Tricalcium Phosphate Solubilization Research Articles

Phosphate solubilizing Pseudomonas and Bacillus combined with rock phosphates promoting tomato growth and reducing bacterial canker disease.

Nowadays, sustainable agriculture approaches are based on the use of biofertilizers and biopesticides. Tomato (Solanum lycopersicum L.) rhizosphere could provide rhizobacteria with biofertilizing and biopesticide properties. In this study, bacteria from the rhizosphere of tomato were evaluated in vitro for plant growth promotion (PGP) properties. Five Pseudomonas isolates (PsT-04c, PsT-94s, PsT-116, PsT-124, and PsT-130) and one Bacillus isolate (BaT-68s), with the highest ability to solubilize tricalcium phosphate (TCP) were selected for further molecular identification and characterization. Isolates showed phosphate solubilization up to 195.42 μg mL-1. All isolates showed phosphate solubilization by organic acid production. The six isolates improved seed germination and showed effective root colonization when tomato seeds were coated with isolates at 106 cfu g-1 in axenic soil conditions. Furthermore, the selected isolates were tested for beneficial effects on tomato growth and nutrient status in greenhouse experiments with natural rock phosphate (RP). The results showed that inoculated tomato plants in the presence of RP have a higher shoot and root lengths and weights compared with the control. After 60 days, significant increases in plant Ca, Na, P, protein, and sugar contents were also observed in inoculated seedlings. In addition, inoculated tomato seedlings showed an increase in foliar chlorophyll a and b and total chlorophyll, while no significant changes were observed in chlorophyll fluorescence. In greenhouse, two Pseudomonas isolates, PsT-04c and PsT-130, showed ability to trigger induced systemic resistance in inoculated tomato seedlings when subsequently challenged by Clavibacter michiganensis subsp. michiganensis, the causal agent of tomato bacterial canker. High protection rate (75%) was concomitant to an increase in the resistance indicators: total soluble phenolic compounds, phenylalanine-ammonia lyase, and H2O2. The results strongly demonstrated the effectiveness of phosphate-solubilizing bacteria adapted to rhizosphere as biofertilizers for tomato crops and biopesticides by inducing systemic resistance to the causal agent of tomato bacterial canker disease.

Understanding the Molecular Mechanism of PGPR Strain Priestia megaterium from Tea Rhizosphere for Stress Alleviation and Crop Growth Enhancement

The study aimed to assess the plant growth-promoting (PGP) capabilities and abiotic stress tolerance of strain IHB B 7164 with a focus on identifying associated genes through genomic analysis. Isolated from the tea rhizosphere, strain underwent screening for multiple PGP traits and stress tolerance against various abiotic factors. Taxonogenomic analysis of the complete genome identified the bacterium as Priestia megaterium exhibiting high similarity (97.04 % ANI, 74.3 % in silico DDH) to P. megaterium ATCC 14581. Functional annotations of the genome highlighted gene clusters associated with PGP traits and stress tolerance substantiating the strain's potential in promoting plant growth under stress conditions. The strain demonstarted robust growth and PGP activities under stressed culture conditions such as acidity, temperature fluctuations, desiccation, salinity, and exposure to calcium, aluminum, and iron salts, affirming its status as a stress-tolerant rhizobacterium. Screening of PGP traits under acidic conditions revealed phosphate solubilization, ACC-deaminase activity and production of IAA-like auxins. Notably gluconic and oxalic acids were consistently detected during solubilization of tri-calcium phosphate (TCP), aluminum phosphate (Al-P), and iron phosphate (Fe-P). Inoculation with the strain led to significant enhancements in tea nursery plants including a 9 % increase in plant height, 10 % increase in leaf number, and substantial improvements in leaf fresh and dry weights. Similarly, pea and wheat yields recorded notable increases of 16.9 % and 18.3 %, respectively under field conditions. These findings underscore the efficacy of P. megaterium strain IHB B 7164 as an abiotic stress-tolerant and broad-spectrum plant growth promoting rhizobacteria (PGPR) capable of enhancing plant growth and productivity across diverse agricultural settings.

Screening Plant Growth-Promoting Bacteria with Antimicrobial Properties for Upland Rice.

