Phosphate Solubilizing Ability Research Articles

Broad-spectrum pH functional chitosan-phosphatase beads for the generation of plant-available phosphorus: utilizing the insoluble P pool.

Utilization of organic phosphates and insoluble phosphates for the gradual generation of plant-available phosphorus (P) is the only sustainable solution for P fertilization. Enzymatic conversions are one of the best sustainable routes for releasing P to soil. Phosphatase enzyme aids in solubilizing organic and insoluble phosphates to plant-available P. We herein report the preparation of highly functional chitosan beads co-immobilized with acid phosphatase and alkaline phosphatase enzymes via a glutaraldehyde linkage. The dual enzyme co-immobilized chitosan beads were characterized using Fourier-transform infrared (FTIR), thermogravimetric (TGA), and scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analyses to confirm the immobilization. The co-immobilized system was found to be active for a broader pH range of ∼4-10 than the individually bound enzymes and mixed soluble enzymes. The bound matrix exhibited pH optima at 6 and 9, respectively, for acid and alkaline phosphatase and a temperature optimum at 50°C. The phosphate-solubilizing abilities of the chitosan-enzyme derivatives were examined using insoluble tri-calcium phosphate (TCP) for wide pH conditions of 5.5, 7, and 8.5 up to 25 days. The liberation of phosphate was highest (27.20mg/mL) at pH 5.5 after the defined period. The residual soil phosphatase activity was also monitored after 7days of incubation with CBE for three different soils of pH ∼5.5, 7, and 8.5. The residual phosphatase activity increased for all the soils after applying the CBE. The germination index of the Oryza sativa (rice) plant was studied using different pH buffer media upon the application of the CBE in the presence of tri-calcium phosphate as a phosphate source. Overall, the dual-enzyme co-immobilized chitosan beads were highly effective over a wide pH range for generating plant-available phosphates from insoluble phosphates. The chitosan-enzyme derivative holds the potential to be used for sustainable phosphorus fertilization with different insoluble and organic phosphorus sources.

Diversity of endophytic bacterial community in rice roots and their roles in phosphate solubilization and plant growth

Root endophytic bacteria have significant beneficial effects on plant growth and health, while specific coexisting pathogenic bacteria can cause various diseases. In this study, we assessed the diversity and cultivability of the endophytic bacterial community in rice roots with a focus on their capacity for phosphate solubilization and impact on plant growth. Employing PacBio Single Molecule Real-Time (SMRT) and Sanger sequencing, we generated 16S rRNA gene libraries using metagenomic DNA extracted from the roots of three field-grown rice plants, along with genomic DNA from 156 associated bacterial isolates. QIIME 2-based microbiome analysis revealed dominant classified species at diverse taxonomic levels, including Arcobacter marinus, Paraburkholderia kururiensis, Lactobacillus plantarum, and Lactobacillus brevis. Furthermore, we effectively isolated 25.97% of rice root endophytic bacteria, with a notable 33.33% of pure culture endophytic bacteria exhibiting phosphate solubilization abilities. Finally, we revealed the inhibitory role of Burkholderia vietnamiensis and the growth promoting role of Paraburkholderia kururiensis subsp. Kururiensis in both the monocot model Brachypodium distachyon and the dicot Arabidopsis thaliana. Our study provided novel insight into the microbiome structure in rice roots and its potential to benefit rice cultivation and enhance overall crop health.

Rhizospheric Fungal spp. of Tomato (Solanum lycopersicum L.) and Their Effect on Tomato Plant Growth and on Alternaria solani, the Causative Agent of Early Blight of Tomato

