Phosphate Solubilization Potential Research Articles

Phosphate solubilization potential of PSB: an advance approach to enhance phosphorous availability for phytostimulation.

Rhizosphere engineering approach is considered a quantum leap in plant sciences. The current study focused on investigating rhizobacterial efficiency to mobilize bioavailable phosphate from insoluble-phosphate source. Four efficient phosphate-solubilizing bacterial isolates, i.e., Pseudomonas songnenensis (GR3), Stutzerimonas stutzeri (HH2), Bacillus bingmayongensis (KH3), and Achromobacter aegrifaciens (MH1) were selected for the current study. Interactions between various physiological parameters and phosphate solubilization efficiency of isolates revealed that glucose significantly facilitated phosphorus solubilization at 37 ℃, with media having pH 7 and 0.5% phosphorous. Additionally, positive correlation among P-solubilization potential, acids produced, and pH was observed. Plant microbe-interaction analysis was performed to evaluate the efficiency of these bacterial isolates on various morpho-physiological responses of Zea mays L. For this purpose, various concentrations of tricalcium phosphate (TCP) (0, 10, 20, 30, 40, and 50mM) were applied to plants in the presence and absence of bacterial isolates. The results showed that lower phosphate levels (10 and 20mM) trigger shoot development and improve plant weight and leaf formation whereas higher phosphate concentrations (30mM and above) stimulated the development of longer root system. The bacterial isolates, KH3 and HH2, were observed as efficient phosphate-solubilizing bacteria (PSB) that positively stimulated various plant growth and biochemical attributes over untreated plants. At lower phosphate levels, substantial increase of 92, 65, and 200% in shoot length, fresh weight, and number of leaves was recorded with bacterial isolate HH2, whereas, at 30mM TCP, increase of 165% was observed in root length of plants treated with bacterial isolate KH3 compared to control. Similarly, at lower phosphate levels, increment of 57.3, 76.7, and 217% in phosphate, protein, and auxin content was recorded in plants treated with bacterial isolate HH2, and increase of 188.8% in total soluble carbohydrates was observed in plants treated with bacterial isolate KH3 as compared to control. Contrarily, increment in total chlorophyll content was most substantial (207%) by the bacterial isolate KH3 when provided with 30mM TCP. Hence, the current study reviled that the use of these phosphates (KH3 and HH2)-solubilizing PGPR, as an efficient phytostimulator used for crop production in the replacement of chemical fertilizers, is carcinogenic and deteriorating our eco-system.

Soil phosphorus cycling microbial functional genes of monoculture and mixed plantations of native tree species in subtropical China.

Transforming coniferous plantation into broadleaved or mixed broadleaved-coniferous plantations is the tendency of forest management strategies in subtropical China. However, the effects of this conversion on soil phosphorus (P) cycling microbial functional genes are still unknown. Soil samples were collected from 0-20, 20-40, and 40-60 cm (topsoil, middle layer, and subsoil, respectively) under coniferous Pinus massoniana (PM), broadleaved Erythrophleum fordii (EF), and their mixed (PM/EF) plantation in subtropical China. Used metagenomic sequencing to examine the alterations of relative abundances and molecular ecological network structure of soil P-cycling functional genes after the conversion of plantations. The composition of P-cycling genes in the topsoil of PM stand was significantly different from that of PM/EF and EF stands (p < 0.05), and total phosphorus (TP) was the main factor causing this difference. After transforming PM plantation into EF plantation, the relative abundances of P solubilization and mineralization genes significantly increased in the topsoil and middle layer with the decrease of soil TP content. The abundances of P-starvation response regulation genes also significantly increased in the subsoil (p < 0.05), which may have been influenced by soil organic carbon (SOC). The dominant genes in all soil layers under three plantations were phoR, glpP, gcd, ppk, and ppx. Transforming PM into EF plantation apparently increased gcd abundance in the topsoil (p < 0.05), with TP and NO3 --N being the main influencing factors. After transforming PM into PM/EF plantations, the molecular ecological network structure of P-cycling genes was more complex; moreover, the key genes in the network were modified with the transformation of PM plantation. Transforming PM into EF plantation mainly improved the phosphate solubilizing potential of microorganisms at topsoil, while transforming PM into PM/EF plantation may have enhanced structural stability of microbial P-cycling genes react to environmental changes.

