Indole Acetic Acid Production Research Articles

Mitigation of Salinity Stress on Soybean Seedlings Using Indole Acetic Acid-Producing Acinetobacter pittii YNA40

Soybean is an important oil crop with multiple uses. Soybeans can grow in various soil types and climates; however, salt stress reduces their yield. Plant growth-promoting microorganisms are an environmentally benign way to combat stress and boost plant tolerance. In the present study, we have identified plant growth-promoting bacteria that can produce indole acetic acid (IAA) and induce distinct growth characteristics in soybean plants under salt stress. The YNA40 isolate was identified as Acinetobacter pittii through 16S rRNA sequencing and phylogenetic analysis. A pure culture of Acinetobacter pittii YNA40 was subjected to chromatographic and mass spectrometry selected-ion monitoring (GC-MS/SIM) for IAA quantification. The results revealed that the YNA40 bacterial strain showed a significantly higher IAA concentration (473.88 ng/mL) at 4% sodium chloride (NaCl). Moreover, in a salt-stress condition, inoculation with Acinetobacter pittii YNA40 was able to induce increased shoot length (23.48%), shoot weight (24%), root length (2.47%), and root weight (44.82%) compared to the uninoculated control. Therefore, soybean seedlings were inoculated with YNA40 to examine their potential for promoting growth and reprogramming after salt stress. Inoculation with YNA40 isolates mitigated the salt stress and significantly improved the growth of the plant, enhanced the chlorophyll contents, and improved the quantum efficiency of chlorophyll fluorescence, total phenolic content, flavonoid content, the diphenyl-1-picrylhydrazyl (DPPH) activity, and antioxidant activities of soybean plants during and after salt stress. The present research demonstrated that the application of the YNA40 isolate is promising for reducing salt stress in soybean plants and helps plants grow better in a salt-stressed environment.

Plant-beneficial Streptomyces dioscori SF1 potential biocontrol and plant growth promotion in saline soil within the arid and semi-arid areas.

Environmental challenges like salinity, drought, fungal phytopathogens, and pesticides directly or/and indirectly influence the environment and agricultural yields. Certain beneficial endophytic Streptomyces sp. can ameliorate environmental stresses and be utilized as crop growth promoters under adverse conditions. Herein, Streptomyces dioscori SF1 (SF1) isolated from seeds of Glycyrrhiza uralensis tolerated fungal phytopathogens and abiotic stresses (drought, salt, and acid base). Strain SF1 showed multifarious plant growth promotion characteristics, including the production of indole acetic acid (IAA), ammonia, siderophores, ACC deaminase, extracellular enzymes, the ability of potassium solubilization, and nitrogen fixation. The dual plate assay showed that strain SF1 inhibited 63.21 ± 1.53%, 64.84 ± 1.35%, and 74.19 ± 2.88% of Rhizoctonia solani, Fusarium acuminatum, and Sclerotinia sclerotiorum, respectively. The detached root assays showed that strain SF1 significantly reduced the number of rotten sliced roots, and the biological control effect on sliced roots of Angelica sinensis, Astragalus membranaceus, and Codonopsis pilosula was 93.33%, 86.67%, and 73.33%, respectively. Furthermore, the strain SF1 significantly increased the growth parameters and biochemical indicators of adversity in G. uralensis seedlings under drought and/or salt conditions, including radicle length and diameter, hypocotyl length and diameter, dry weight, seedling vigor index, antioxidant enzyme activity, and non-enzymatic antioxidant content. In conclusion, the strain SF1 can be used to develop environmental protection biological control agents, improve the anti-disease activity of plants, and promote plant growth in salinity soil within arid and semi-arid regions.

Optimization of Indole-3-acetic acid production by Bacillus velezensis isolated from Pyrus rhizosphere and its effect on plant growth