Tomato (Solanum lycopersicum L.) is a widely consumed crop throughout the world including Sri Lanka. Use of agrochemicals for enhanced yields and managing diseases associated with tomato results in deleterious impacts on soil microflora, fauna and leads to human health problems. A possible alternative is the use of rhizospheric microorganisms, as they are reported to improve productivity and protect various crops. Hence this study aimed to isolate rhizospheric fungal assemblages of tomato plants and evaluate their ability to solubilize phosphate while, controlling Alternaria solani, the causative agent of Early Blight of tomatoes. Rhizospheric fungi were isolated from commercial tomato cultivations in two agro-ecological zones (WM3b and IM2b), using soil dilution plate technique. Composite samples of soil attached to the root systems of five healthy plants, uprooted from each field were prepared and 10 g of each sample was used for the isolations. Twenty-seven fungal genera were isolated and Trichoderma and Penicillium were the frequently isolated genera. Phosphate solubilization ability of each fungal species was evaluated using Pikovskaya's agar and liquid medium, and four isolates (Eupenicillium sp., Talaromyces purpureogenus, Paecilomyces sp., and Purpureocillium lilacinum) with the highest phosphate solubilizing abilities were evaluated on tomato plant growth under greenhouse condition. The inocula of each fungal sp. were prepared by adding fifteen, 6mm diameter mycelial discs from each 5-day-old culture into polypropylene bags containing 90 g of sterile rice husk medium and incubated for 02 weeks at room temperature. Each pot contained a 4.6 kg layer of non- sieved sterilized potting medium (Sand: topsoil: Compost at 2:1:1 ratio) and a 2.5 kg layer of sieved medium on top, which was mixed with 15 g of inoculum. Three-week old, healthy tomato seedlings (variety-Bathiya) were planted (with 3 replicates) and allowed to grow with regular watering. Control pots contained potting medium with uninoculated sterile rice husk. Growth parameters such as Root and shoot lengths, fresh and dry weights of roots, shoots, and leaves were evaluated at 02-week intervals for 02 months and the results were analysed using ANOVA with Tukey‘s pairwise comparison. Plants treated with T. purpureogenus and P. lilacinum showed significant increases (p≤0.05) in all growth parameters in every evaluation. Dual culture plate assay on the Potato Dextrose Agar was used to test the effect of rhizospheric fungal spp. on the radial colony growth of A. solani, and Eupenicillium sp. showed the highest percentage inhibition (85.09±5.68%). Microscopic observations of inhibition zones between two colonies showed the presence of coils, loops, knobs, and haustoria, formed by inhibitory rhizospheric fungal species. Assays for Chitinase and Glucanase enzyme production showed that Mortierella sp.-1, P. lilacinum, Trichoderma sp.-1, and Acremonium sp. were the highest chitinase producers, whereas P. lilacinum was the highest glucanase producer. These results indicate the ability of some rhizospheric fungal species of tomato to increase the growth of tomato plants significantly by phosphate solubilization and ability to inhibit the growth of foliar pathogen A. solani under in vitro conditions. 
 Keywords: Rhizospheric fungi, Phosphate solubilization, Dual culture plate, Plant growth parameters

Screening and biodiversity analysis of cultivable inorganic phosphate-solubilizing bacteria in the rhizosphere of Hydrilla verticillata.

The inorganic phosphate-solubilizing bacteria (IPB) in the rhizosphere of Hydrilla verticillata can convert insoluble inorganic phosphorus in the environment into soluble phosphorus that can be directly absorbed and utilized by Hydrilla verticillata. In this research, the roots and rhizosphere sediments of Hydrilla verticillata were collected from high-organic matter urban landscape water. The National Botanical Research Institute's Phosphate growth medium (NBRIP medium) was used to screen for efficient cultivable IPB. The 16S rRNA gene sequence analysis was used to determine the taxonomic affiliation of the strains, and ammonium molybdate spectrophotometry was used to detect the phosphate-solubilizing ability of the strains. The results show that a total of 28 IPB strains with good phosphate-solubilizing effect are obtained from the roots and rhizosphere sediments of Hydrilla verticillata. These IPB strains belong to two phyla, four orders, seven classes, nine families, and nine genera. Among these, Bacillus and Acinetobacter are the dominant genera, and the strains SWIH-7, SWIP-6, SWIP-7, SWIP-13, SWIP-15 and SWIP-16 are potential new species. The IPB strains isolated and screened in this research are rich in diversity, with potential new species and stable phosphate-solubilizing characteristic. These IPB strains are suitable for further development as microbial bacterial agents, which can be applied to promote the recovery of submerged plants in polluted water with high-organic matter, treatment of polluted water and ecological restoration of water.

