Phosphate Solubilization Efficiency Research Articles

Bacterial Strain Improvement via Random Physical Mutation to Improve Phosphate Solubilization Efficiency for Sustainable Crop Growth

Phosphorus deficiency in soil due to cation-mediated fixation reduces agricultural output from otherwise fertile lands. Phosphate solubilizing bacteria can solubilize this immobilized phosphate. The goal of this study was to use random UV mutagenesis to improve the phosphate solubilizing efficiency of the bacterial strains isolated from agriculture soils of Jaipur, Rajasthan. The phosphate solubilizing capacity was determined using the colorimetric chlorostannous reduced molybdo phosphoric acid blue method. When UV treated for 40, 50, and 60  min. Strain B5 depicted 58.54 %, 133.27 %, and 159.09 % enhanced phosphate solubilization, respectively, in the phylogenetic tree constructed using 16S rRNA gene sequencing, the isolate B5 clustered with Pseudomonas putida strains. Thus wild strains such as Pseudomonas sp. and Bacillus sp. can be mutagenically exploited to avail incapacitated phosphorus in soil. This can be an ecologically desired elucidation; however, more research is needed to investigate the underlying mechanisms involved and their repercussions.

Mineral Solubilizing Rhizobacterial Strains Mediated Biostimulation of Rhodes Grass Seedlings.

Minerals play a dynamic role in plant growth and development. However, most of these mineral nutrients are unavailable to plants due to their presence in fixed forms, which causes significant losses in crop production. An effective strategy to overcome this challenge is using mineral solubilizing bacteria, which can convert insoluble forms of minerals into soluble ones that plants can quickly assimilate, thus enhancing their availability in nutrient-depleted soils. The main objective of the present study was to isolate and characterize mineral solubilizing rhizobacteria and to assess their plant growth-promoting potential for Rhodes grass. Twenty-five rhizobacterial strains were isolated on a nutrient agar medium. They were characterized for solubilization of insoluble minerals (phosphate, potassium, zinc, and manganese), indole acetic acid production, enzymatic activities, and various morphological traits. The selected strains were also evaluated for their potential to promote the growth of Rhodes grass seedlings. Among tested strains, eight strains demonstrated strong qualitative and quantitative solubilization of insoluble phosphate. Strain MS2 reported the highest phosphate solubilization index, phosphate solubilization efficiency, available phosphorus concentration, and reduction in medium pH. Among tested strains, 75% were positive for zinc and manganese solubilization, and 37.5% were positive for potassium solubilization. Strain MS2 demonstrated the highest quantitative manganese solubilization, while strains MS7 and SM4 reported the highest solubilization of zinc and potassium through acidifying their respective media. The strain SM4 demonstrated the most increased IAA production in the presence and absence of L-tryptophan. The majority of strains were positive for various enzymes, including urease, catalase protease, and amylase activities. However, these strains were negative for coagulase activity except strains SM7 and MS7. Based on 16S rRNA gene sequencing, six strains, namely, SM2, SM4, SM5, MS1, MS2, and MS4, were identified as Bacillus cereus, while strains SM7 and MS7 were identified as Staphylococcus saprophyticus and Staphylococcus haemolyticus. These strains significantly improved growth attributes of Rhodes grass, such as root length, shoot length, and root and shoot fresh and dry biomasses compared to the uninoculated control group. The present study highlights the significance of mineral solubilizing and enzyme-producing rhizobacterial strains as potential bioinoculants to enhance Rhodes grass growth under mineral-deficient conditions sustainably.

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.