Indole-3-acetic acid (IAA) is an important plant growth promoting hormone produced as secondary metabolite by many microorganisms. The current study aims to optimize conditions for IAA production by a rhizobacterial isolate and evaluation of its effect on plant growth. Seven bacterial isolated were purified from the rhizosphere of pear-tree and screened for IAA production and optimum production medium. The most potent bacterial isolate (S5) was selected for further investigations and molecularly identified using (16S rRNA). The selected isolate was identified as Bacillus velezensis strain MOST-IAA and given the accession number (ON792392.1) in National Center for Biotechnology Information (NCBI). For maximum IAA productivity, twenty one nutritional factors were screened for their significance on IAA using Placket Burman design and the significant factors were used for statistical modeling of the production conditions using Box-Behnken design. The produced model and optimization resulted in maximum IAA (56.60 μg/ml) at: 4.41 g/l, D(+) mannose; 8.66 g/l, mannitol; 0.93 g/l, tryptophan; 5.88 g/l, potassium nitrate; 1.29 g/l, ammonium chloride; 28.5 °C, temperature and 7.69, initial pH with correlation of 94.76% to the theoretical results. The produced IAA has been extracted and used in irrigation of barley seed for 10 days. Data showed significant differences among the test and control barley, especially in the length of the produced roots. Bacillus velezensis can be used to increase the soil fertility or biotechnologically used for production of IAA to be applied for plant growth improvement.

Lysinibacillus spp.: an IAA-producing endospore forming-bacteria that promotes plant growth

Lysinibacillus is a bacterial genus that has generated recent interest for its biotechnological potential in agriculture. Strains belonging to this group are recognized for their mosquitocidal and bioremediation activity. However, in recent years some reports indicate its importance as plant growth promoting rhizobacteria (PGPR). This research sought to provide evidence of the PGP activity of Lysinibacillus spp. and the role of the indole-3-acetic acid (IAA) production associated with this activity. Twelve Lysinibacillus spp. strains were evaluated under greenhouse conditions, six of which increased the biomass and root architecture of corn plants. In most cases, growth stimulation was evident at 108 CFU/mL inoculum concentration. All strains produced IAA with high variation between them (20–70 µg/mL). The bioinformatic identification of predicted genes associated with IAA production allowed the detection of the indole pyruvic acid pathway to synthesize IAA in all strains; additionally, genes for a tryptamine pathway were detected in two strains. Extracellular filtrates from all strain’s cultures increased the corn coleoptile length in an IAA-similar concentration pattern, which demonstrates the filtrates had an auxin-like effect on plant tissue. Five of the six strains that previously showed PGPR activity in corn also promoted the growth of Arabidopsis thaliana (col 0). These strains induced changes in root architecture of Arabidopsis mutant plants (aux1-7/axr4-2), the partial reversion of mutant phenotype indicated the role of IAA on plant growth. This work provided solid evidence of the association of Lysinibacillus spp. IAA production with their PGP activity, which constitutes a new approach for this genus. These elements contribute to the biotechnological exploration of this bacterial genus for agricultural biotechnology.

Studies on Isolation of Plant Growth Promoting Azotobacter spp from Soil Samples

Soil is the heterogeneous mixture of different kinds of microorganisms. Soil provides nutritive environment for the growth of microorganisms. One of the soil microbes is Azotobacter. The aim of present study was to isolate plant growth promoting Azotobacter spp. In the present study, 25 soil samples were collected from different locations of Akola and Akot region. In the study, 10 Azotobacter spp. were isolated. Azotobacter spp. was checked for phosphate solubilizing ability, stress tolerance (Temperature, pH, Salt), Nitrate Reduction, Cyst formation by using Burks medium and Indole Acetic Acid production using L- Tryptophan. Amongst the 10 isolates all were found to reduced nitrate, NH3 formation ability and IAA production, while two isolates H3 and C5 were only found to be have phosphate solubilizing ability. The seed germination test was also performed, Azotobacter showed promising results on the moth beans. The result reveals that Azotobacter could be a better source for crop improvement and soil fertility over the use of chemical fertilizers.

EXPLORING THE PLANT GROWTH PROMOTION AND ANTAGONISTIC PROPERTIES OF LACTIC ACID BACTERIA: A COMPREHENSIVE STUDY

Lactic acid bacteria (LAB) are known for their various beneficial properties, including plant growth promotion and antagonistic effects against plant pathogens. In this study, we aimed to explore the plant growth promotion and antagonistic properties of LAB isolated from various sources. The LAB isolates were screened for their ability to produce indole acetic acid (IAA), phosphate solubilization, siderophore production, and antagonistic effects against plant pathogens. The results showed that most of the LAB isolates exhibited plant growth promotion properties, with the ability to produce IAA and solubilize phosphate. Moreover, some of the LAB isolates also showed strong antagonistic effects against plant pathogens, such as Fusarium oxysporum, Pythium ultimum, and Rhizoctonia solani. The study suggests that LAB can be a potential biocontrol agent for plant diseases while promoting plant growth.