The Plant Growth Promoting Potential of Saline Tolerant Rhizobacteria under In vitro Saline Stressed Conditions

Since the beginning of agricultural operations, soil salinity has been one of the most significant abiotic variables limiting agricultural production. Saline tolerant plant growth-promoting rhizobacteria (PGPR) enhance nutrient equitation and soil enzyme activities, which serve as indicators of soil biological health, and help to correct nutritional imbalances in plants. Potential bioinoculants for boosting crop yield in saline agriculture include saline tolerant plant growth-promoting rhizobacteria (PGPR). Therefore, in the present study the potential saline tolerant rhizobacteria isolated from saline patches of Karnataka were screened for Exopolysacchride production and Phosphate solubilization and phytohormone production potential under in vitro saline conditions. The results revealed that among the eight organisms were the highest EPS production, phosphate solubilization and phytohormone production recorded by Bacillus subtilis GAN-4 and Staphylococcus cohnii MAN-3 under both normal and saline stressed conditions compared to other organisms. Therefore,these strains show potential as plant growth-promoting rhizobacteria (PGPR) for mitigating salinity in saline agriculture.

Exploring the Phosphate Solubilization Potential of Rhizobia Isolated from Sesbania grandiflora

Rhizobia, are known to exhibit the ability to solubilize phosphate (P) in the soil, apart from their primary function of nitrogen fixation. Hence this study was conducted to evaluate and characterize rhizobia isolates obtained from root nodules of Sesbania grandiflora for their potential in P solubilization. Two experiments were conducted under laboratory conditions arranged in a Complete Randomized Design (CRD) with three replicates. All data were analyzed using analysis of variance (ANOVA) and means were separated using the LSD test. Four bacterial strains (a,b,c,d) were isolated from root nodules using the trap plant method. They were initially identified as Rhizobia based on morphology and authenticated through gram staining, acid-alkaline tests, Congo Red Yeast Mannitol Agar (CRYMA), and Bromothymol blue Yeast Mannitol Agar (BRYMA) tests. The most effective rhizobia for P solubilization was identified based on the Phosphorus Solubilization Index (PSI) and solubilized P in Pikovaskya (PVK) solid and liquid media. Subsequently, optimization of PVK liquid media was conducted for effective P solubilizer, varying with carbon (C), nitrogen (N), and P sources. All isolates were gram-negative and exhibited acid production, authenticated as rhizobia. The significantly (p&lt;0.05) highest PSI was recorded with isolate “c” and it also exhibited the highest (p&lt;0.05) solubilized P. The isolate “c” showed potassium dihydrogen phosphate (35.1±0.46 ppm), glucose (25.47±0.49 ppm), and ammonium sulfate (3.20±0.17 ppm) as the optimum sources of P, C, and N, respectively, for achieving significantly higher phosphorus solubilization in PVK medium by thriving rhizobia “c” as an effective phosphorus solubilizer. However, further field studies are required to assess performance of rhizobia “c” before introducing it as a P solubilizing inoculum.

Genomic insight of phosphate solubilization and plant growth promotion of two taxonomically distinct winter crops by Enterobacter sp. DRP3.