This study explores beneficial bacteria isolated from the roots and rhizosphere soil of Khao Rai Leum Pua Phetchabun rice plants. A total of 315 bacterial isolates (KK1 to KK315) were obtained. Plant growth-promoting traits (phosphate solubilization and indole-3-acetic acid (IAA) production), and antimicrobial activity against three rice pathogens (Curvularia lunata NUF001, Bipolaris oryzae 2464, and Xanthomonas oryzae pv. oryzae) were assessed. KK074 was the most prolific in IAA production, generating 362.6±28.0 µg/ml, and KK007 excelled in tricalcium phosphate solubilization, achieving 714.2±12.1 µg/ml. In antimicrobial assays using the dual culture method, KK024 and KK281 exhibited strong inhibitory activity against C. lunata, and KK269 was particularly effective against B. oryzae. In the evaluation of antimicrobial metabolite production, KK281 and KK288 exhibited strong antifungal activities in cell-free supernatants. Given the superior performance of KK281, taxonomically identified as Bacillus sp. KK281, it was investigated further. Lipopeptide extracts from KK281 had significant antimicrobial activity against C. lunata and a minimum inhibitory concentration (MIC) of 3.1 mg/ml against X. oryzae pv. oryzae. LC-ESI-MS/MS analysis revealed the presence of surfactin A in the lipopeptide extract. The crude extract was non-cytotoxic to the L-929 cell line at tested concentrations. In conclusion, the in vitro plant growth-promoting and disease-controlling attributes of Bacillus sp. KK281 make it a strong candidate for field evaluation to boost plant growth and manage disease in upland rice.

Isolation and Identification of Acer truncatum Endophytic Fungus Talaromyces verruculosus and Evaluation of Its Effects on Insoluble Phosphorus Absorption Capacity and Growth of Cucumber Seedlings.

The symbiosis between endophytic fungi and plants can promote the absorption of potassium, nitrogen, phosphorus, and other nutrients by plants. Phosphorus is one of the indispensable nutrient elements for plant growth and development. However, the content of available phosphorus in soil is very low, which limits the growth of plants. Phosphorus-soluble microorganisms can improve the utilization rate of insoluble phosphorus. In this study, Talaromyces verruculosus (T. verruculosus), a potential phosphorus-soluble fungus, was isolated from Acer truncatum, a plant with strong stress resistance, and its phosphorus-soluble ability in relation to cucumber seedlings under different treatment conditions was determined. In addition, the morphological, physiological, and biochemical indexes of the cucumber seedlings were assessed. The results show that T. verruculosus could solubilize tricalcium phosphate (TCP) and lecithin, and the solubilization effect of lecithin was higher than that of TCP. After the application of T. verruclosus, the leaf photosynthetic index increased significantly. The photosynthetic system damage caused by low phosphorus stress was alleviated, and the root morphological indexes of cucumber seedlings were increased. The plant height, stem diameter, and leaf area of cucumber seedlings treated with T. verruculosus were also significantly higher than those without treatment. Therefore, it was shown that T. verruculosus is a beneficial endophytic fungus that can promote plant growth and improve plant stress resistance. This study will provide a useful reference for further research on endophytic fungi to promote growth and improve plant stress resistance.

Exploration and Characterization of High-Efficiency Phosphate-Solubilizing Bacteria Isolates from Chickpea Rhizospheric Soil

The study was conducted during April, 2021 to June, 2022 to study the isolation and identification of high effective strains of phosphate solubilizing bacteria and evaluation the ability to solubilize tricalcium phosphate in vitro. Microorganisms that live in soil are actively involved in the carbon, nitrogen, sulphur, and phosphorus cycles in nature, enabling them to maintain ecological balance. Phosphate-solubilizing microbes are used as agricultural biofertilizers and play an essential role in plant nutrition by enhancing phosphate uptake. Phosphate is one of the most important macronutrients necessary for the growth and development of plants. Numerous microorganisms present in the rhizosphere solubilize insoluble phosphorus, making it readily available to plants. Fourteen phosphate-solubilizing bacterial colonies were identified on Pikovskaya’s agar medium, containing insoluble tricalcium phosphate (TCP) from rhizospheric soil. Among them, eight colonies showing clear halo zones around the microbial growth were considered as phosphate-solubilizing. All isolates showing the highest phosphate solubilization index (PSI), ranging from 2.8 to 4.03, were selected for further qualitative and quantitative studies. Out of these eight potent isolates, two strains showed the maximum PSI: V7 (4.03) and V8 (3.85) in agar plates, along with a high production of soluble phosphate, measuring 448.03 and 441.43 mg l-1, and a greater reduction in pH in the broth culture. The morphological, biochemical, and molecular identification of V7 and V8 strains revealed them to belong the Acinetobacter and Paenibacillus genera, respectively, and were phylogenetically close to Acinetobacter baumannii and Paenibacillus lautus species.

