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.

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.

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.

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.

Genomic, LC-MS, and FTIR Analysis of Plant Probiotic Potential of Bacillus albus for Managing Xanthomonas oryzae via Different Modes of Application in Rice (Oryza sativa L.).

Xanthomonas oryzae causes tremendous damage in rice plants (Oryza sativa L). Therefore, this study is focused on siderophore-producing Bacillus albus (CWTS 10) for managing BLB disease caused by X. oryzae. Both B. albus and its crude siderophore (methanolic and diethyl ether) extracts inhibited X. oryzae (10-12 mm). Fourier transform infrared spectroscopy (FTIR) analysis of the extracts indicated the presence of catecholate siderophore functional groups. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed the presence of antimicrobial compounds such as 2-deoxystreptamine, miserotoxin, fumitremorgin C, pipercide, pipernonaline, gingerone A, and deoxyvasicinone. Complete genome sequencing revealed the gene clusters for antibiotic, siderophore, antibacterial, antifungal, and secondary metabolite production. An in vivo study revealed that bacteria (CWTS 10) and their siderophore extracts effectively inhibited X. oryzae. The mode of application of bacterial or siderophore extracts in terms of DI and DSI percentage was as follows: soak method > inoculation method > spray method. In addition to providing enhanced antagonistic activity, there was a significant increase in root and shoot length and weight (wet and dry) of treated plants compared to control plants challenged with X. oryzae. Thus, the results clearly indicate that siderophore-producing B. albus and its siderophore extracts strongly inhibited X. oryzae. However, further field experiments are required before being formulated to protect rice crops from X. oryzae.

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.

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.

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.

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.

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.

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.

Secondary metabolites from methylotrophic bacteria: their role in improving plant growth under a stressed environment.

Climate change is considered a natural disaster that causes the ecosystem to fluctuate and increase temperature, as well as the amount of UV radiation (UV-A and UV-B) on the Earth's surface. Consequently, greenhouse gases such as chlorofluorocarbons, methane, nitrogen oxide, and carbon dioxide have become obstacles to the development of sustainable agriculture. To overcome environmental stress such as phytopathogens, drought, salinity, heavy metals, and high-low temperatures, the utilization of microorganisms is a viable option. The synthesis of secondary metabolites by methylotrophic bacteria improves plant metabolism, enhances tolerance, and facilitates growth. The genus Methylobacterium is a pink-pigmented facultative methylotrophs which abundantly colonizes plants, especially young leaves, owing to the availability of methanol. Secondary metabolites such as amino acids, carotenoids, hormones, antimicrobial compounds, and other compounds produced by methylotrophic bacteria enhance plant metabolism under stress conditions. Therefore, in this review, we discuss the role of secondary metabolites produced by methylotrophic bacteria and their role in promoting plant growth under stress.

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.

In silico analysis of Typha domingensis Pers. phytocompounds against wound healing biomarkers and ascertaining through in vitro cell migration assay.

Typha domingensis Pers. is known for its medicinal properties. Although traditionally T. domingensis Pers. has been used for wound healing, yet scientific investigations reporting its ability to heal wounds are lacking. Phytochemical profiling of T. domingensis Pers. inflorescence crude extract was carried out by LC-MS analysis. Ten phytochemicals were selected for in silico analysis based on retention time, mass-to-charge ratio and resolution of mass spectrum. Molecular docking of all ten compounds was done against selected wound healing biomarkers viz., interleukin 6(IL-6), interleukin ß (IL-ß), insulin-like growth factor tyrosine kinase receptor (IGF-1R) and transformation growth factor ß (TGF-ß). Based on this, catechin, mesalazine and piperazine were subjected for in vitro cell migration assay (3T3 L1 mouse fibroblast cell line) to assess their wound healing potentials. Molecular docking revealed that mesalazine, catechin, and piperazine have potential ligands based on lowest docking energy (ranging from - 4.1587 to - 0.972), Glide E score (ranging from - 26.929 to - 57.882), Glide G score (ranging from - 4.16 to - 7.972) and numbers of hydrogen bonds compared to other compounds studied. The migration assay revealed that, compared to control (52.5%), T. domingensis Pers. inflorescence crude extract showed maximum wound healing potential (80%) followed by Catechin (66.8%) Mesalazine (58.3%) and Piperazine (51.2%). The combined in silico and in vitro approach opens new dimension for designing innovative therapeutics to manage different types of wounds.

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.

Role of ACC deaminase producing bacteria for abiotic stress management and sustainable agriculture production.

