11.24 t/ha) strains showed significantly higher yield and disease reduction on par with chemical control (11.81 t/ha). However, there was an increase in the yield with respect to uninoculated control except the isolate BETS5 (9.09 t/ha). Therefore, the isolates BETS11 and BETR11 may be used as efficient biofertilizer and bio-control agent for tomato production in the Island agricultural ecosystem.

Influence of salt tolerant Trichoderma spp. on growth of maize (Zea mays) under different salinity conditions.

In the present study, a total of 70 Trichoderma spp. were isolated from the rhizosphere soils of vegetable and spice crops that were grown in Andaman and Nicobar Islands, India. Initial screening of Trichoderma spp. for salt tolerant properties showed 32 isolates were able to tolerate 10% NaCl. Furthermore, these isolates were screened for their potential plant growth-promoting characteristics such as IAA production, phosphate solubilization, and siderophore production. Among 32 isolates, nine isolates were able to produce IAA, siderophore, and solubilize phosphate. Jar trial was carried out on maize under axenic conditions at 1.67, 6.25, 11.25, 17.2, and 22.9 dS m-1 salt stress using the best nine isolates. Three isolates (TRC3, NRT2, and THB3) were effective in improving germination percentage, reducing reduction percentage of germination (RPG) and also in increasing the shoot and root length under axenic conditions. These three isolates were further tested under pot trial at 52 (sea water), 27, 15, 7, and 1.67 dS m-1 . TRC3 was found to be the most effective isolate compared to the other isolates and significantly increased the physiological parameters like shoot, root length, leaf area, total biomass, and stem and leaf fresh weight at all stress levels. Similarly, total chlorophyll content also increased by TRC3 over control. All three isolates, NRT2, TRC3, and THB3 showed lower accumulation of malondialdehyde (MDA) content whereas, proline and phenol content were higher than the uninoculated control plants under both normal and saline conditions. The results suggest that these isolates could be utilized for the alleviation of salinity stress in maize.

Siderophore-producing bacteria mitigate cobalt stress in black gram (Vigna mungo L.), and the mitigation strategies are associated with iron concentration.

Cobalt (Co) is considered an essential element in agriculture as it is an important constituent of vitamin B12. Due to natural and anthropogenic factors, heavy metals, especially Co, accumulate in agricultural fields, but their high exposure produces ramifications in crop plants, thereby reducing crop yield and biomass. Excessive Co in plants causes oxidative stress, and as the stress progresses, Co competes with iron (Fe) thereby decreasing chlorophyll content and resulting in Fe deficiency in plants. A major concern is to counter the Co toxicity. Therefore, the current study aimed to mitigate Co-stress or Co-toxicity by using siderophore producing microbes and simultaneously mobilize Co and iron (Fe) in required amounts. In this study, 250 bacteria were isolated from agricultural and non-agricultural soils and screened for siderophore production. Initial siderophore screening revealed that 28.8% of the isolates produced siderophore. Subsequent screening for Co-tolerance showed that 16 isolates were tolerant to up to 20,000 ppm of Co and produced ACC deaminase, siderophore (96.82-99.67%), indole-3-acetic acid (15.15-70.55 µg/mL) and phosphate solubilisation (39.33-142.67 µg/mL). A plate assay (200 mM Co stress) revealed that four isolates (KSBTS 12, SBTS 12, CWTS 5 and CWTS 10) enhanced the growth of black gram (Vigna mungo L.). Furthermore, evaluation in pot studies (2000 ppm Co stress) revealed enhanced root (60.69-174.24%) and shoot length (3.27-143.96%) compared to the control. Inoculated plants also enhanced the uptake of nitrogen (37.33-42.36 mg/g) and phosphorous (3.12-3.92 mg/g), chlorophyll content (7.60-22.97 mg/g), siderophore quantity in the soils (282.41-331.53%) and the soil respiration activity such as hydrolysis of fluorescein diacetate (11.33-24.88 µg/g), dehydrogenase enzyme (109.76-197.26 µg/g) and alkaline phosphatase (631.53-918.20 µg/g). In conclusion, CWTS 5 (Bacillus subtilis) and CWTS 10 (Bacillus albus) can be used to mitigate Co-stress and mobilize Co and Fe in plants.

Microbial volatile compounds (MVCs): an eco-friendly tool to manage abiotic stress in plants.

Microbial volatile compounds (MVCs) are produced during the metabolism of microorganisms, are widely distributed in nature, and have significant applications in various fields. To date, several MVCs have been identified. Microbial groups such as bacteria and fungi release many organic and inorganic volatile compounds. They are typically small odorous compounds with low molecular masses, low boiling points, and lipophilic moieties with high vapor pressures. The physicochemical properties of MVCs help them to diffuse more readily in nature and allow dispersal to a more profound distance than other microbial non-volatile metabolites. In natural environments, plants communicate with several microorganisms and respond differently to MVCs. Here, we review the following points: (1) MVCs produced by various microbes including bacteria, fungi, viruses, yeasts, and algae; (2) How MVCs are effective, simple, efficient, and can modulate plant growth and developmental processes; and (3) how MVCs improve photosynthesis and increase plant resistance to various abiotic stressors.