Study of rhizospheric microbiome-mediated plant growth promotional attributes currently highlighted as a key tool for the development of suitable bio-inoculants for sustainable agriculture purposes. In this context, we have conducted a detailed study regarding the characterization of phosphate solubilizing potential by plant growth-promoting bacteria that have been isolated from the rhizosphere of a pteridophyte Dicranopteris sp., growing on the lateritic belt of West Bengal. We have isolated three potent bacterial strains, namely DRP1, DRP2, and DRP3 from the rhizoids-region of Dicranopteris sp. Among the isolated strains, DRP3 is found to have the highest phosphate solubilizing potentiality and is able to produce 655.89 and 627.58µg ml-1 soluble phosphate by solubilizing tricalcium phosphate (TCP) and Jordan rock phosphate, respectively. This strain is also able to solubilize Purulia rock phosphate moderately (133.51µg ml-1). Whole-genome sequencing and further analysis of the studied strain revealed the presence of pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase gdh gene along with several others that were well known for their role in phosphate solubilization. Further downstream, quantitative reverse transcriptase PCR-based expression study revealed 1.59-fold upregulation of PQQ-dependent gdh gene during the solubilization of TCP. Root colonization potential of the studied strain on two taxonomically distinct winter crops viz. Cicer arietinum and Triticum aestivum has been checked by using scanning electron microscopy. Other biochemical analyses for plant growth promotion traits including indole acetic acid production (132.02µg ml-1), potassium solubilization (3mg l-1), biofilm formation, and exopolymeric substances productions (1.88-2.03µg ml-1) also has been performed. This study highlighted the active involvement of PQQ-dependent gdh gene during phosphate solubilization from any Enterobacter group. Moreover, our study explored different roadmaps for sustainable farming methods and the preservation of food security without endangering soil health in the future.

Unlocking the Potential of Plant Growth-Promoting Rhizobacteria to Enhance Drought Tolerance in Egyptian Wheat (Triticum aestivum)

Plant growth-promoting rhizobacteria (PGPRs) represent a promising strategy for enhancing plant resilience and yields under drought-stress conditions. This study isolated and characterized PGPR from wheat rhizosphere soil in Egypt. Four PGPR strains were evaluated for an array of plant growth-promoting traits, including IAA production, biofilm formation, siderophore production, nitrogen fixation, ACC deaminase activity, phosphate solubilization, and antagonistic potential. Molecular identification via 16S rRNA sequencing classified three isolates (MMH101, MMH102, and MMH103) within the Bacillus genus and one isolate (MMH104) as Myroides sp. Greenhouse experiments examined the effects of PGPR inoculation on the drought-stressed Egyptian wheat cultivar, Gimmeza-9. Wheat plants inoculated with PGPR isolates showed dramatic improvements in growth parameters and stress tolerance indicators compared to non-inoculated controls when subjected to a 10-day drought period, with Bacillus rugosus (MMH101) inoculation resulting in increases of 61.8% in fresh biomass, 77.2% in dry biomass, 108.5% shoot length, and 134.9% root length. PGPR treatments also elevated the chlorophyll and proline content while reducing malondialdehyde levels. The findings demonstrate the effectiveness of PGPR inoculation in enhancing the morphology, physiology, and drought stress resilience of wheat. Isolated PGPR strains hold promise as biofertilizers for improving cereal productivity under water-deficit conditions.

Phytoremediation of Arsenic (As) in rice plants, mediated by Bacillus subtilis strain IU31 through antioxidant responses and phytohormones synthesis