Groundnut harbours non-nodulating non-rhizobial plant growth-promoting bacterial endophytes.

The present study was carried out to assess the growth-promoting ability of non-rhizobial endophytes in groundnut (Arachis hypogaea). Thirteen endophytic bacteria with different morphologies were isolated from the root and nodules of groundnut. These isolates significantly enhanced the growth of groundnut in sterilised vermiculite, though the isolates were unable to nodulate the host plant. The endophytic nature of these isolates was confirmed by their re-isolation from the sterilised and macerated roots of the plants. The isolates exhibited in vitro tricalcium phosphate and zinc solubilization, production of siderophores, auxins and ammonia as well as growth on different nitrogen-free media. The phosphate solubilization and auxin production varied from 50 to 196 and 17 to 71µg/ml, respectively by the isolates. Based on phenotypic tests and 16S rRNA gene sequencing, four potential strains were identified as Klebsiella sp. R3, Pseudomonas putida R6, Klebsiella oxytoca GRE5 and Pseudomonas proteolytica GRE6. A significant increase in plant growth, chlorophyll content, nodule count and shoot nutrient content of groundnut was observed with these bacterial inoculations over the uninoculated control in greenhouse. The bacterial treatments resulted in increased N, P and K content in the shoot up to 87, 96 and 44%, respectively, over the control. Physico-chemical properties and available nutrient content of soil were also improved on bacterial inoculations. The results indicated that groundnut harbours beneficial non-rhizobial bacterial endophytes with the potential to be used as microbial inoculants in groundnut. Klebsiella oxytoca as a non-nodulating nodule endophyte of groundnut is reported for the first time.

Isolation and Phenotypic Microarray Profiling of Different Pseudomonas Strains Isolated from the Rhizosphere of Curcuma longa L.

In the present study, different Pseudomonas strains were isolated from the rhizospheric soil of Curcuma longa (turmeric) and further identified and characterized based on morphological, biochemical, and molecular characteristics through the 16S rRNA gene sequencing analysis. The identified bacterial strains belong to the Pseudomonas genus viz. Pseudomonas sp. CL10, Pseudomonas sp. CL11, and P. fluorescence CLI4. However, the isolated strains tested positive for IAA production, siderophore production, and the solubilization of tricalcium phosphate during plant growth promoting traits analysis. Further phenotype microArray (PM) technology was used to evaluate the antibiotic and chemical sensitivity of the isolated bacterial strains. The antibiotics phleomycin, oxacillin, vancomycin, novobiocin, spiramycin, and rifampicin, as well as chemicals like, 5-7 dichloro-8-hydroxy quanaldine, 5-7 dichloro-8-hydroxyquinoline, domophenbrobide, and 3-5 dimethoxy benzyl alcohol, showed resistance in all the rhizobacterial strains. However, upon further detailed study, Pseudomonas sp. CL10 exhibited resistance to thirteen antibiotics, CL11 to fourteen, and CL14 showed resistance against seventeen antibiotics and chemical classes. The results of the study indicate that some of these strains can be used as bioinoculum to enhance the plant growth and health.

Plant growth promotion of radish by rhizosphere dwelling bacteria

The present study was carried out with the aim to develop a plant growth-promoting rhizobacterial inoculant for improving the growth of radish. A total of 20 rhizobacteria were isolated and then tested for multifarious plant growth-promoting traits. The isolates exhibited tricalcium phosphate and zinc solubilization, production of siderophores, auxins, ammonia and growth on different nitrogen free medium. Out of 20 isolates, two potential bacterial isolates (RM3 and RL3) were selected on the basis of PGP traits for evaluation of their potential to promote growth of radish under pot conditions. In green house experiment, these isolates when used as consortium showed a significant improvement in soil enzymatic activities (viz. dehydrogenase: 12.99 µg TPF formed h-1 g of soil-1, alkaline phosphatase: 11.94 µg PNP formed h-1 g of soil-1 and urease: 401.65 µg urea hydrolyzed formed h-1g of soil-1) and plant growth parameters (shoot length: 38.76 cm, leaf area: 267cm2, fresh leaf weight:106.05 g, dry leaf weight:1.23 g, number of leaves per plant: 23, fresh root weight:111.69 g, dry root weight: 2.06 g, root length: 34.04 cm and root diameter: 3.33 cm) relative to control as well as other bioinoculants. These bacteria were tentatively identified as Bacillus (RM3) and Pseudomonas (RL3) on the basis of biochemical tests.