Phosphate Solubilizing Bacteria (PSB) Isolation from Tomato Rhizospheres at Koka District, Ethiopia

Phosphorous is an essential macronutrient for plant growth and development. Most of the soil is deficient in plant available phosphorous and due to economic limitations majority of Ethiopian farmers applied inadequate fertilizers. It is essential to stabilize a mechanism to access P for plants with an efficient, cheap, and eco-friendly approach for enhanced crop growth and production. The main objective of this study was to screen efficient phosphate solubilizing bacteria from tomato rhizosphere soil. Using halo zone formation on PVK agar medium, more than 400 PSB isolates were isolated from 13 rhizosphere soil samples. By evaluating SI, texture in the culture-re-culturing process, liquid medium pH change efficiency and growth rate, upmost three promising PSB isolates (K-1-29, K-10-27, and K-10-41) were selected. Incubation of the isolates in PVK broth for five days showed significant pH reduction. For instance, isolate K-10-41 showed significant pH change (4.02) which indicates the organic acid production. Isolation and evaluation of efficient phosphate solubilizing bacteria maintain soil fertility, promote plant growth, induce plant response to pathogens, reduce agrochemical consumption and promote sustainable agriculture. Therefore, these selected PSB isolates need further detailed study for taxonomic identification, plant growth promotion, host range, and phytopathogen response. Local isolation improves environmental adaptation and indigenous competition.

The combined Application of Iron and Phosphate Solubilizing Bacteria to enhance Wheat (Triticum aestivum L.) growth and yield

This study had the objective of evaluating the efficiency of prepared iron and phosphate biofertilizers in improving wheat growth and yield. To isolate bacteria that dissolve iron and phosphate, different soil samples were collected from the Erbil governorate, a total of eighteen iron solubilizing bacteria were selected on a modified agar medium and all isolates belonged to Pseudomonas fluorescence. Twenty-two isolates of phosphate solubilizing bacteria were recognized and referred to P. putida, P.fluorescens, and Bacillus megaterium using microscopical, cultural, physiological and molecular tests. According to iron and phosphate solubilizing efficiency test, the most efficient isolate of iron solubilizing bacteria (Pfl3) and P-solubilizin bacteria (Ppu2, Bm14) were selected for biofertilizers preparation  Local and imported iron and phosphate biofertilizers were applied in pot experiment. Most biofertilizers were significantly increased yield components of wheat plants. Maximum shoot length, root length, tillers number,1000 seed weight, spike number and yield (99.60cm, 58.95cm, 22, 38.75g. 20, 5.52 ton/ha  respectively) were recorded by incoculation with P. Flourence + P. putida +B. megatrium significantly higher than uninoculated control and treatments with imported biofertilizer. It can be concluded that local iron and phosphate solubilizing bacterial isolates can be used for Fe and P biofertilizers.  &nbsp

ISOLATION AND MOLECULAR CHARACTERIZATION OF PHOSPHATE SOLUBILIZING BACTERIA FROM RHIZOSPHERIC SOILS OF TROPICAL LOWLAND RICE

Phosphate-solubilizing bacteria (PSB) can promote the dissolution of insoluble phosphorus in soil, enhancing the availability of soluble P and reducing the consumption of fertilizer and aid in sustainable agricultural development. The phosphate solubilising bacteria were isolated from the rhizospheric soils of the experimental site located in the ICAR-National Rice Research Institute's experimental farm in Cuttack, India. & the population of PSBs varied between 1-22.5 cfu/gm*104 and higher in DSR (Direct seeded rice) compared to TPR (Transplanted rice). Phosphate solubilization efficiency (PSE) of the isolates gave better result in Pikovskaya’s agar medium plates i.e. 188.9% in K6 (Kasalath, P80, DSR) rather than National Botanical Research Institute’s Phosphate growth medium (NBRIP) i.e. 73.3% for K6. The highest PSE% in C sources was found in lactose i.e. 166.7% for the isolate K9 (Kasalath, P0, DSR) and 180.0% for the isolate D17 (Dular, P80, TPR) for potassium nitrate as N source. The morphological study by staining characteristics showed that all the isolates were gram negative and cocci except D19 (Dular, P80, TPR) which was gram positive and rod shaped. Amplified fragments of oligonucleotide primers in RAPD characterization showed 51.81% polymorphism and 44.54% monomorphism. Based on dendrogram all the isolates were placed in group A except S11 (Dular, P80, TPR) which was placed in major group B showing great variation from all other isolates and group A consists of 6 minor groups in which minor group A6 was the largest containing 5 isolates i.e. Kasalath, P40, DSR (S13), Kasalath, P80, DSR (S14, S15, S16) & IR36, P40, DSR (S17).
  