Eksplorasi Potensi Bacillus spp. sebagai Bakteri Pemacu Pertumbuhan Tanaman di Hutan Primer Resort Kembang Kuning

Kembang Kuning resort is one of the Mount Rinjani National Park Resorts that have high biodiversity, so it has the potential for plant growth-promoting bacteria. Bacillus sp. is one species of bacteria that has great potential as a plant growth-promoting bacteria. The purpose of this study was to isolate and determine the ability of phosphate solubilization, nitrogen-fixing and anti-fungal activity of Bacillus spp. isolated from the Primary Forest of Kembang Kuning Resort, Gunung Rinjani National Park. This research is an exploratory study consisting of the isolation of Bacillus sp., phosphate solubilization test with spot inoculation method on Pikovskaya Agar media, qualitative nitrogen fixing test using Jensen's Nitrogen - Free media, and anti-fungal activity test against Fusarium sp. with dual culture method. There were 21 isolates of the genus Bacillus successfully isolated in this study. The phosphate solubilization test showed that 16 bacterial isolates could solubilize phosphate, where the highest phosphate solubilization index was produced by isolate P3.1 namely 0,52. A total of one isolate, namely isolate P3.1, can fix nitrogen on Jensen's Nitrogen-Free medium. In the anti-fungal test against Fusarium sp., three bacterial isolates were obtained that were able to inhibit the growth of Fusarium sp., where the highest antagonism was produced by isolate P2.8 which was 46,66%. Bacillus spp. isolated from Kembang Kuning Resort has potential as PGPB in terms of crop protection.

Phosphate solubilization and plant growth properties are promoted by a lactic acid bacterium in calcareous soil.

On the basis of good phosphate solubilization ability of a lactic acid bacteria (LAB) strain Limosilactobacillus sp. LF-17, bacterial agent was prepared and applied to calcareous soil to solubilize phosphate and promote the growth of maize seedlings in this study. A pot experiment showed that the plant growth indicators, phosphorus content, and related enzyme activity of the maize rhizospheric soils in the LF treatment (treated with LAB) were the highest compared with those of the JP treatment (treated with phosphate solubilizing bacteria, PSB) and the blank control (CK). The types of organic acids in maize rhizospheric soil were determined through LC-MS, and 12 acids were detected in all the treatments. The abundant microbes belonged to the genera of Lysobacter, Massilia, Methylbacillus, Brevundimonas, and Limosilactobacillus, and they were beneficial to dissolving phosphate or secreting growth-promoting phytohormones, which were obviously higher in the LF and JP treatments than in CK as analyzed by high-throughput metagenomic sequencing methods. In addition, the abundance values of several enzymes, Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology, and Carbohydrate-Active Enzymes (CAZys), which were related to substrate assimilation and metabolism, were the highest in the LF treatment. Therefore, aside from phosphate-solubilizing microorganisms, LAB can be used as environmentally friendly crop growth promoters in agriculture and provide another viable option for microbial fertilizers. KEY POINTS: • The inoculation of LAB strain effectively promoted the growth and chlorophyll synthesis of maize seedlings. • The inoculation of LAB strain significantly increased the TP content of maize seedlings and the AP concentration of the rhizosphere soil. • The inoculation of LAB strain increased the abundances of the dominant beneficial functional microbes in the rhizosphere soil.