Unlocking the potential of rhizobacteria in Moroccan vineyard soils: Biocontrol of grapevine trunk diseases and plant growth promotion

Rhizospheric bacteria isolated from the root system of Vitis vinifera plants in Morocco were evaluated for their activities against fungi associated with grapevine trunk diseases namely Diplodia mutila, Neoscytalidium dimidiatum, Trichothecium roseum, and Neopestalotiopsis vitis. Those pathogens cause grapevine decline and impede growth and are known as the greatest threat to production worldwide. Among a collection of 196 rhizobacteria, twenty-four isolates exhibited potential antifungal activity against all the tested fungal pathogens. Based on the partial 16S rDNA genes, different genera were identified namely Bacillus, Pseudomonas, Achromobacter, Ensifer, and Brucella. In particular, Bacillus halotolerans (JFM-64 and JMS-14), Pseudomonas koreensis (JRSK-45), and Ensifer adhaerens (JRSK-84) were found to be the most effective strains. Furthermore, the potential of bacterial isolates to promote plant growth was assessed. The funding revealed that of twenty-four antagonist rhizobacteria, seventeen displayed protease and chitinase production, while fifteen, thirteen, and twelve bacteria demonstrated the production of amylase, cellulase, and pectinase respectively. Furthermore, thirteen bacterial isolates produced hydrocyanic acid (HCN), sixteen isolates harbor the ability to solubilize tricalcium phosphate and seventeen were able to produce siderophores and indole acetic acid (IAA). The results of the current study showed that the most effective bacterial isolates could exhibit traits other than Plant Growth-Promoting Rhizobacteria (PGPR). Our results showed that the bacterization of B. napus seedlings with the selected bacteria improved plant growth when compared to untreated controls. Autoclaved grape wood assays were used to further confirm the in vitro results. The growth of Diplodia mutila, Neopestalotiopsis vitis, Neoscytalidium dimidiatum, and Trichothecium roseum was effectively reduced by rhizobacterial isolate Pseudomonas koreensis (JRSK-45) by 97.31, 97.14, 94.17, and 91.91%, respectively. This study highlights the potential of specific rhizobacteria as a promising approach to controlling fungal trunk pathogens associated with grapevine decline.

Promoting the growth of Sulla flexuosa L. by endophytic root nodule bacteria authors and affiliations.

Legume plants rely upon multipartite interactions between rhizobia and bacterial endophytes within root nodules to facilitate plant growth. This study aimed to isolate and identify indigenous endophytic bacteria from root nodules of Sulla aculeolata L. in Northeast Morocco. Based on their tri-calcium phosphate (TCP) solubilization capacity, five endophytes were chosen for further evaluation of their plant growth traits. All isolates were hydrogen cyanide (HCN) and siderophore producers, while only BCH24 tested positive for ACC deaminase activity. Indole-3-acetic acid (IAA) synthesis ranged from 1.27 mgL- 1 to 2.89 mgL- 1, while soluble phosphate concentrations was between 7.99mg L- 1 and 110.58mg L- 1. Additionally, all the endophytes were able to produce more than two lytic enzymes. Based on the analysis of 16S rRNA gene sequences five isolates were identified as Enterobacter sp (BCH13, BCH2), Pseudomonas sp (BCH16, BCH24), and Serratia sp (BCH10). The strains inhibited the growth of three phytopathogenic fungi, with BCH13 exhibiting the highest rate against Aspergillus ochraceus (45%), followed by BCH24 against Fusarium oxysporum (40%) and Botrytis cinerea (35%), respectively. In vivo inoculation of halotolerant strains Enterobacter hormaechei (BCH13) and Pseudomonas moraviensis (BCH16) under gnotobiotic conditions revealed that co-inoculation with Rhizobium sullae KS6 improved plant development compared to single inoculation, making it a promising eco-friendly bio-inoculant for legume Sulla flexuosa L. production.