Isolation, Solubilization of Inorganic Phosphate, and Production of Organic Acids by Individual and Co-inoculated Microorganisms

Phosphate solubilizing microorganisms (PSMs) mineralize phosphate (PO4³−) to make phosphorous available for plant uptake. This study is designed to isolate the PSMs from the subtropical environmental samples. Total 35 bacterial and 18 fungal isolates were found to be effective P solubilizers depend on their ability of P solubilization that were determined qualitatively and quantitatively using National Botanical Research Institute Phosphorus media. Efficient PSMs that were solubilizing phosphate in maximum amount were identified as Pseudomonas aeruginosa, Serratia marcescens, Pseudomonas mosselii, Bacillus licheniformis, Bacillus subtilis, Bacillus species, Aspergillus flavus, Aspergillus foetidus, Aspergillus niger, Aspergillus tubingensis, and Penicillium chrysogenum. Among them, A. tubingensis was observed as the most efficient phosphate solubilizing strain. For the first time, combined phosphate solubilization activity of A. tubingensis with other efficient phosphate solubilizers was checked and found that A. tubingensis and P. aeruginosa acted synergistically and solubilized phosphate in increased amount. High-performance liquid chromatography results revealed that A. tubingensis produced variety of organic acids including succinic, gluconic, oxalic, and citric acids. Scanning electron microscopy results confirmed the presence of firmly attached large fungal hyphae on tri-calcium phosphate (Ca3(PO4)2). Thus, the results suggest that the use of these PSMs either single or combined as bioinoculants will help to increase the availability of soluble phosphorous.

Phosphate solubilization and plant growth promotion by two Pantoea strains isolated from the flowers of Hedychium coronarium L.

Phosphorus (P) is an essential macronutrient for plants and is considered as one of the limiting nutrients to plants. The majority of P in the soil is found in the form of insoluble phosphate complexes, making the P unavailable for plants. In the present study, we report two highly efficient phosphate solubilizing bacteria isolated from the closed flower ofHedychium coronariumL., a medicinal plant commonly known as Gulbakawali. Based on morphological, biochemical, and molecular characterization, the two bacterial isolates were identified as genusPantoeaand designated as HCF6 and HCF9. Both these isolates efficiently solubilize tricalcium phosphate [Ca3(PO4)2] present in National Botanical Research Institute’s Phosphate (NBRIP) medium by releasing soluble phosphate up to 2000 μg ml-1and also partially solubilize aluminium phosphate (AlPO4). HCF6 and HCF9 possess several plant growth promoting traits and were evaluated for plant growth promotion ability using sand as a growth medium. Wheat plants treated with the bacterial isolates had increased root and shoot length and plant dry mass and accumulated higher inorganic phosphate in the plant tissue suggesting their role in mobilizing soluble P from insoluble P-complexes. Overall, our findings suggest that both thesePantoeaisolates (HCF6 and HCF9) represent promising candidates as bioinoculants.