Effect of fluorescent Pseudomonas on plant growth promotion of Aloe vera

Modern agriculture practices heavily depend on the application of chemical fertilizers and continuous application disturbs the soil quality and health. Fluorescent Pseudomonas are the well characterized group of bacteria proficient in plant growth promotion and have excellent phosphate solubilizing abilities and solubilize insoluble phosphate to plants available form via secretion of organic acids. This study focused on the phosphate solubilization ability of Pseudomonas, arouse of Aloin-A molecule, gluconic acid production, as well as biometric parameters of key medicinal plant, the Aloe vera (Aloe barbadensis). Two strains (P. putida and Pseudomonas sp.) were found very effective PSBs and solubilized 236.73 and 153.73 mg L−1 phosphate, respectively. High-performance liquid chromatography analysis (HPLC) showed the production of gluconic acid (GA). P. putida and P. sp. produced 23970 ± 231 and 21538 ± 129 mg L−1 GA, respectively. Inoculation of the plants with consortium of P. putida and Pseudomonas sp. enhanced the plant growth, soil available P and phosphate uptake in plants than individual inoculation. An increase in aloin-A content (18.15 and 28.71 fold) was recorded in A. barbadensis treated with a PSB consortium in a soil amended without and with TCP (tricalcium phosphate), respectively. P-uptake ultimately enhances the aloin-A synthesis and biomass of plant. Therefore, agronomic attributes of Aloe vera plants can be improved for used as a medicinal plant through application of potent Fluorescent Pseudomonas.

Competition and co-association, but not phosphorous availability, shape the benefits of phosphate-solubilizing root bacteria for maize (Zea mays).

Predicting the conditions under which rhizobacteria benefit plant growth remains challenging. Here we tested the hypothesis that benefits from inoculation with phosphate-solubilizing rhizobacteria will depend upon two environmental conditions: phosphate availability and competition between bacteria. We used maize-associated rhizobacteria with varying phosphate solubilization ability in experiments in soil, sterilized soil and gnotobiotic microcosms under conditions of varying orthophosphate availability, while we manipulated the intensity of competition by varying the number of isolates in plant inocula. Growth promotion by microbes did not depend on phosphate availability but was affected by interactions between inoculants: the beneficial effects of one Serratia isolate were only detectable when plants were inoculated with a single strain and the beneficial effects of a competition-sensitive Rhizobium was only detectable in sterilized soil or in microcosms inoculated with single strains. Moreover, microcosm experiments suggested that facilitation of a parasitic isolate, not competitive interactions between bacteria, prevented plants from gaining benefits from a potential mutualist. Competition and facilitation affected colonization of plants in microcosms but growth promotion by Serratia was more affected by inoculation treatment than culturable densities on roots. Experimental manipulation of seed inocula can reveal whether plant growth stimulation is robust with respect to competition, as well as the ecological strategies of different rhizobacteria. From an applied perspective, phosphate solubilization may not provide the mechanism for bacterial growth promotion but may indicate mutualistic potential due to phylogenetic associations. Importantly, benefits to plants are vulnerable to interactions between rhizobacteria and may not persist in mixed inoculations.

Characterization of halotolerant phosphate-solubilizing rhizospheric bacteria from mangrove (Avicennia sp.) with biotechnological potential in agriculture and pollution mitigation

Mangroves represent intricate and ever-changing ecosystems, exhibiting fluctuations in water level, salinity, and nutrient (such as NPK) availability as well as a wide array of unique bacterial communities. Microbial interactions in different components (e.g., tree roots) of the mangrove ecosystem are crucial to understand the ecosystem functioning for potential application in pollution mitigation and agricultural production. This study aimed to isolate phosphate-solubilizing bacteria (PSB) from the rhizosphere sediment of mangrove (Avicennia sp.) in terms of heavy metals (HMs) and salinity tolerance as well as plant growth promoting (PGP) traits, where the effective PSB were used on Brassica chinensis for their seed priming and growth under salinity stress. The effective two PSB isolates were identified by 16S rRNA, where JKD01 and JKD02 were closely related (99%) to Enterobacter cloacae (OQ271412) and Kocuria rhizophila (OQ271413), respectively. Both the strains exhibited phosphate solubilization, IAA, NH3, and EPS production ability as well as HMs resistant ability where, E. cloacae (OQ271412) and K. rhizophila (OQ271413), are effectively remove the Cu from the water with 33.23% and 27.54%, respectively. The FTIR results showed functional group shifts (carboxyl, phosphate, and amino) in Cu-treated bacterial biomass and intracellular Cu presence, indicating the involvement of Cu in the bio-sorption and intracellular bioaccumulation process, respectively. The findings suggested PSB tolerance to salinity and HMs are present in mangroves, making them a valuable source for isolating effective bacteria to reduce stress in plants, lower HMs accumulation in mangroves, and aid in the bioremediation of HMs-contaminated environments.