Isolation and characterization of phosphate-solubilizing bacterium Pantoea rhizosphaerae sp. nov. from Acer truncatum rhizosphere soil and its effect on Acer truncatum growth.

The Acer truncatum Bunge, widely distributed in North China, shows excellent tolerance to low-P soils. However, little information is available on potential phosphate-solubilizing bacterial (PSB) strains from the A. truncatum rhizosphere. The objectives of this work were to isolate and characterize PSB from A. truncatum rhizosphere soil and to evaluate the effect of inoculation with the selected strain on A. truncatum seedlings. The strains were characterized on the basis of phenotypic characteristics, carbon source utilization pattern, fatty acid methyl esters analysis, 16S rRNA gene and the whole-genome sequence. A Gram-negative and rod-shaped bacterium, designated MQR6T, showed a high capacity to solubilize phosphate and produce indole-3-acetic acid (IAA) and siderophores. The strain can solubilize tricalcium phosphate (TCP) and rock phosphate (RP), and the solubilization of TCP was about 60% more effective than RP. Phylogenetic analyses based on the 16S rRNA gene and whole-genome sequences revealed that strain MQR6T formed a distinct phyletic lineage as a new species within the genus Pantoea. The digital DNA-DNA hybridization value between strain MQR6T and the closely related strains was 19.5-23.3%. The major cellular fatty acids were summed feature 3 (C16:1ω7c and/or C16:1ω6c), summed feature 8 (C18:1ω6c and/or C18:1ω7c), C14:0, C16:0, and C17:0 cyclo. Several genes related to IAA production, phosphonate transport, phosphate solubilization and siderophore biogenesis were found in the MQR6T genome. Furthermore, inoculation with the strain MQR6T significantly improved plant height, trunk diameter, dry weight and P accumulation in roots and shoot of A. truncatum seedlings compared to non-inoculated control. These plant parameters were improved even further in the treatment with both inoculation and P fertilization. Our results suggested that MQR6T represented a new species we named Pantoea rhizosphaerae, as a plant growth-promoting rhizobacterium that can solubilize inorganic P and improve growth of A. truncatum seedlings, emerging as a potential strategy to improve A. truncatum cultivation.

An insight into the role of the organic acids produced by Enterobacter sp. strain 15S in solubilizing tricalcium phosphate: in situ study on cucumber

BackgroundThe release of organic acids (OAs) is considered the main mechanism used by phosphate-solubilizing bacteria (PSB) to dissolve inorganic phosphate in soil. Nevertheless, little is known about the effect of individual OAs produced by a particular PSB in a soil–plant system. For these reasons, the present work aimed at investigating the effect of Enterobacter sp. strain 15S and the exogenous application of its OAs on (i) the solubilization of tricalcium phosphate (TCP), (ii) plant growth and (iii) P nutrition of cucumber. To this purpose two independent experiments have been performed.ResultsIn the first experiment, carried out in vitro, the phosphate solubilizing activity of Enterobacter 15S was associated with the release of citric, fumaric, ketoglutaric, malic, and oxalic acids. In the second experiment, cucumber plants were grown in a Leonard jar system consisting of a nutrient solution supplemented with the OAs previously identified in Enterobacter 15S (jar’s base) and a substrate supplemented with the insoluble TCP where cucumber plants were grown (jar’s top). The use of Enterobacter 15S and its secreted OAs proved to be efficient in the in situ TCP solubilization. In particular, the enhancement of the morpho-physiological traits of P-starved cucumber plants was evident when treated with Enterobacter 15S, oxalate, or citrate. The highest accumulation of P in roots and shoots induced by such treatments further corroborated this hypothesis.ConclusionIn our study, the results presented suggest that organic acids released by Enterobacter 15S as well as the bacterium itself can enhance the P-acquisition by cucumber plants.

The effects of herbicide application on two soil phosphate solubilizing bacteria: Pantoea agglomerans and Serratia rubidaea.