Isolation of phosphate solubilizing fungus from rice fields of Odisha for agro‐ecological sustainable agriculture

AbstractPhosphorus (P), the second most essential nutrient, plays a remarkable role in energy transfer, storage, plant growth, and development. It is the least mobile and accessible to plants in most soil conditions as compared to the other key nutrients. Phosphate‐solubilizing fungus (PSF) plays a vital role in supplying phosphorous to plants from the soil. Hence this research intends to assess the phosphorous and nutritional status of collected soil samples as well as isolation of potential fungal strains. Twelve soil samples were taken from three costal districts of Odisha (Bhadrak, Jajpur, and Balasore). All six key soil parameters like pH, electrical conductivity, organic carbon, nitrogen, phosphorous, and potassium were examined for correlation and found to be significantly associated with each other. Fungal colonies were enumerated, grown and pure colonies were found. A total of four potential fungal strains were isolated, screened from rhizospheric soil and evaluated for their phosphate solubilization efficiency on Pikovskaya's agar selective media. They produce the halo zones around their colony approximately 3.3 cm (PRF2), 2.96(PRF3), and 3.06(PRF4) cm within 10 days of incubation. Aspergillus niger was a highly efficient strain in solubilizing phosphate with the solubilization index (SI) of 3.56 cm and also showed the greatest drop in pH in the PVK broth containing rock phosphate.

Phosphate mining activities affect crop rhizosphere fungal communities

Phosphate mining releases heavy metals into the surrounding environment. In this study, the effects of phosphate mining on rhizosphere soil fungi in surrounding crops, including Lactuca sativa var. angustata, Glycine max (L.) Merr., and Triticum aestivum L., were assessed. Phosphate mining significantly reduced the crop rhizosphere fungal diversity (P < 0.05). The relative abundances of Fusarium and Epicoccum increased in mining rhizosphere soil compared with the baseline. Beta diversity analysis indicated that phosphate mining led to the differentiation of fungal community structure in plant rhizospheres. Guild analysis indicated that different plant rhizosphere fungi developed various guilds in response to phosphate mining stress. Nine fungi were isolated from soil samples, with solubilization index values ranging from 1.1 to 2.5. Two efficient phosphate solubilizers, Epicoccum nigrum and Fusarium verticillioides, were enriched in phosphate mining rhizosphere soil samples. The dissolution kinetics of inorganic phosphorus and alkaline phosphatase activity assay showed strong phosphorus dissolution ability of the isolated fungi. Penicillium aculeatum, Trichoderma harzianum, Chaetomium globosum, and F. verticillioides showed strong tolerance to multiple heavy metals. This study furthers our understanding of how rhizosphere fungal ecology is affected by phosphate mining and provides important resources for the remediation of phosphate mining soil pollution.

Modulation in Biofertilization and Biofortification of Wheat Crop by Inoculation of Zinc-Solubilizing Rhizobacteria.

Zinc is an important micronutrient needed for the optimum growth and development of plants. Contrary to chemical zinc fertilizers, the use of zinc-solubilizing bacteria is an environmentally friendly option for zinc enrichment in edible parts of crops. This study was conducted with the objective of selecting potential zinc-solubilizing rhizobacteria from the rhizosphere of chickpea grown in soils of eastern Uttar Pradesh and further assessing their impact on the magnitude of zinc assimilation in wheat crops. Among 15 isolates, CRS-9, CRS-17, CRS-30, and CRS-38 produced net soluble zinc in broth to the tune of 6.1, 5.9, 5.63, and 5.6 μg ml–1, respectively, in zinc phosphate with the corresponding pH of 4.48, 5.31, 5.2, and 4.76. However, the bacterial strains CRS-17, CRS-30, CRS-38, and CRS-9 showed maximum zinc phosphate solubilization efficiency of 427.79, 317.39, 253.57, and 237.04%, respectively. The four bacterial isolates were identified as Bacillus glycinifermentans CRS-9, Microbacterium oxydans CRS-17, Paenarthrobacter nicotinovorans CRS-30, and Bacillus tequilensis CRS-38 on the basis of morphological and biochemical studies and 16S rRNA gene sequencing. Bacterial inoculants significantly colonized the roots of wheat plants and formed a biofilm in the root matrix. These strains significantly increased seed germination (%) and vigor indices in wheat grown under glasshouse conditions. After 30 days of sowing of wheat under microcosm conditions, eight zinc transporter (TaZIP) genes were expressed maximally in roots, with concomitant accumulation of higher zinc content in the bacterially treated plant compared to the absolute control. Out of the four strains tested, two bacteria, B. tequilensis CRS-38 and P. nicotinovorans CRS-30, improved seed germination (%), vigor indices (2–2.5 folds), plant biomass, grain yield (2.39 g plant–1), and biofortificated grains (54.25 μg g–1Zn) of wheat. To the best of our knowledge, this may be the first report on the presence of zinc solubilization trait in B. glycinifermentans CRS-9, M. oxydans CRS-17, and P. nicotinovorans CRS-30.