Bacteria-assisted phytoremediation uses bacteria to promote plant health and improve its ability to remediate toxic heavy metals like Arsenic (As). Here, we isolated rhizobacteria and identified them as Bacillus subtilis strain IU31 using 16S rDNA sequencing. IU31 showed phosphate solubilization potential on Pikovskaya agar medium and produced siderophores, which were detected on Chromium Azurol-S (CAS) agar medium. Indole-3-acetic acid (IAA) and gibberellins (GAs), namely GA1, GA3, GA4, GA7, GA9, GA12, GA15, and GA24, were quantified by GC/MS-SIM analysis. The expression levels of genes involved in GA and IAA biosynthesis, such as cyp112, cyp114, trpA, and trpB, were assessed using semi-quantitative RT-PCR. Plant bioassays showed that As at a 15 mg/kg concentration reduced plant growth, chlorophyll content, and biomass. However, IU31 inoculation significantly improved plant growth dynamics, enhancing As accumulation by up to 50% compared with uninoculated plants. IU31 inoculation induced the bioconcentration factor (BCF) and bioaccumulation factor (BAF) of As in plants compared to uninoculated plants, but the translocation factor (TF) of As was unaffected by IU31 inoculation. IU31 inoculation effectively restored glutathione-S-transferase (GST) and catalase (CAT) enzyme activities, as well as glutathione (GSH) and hydrogen peroxide concentrations to nearly normal levels, which were significantly elevated in plants exposed to As stress. These results show that IU31 improves plant health and growth by producing IAA and GAs, which might contribute to the uptake and detoxification of As.

In vitro and in silico study for plant growth promotion potential of indigenous Ochrobactrum ciceri and Bacillus australimaris

Abstract Insights into plant and bacterial associations, along with their genome mining, have paved the way for the improvement of the agriculture sector. Initially, 69 morphologically different bacterial strains were isolated from 6 different extreme environment samples. For in vitro screening of plant growth-promoting bacteria, auxin, hydrogen cyanide, and antibiotic production along with phosphate solubilization potential was estimated. Only 15 strains exhibited noteworthy production of plant growth-promoting compounds. Ochrobactrum ciceri CS-10 fostered Triticum aestivum and Zea mays seedling root growth remarkably (104.12 and 159%, respectively), while Bacillus australimaris TP-10 significantly increased the number of leaves in T. aestivum (166.66%) and Z. mays (133.33%) seedlings. These strains also boosted seedling biochemical traits, like indole acetic acid, peroxidase, and soluble protein content. Particularly, O. ciceri elevated peroxidase content greatly in T. aestivum (249.7%) and Z. mays (260.5%). Scanning electron micrographs of inoculated roots revealed the aggregation of cells at the roots of Z. mays, whereas single cells/micro-colonies were observed on T. aestivum roots. For in silico analysis, AntiSMASH was used for genome mining of the environmental Ochrobactrum sp. and B. australimaris reference genome. This genome mining unveiled diverse gene clusters encoding; terpenes, beta-lactones, acyl-amino-acids, aryl polyenes, lanthipeptide, and siderophores, etc. Two common biosynthetic gene clusters (terpenes and beta-lactones) were identified in these strains, which can act as plant growth promoters. This symbiotic plant–bacteria relationship has promising ecological and economic implications, offering avenues for beneficial applications.

Phosphate solubilization potential and molecular identification of bacterial isolates from soils with sugarcane cultivation

A study on the composition and physiology of the microbiota of soils subjected to vinasse irrigation may be important in the discovery of products of biotechnological interest, since this residue increases microbial activity in the environments where it is applied. The objective of this work was to carry out the molecular characterization, through the sequencing of the 16S rRNA gene of four bacterial isolates obtained from sugarcane agricultural soils with vinasse management, as well as to evaluate the phosphate solubilization capacity and to relate the results with good practices in agriculture. Isolate LGA01-EV05 showed high sequence similarity with Curtobacterium albidum. The isolate LGA02-EV08 shows similarity with Brevibacillus nitrificans, the isolates LGA03-V20B and LGA04-V20G showed a high degree of similarity among themselves and with Sinomonas soli. Regarding the potential for phosphate solubilization, the four isolates demonstrated efficiency for this function. It was observed that there was no statistical difference between the LGA02-EV08 and LGA04-V20G groups, being the best solubilizing bacteria, with a yield about four times higher than the LGA03-V20B group, the worst among those analyzed.