Symbiotic effectiveness, abiotic stress tolerance and phosphate solubilizing ability of new chickpea root-nodule bacteria from soils in Kununurra Western Australia and Narrabri New South Wales Australia

AimsTo assess the symbiotic effectiveness, tolerance to abiotic stress factors and phosphate solubilizing ability of new chickpea root-nodule bacteria.MethodsSymbiotic effectiveness, abiotic stress tolerance and phosphate solubilizing ability of ten new chickpea rhizobial strains collected from soils were evaluated using laboratory and glasshouse experiments.ResultsSix of the ten strains were symbiotically efficient with diversity between those and the commercial chickpea strain CC1192. High temperatures significantly affected strain survival in liquid and peat carrier. Peat carrier offered greater protection. Above 37 °C, strain infectivity decreased with no correlation between strain origin and their infectivity after exposure. Three of the new strains and CC1192 produced optimum growth and survival at pH 6.8 and at two lower pH’s of 4.4 and 5.4 were able to neutralize the growth medium while the other seven strains at high pH were able to either neutralize or acidify the growth medium. Strain survival was significantly higher at increased salt concentrations of NaCl compared to CaCl2. At 3% NaCl concentration, 8 strains survived while at 3% CaCl2 only 3 survived. Many strains were resistant to more than one antibiotic. All strains were able to solubilize phosphate. The ratio between the most efficient strain and the least was 3:1.ConclusionsChickpea rhizobia strains sourced from soils in Narrabri New South Wales and Kununurra in Western Australia differed in expressed traits from the commercial strain CC1192. These unique traits could provide additional tools for rhizobial strain selection to benefit chickpea production in different soil environments.

Isolation, screening, and characterization of plant growth enhancing endophytic bacteria from halophytic Heliotropium curassavicum L. collected from salt stress areas of Srikakulam, Andhra Pradesh

Farmers use excessive chemical fertilizers to boost crop productivity to meet growing agricultural demands. However, this practice is costly and environmentally hazardous. Sustainable increase in crop yield can be achieved through alternatives like microbial-based fertilizers. In the quest to identify plant growth-promoting endophytic bacteria, the present study was carried out and selected unexplored halophytic plant Heliotropium curassavicum L. Thirteen endophytic bacterial strains were isolated from both aerial and root portions of H.curassavicum. These isolates were tested for salt tolerance, enzyme production, and synthesis of growth-promoting secondary metabolites, like Indole-3-acetic acid (IAA) and phosphate solubilization . Most of the isolates belonged to the Bacillus family, exhibiting varying Gram staining and biochemical reactions. The majority are Gram-positive bacteria, non-motile, spore formers, and exist in two cells or chains. All isolates could tolerate up to 10% NaCl concentration and a temperature of 42°C. Based on phenotypic, bio-chemical characteristics, isolate HCR3 showed promising properties in synthesizing IAA and phosphate solubilization abilities. The isolate HCR3 grew well upto 10% NaCl concentration and also 42°C temperature. Based on molecular characterization by using 16S rRNA gene-based analysis HCR3 isolate was identified and belonged to the Genus Pseudomonas with the highest similarity index with Pseudomonas khazarica sp. HCR3 showed IAA production of 37µg ml-1, had a phosphate solubilization ability of 3.5 ppm, and recorded protease activity on gelatin medium. The findings highlight the potential of HCR3 and other strains from halophytic H. curassavicum L. to enhance plant growth through secondary bioactive metabolites, offering eco-friendly solutions for sustainable agriculture.

Pseudomonas mosselii improves cold tolerance of Asian rice (Oryza sativa L.) in a genotype-dependent manner by increasing proline in japonica and reduced glutathione in indica varieties.