Diversity and Phosphate Solubilization Efficiency of Phosphate Solubilizing Bacteria Isolated from Semi-Arid Agroecosystems of Eastern Kenya.

Phosphorus (P) is a major nutrient required for plant growth but it forms complexes with other elements in soil upon application. A cost-effective way of availing P to plants is by use of Phosphate Solubilizing Bacteria (PSB). There is a wide range of PSB suited for diverse agro-ecologies. A large part of Eastern Kenya especially the lower altitude regions are semi-arid with nutrient depleted soils and predominated by low-income smallholders farmers who do not afford costly inorganic fertilizers. To alleviate poor soil nutrition in this agroecosystem, we sought to study the diversity of phosphate solubilizing bacteria and their phosphate solubilization efficiency. The bacteria were selectively isolated in Pikovskaya’s agar media. Bacterial colonies were enumerated as Colony Forming Units and morphological characterization determined by analyzing morphological characteristics. Genetic characterization was determined based on sequencing of 16S rRNA. A total of 71 PSB were isolated and they were placed into 23 morphological groups. Correlation analysis showed a negative correlation between phosphate solubilizing bacteria and the levels of phosphorus, iron, calcium, magnesium and soil pH. Analysis of 16S rRNA sequences revealed that the genetic sequences of the isolates matched the strains from the genera Burkholderia, Pseudomonas, Bacillus, Enterobacter, Pantoea, Paraburkholderia, Cronobacter, Ralstonia, Curtobacterium, and Massilia deposited in NCBI Database. Analysis of Molecular Variance showed that variation within populations was higher than that of among populations. Phosphate solubilization index values ranged between 1.143 and 5.883. Findings on biodiversity of phosphate solubilizing bacteria led to identification of 10 candidate isolates for plant growth improvement and subsequently, bio-fertilizer development.

Phosphate Solubilization Potential of Rhizosphere Soil Bacteria and their Possible Use as Biofertilizers

PHOSPHORUS is second only to Nitrogen as the most limiting element for plant growth. The concentration of soluble P in soil is usually very low, however, more than 80% of P becomes immobile and unavailable for plant uptake. The development of a biological alternative to chemical fertilizers is of great importance for the improvement of agriculture as well as the protection of the environment. The present study investigated thirteen efficient inorganic-phosphate solubilizing bacteria (PSB) isolated from various rhizospheric soil samples collected from El-Bekaa, Lebanon. Two isolates (Pseudomonas sp. HD and Escherichia sp. HD), exhibited the highest phosphate solubilization percentages of 76.60 and 88.21%, respectively. Application of the Plackett-Burman design resulted in phosphate solubilization efficiency of 79.08 and 93.77% for Pseudomonas sp. HD and Escherichia sp. HD, respectively. In vitro cultivation of different plants was applied to reflect the relative importance of Pseudomonas sp. HD and Escherichia sp. HD as biofertilizers on growth parameter of melon (Cucumis melo var. inodorus), horse-bean (Vicia faba), cucumber (Cucumis sativus), Armenian cucumber (Cucumis melo var. flexuosus), bean (Phaseolus vulgaris) and squash (Cucurbita pepo). The best growth parameters of the studied plants where observed where seeds were soaked in water and Ca3(PO4)2 with Pseudomonas sp. HD and Escherichia sp. HD.