Arthospira platensis and Bacillus subtilis Synergies for Sustainable Agriculture

The aim of this study is to analyze the biofertilizer value of B. subtilis by estimating its phosphate solubilizing potential and its antagonistic activity against pathogenic strains of E. coli and Bacillus cereus. Prolonged use of chemical fertilizers have adverse effects on the soil and through food chain they cause hazards to organisms including humans. Moreover pests and pathogenic microbes are becoming immune to the chemical pesticides and herbicides. Hence the need of biofertilizers that are ecofriendly and good biocontrol agents are gaining importance. Use of biofertilizers leads us towards the path of sustainable agriculture yielding better productivity without compromising the fertility of agricultural fields. Bacillus subtilis is a PGPR (Plant growth promoting rhizobacteria) capable of phosphate and zinc solubilizing and it increases the bioavailability of nutrients to the plants. Due to its antagonistic nature, B. subtilis can be utilized in biocontrol management practices. Arthospira platensis is a well explored microalgal species that is rich in micronutrients and a wide array of amino acids that has immense biofertilizer value. The methodology involves UV spectrometric estimation of bioavailable phosphate in Pikovskaya’s broth at 690nm and percentage of inhibition of B. subtilis against E. coli and Bacillus cereus using OD600values. Evidences for utilizing mixed culture of A. platensis and B. subtilis as biofertilizer are explored from literature. B. subtilis strain AMLA5 isolated from oil contaminated soil from Coimbatore had phosphate solubilizing potential of 1.3ppm and showed good antagonistic effects against E. coli and B. cereus. The NCBI genebank accession number of the strain SUB13179211 AMLA5 is OQ874086 that showed 99.77% sequence identical to Bacillus subtilis. This strain was a surfactin producer that utilized A. platensis as its economical substrate. A. platensis &amp; B. subtilis are GRAS level organisms that can be utilized in agriculture as biofertilizer as mixed culture. The synergism existing between these two organisms can be exploited in multiple sectors

Phosphate solubilization potential of rhizosphere fungi isolated from satoimo taro plant

Phosphorus is an essential nutrient required by plants for their growth and development. Phosphates bioavailability in nature is approximately 95-99% but insoluble, therefore the plant can not simply use them. The alternative to overcome phosphate deficiency is by utilizing phosphate solubilizing fungi. This research is aimed at selecting and characterizing phosphate solubilizing fungi in rhizosphere of saitomo taro (Colocasia esculenta var antiquorum). The test on isolate ability to solubilize phosphate was conducted through qualitative and quantitative. Qualitative was carried out by counting index of phosphate solubilization on solid Pikovskaya while quantitative was through counting concentration of phosphate solubilization through spectrophotometry at wave length 693 nm. The result of qualitative test showed that the highest index of phosphate solubilisation was 1.08 at isolate RTP25 while quantitative demonstrated that isolate RTP16 released highest concentration of phosphate solubilization with the amount 12.78 µgl−1. Isolate RTP 25 (by Trichoderma sp) and RTP16 (by Aspergillus sp) be potential to be developed as phosphate biofertilizer.

Multifarious characteristics of sulfur-oxidizing bacteria residing in rice rhizosphere.

Sulfur-oxidizing bacteria (SOB) are versatile microorganisms known for their ability to oxidize various reduced sulfur compounds, namely, elemental sulfur (S0), hydrogen sulfide (H2S), tetrathionate (S4O62-), and trithionate (S3O62-) to sulfate (SO42-). In this study, out of twelve SOB isolates from rice rhizosphere, five were screened based on their sulfur oxidation potential, viz., SOB1, SOB2, SOB3, SOB4, and SOB5, and were identified as Ochrobactrum soli SOB1, Achromobacter xylosoxidans SOB2, Stenotrophomonas maltophilia SOB3, Brucella tritici SOB4, and Stenotrophomonas pavanii SOB5, respectively. All the isolates displayed chemolithotrophic nutritional mode by consuming thiosulfate and accumulating trithionate and tetrathionate in the growth medium which is ultimately oxidized to sulfate. The strains were authenticated with the production of thiosulfate oxidizing enzymes such as rhodanese and sulfite oxidase. Despite their tendency to oxidize reduced sulfur compounds, B. tritici SOB4 and S. pavanii SOB5 were also found to possess phosphate and zinc solubilization potential, acetic acid, and indole acetic acid (IAA) production and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The presence of sulfanyl (R-SH) groups was noticed in the A. xylosoxidans SOB2. Elemental sulfur conversion into sulfate was noted in the S. maltophilia SOB3, and hydrogen sulfide conversion into sulfate was observed in the Ochromobacter soli SOB1. Sulfur oxidation potential coupled with beneficial properties of the isolates widen the knowledge on SOB.