Plants are immobile and are exposed to various biotic and abiotic stresses, including heat, cold, drought, flooding, nutrient deficiency, heavy metal exposure, phytopathogens, and pest attacks. The stressors significantly affect agricultural productivity when exceed a certain threshold. It has been reported that most of the stressed plants are reported to have increased ethylene synthesis from its precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Ethylene is a plant hormone that plays a vital role in the regulation of various physiological processes, such as respiration, nitrogen fixation, and photosynthesis. The increment in the plant hormone ethylene would reduce plant growth and development, and if the ethylene level increased beyond the limit, it could also result in plant death. Therefore, plant growth-promoting bacteria (PGPB) possessing ACC deaminase activity play an essential role in the management of biotic and abiotic stresses by hydrolysing 1-aminocyclopropane-1-carboxylic acid using ACC deaminase. In this review, the importance of ACC deaminase-producing bacteria in promoting plant growth under various abiotic stressors is discussed.

Predatory activity of Acanthamoeba sp genotype T4 on different plant growth-promoting bacteria and their combined effect on rice seedling growth.

Heterotrophic protists play a crucial role in plant growth promotion via nutrient cycling and shift in microbial community composition in the soil ecosystem. Selective predation pressure by protists contributes to the evaluation of plant beneficial traits in rhizospheric bacteria. However, not always all plant growth-promoting bacterial (PGPB) strains are benefitted by predation. This study aimed to examine the predatory effect of Acanthamoeba sp genotype T4 on a range of PGPB strains and their combined impact on early rice seedling growth. Acanthamoeba sp isolated from rice rhizosphere soils were used to assess predation against several PGPB such as Pseudomonas, Bacillus, Enterobacter, Morganella, Stenotrophomonas, Providencia, and Lysinibacillus on Nutrient Yeast Extract agar (NYE) plate. The controlled experiment on the germinated rice seeds (Oryza sativa L.) grown in Petri dishes containing each PGPB strain and Acanthamoeba sp was performed to evaluate the combined impact on plant performance. The PGPB-Acanthamoeba combined treatments in Petri dishes showed significant rice seedling growth compared to PGPB alone, non-PGPB and control. Our results indicated the positive but different impact of Acanthamoeba sp with different PGPB species on early rice plant growth. Further in-depth research should be carried out with diverse protists and PGPB species to assess which protist species can be linked to enhancement of indigenous soil PGPB for improved plant growth.

Effect of zinc-resistant Lysinibacillus species inoculation on growth, physiological properties, and zinc uptake in maize (Zea mays L.).

Soil contamination by heavy metals is one of the major abiotic stresses that cause retarded plant growth and low productivity. Among the heavy metals, excessive accumulations of zinc (Zn) cause toxicity to plants. The toxicity caused by Zn could be managed by application of Zn-tolerant plant growth-promoting (PGP) bacteria. In this study, five Zn-tolerant bacteria (100-400 mg-1 Zn resistant) were selected and identified as Lysinibacillus spp. based on 16S rRNA gene sequencing. The PGP properties of the Lysinibacillus spp. showed the production of indole acetic acid (60.0-84.0 µg/ml) and siderophore, as well as solubilization of potassium. Furthermore, the isolates were evaluated under greenhouse condition with 2 g kg-1 Zn stress and without Zn stress along with control on Zea mays. The results showed that Lysinibacillus spp. coated seeds enhanced plant growth attributes and biomass yield in both conditions compared with control plants. The enhancement of root growth ranged from 49.2 to 148.6% and shoot length from 83.3 to 111.7% under Zn-stressed soils. Also, the inoculated seedlings substantially enhanced chlorophyll a and b, proline, total phenol, and ascorbic acid. The uptake of Zn by maize root ranged from 31.5 to 210.0% compared with control plants. Therefore, this study suggested that the tested Zn-tolerant Lysinibacillus spp. may be used for cultivation of Z. mays in Zn-contaminated agricultural lands.

Isolation and characterization of Lactococcus garvieae from the fish gut for in vitro fermentation with carbohydrates from agro-industrial waste.

This study focused on agro-industrial waste such as fruit peels by extracting prebiotics as a carbon source for lactic acid bacteria (LAB). Four strains of LAB were selected from Oreochromis niloticus (B2 and B3) and Nemipterus japonicas (R4 and R5), and identified as Lactococcus garvieae through 16S rRNA gene sequencing. The analysis of probiotic characteristics revealed that all four strains were able to tolerate sodium chloride (up to 7 %), bile salt (up to 3 %), and broad range of pH (2-9). Further, analysis of polysaccharide contents in the agro-industrial waste materials such as peels of pineapple, orange, lemon, sugarcane, pomegranate, and sweet lemon revealed that the concentration ranged from 3.91-163.85 mg/g. It was observed that orange peels (20.38-140.99 mg/g), sweet lemon peels (22.03-161.93 mg/g), and pomegranate peels (38.19-163.85 mg/g) yielded maximum indigestible polysaccharide. Evaluation of synbiotic combination of probiotic and prebiotic revealed that L. garvieae strains had better fermentation efficiency with orange, sweet lemon, and pineapple compared to lemon, sugarcane, and pomegranate. In nutshell, different types of agro-industrial waste evaluated in this research were found to be a cheap and fermentable carbon sources for LAB. Further study should be conducted to analyze this symbiotic combination as feed supplements for fish in aquaculture as well as various fermentation industries.