Ornamental plant Pachystachys lutea as a source of promising endophytes for plant growth and phytoprotective activity

Endophytes are growth-promoting agents capable of synthesizing phytohormones, uptaking nutrients, and controlling pathogens. There is a strong potential to exploit them in the agriculture field like biofertilizers and biocontrol agents. In this work, we aimed to evaluate endophytic fungi isolated from Pachystachys lutea for their potential to solubilize phosphate, synthesise indole acetic acid (IAA), antagonize phytopathogens, and promote plant growth under greenhouse conditions. The phosphate solubilization efficiency was assessed on Pikovskaya’s agar medium. For analysis of IAA production, mycelia plugs of endophytes were cultured in Potato Dextrose Broth medium supplemented with L-tryptophan, with Salkowski Reagent, and the absorbance of the culture was measured. The antagonism evaluation of strain Alternaria sp. PL75 against phytopathogens was performed using the paired-culture technique. The promotion of plant growth provided by Alternaria sp. PL75 was evaluated in tomato plants. All strains evaluated were able to solubilize phosphate; however, the strain Alternaria sp. PL75 was the most effective (4.29). Two strains, Nemania sp. PL27 and Alternaria sp. PL75, produced 1.86 and 1.73 μg mL-1 of IAA, respectively. In the antagonism assay, the endophyte Alternaria sp. PL75 and its fungal extract showed the best results against the pathogen Moniliophthora perniciosa. The greenhouse experiment result showed the endophyte Alternaria sp. PL75 increased the plantlets emergency speed index and the percentage of germination from 60 to 81.63%. It was also observed a statistical significance in the shoot length of the treated plants with the endophyte suspension (55.38 cm) compared to the control (41.67 cm).

Halotolerant Endophytic Bacterium Serratia rubidaea ED1 Enhances Phosphate Solubilization and Promotes Seed Germination

Quinoa is renowned for its nutritional value and ability to withstand harsh environmental conditions such as salinity. In the present work, we isolated 34 phosphate solubilizing endophytic bacteria associated with the roots of quinoa plants. Based on phosphate solubilization efficiency and biochemical characterization, we selected one isolate named ED1. Ribotyping using partial 16S RNA gene analysis revealed that the selected isolate shares 99.7% identity with Serratia rubidaea. Plant growth promoting (PGP) studies showed that the ED1 strain solubilized complexed forms of phosphate (Ca3(PO4)2). Zinc release from ZnO, Zn3(PO4)2, or ZnCO3 revealed the efficient ZnO solubilization by the ED1 strain. Except for proteases, the strain ED1 produced siderophores, cellulase, ammonia and exhibited oligonitrophilic features. Indole acetic acid (IAA) production was detected with and without the L-tryptophan precursor. Next, we demonstrated that the ED1 strain tolerated 1.5 M NaCl final concentration and exhibited intrinsic resistance to seven antibiotics frequently prescribed for medical use. Moreover, we found that ED1 strain withstood 2 mg/L of Cadmium and 1 mg/L of either Nickel or Copper. Furthermore, we observed that S. rubidaea ED1 stimulated quinoa seeds germination and seedlings growth under salt stress conditions. Lastly, we discuss the advantages versus disadvantages of applying the S. rubidaea ED1 strain as a beneficial agent for salty and/or heavy metals contaminated soils.

Phosphate solubilization and multiple plant growth promoting properties of Mesorhizobium species nodulating chickpea from acidic soils of Ethiopia.