The application of synthetic pesticides is one of the fastest acting tools at farmers' disposal to prevent and mitigate the threats posed by plant pests in agriculture. However, the effects of these above-ground applications of pesticides are known to be detrimental to some belowground, non-target soil biota. At present, the effects many pesticides have on key functional microbial groups associated with phosphate (P) solubilization in the soil are still largely unknown. The purpose of this study was to compare the effects of two herbicides, glyphosate, and paraquat, on phosphate solubilizing bacteria (PSB) with and without pH adjustment (after herbicide addition) since pH is a major indicator of P solubilization. In our assay, two PSB strains (Pantoea agglomerans and Serratia rubidaea) were chosen to assess their ability to solubilize tricalcium phosphate (TCP) by using the vanadate-molybdate method (to measure the amount of P solubilized) in the presence of glyphosate (5.4 g/L and 10.8 g/L) or paraquat (2 g/L and 4 g/L) separately. To assess the effect of PSB treated by the herbicides, a growth experiment using PSB inoculated wheat seedlings was performed under greenhouse conditions (25 °C, light 16 h/8 h dark). After four weeks, wheat above-ground growth parameters were measured. Our results showed that even under recommended doses of glyphosate (5.4 g/L) and paraquat (2 g/L), a decrease in P solubilization activity was observed in P. agglomerans and S. rubidaea. Whilst paraquat affected TCP solubilization more than glyphosate with and without pH adjustment, there was a significant decrease (p < 0.05) in TCP solubilization, up to 39% and 93% in the presence of glyphosate and paraquat, respectively, for S. rubidaea, and up to 45% and 95% in the presence of glyphosate and paraquat, respectively, for P. agglomerans. The effect of the herbicides on the PSB had the same results as in the greenhouse test on wheat seedling growth, confirming that these herbicides have both above and belowground negative effects, despite being used at recommended doses.

Novosphingobium kaempferiae sp. nov., a phosphate-solubilizing bacterium isolated from stem of Kaempferia marginata Carey.

A Gram-stain-negative, aerobic, rod-shaped, non-spore-forming and yellow-pigment-producing bacterium, designated as Sx8-5T, was isolated from stem tissue of Kaempferia marginata Carey in Kanchanaburi Province, Thailand. The strain exhibited tricalcium phosphate solubilizing activity. Its taxonomic position was investigated using a polyphasic approach. Sx8-5T grew at 25-37 °C (optimum 30 °C), pH 6-9 (optimum 7) and with 0 and 1% NaCl (optimum 0 %). According to the 16S rRNA gene phylogeny, Sx8-5T represents a member of genus Novosphingobium and shared the highest sequence similarities to Novosphingobium barchaimii LL02T of 99.4 % and shared sequence similarities with other species of the genus Novosphingobium of less than 99.4 %. The whole-genome size was 5.7 Mb, comprised of one contig, with a DNA G+C content of 66 %. The average nucleotide identity using BLASTn (ANIb) or MUMMER (ANIm) values for whole genome comparisons between Sx8-5T and Novosphingobium barchaimii LL02T and six closely related type strains were 72.33-82.14 % and 83.82-87.38 %, respectively, and the digital DNA-DNA hybridization (dDDH) values ranged from 21.0 to 28.6% when compared with the type strains of the members of the genus Novosphingobium. Major fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c), C16 : 0 and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), respectively. Polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylglycerol, unidentified phospholipids and unidentified polar lipids. The major isoprenoid quinone was Q-10. According to results obtained using a polyphasic approach, Sx8-5T represents a novel species of the genus Novosphingobium, the name Novosphingobium kaempferiae sp. nov. is proposed. The type strain is Sx8-5T (=JCM 35076T =TBRC 15600T).

Characterization of Paenibacillus spp. CBRM17 as antagonist of phytopathogenic fungi and growth promoter of Capsicum chinense Jacq.

Studies of the plant-microorganism relationship have made it posible to explore the potential of rhizospheric bacteria to improve the health and quality of plants. In the present study, Paenibacillus sp. CBRM17 was characterized in vitro for its ability to inhibit the growth of phytopathogenic fungi that cause diseases in horticultural crops in the tropics, finding a reduction in the mycelial growth of Alternaria, Fusarium and Helmintosphorium strains in the range of 50 to 70 %, additionally its biochemical properties related to the promotion of plant growth were characterized, registering the production of 0.36 µg/mL of indole acetic acid (IAA), the solubilization of tricalcium phosphate with solubilization index (SI) of 2.41 mm and solubilization efficiency (SE) of 140.6 %, producing in the supernatant 63.5 mg/L of soluble phosphorus, in addition to being positive for ACC deaminase activity. Inoculations trials of habanero chili (Capsicum chinense Jacq.) seeds with Paenibacillus sp. CBRM17 showed its potential to be used as an inoculant in the growth promotion of this crop, since it increased all growth variables; increasing the total fresh and dry biomass by 93.3 and 96.4 %, respectively.