Cold stress is an important factor limiting rice production and distribution. Identifying factors that contribute to cold tolerance in rice is of primary importance. While some plant specific genetic factors involved in cold tolerance have been identified, the role of the rice microbiome remains unexplored. In this study, we evaluated the influence of plant growth promoting bacteria (PGPB) with the ability of phosphate solubilization on rice cold tolerance and survival. To reach this goal, inoculated and uninoculated 2-week-old seedlings were cold stressed and evaluated for survival and other phenotypes such as electrolyte leakage (EL) and necessary elements for cold tolerance. The results of this study showed that of the five bacteria, Pseudomonas mosselii, improved both indica and japonica varietal plants' survival and decreased EL, indicating increased membrane integrity. We observed different possible cold tolerance mechanisms in japonica and indica plants such as increases in proline and reduced glutathione levels, respectively. This bacterium also improved the shoot growth of cold exposed indica plants during the recovery period. This study confirmed the host genotype dependent activity of P. mosselii and indicated that there is an interaction between specific plant genes and bacterial genes that causes different plant responses to cold stress.

Isolasi Bakteri Fiksasi Nitrogen dan Fosfat pada Limbah Cair Karet (Hevea brasiliensis)

This research aims to determine which bacteria are capable of fixing nitrogen and dissolving phosphate in liquid rubber waste in Perdamean Village, Labuhanbatu Regency. The research method used was the description method with bacterial isolation techniques, then testing was carried out, namely the nitrogen fixation ability test and the phosphate solvent ability test. The results of the research showed that bacterial isolates capable of fixing nitrogen were found to have high absorbance values, namely 1,340 ABS. In the phosphate solubilizing ability test, there were 2 isolates that were unable to dissolve phosphate. In conclusion, isolating nitrogen and phosphate fixing bacteria in liquid rubber waste is a way to prevent pollution and destruction of the ecosystem in the environment.
 
 Keywords: Nitrogen Fixation, Rubber Liquid Waste, Phosphate Solvents

Effects of Phosphorus-dissolving Dark Septate Endophytes on the Growth of Blueberry.

Dark septate endophytes (DSEs) are widely distributed and improve plant growth. DSEs secrete large amounts of enzymes to mineralize insoluble phosphorus in soil and convert it into soluble phosphorus, promoting plant uptake of phosphorus. However, the effects of DSEs with phosphate-solubilizing ability on host plants need further study. In this study, phosphorus-dissolving DSEs were screened for growth-promoting effects. We isolated, identified and characterized three DSE species (Thozetella neonivea, Pezicula ericae and Hyaloscyphaceae sp.) showing phosphate-solubilizing ability. The impact of single, dual or triple inoculation of DSEs on blueberry plant characteristics was studied. Their effects on colonization intensity, seedling biomass, nutrients in plants and soil, and activities of plant resistance enzymes and soil enzymes were markedly upregulated relative to the control (P < 0.05). The available phosphorus and acid phosphatase levels in different combinations were significantly increased. These findings indicate that the application of the three DSEs may be valuable in facilitating the cultivation of blueberry with a higher biomass and improved plant quality.

Isolation, Characterization, and Investigation on Potential Multi-trait Plant Growth Promoting Rhizobacteria from Wild Banana (Musa itinerans) Rhizospheric Soil

The undertaken study was conducted to isolate and characterize the plant growth promoting rhizobacteria from the rhizospheric soil of Musa itinerans collected from Zaphumi village, Nagaland, Northeast India. The purified bacterial isolates were screened for plant growth-promoting traits namely phosphate solubilization, IAA production, siderophore production, and ammonia production. Out of the 25 isolates, the three best isolates with maximum growth promoting traits were selected and considered for further study for heavy metal and salinity tolerance. All three isolates were able to produce siderophore, whereas, only isolate EZ30 was able to produce IAA. Phosphate solubilization ability was the highest in EZ27 (272.89±2.46), followed by EZ30 (109.70±5.47) and EZ11(89.12±1.87). The isolates also exhibited variable levels of cadmium (30- 280µg/ml) and salinity resistance (2-14%). Based on 16S-rRNA gene sequence analysis, these bacterial isolates were identified as Kosakonia arachidis, Pseudomonas putida and Pseudomonas monteilii. The highest salinity tolerance was shown by P. putida (14%), whereas K. arachidis (4%) and P. monteilii (4%) exhibited similar level of tolerance. The cadmium tolerance was the highest for P. monteilii (280 µg/ml), followed by K. arachidis (80 µg/ml) and P. putida (30 µg/ml). Inoculation of Cicer arietinum L. with these three isolates significantly enhanced the growth parameter such as shoot and root length (p≤ 0.05), root and shoot fresh weight and dry weight (p≤ 0.05), except for EZ27 and EZ11 where there was no significant difference in shoot dry weight (p≥ 0.05). Overall, the three selected PGPR strains showed potential biofertilizer traits (phosphate solubilizing, IAA producing, siderophore production, salinity, and cadmium tolerant) to be used in the agricultural fields promoting sustainable practices.