Functional characterization and molecular fingerprinting of potential phosphate solubilizing bacterial candidates from Shisham rhizosphere

Phosphate solubilizing bacteria (PSB) are important role players in plant growth promotion. In the present study, we aimed to screen the functionally active phosphate solubilizing bacteria (PSB) associated with Dalbergia sissoo Roxb. (Shisham) from different provenances. Screening for phosphate solubilization was done on Pikovskaya's agar, and 18 bacteria positive for the tri-calcium phosphate (Ca3(PO4)2 solubilization showing visible dissolution halo zones were identified. All 18 isolates showed zinc solubilization, indole acetic acid (IAA), siderophore, and hydrogen cyanide (HCN) production. The morphological and biochemical characterization with 16S rDNA gene-based phylogenetic analysis identified bacterial strains as belonging to the genus Pseudomonas, Klebsiella, Streptomyces, Pantoea, Kitasatospora, Micrococcus, and Staphylococcus. Among all the isolates, one of the isolates named L4, from Lacchiwala region was the most efficient P solubilizer with a high P solubilization index (4.75 ± 0.06) and quantitative P solubilization activity (891.38 ± 18.55 μg mL−1). The validation of phosphate solubilization activity of PSB isolates was done by amplification of the Pyrroloquinoline quinone (PQQ) genes, pqqA and pqqC. Based on this study, we have selected the bacterial strains which are efficient phosphate solubilizers and could be economical and eco-friendly in plant growth promotion, disease suppression, as an antioxidant, and for subsequent enhancement of yield.

Rhizobacteria Bacillus spp. enhance growth, influence root architecture, physiological attributes and canopy temperature of mustard under thermal stress

In arid and semi-arid regions, high temperature stress is one of the most common abiotic stresses affecting plant growth and development, as well as agricultural output. Growth and establishment of mustard, an important oilseed crop, is affected due to increased incidences of higher-than-normal temperatures during sowing of the crop. In the present study, we screened rhizobacterial isolates for their thermotolerance. Under high temperature stress, three thermotolerant rhizobacterial cultures were assessed for their plant growth promoting activities. There was beneficial effect of high temperature on their indole acetic acid and gibberellic acid production abilities. A pot experiment was conducted to evaluate the effect of the three rhizobacterial strains on mustard growth under high temperature stress. Inoculation with the rhizobacteria significantly improved plant biomass, root architecture and physiological attributes – relative water content, membrane stability index and chlorophyll content. There were lowering of hydrogen peroxide content and lipid peroxidation. Increased total leaf area and lowering of canopy temperature was observed in the inoculated plants, under high temperature. Significant positive correlation was observed between plant biometric traits and most of the physiological attributes, while negative correlation was observed with lipid peroxidation and hydrogen peroxide content. Under both no stress and high temperature stress, response to inoculation with Bacillus sp. strain MRD-17 was markedly more than the other rhizobacterial strains. Thus, these rhizobacteria were able to enhance thermotolerance of mustard during early stages of growth. As a result, thermotolerant rhizobacteria with plant growth-promoting activity can be utilized to alleviate high temperature stress in crops.

Taxonomic, metabolic traits and species description of aromatic compound degrading Indian soil bacterium Pseudomonas bharatica CSV86T

A soil bacterium, strain CSV86T isolated from a petrol station in Bangalore, India displays a unique carbon source utilization hierarchy with preferential utilization of various genotoxic aromatic compounds over glucose. Cells were Gram-negative, motile rods, oxidase- and catalase-positive. Strain CSV86T possess a 6.79 Mb genome with 62.72 G + C mol%. 16S rRNA gene phylogeny relates strain CSV86T to the genus Pseudomonas, with highest similarity to Pseudomonas japonica WLT (99.38%). Multi-locus sequence analyses of gyrB-rpoB-rpoD-recA and 33 ribosomal proteins (rps) displayed overall low similarities to its phylogenetic relatives with poor similarity score (6%). Average nucleotide identity (ANI) and in-silico DNA-DNA hybridization (DDH) showed poor (87.11% and 33.2%, respectively) genomic relatedness of strain CSV86T to its closest relatives, indicating genomic distinctiveness. The major cellular fatty acids were 16:0, 17:0cyclo, summed-feature-3 (16:1ω7c/16:1ω6c) and −8 (18:1ω7c). Further, differential abundance of 12:0, 10:0 3-OH and 12:0 3-OH and phenotypic differences distinguished strain CSV86T from closest relatives, hence designated as Pseudomonas bharatica. The unique aromatic degradation ability, resistance to heavy metals, efficient nitrogen-sulfur assimilation, beneficial eco-physiological traits (production of indole acetic acid, siderophore and fusaric acid efflux) and plasmid-free genome suggest strain CSV86T to be a model organism for bioremediation and ideal host for metabolic engineering.