Growth Promoting Potential of Phosphate Solubilizing Enterobacter Cloaca and Enterobacter Hormaechei on Maize and Cowpea Seedlings

Introduction: Phosphorus plays a range of functions in the proper growth and development of plants. Numerous microbial species, including bacteria, fungi, actinomycetes, and even algae have been found to play a crucial role in the solubilization of phosphate. This study was therefore aimed at exploring the growth-promoting potential of phosphate solubilizing Enterobacter species on maize and cowpea seedlings. Methods: Five strains that showed remarkable phosphate solubilization potential were used for the study. The bacterial isolates consist of three strains of Enterobacter cloaca and two strains of Enterobacter hormaechei. Growth promotion studies were carried out under laboratory conditions (in blotters) and green house (soil environment). In the blotter study, percent germination, germination index, germination time, germination rate, and vigor index were estimated, while shoot and root lengths, number of leaves, and wet weight were estimated in the greenhouse study. Results: In both seedlings, percent germination, germination index, and vigor index showed significantly higher values in seeds primed with the isolates than in the water-treated seeds (p≤ 0.05). Throughout the period of planting, the shoot and root lengths of the isolate-treated seedlings showed significantly higher values than the untreated control setups. This observation was irrespective of the maize and cowpea seedlings. In both seedlings, shoot and root lengths were directly proportional to days of growth. The bacterial strains showed significantly higher growth promoting potential on the seedlings. Conclusion: Therefore, the availability of these phosphate solubilizing microorganisms in the soil could enhance the growth of the seeds.

Isolation and Characterization of Thermotolerant Mungbean (Vigna Radiata L.) Rhizobial Isolate As Biofertilizer

Rhizobia act as primary nitrogen fixing microorganisms in the root of leguminous plants. Efficient rhizobia are helpful in increasing productivity of legumes. In the present investigation a total of twenty rhizobial isolates were retrieved from root nodules of mungbean plants growing in field during summer season. On evaluation of plant growth promoting traits of all rhizobial isolates it was found that rhizobial isolate HSR1 had maximum indole acetic acid (IAA) production (58.83 μg/ml), ammonia excretion (4.78 μg/ml) and phosphate solubilization potential. Other plant growth promoting traits like aminocyclopropane- 1-carboxylic acid (ACC) deaminase activity, siderophore production and hydrogen cyanide (HCN) production were also exhibited by isolate HSR1. This isolate was able to survive 45ºC and exhibited plant growth promoting traits at high temperature. Genomic DNA extracted from isolate HSR1 was subjected to amplification of 16S rRNA gene for identification. The similarity searching of the sequence obtained after 16S rRNA gene sequencing showed 99% similarity with Sinorhizobium sp. T25, which was confirmed by morphological and biochemical tests. Presence of good plant growth promoting traits makes HSR1 a promising strain to be developed as biofertilizer to improve soil fertility and plant growth. Bangladesh J. Bot. 52(2): 217-224, 2023 (June)

Bacillus strains exhibit various plant growth promoting traits and their biofilm-forming capability correlates to their salt stress alleviation effect on maize seedlings.