Ignatzschineria cameli Strain KAUPDF7-A First Report on Plant Growth Promoting Rhizobacteria (PGPR) from the Post-flood Affected Soils of Kerala

Background: Kerala flood in 2018 and 2019 had reduced the yield in many agricultural plots of Attapadi, Kerala, India. The scope of the study was to identify the potential native plant growth promoting rhizobacteria from the post flood-affected sites to rejuvenate the nutrient depleted soils. Methods: The present study was carried out in the department of agricultural microbiology, College of Agriculture, Kerala Agricultural University, Vellanikara, Kerala during 2020-2022. Bacteria were isolated from post flood-affected agricultural soils of Attapadi in Palakkad district of Kerala, India. Three morphologically distinct isolates were screened for cellulase, laccase and dehydrogenase to select the best bacterial isolate that could produce the multifunctional enzymes for rejuvenation of flood-affected soils. The isolate were also screened for plant growth promotion traits such as; indole acetic acid (IAA), phosphate solubilizing ability, nitrogen fixing ability and potassium solubilizing ability. Result: The most promising isolate was identified as Ignatzschineria cameli, which was found to be a high indole acetic acid producer along with phosphate and potassium solubilizing ability and revealed as the first report of PGPR from post flood-affected soils of Kerala.

Isolation of Phosphate Solubilizing Bacteria Around Bamboo (Bambusa vulgaris) Clumps Using Natural Media Trap Method

Bamboo plant is a potential source of plant growth promoting bacteria (PGPB). Phosphate solubilizing ability is an important characteristic of PGPB. This study aims to isolate phosphate solubilizing bacteria around the bamboo clumps using natural media. The bacteria around the bamboo clumps are trapped using natural media. The media consist of 70 gram cooked rice and 70 gram banana peel. The media were stored in plastic boxes with four types of treatments: 1) tightly closed, 2) covered with tissue, 3) covered with banana leaves, and 4) uncovered (open). Those plastic boxes are placed around the bamboo clump and left for up to 5 days. The trapped phosphate solubilizing bacteria were isolated using Pikovskaya agar. A total of 17 isolates of phosphate solubilizing bacteria were successfully trapped, 8 isolates in cooked rice and 9 isolates in banana peel. The isolates showed a phosphate solubilization index, ranging from 0,2 to 1,40. The isolate NN01 has the highest ability to solubilize phosphate. This isolate was trapped in a cooked rice with an open plastic box condition. NN01 is a Gram positive rod-shaped bacterium. In this study it was revealed that the area of ​​the bamboo clumps is inhabited by various types of bacteria. The natural media of cooked rice and banana peels have a good ability to trap potential phosphate solubilizing bacteria around the bamboo clumps.