The main purpose of this study was to screen and select strains from seven Mesorhizobiumspp. for efficient phosphate solubilizing and other plant growth-promoting traits. Mesorhizobium species were tested for their ability to dissolve inorganic phosphate sources and multiple plant growth-promoting attributes. From a total of 62Mesorhizobiumstrains, 47(76%) strains formed clear zones with an average PSI of 1.9-2.7 on Pikovskaya's agar plate. The selected strains also released soluble phosphorus [125-150 P (µgml-1)] from tri-calcium phosphate and low level of phosphorous i.e., 15.4µg/ml and 14.5µg/ml from inorganic ferrous and aluminum phosphates, respectively, in a liquid medium after 4days of incubation. The release of soluble P was significantly (P < 0.01) correlated with a drop in pH of the medium. Moreover, screening for multiple plant growth-promoting attributes showed that 40, 28, 26, 21, and 38% of the strains were capable of producing indole-3-acetic acid, hydrogen cyanide, siderophores, ACC deaminase, and antagonism against Fusarium oxysporum f.sp. ciceris under in vitro conditions. TheMesorhizobium strains were endowed with the presence of ACC deaminase which was rarely reported elsewhere. All taken together, the acidic soils harbor numerous and more diverse phosphate solubilizing and plant growth-promoting Mesorhizobium spp. However, greenhouse and field conditions can be further studied within the context of improving chickpea production in Ethiopia.

Isolation and Characterization of Phosphate Solubilizing Microbes from Rock Phosphate Mines and Their Potential Effect for Sustainable Agriculture

Continuous application of phosphate (P) mineral to soil renders apatite addition during each crop growing season which is of great concern from a sustainable agriculture viewpoint. Use of efficient phosphate solubilizing microbes (PSB) is one of the most effective ways to solubilize this apatite mineral in the soil. The current study targeted hydroxyapatite mines to explore, isolate and characterize efficient P solubilizers to solubilize apatite in the soil. Efficiency of isolated microbes to solubilize rock phosphate (hydroxyapatite) and tri-calcium phosphate (TCP) as well as indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate deaminase (ACC) activity were tested. Identification and phylogenetic analysis of bacterial and fungal isolates were carried out by 16S rRNA and internal transcribed spacer (ITS) rDNA sequence analyses, respectively. The isolated bacterial strains were identified as Staphylococcus sp., Bacillus firmus, Bacillus safensis, and Bacillus licheniformis whereas fungal isolates were identified as Penicillium sp. and Penicillium oxalicum. Results showed that the impact of identified strains in combination with three phosphate fertilizers sources (compost, rock phosphate and diammonium phosphate (DAP)) was conspicuous on maize crop grown in pot. Both bacterial and fungal strains increased the P uptake by plants as well as recorded with higher available P in post-harvested soil. Penicillium sp. in combination with compost resulted in maximum P-uptake by plants and post-harvest soil P contents, compared to other combinations of P sources and bio-inoculants. Screening and application of efficient P solubilizers can be a better option to utilize the indigenous phosphate reserves of soil as well as organic amendments for sustainable agriculture.

Characterization and Mechanisms of Biosolubilization of Rock Phosphate by Microbes Isolated from Mahanadi Estuary, Odisha, India

Microbial solubilization of rock phosphate (RP) considered being an alternative to chemical phosphorous (P) fertilizer, causing high costs and environmental pollution. This work aimed to isolate efficient phosphate solubilizing strains from the estuary region of the Mahanadi river to check their RP solubilizing efficiency, and the mechanisms were discussed. Two strains of bacteria (Bacillus thuringenesis P0B11 and Lysinobaccillus fusiformis P0B28) and a fungus (Aspergillus aculeatus P0F3) were the most effective strain solubilizing RP. This is the first report of RP solubilization by L. fusiformis P0B28 and the first report of in vitro stearic acid production during RP solubilization. In particular, the potent strain A. aculeatus P0F3 produced the highest soluble P (345.6 mg/l) on 5th day. The soluble P concentration showed a significant negative correlation (r = − 0.88, p ≤ 0.01) with the pH, while it is positively correlated with the growth of B. thuringenesis P0B11 (r = 0.87, p ≤ 0.01), L. fusiformis P0B28 (r = 0.55, p ≤ 0.01) and A. aculeatus P0F3 (r = 0.96, p ≤ 0.01), respectively. The P release process from rock phosphate fit the first-order kinetics model well (R2 = 0.8046–0.8401). Organic acids produced by the isolates found to be the major mechanism for RP solubilization by supplying H+ ions and organic anions. High P concentration was related to the high corroded structure formation on the RP surface, reduction in all mineral peak intensities and a large decrease in the intensity of vibrational bands of calcite and fluorapatite confirmed by SEM, XRD, and FTIR, respectively.