Soil salinity interferes with plant growth and development. Bacillus genus has been used to increase the growth and productivity of a wide variety of crops by alleviating the effects of salt stress. A total of thirty two Bacillus isolates were obtained from maize rhizosphere, and their plant growth-promoting (PGP) traits and biocontrol activities were tested. Bacillus isolates displayed varying degrees of PGP properties-the production of extracellular enzymes, indole acetic acid, hydrogen cyanide, phosphate solubilization, biofilm formation, and antifungal potential against several fungal pathogens. The phosphate-solubilizing isolates belong to B. safensis, B. thuringiensis, B. cereus, and B. megaterium species. Each Bacillus isolate demonstrated different levels of antifungal activity against the fungal pathogens tested. Biofilm production by some salt-tolerant isolates significantly increased at elevated levels of NaCl (p<0.05). The strains B. safensis B24, B. halotolerans B7/B18, B. subtilis B26, and B. thuringiensis B10 significantly increased the length of root (by 32.7-38.2%) and shoot (by 19.5-29.8%) of maize (p<0.05). Maize plants treated with some Bacillus strains displayed significantly greater chlorophyll content with an increase of 26.7-32.1% (p<0.05). Among PGP properties, enhanced biofilm formation played a more important role in maize growth under higher salinity. These salt-tolerant biofilm-forming strains could be efficiently used as bio-inoculant for maize under salinity stress.

The potency of soil bacteria on soil phosphorus solubilization and IAA production for innovation on sustainable Melon (Cucumis melo) production through biofilm biofertilizer

To fulfils the demand of melons (Cucumis melo), it requires intensive maintenance by agrochemical products. If this is done continuously, it will lead to soil degradation and disrupt the sustainable food supply. Therefore, an innovation is needed to maintain the sustainable food supply using biofilm biofertilizer technology. This study aims are to determine the potential of bacteria isolated from melon rhizosphere to solubilize phosphate and producing indole acetic acid (IAA) so that it can be developed into biofilm biofertilizer. Soil samples were taken from three melon gardens owned by farmers located in Sragen Regency, Karanganyar Regency and Wonogiri Regency, Central Java. In the laboratory, the soil bacteria then isolated from the soil using the dilution method. The isolates obtained then tested for their ability to solubilize phosphate and produce IAA. Phosphate is an essential nutrient for plant growth and IAA is plant growth promoting. The results showed that the highest phosphate solubilization potential was produced by bacterial isolate SRG 1A with a halo zone ratio of 1.957 and the highest concentration of IAA was produced by bacterial isolate WNG 1B with a value of 6.151 ppm. Based on the ability of the bacteria, indicates that the obtained bacterial isolates have the potential to be developed as a biofilm biofertilizer to help the growth of melon plants because it has the potency to solubilize soil nutrient and produce IAA.

16S rRNA gene‐based identification and plant growth‐promoting potential of cultivable endophytic bacteria

AbstractEndophytic bacteria play essential roles in plant growth and fitness through nitrogen fixation, nutrient solubilization, and phytohormone production. However, the plant growth‐promoting (PGP) potential of endophytic microorganisms inhabiting vegetables is underexplored. Thus, this study investigated the endophytic bacteria of vegetable crops for their PGP properties using the culture‐dependent technique. Recovered isolates were identified by sequencing the partial 16S rRNA gene using Sanger sequencing. The isolated endophytic bacteria belonged to 15 genera and 39 different species. Bacillus, Enterobacter, Pantoea, and Pseudomonas were the predominant genera and had high phosphate solubilization and siderophore production potential. The isolates differentially produced indole‐3‐acetic acid and ammonium in the range 0.14–44.48 μg mL–1 and 0.77–93.24 mg L–1, respectively. Pseudomonas azotoformans, Stenotrophomonas maltophilia, and Serratia liquefaciens showed a high level of siderophore production, which was not significantly (p &gt; 0.05) different across the plant and organ types. More than 21% of endophytes could produce gelatinase, protease, amylase, and cellulase, contributing to their diverse ecosystem functions. Bacterial density and species composition varied across the vegetable species, organs, and farm locations but were higher in the stems compared with other organs. However, the vegetable organ had no significant (p &gt; 0.05) influence on the bacterial population density, except for the interaction of plant species and organs. Overall, this study provides basic knowledge about the cultivable endophytic bacterial community of vegetables and reveals diverse endophytic bacteria useful in bioinoculant formulations for improving crop productivity.