Isolation and characterization of halotolerant plant growth promoting rhizobacteria from mangrove region of Sundarbans, India for enhanced crop productivity.

Halotolerant plant growth promoting rhizobacteria (PGPR) are beneficial microorganisms utilized to mitigate the biotic and abiotic stresses in plants. The areas of Sundarban mangroves of West Bengal, India have been reported to be rich in halotolerant microflora, yet major area remains unexplored. The present study, therefore, aims to map down the region-specific native microbial community potent of salt tolerance, plant growth promoting (PGP) activity and antagonistic activity against fungal pathogens. Bacterial samples were isolated from the saline soil of the Sundarban mangroves. A total of 156 bacterial samples were isolated and 20 were screened for their salt tolerance potential. These isolates were characterised using morphological, biochemical, and molecular approaches. Based on 16s rRNA sequencing, they were classified into 4 different genera, including Arthrobacter sp. (01 isolate), Pseudomonas plecoglossicida (01 isolate), Kocuria rosea (01 isolate), and Bacillus (17 isolates). The halotolerant isolates which possessed plant growth promoting traits including phosphate, and zinc solubilization, indole acetic acid production, siderophore, and ammonia generation were selected. Further, the effect of two halotolerant isolates GN-5 and JR-12 which showed most prominent PGP activities was evaluated in pea plant under high salinity conditions. The isolates improved survival by promoting germination (36 to 43%) and root-shoot growth and weight of pea plant in comparison to non-inoculated control plants. In a subsequent dual culture confrontation experiment, both these halo-tolerant isolates showed antagonistic activities against the aggressive root rot disease-causing Macrophomina phaseolina (Tassi) Goid NAIMCC-F-02902. The identified isolates could be used as potential bioagents for saline soils, with potential antagonistic effect on root rot disease. However, further studies at the physiological and molecular level would help to delineate a detail mechanistic understanding of broad-spectrum defence against salinity and potential biotic pathogen.

Plant Growth-promoting Ability and Pathogen Inhibitory Effect of Actinomycetes Isolated from Fecal Pellets of the Giant Millipede Thyropygus resimus (Diplopoda)

The microbial properties of millipede fecal pellets have been studied mainly in Glomerida (pill millipedes), and much less in the significant majority of other millipede groups. Therefore, the present study examined actinomycetes isolated from the fecal pellets of the non-glomerid giant millipede Thyropygus resimus Attems, 1938 (Spirostreptida) to (1) test their plant growth-promoting ability, and (2) evaluate their potential to control and inhibit plant pathogenic microorganisms. Millipedes were collected from Phu Kum Khao, Kalasin Province, Thailand. A total of 59 actinomycete isolates were obtained and identified as belonging to the genus Streptomyces using 16S rRNA sequencing. The plant growth-promoting properties of the isolates were tested by screening four characteristics: nitrogen fixation, phosphate solubility, siderophore production, and indole-3-acetic acid (IAA) production. A nitrogen-fixation test on nitrogen-free solid malate media (NFM) showed that 54 isolates were capable of fixing nitrogen. Phosphate solubility was tested on double-layered glucose yeast extract agar (GYA) medium containing tricalcium phosphate. This showed that 42 isolates formed a clear zone around the colonies due to phosphate dissolution. Siderophore production was tested on chrome azurol sulfate (CAS) agar. This showed that 55 isolates could grow on this medium and form clear yellow to orange zones around their colonies. IAA production tests revealed that 41 isolates could produce IAA. Based on the combined results of these four tests, eight of the 59 isolates were the most effective in promoting plant growth: KLS-AC04, KLD-AC01, KLD-AC02-1, KLD-AC08, KLD-AC09, KLD-AC16, KLD-AC29-1, and KLD-AC30. Seventeen isolates inhibited the growth of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight disease in rice, more effectively than rifampicin (100 ppm), with isolate KLS-AC02-1-1 being the most effective (inhibition zone, 58.25 mm in diameter). Therefore, these isolates can be used for growth promotion and rice disease control in the future.