Effect of pH and Carbon Source on Phosphate Solubilization by Bacterial Strains in Pikovskaya Medium.

Phosphate-solubilizing bacteria (PSB) transform precipitated inorganic phosphorus into soluble orthophosphates. This study evaluated the efficiency of tricalcium and iron phosphate solubilization in Pikovskaya medium using five bacterial strains (A1, A2, A3, A5, and A6) cultured in acidic and alkaline pH levels. The bacterial strain that proved to be more efficient for P solubilization and was tolerant to pH variations was selected for assessing bacterial growth and P solubilization with glucose and sucrose in the culture medium. The bacterial strains were identified through 16S rRNA gene sequencing as Pseudomonas libanensis A1, Pseudomonas libanensis (A2), Bacillus pumilus (A3), Pseudomonas libanensis (A5), and Bacillus siamensis (A6). These five bacterial strains grew, tolerated pH changes, and solubilized inorganic phosphorus. The bacterial strain A3 solubilized FePO4 (4 mg L-1) and Ca3(PO4)2 (50 mg L-1). P solubilization was assayed with glucose and sucrose as carbon sources for A3 (Bacillus pumilus MN100586). After four culture days, Ca3(PO4)2 was solubilized, reaching 246 mg L-1 with sucrose in culture media. Using glucose as a carbon source, FePO4 was solubilized and reached 282 mg L-1 in six culture days. Our findings were: Pseudomonas libanensis, and Bacillus siamensis, as new bacteria, can be reported as P solubilizers with tolerance to acidic or alkaline pH levels. The bacterial strain B. pumilus grew using two sources of inorganic phosphorus and carbon, and it tolerated pH changes. For that reason, it is an ideal candidate for inorganic phosphorus solubilization and future production as a biofertilizer.

Bioprospecting of Multi Trait Plant Growth Promoting Bacillus altitudinis from Phosphate Rich Soil

Phosphate Solubilizing Bacteria (PSB) has the natural ability to liberate unavailable phosphorus (as a result of microbial metabolism extracellularly) from soil, rocks, and mines thereby increasing its availability for plants. The main mechanism behind this is the production of mineral dissolving compounds, such as organic acids, protons, hydroxyl ions, and CO2. The current study was conducted to explore the potential of a phosphate solubilizing bacteria which are isolated from rock phosphate mine in Rajasthan for enhancing the growth of Zea mays (maize) plants. Out of total of 137 bacterial isolates, one bacterial isolate RJ-11 was found to have multiple plant growth promoting (PGP) properties. Its phosphate solubilization ability was observed with solubility index (PSI) of 5.15. The potential isolate RJ-11 was found to solubilize tri calcium phosphate (Ca3(PO4)2) at a rate of 790.67 mg L-1. RJ-11 was found positive for potash solubilization, zinc solubilization, and siderophore production. On the basis of morphological and molecular characterization, isolate RJ-11 was identified as Gram positive bacterium, Bacillus altitudinis. LabID-B197 was assigned to B. altitudinis for further greenhouse pot experiments. Greenhouse pot experiments demonstrated that maize plants inoculated with B197 incorporated more phosphate which was observed as increase in germination percentage, increased shoot length (155%) and root length (45%), and much higher biomass weights than those plants without any added bacteria or controls. The result of present study indicates that B. altitudinis is a unique bacterium with multiple plant growth promoting properties and could act as potential bio fertilizer to improve the plant growth and develop cost-effective and sustainable agriculture practices.

Impact Assessment of Varied Agroclimatic Conditions on Phosphate Solubilization Potential of Fungi in Fermentation and Soil-Plant System

In this work, two phosphate solubilizing fungi viz., Aspergillus tubingensis S33 and A. niger S36 were studied under different physiochemical and nutritional parameters in the lab, and in vitro under soil-plant experiments at two very distinct agro-climatic conditions viz., Banasthali, Tonk (Rajasthan), and Dwarahat, Almora (Uttarakhand), India. Phosphate-solubilizing capability was checked with different carbon and nitrogen sources. Maltose, glucose, and fructose were optimal carbon source in A. tubingensis S33 while fructose in the case of A. awamori S33. Amongst nitrogen sources, S33 showed maximum phosphate solubilization with ammonium sulfate while, S36 with ammonium sulfate and sodium nitrate. Ammonium was more stimulating than nitrate as the chief nitrogen source. In vivo experiments revealed that solubilization was noticeable at all the temperatures, but optimal temperature was 25–35℃. The optimal initial pH for Tricalcium Phosphate (TCP) solubilization was 8.0. The ideal concentration of TCP for solubilization was 7.5 g∙l−1. The application of both strains in two different geographical sites exhibited a significant (p<0.05) rise in wheat growth, grain yield, and available Phosphorus (P). Fungal inoculation with TCP amendment exhibited a more notable effect on growth, yield, and soil fertility than control. This study support that these isolates will be able to work efficiently in varied climatic conditions and will show consistent efficiency on field application.