The rhizosphere microbiome and growth-promoting rhizobacteria of the Brazilian juçara palm

Juçara palm (Euterpe edulis Mart.) is a native species of great ecological and economic importance that occurs in the Brazilian Atlantic Forest. The illegal harvesting of wild juçara palm heart has brought the species onto the endangered species list. Thus, this study aims to isolate, characterize, and select native bacterial strains associated with E. edulis and estimate the correlation between soil properties and diversity. In total, out of 190 isolates obtained of E. edulis, 110 were rhizosphere isolates, and 80 were root endophytic isolates that were screened for plant growth-promoting traits. The communities associated with juçara palm mainly include the genera Pseudomonas, Stenotrophomonas, Burkholderia, Rhizobium, and Gluconobacter. The diversity indices vary from 1.60 to 1.95, and it was found that soil phosphorus was most closely related to bacterial diversity, while clay, pH, and potassium had an inverse correlation with bacterial diversity. Out of the total bacterial isolates, 42.2% were found to be efficient phosphate solubilizers among which the Burkholderia genus was the most common, and the genus Pseudomonas was the most frequent among the siderophore-producing isolates (14.6%). Moreover, the Burkholderia and Pseudomonas were the most capable of producing auxins (80.2%); they were followed by Gluconobacter. In this regard, the isolation, identification, and the diversity of plant growth-promoting bacteria, which combine the ability to fix nitrogen with the production of substances capable of promoting the plant growth, in the future, can be of substantial help to the juçara palm cultivation.

Colonization by multi-potential Pseudomonas aeruginosa P4 stimulates peanut (Arachis hypogaea L.) growth, defence physiology and root system functioning to benefit the root-rhizobacterial interface

The beneficial associations between Arachis hypogaea L. (peanut) and fluorescent Pseudomonas species have been poorly explored despite their predominance in the peanut rhizosphere. The present study explores the mutually beneficial interactions between peanut roots and P. aeruginosa P4 (P4) in terms of their impact on plant growth, defence physiology and the root-rhizobacterial interface. The efficient phosphate solubilizer P4 exhibited biocontrol abilities, including the production of siderophores, pyocyanin, indole-3-acetic acid and hydrogen cyanide. The bacterization of peanut seeds with multi-potential P4 significantly enhanced in vitro seed germination and seedling vigour. Under sand-based gnotobiotic (10 days post-inoculation) and sterile soil-based cultivation systems (30 days post-inoculation), sustained P4 colonization enhanced the peanut root length and dry plant biomass. The subsequent increase in catalase, polyphenol oxidase and phenylalanine ammonia lyase activities with increased phenolic contents in the peanut roots and shoots suggested the systemic priming of defences. Consequently, the altered root exudate composition caused enhanced chemo-attraction towards P4 itself and the symbiotic N2-fixing Bradyrhizobium strain. Co-inoculating peanuts with P4 and Bradyrhizobium confirmed the improved total bacterial colonization (∼2 fold) of the root tip, with the successful co-localization of both, as substantiated by scanning electron microscopy. Collectively, the peanut-P4 association could potentially model the beneficial Pseudomonas-driven multi-trophic rhizosphere benefits, emphasizing the plausible role of non-rhizobium PGPR in promoting N2 fixation.