Penicillium citrinum, a Drought-Tolerant Endophytic Fungus Isolated from Wheat (Triticum aestivum L.) Leaves with Plant Growth-Promoting Abilities.

Endophytic fungi have recently garnered significant attention as next-generation bioinoculants due to their plausible role in ameliorating abiotic and biotic stresses. This adaptation is achieved via various signalling molecules and mechanisms established by these symbionts with their hosts. The present study screened 61 endophytic isolates of culturable mycobiome associated with wheat variety PBW725 during their crop cycle. Three endophytic isolates exhibited a minimum reduction in their growth and maximum biomass production during the drought stress developed using polyethylene glycol 6000. Further, these isolates also exhibited plant growth promoting properties by virtue of the production of indole acetic acid, gibberellic acid and ammonia. These isolates also exhibited the propensity to solubilise phosphate and zinc, produce siderophores and further exhibit extracellular enzymatic activities, contributing to plants' adaptability to abiotic stresses. The best isolate amongst the three was #5TAKL-3a, identified as Penicillium citrinum based on multilocus phylogenetic analysis. The isolate as a bioinoculant enhances various biochemical and physiological properties in planta. Hence our studies indicate that Penicillium citrinum #5TAKL-3a is a potential candidate bioinoculant for field trials to improve the adaptability of the wheat plant under drought stress.

Antagonistic bacteria against Fusarium spp. isolated from sclerotia of Claviceps gigantea in maize (Zea mays)

Fungal sclerotia house native bacterial populations of interest for biological control of plant pathogenic fungi. The objectives of this research were: i) to explore the bacterial populations associated with Claviceps gigantea sclerotia in maize from six locations in the State of Mexico, ii) to evaluate the in vitro antagonism of these bacterial populations against three species of Fusarium phytopathogens of maize, iii) to molecularly identify the more efficient antagonists and characterize the in vitro production of metabolites. Bacterial populations in the sclerotia were calculated by direct plate count; in vitro antagonism against Fusarium graminearum, F. sublgutinans, and F. verticillioides was evaluated by confrontation in Waksman agar medium. Antagonistic bacteria were identified by partial sequencing of 16S rRNA gene and evaluated in vitro for the production of indole-3 acetic acid, siderophores, lipolytic and proteolytic activity, and mineral phosphate solubilization. The bacterial density ranged from 2.023 to 2.397 Log10UFC g-1 of sclerotia. Twenty-two strains showed in vitro antagonism against at least one Fusarium species and were identified as members of the genera Bacillus, Delftia, Micromonospora, Pseudomonas, Sphingobacterium, Staphylococcus, and Stenotrophomonas. The 22 antagonists showed in vitro lipolytic, proteolytic, siderophore-producing and phosphate-solubilizing activity; only 12 (55%) produced indole-3-acetic acid. Bacillus subtilis (BA1), Pseudomonas syringae (BA2), and Bacillus amyloliquefaciens (BA18) strains were antagonists against the three Fusarium species and produced all the metabolites evaluated.

Bioprospeksi Bakteri Asal Akar Nanas (Ananas comosus L. Merr) Lahan Gambut Kayu Agung, Sumatra Selatan, sebagai Agen Biostimulan dan Bioprotektan

Pineapple (Ananas comosus L. Merr) is a plant that can live well on nutrient-poor lands such as peatlands. However, plant resistance to nutrient-poor conditions is caused by symbiosis with endophytic bacteria capable of plant growth-promoting bacteria (PGPB) through biostimulant and bioprotective mechanisms. This study aims to characterize the potential of endophytic bacteria from pineapple roots from peatlands as biostimulants and bioprotective agents. Thirteen endophytic bacteria from pineapple root were characterized by their ability as biostimulants through phosphate dissolution tests using Pikovskaya media qualitatively and quantitatively, and the production of indole-3-acetic acid (IAA) upon additional 0.1% tryptophan. Furthermore, bacteria as bioprotectors were characterized by qualitative production of chitinase enzyme and antifungal tests against Fusarium proliferatum using dual culture techniques. The results showed the presence of 2 positive bacteria in all tests, namely the ANAP3 and ANAP5 isolates. ANPA3 bacteria show the highest activity in IAA production (26.3 ppm), and the highest antifungal activity in inhibiting F. proliferatum, with an inhibitory index reaching 52.6%. Meanwhile, ANAP5 is an endophytic bacterium with the highest phosphate dissolving activity, with a dissolved phosphate value of 253.5 ppm. This finding shows that some endophytic bacteria from pineapple roots on peatlands can be biostimulants and bioprotectors that can be developed as PGPB.
 