Screening of salt tolerant endophytic bacteria with plant growth promoting characters isolated from Acanthus ilicifolius L., a species of mangrove ecosystem located at Corangi wildlife sanctuary, Andhra Pradesh

Mangroves harbour many beneficial microorganisms in their rhizosphere, phyllosphere and endophytically, which forms an ideal ecological habitation for isolating halotolerant endophytic bacteria with unique characteristics. Endophytes can produce numerous bioactive secondary metabolites and phytohormones, which may be directly or in some way beneficial to the host plant. The present study aimed to identify novel endophytes capable of producing plant growth-promoting substances. The mangrove plants Acanthus ilicifolius L. at Corangi Wildlife Sanctuary were selected, and their leaves and roots were collected for endophyte isolation. Eight isolates from the leaves and roots were collected, purified and preserved. All these isolates were subjected to morphological, phenotypical and biochemical studies. Isolates were grown best at 3% NaCl nutrient agar and could tolerate salinity upto 8%NaCl. Most of them could grow upto 42°C. The majority were gram’s positive, motile, aerobic, rod-shaped and some were gram’s negative, rod-shaped organisms. Many of the endophytic organisms had the ability to synthesize Indole-3-acetic acid(IAA) varied from 0.7 µg/ml (AIL1) to 51.0 µg/ml (AIL2) and the highest phosphate solubilizing ability was recorded with AIR3 (3.71 ppm) followed by AIR4 (3.00 ppm) and lowest was recorded by AIL4 (1.80 ppm). Among total isolates, AIL2 (51µg/ml) showed promising potential in producing IAA and had phosphate solubilization ability. Based on 16S ribosomal RNA molecular method the isolate AIL2 was identified as Bacillus altitudinis. This is the first to report that B.altitudinis strain AIL2 isolated from A.ilicifolius L. could produce IAA, which can be used as a bioinoculant in agriculture and allied sector.

Potential effect of key soil bacterial taxa on the increase of rice yield under milk vetch rotation.

Legume crop rotation is often adopted in rice cultivation to improve soil productivity. However, little is known about the role of microbes under legume rotation in affecting soil productivity. To elucidate this, a long-term paddy cropping experiment was set up to study the relationship between crop yield, soil chemical properties, and key microbial taxa under a double-rice and milk vetch rotation. Milk vetch rotation significantly improved soil chemical properties compared to no fertilization treatment, and soil phosphorus was a major factor correlated with crop yield. Long-term legume rotation increased soil bacterial alpha diversity and changed soil bacterial community. After milk vetch rotation, the relative abundances of Bacteroidota, Desulfobacterota, Firmicutes, and Proteobacteria increased while those of Acidobacteriota, Chloroflexi, and Planctomycetota decreased. Moreover, milk vetch rotation increased the relative abundance of phosphorus-related gene K01083 (bpp), which was significantly correlated with soil phosphorus content and crop yield. Network analysis showed that taxa of Vicinamibacterales were positively correlated with total phosphorus and available phosphorus, which was a potential taxon contributing to the availability of soil phosphorus stock. Our results indicated that milk vetch rotation could enrich key taxa with latent phosphate-solubilizing ability, increase the content of soil available phosphorus, and finally enhance crop yield. This could provide scientific guidance for better crop production.

Plant-growth promoting activity of three fungal endophytes isolated from plants living in dehesas and their effect on Lolium multiflorum

Endophytic fungi have been demonstrated to produce bioactive secondary metabolites, some of which promote plant growth. Three endophytic fungi isolated from healthy plants living in dehesas of Extremadura (Spain) were identified and evaluated for their ability to produce phytohormone-like substances, antioxidant activity, total polyphenol content, phosphate solubilization ability and siderophore and ammonia production. The filtrates and extracts produced by the three endophytes were applied to Lolium multiflorum seeds and seedlings under both in vitro and greenhouse conditions, to analyse their influence on plant growth traits such as germination, vigour index, chlorophyll data, number and length of leaves and roots, and dry weight. All three endophytes, which were identified as Fusarium avenaceum, Sarocladium terricola and Xylariaceae sp., increased the germination of L. multiflorum seeds by more than 70%. Shoot and root length, plant dry weight and the number of roots were positively affected by the application of fungal filtrates and/or extracts, compared with controls. The tentative HPLC–MS identification of phytohormone-like substances, such as gibberellin A2 and zeatin, or the antioxidant acetyl eugenol, may partially explain the mechanisms of L. multiflorum plant growth promotion after the application of fungal filtrates and/or extracts.