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.

Pseudomonas aeruginosa and Bacillus cereus Isolated from Brazilian Cerrado Soil Act as Phosphate-Solubilizing Bacteria

The phosphate-solubilizing microorganism is essential for soil quality and plant development and can serve as an alternative to reduce such Brazilian needs for importing phosphate overseas. Here, we isolated and selected bacteria from Brazilian Cerrado soils capable of solubilize phosphate. We obtained 53 bacteria isolates, of which 23 could solubilize phosphate at a pH of 7.0, 17 could solubilize phosphate at a pH of 6.0, and 8 could solubilize at a pH of 5.5. Using 16S rRNA gene sequences, we identified nine bacteria species clustered in four groups: Bacillus sp., Pseudomonas sp., Priestia sp., and Klebsiella sp. Our results revealed that the UFT01 (P. aeruginosa) and UFT42 (B. cereus) isolates exhibited the best phosphate solubilization performance at all tested pH values. We further recorded higher levels of solubilization and phosphate availability six days after the soil inoculation with P. aeruginosa, and enzymatic analysis of the soil samples revealed that the P. aeruginosa-inoculated samples resulted in four-fold higher enzymatic activities when compared to non-inoculated soils. The B. cereus soil inoculation increased β-glucosidase activities and resulted in reduced the activities of arylsulfatase. Altogether, our findings demonstrated that P. aeruginosa and B. cereus isolated from Cerrado soils showed high phosphate solubilization potential.

Molecular Characterization and Mineralizing Potential of Phosphorus Solubilizing Bacteria Colonizing Common Bean (Phaseolus vulgaris L.) Rhizosphere in Western Kenya.

Phosphorus solubilizing bacteria (PSB) are a category of microbes that transform insoluble phosphates in soil into soluble forms that crops can utilize. Phosphorus in natural soils is abundant but poorly soluble. Hence, introducing PSB is a safer way of improving its solubility. The aim of this study was to genetically characterize and determine the mineralization capability of selected PSB colonizing rhizospheres of common beans in Western Kenya. Seven potential phosphorus solubilizing bacteria (PSB) were isolated from various subregions of Western Kenya. 16S ribosomal RNA gene sequencing and National Center for Biotechnology Information (NCBI), Basic Local Alignment Search Tool (BLAST) identified the isolates. The phosphate solubilization potential of the isolates was evaluated under agar and broth medium of National Botanical Research Institute's phosphate (NBRIP) supplemented with tricalcium calcium phosphate (TCP). Identified isolates were as follows: KK3 as Enterobacter mori, B5 (KB5) as Pseudomonas kribbensis, KV1 as Enterobacter asburiae, KB3 as Enterobacter mori, KK1 as Enterobacter cloacae, KBU as Enterobacter tabaci, and KB2 as Enterobacter bugandensis. The strains B5 and KV1 were the most effective phosphorus solubilizers with 4.16 and 3.64 indices, respectively. The microbes converted total soluble phosphate concentration in broth medium which was 1395 and 1471 P μg/mL, respectively. The least performing isolate was KBU with a 2.34 solubility index. Significant (p ≤ 0.05) differences in plant biomass for Rose coco and Mwitemania bean varieties were observed under inoculation with isolates B5 and KV1. PSB isolates found in common bean rhizospheres exhibited molecular variations and isolates B5 and KV1 are the potential in solving the insufficiency of phosphorus for sustainable crop production.