 Keywords: Ananas comosus L. Merr, endophytic bacteria, bioprotectant, biostimulant, Fusarium proliferatum

Exploring potential soybean bradyrhizobia from high trehalose-accumulating soybean genotypes for improved symbiotic effectiveness in soybean.

Drought is the most important factor limiting the activity of rhizobia during N-fixation and plant growth. In the present study, we isolated Bradyrhizobium spp. from root nodules of higher trehalose-accumulating soybean genotypes and examined for moisture stress tolerance on a gradient of polyethylene glycol (PEG 6000) amended in yeast extract mannitol (YEM) broth. In addition, the bradyrhizobial strains were also evaluated for symbiotic effectiveness on soybean. Based on 16S rDNA gene sequences, four bradyrhizobial species were recovered from high trehalose-accumulating genotypes, i.e., two Bradyrhizobium liaoningense strains (accession number KX230053, KX230054) from EC 538828 and PK-472, respectively, one Bradyrhizobium daqingense (accession number KX230052) from PK-472, and one Bradyrhizobium kavangense (accession number MN197775) from Valder genotype having low trehalose. These strains, along with two native strains, viz., Bradyrhizobium japonicum (JF792425), Bradyrhizobium liaoningense (JF792426), and one commercial rhizobium, were studied for nodulation, leghaemoglobin, and N-fixation abilities on soybean under sterilized sand microcosm conditions in a completely randomized design. Among all the strains, D-4A (B. daqingense) followed by D-4B (B. liaoningense) was found to have significantly higher nodulation traits and acetylene reduction assay (ARA) activity when compared to other strains and commercial rhizobia. The bradyrhizobia isolates showed plant growth promotion traits such as indole acetic acid (IAA), exopolysaccharide (EPS), and siderophore production, phosphate-solubilizing potential, and proline accumulation. The novel species B. daqingense was reported for the first time from Indian soil and observed to be a potential candidate strain and should be evaluated for conferring drought tolerance in soybean under simulated stress conditions.

Performance of Plant-Growth-Promoting Rhizobacteria (PGPR) Isolated from Sandy Soil on Growth of Tomato (Solanum lycopersicum L.).

The plant-growth-promoting rhizobacteria (PGPR) in the rhizosphere affect plant growth, health, and productivity, as well as soil-nutrient contents. They are considered a green and eco-friendly technology that will reduce chemical-fertilizer usage, thereby reducing production costs and protecting the environment. Out of 58 bacterial strains isolated in Qassim, Saudi Arabia, four strains were identified by the 16S rRNA as the Streptomyces cinereoruber strain P6-4, Priestia megaterium strain P12, Rossellomorea aquimaris strain P22-2, and Pseudomonas plecoglossicida strain P24. The plant-growth-promoting (PGP) features of the identified bacteria involving inorganic phosphate (P) solubilization, the production of indole acetic acid (IAA), and siderophore secretion were assessed in vitro. Regarding the P solubilization, the previous strains' efficacy reached 37.71%, 52.84%, 94.31%, and 64.20%, respectively. The strains produced considerable amounts of IAA (69.82, 251.70, 236.57, and 101.94 µg/mL) after 4 days of incubation at 30 °C. Furthermore, the rates of siderophore production reached 35.51, 26.37, 26.37, and 23.84 psu, respectively, in the same strains. The application of the selected strains in the presence of rock phosphate (RP) with tomato plants under greenhouse conditions was evaluated. The plant growth and P-uptake traits positively and significantly increased in response to all the bacterial treatments, except for some traits, such as plant height, number of leaves, and leaf DM at 21 DAT, compared to the negative control (rock phosphate, T2). Notably, the P. megaterium strain P12 (T4), followed by R. aquimaris strain P22-2 (T5), revealed the best values related to plant height (at 45 DAT), number of leaves per plant (at 45 DAT), root length, leaf area, leaf-P uptake, stem P uptake, and total plant P uptake compared to the rock phosphate. The first two components of the PCA (principal component analysis) represented 71.99% (PCA1 = 50.81% and PCA2 = 21.18%) of the variation at 45 DAT. Finally, the PGPR improved the vegetative-growth traits of the tomato plants through P solubilization, IAA, and siderophore production, and ameliorated the availability of nutrients. Thus, applying in PGPR in sustainable agriculture will potentially reduce production costs and protect the environment from contamination by chemical fertilizers and pesticides.