Exploring the potential of P solubilizing rhizobacteria for enhanced yield and quality in turmeric (Curcuma longa L.)

The study focused on isolation and characterization of a bevy of phosphorus solubilizing bacteria (PSB) and exploring the effects of the most promising PSB on yield and quality of turmeric. For this purpose, several bacterial strains isolated from the rhizosphere of turmeric grown across India were assessed for their capacity to solubilize tri-calcium phosphate (TCP) and di-calcium phosphate (DCP) under in vitro condition and in liquid medium. The soluble P turnover by the promising PSB was then investigated in soil per se and their effects were further validated in turmeric under both green house and field conditions for two successive years. The results revealed that Bacillus safensis (NCBI-MT192800), B. marisflavi (NCBI-MT 192801), B. cereus (NCBI- MT192803) and Pseudomonas aeruginosa (NCBI-MZ 540872) released significantly greater levels of labile P in the liquid medium due to their capacity to produce appreciable amounts of organic acids (gluconic, α ketogluconic, succinic, oxalic and tartaric). Green house studies on turmeric indicated that soil available P was significantly higher in the treatments involving PSB suggesting enhanced P solubilization and the treatment with B. safensis + 75 % P as rock phosphate (RP) increased rhizome yield by 129.0 % compared to the treatment with 100 % P applied as RP. The positive effects of PSB were also reflected in field experiments, wherein the treatments with combined application of B. safensis with 50 % or 75 % or 100 % P significantly increased soil available P by 143.0 – 246.0 %, rhizome yield by 29.0 – 120.0 %, P uptake by 51.0 – 223.0 % and curcumin content by 30.0 – 32.5 % compared to control (100 % P as RP). The use of B. safensis ensured 25.0 % reduction in exogenous inorganic P application while simultaneously enhancing turmeric yield and quality in P deficient soil.

Molecular Characterization of Plant Growth Promoting Pseudomonas from Rhizosphere of Euphorbia caducifolia Haines

A study was conducted during kharif 2020 at the Department of Microbiology, Chimanbhai Patel College of Agriculture, S. D. Agricultural University for molecular characterization of plant growth promoting Pseudomonas isolates from rhizosphere of Euphorbia caducifolia. Twenty Pseudomonas isolates (designated as PsEc1 to PsEc20) were axenically isolated from rhizospheric soil sample of Euphorbia caducifolia using Pseudomonas Isolation Agar Base (a selective medium). These isolates were tested gram negative, rod shaped, and oxidase positive. All 20 isolates were positive for utilization of maltose, esculin, citrate and malonate whereas these isolates showed varied results for utilization of xylose, fructose, galactose, sucrose and sorbitol. 16Sr DNA sequencing data revealed similarity of the isolates to different species of Pseudomonas, i.e., P. fluroscens (11), P. aeruginosa (3), P. putida (3), P. stutzeri (2) and P. syringe (1). These nucleotide sequences were submitted to the NCBI GenBank database with accession numbers respectively MT775484 to MT775503. The 16S rDNA sequences were aligned and used to reconstruct a phylogenetic tree with bootstrap values using software MEGA 6.06. The phylogenetic tree comprised of three clades. Clade I comprised of sixteen isolates, clade II four isolates and clade III only one isolate. The members of clade I belonged to P. fluorescens, P. putida and P. stutzeri whereas members of clade II comprised of P. aeruginosa. However, clade III consisted of P. syringae. In vitro test showed PsEc17 (P. fluorescens, MT775500) as most efficient in solubilizing tricalcium phosphate (78.53 µg ml-1) and IAA production (78.53 µg ml-1). PsEc17 also proved most efficient and showed 69.5% inhibition of Fusarium oxysporum f. sp. cumini.