Seed endophytic bacterial profiling from wheat varieties of contrasting heat sensitivity.

Wheat yield can be limited by many biotic and abiotic factors. Heat stress at the grain filling stage is a factor that reduces wheat production tremendously. The potential role of endophytic microorganisms in mitigating plant stress through various biomolecules like enzymes and growth hormones and also by improving plant nutrition has led to a more in-depth exploration of the plant microbiome for such functions. Hence, we devised this study to investigate the abundance and diversity of wheat seed endophytic bacteria (WSEB) from heatS (heat susceptible, GW322) and heatT (heat tolerant, HD3298 and HD3271) varieties by culturable and unculturable approaches. The results evidenced that the culturable diversity was higher in the heatS variety than in the heatT variety and Bacillus was found to be dominant among the 10 different bacterial genera identified. Though the WSEB population was higher in the heatS variety, a greater number of isolates from the heatT variety showed tolerance to higher temperatures (up to 55°C) along with PGP activities such as indole acetic acid (IAA) production and nutrient acquisition. Additionally, the metagenomic analysis of seed microbiota unveiled higher bacterial diversity, with a predominance of the phyla Proteobacteria covering >50% of OTUs, followed by Firmicutes and Actinobacteria. There were considerable variations in the abundance and diversity between heat sensitivity contrasting varieties, where notably more thermophilic bacterial OTUs were observed in the heatT samples, which could be attributed to conferring tolerance against heat stress. Furthermore, exploring the functional characteristics of culturable and unculturable microbiomes would provide more comprehensive information on improving plant growth and productivity for sustainable agriculture.

Isolation and Characterization of a Silicate-Solubilizing Bacterial Strain Associated with the Roots of Groundnut (Arachis hypogaea L.)

The aim of this investigation was to isolate groundnut root-associated rhizobacteria and to study their efficiency to solubilize silicate, synthesize indole acetic acid (IAA), encourage plant growth, and promote silicon (Si) uptake and deposit in plants. Based on silica-solubilizing ability and IAA production, a bacterial strain was chosen in the present study for further studies. The bacterial isolate synthesized more quantities of IAA at pH 8. When the soil fertilized with silica was inoculated with this bacterial strain, there was an improvement in overall growth characteristics of groundnut. It was also found that more Si was deposited in plants fertilized with both insoluble silica and bacterial strain. Bacteria isolated in the present study can synthesize more IAA under alkaline conditions, solubilize silicate, and encourage the growth of groundnut.

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

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. 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 (34.80µmol 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 (25.18µmol mL-1), and indole-3-acetic acid (IAA)-like substance (28.59µg 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. Protists may act as regulators of the bacterial activities involved in plant growth promotion and thus enhance plant growth.

Identification and Optimisation of Indole-3-Acetic Acid Production of Endophytic Bacteria and Their Effects on Plant Growth.

Indole-3-acetic acid (IAA) is one of the most physiologically active auxins produced by rhizobacteria and is potentially applied for agriculture. Two endophytic bacteria, VR2 and MG9, isolated from the root of Chrysopogon zizanioides (L.) collected at Cha-Am, and the leaf of Bruguiera cylindrica (L.) Blume collected from a mangrove forest at Ban Laem, Phetchaburi Province, Thailand, were taxonomic characterised based on their phenotypic characteristics and 16S rRNA gene analysis. Strain VR2 was closely related to Enterobacter hormaechei CIP 103441T (99.6% similarity), while strain MG9 was closely related to Bacillus aryabhattai B8W22T (99.9% similarity). Consequently, they were identified as Enterobacter hormaechei and Bacillus aryabhattai, respectively. The IAA production of VR2 and MG9 strains are determined and applied to rice seeds for their root and shoot germination. Strains VR2 and MG9 greatly produced a yield of IAA, 246.00 and 195.55 μg/mL in 1,000 μg/mL of L-tryptophan at pH 6 for 48 h. They showed no significant differences in IAA to root and shoot development. However, the bacterial IAA exhibited potential nearby synthetic IAA, which had a significant effect compared to the control. IAA produced from these two strains might preferably trim down the use of synthetic IAA and could contribute to sustainable agriculture.