Phosphate Solubilization Research Articles

Enhancing phosphate-solubilising microbial communities through artificial selection

Microbial communities, acting as key drivers of ecosystem processes, harbour immense potential for sustainable agriculture practices. Phosphate-solubilising microorganisms, for example, can partially replace conventional phosphate fertilisers, which rely on finite resources. However, understanding the mechanisms and engineering efficient communities poses a significant challenge. In this study, we employ two artificial selection methods, environmental perturbation, and propagation, to construct phosphate-solubilising microbial communities. To assess trait transferability, we investigate the community performance in different media and a hydroponic system with Chrysanthemum indicum. Our findings reveal a distinct subset of phosphate-solubilising bacteria primarily dominated by Klebsiella and Enterobacterales. The propagated communities consistently demonstrate elevated levels of phosphate solubilisation, surpassing the starting soil community by 24.2% in activity. The increased activity of propagated communities remains consistent upon introduction into the hydroponic system. This study shows the efficacy of community-level artificial selection, particularly through propagation, as a tool for successfully modifying microbial communities to enhance phosphate solubilisation.

The combined application of salt-alkali tolerant phosphate solubilizing microorganisms and phosphogypsum is an excellent measure for the future improvement of saline-alkali soils.

The combined application of salt-alkali tolerant phosphate solubilizing microorganisms and phosphogypsum is an excellent measure for the future improvement of saline-alkali soils.

Isolation and Characterization of Phosphorus Solubilizing Bacteria from Millet Rhizosphere in Lafia metropolis

Phosphorus is an essential, but often unavailable nutrient for plant growth in the soil due to its low solubility. Phosphorus solubilizing bacteria (PSB) convert insoluble forms of phosphorus into soluble forms that can be taken up by plants. The study aimed to isolate and characterize PSB from the rhizosphere of millet plants in Lafia, and to evaluate their potential for improving soil fertility and crop productivity. Soil samples were collected from four different locations and plated on Pikovskaya's agar medium. PSB colonies were identified based on their ability to produce clear zones around them. The PSB isolates were further characterized by morphological, biochemical, and molecular methods. The phosphate solubilizing activity and plant growth-promoting traits of the PSB isolates were also assessed. The PSB isolates were tested for their effect on the growth of millet seedlings in pots. The results showed that 16 PSB isolates belonging to four genera (Bacillus, Pseudomonas, Enterobacter, and Klebsiella) were obtained from the soil samples. The PSB isolates exhibited varying degrees of phosphate solubilizing activity, ranging from 11.2 to 81.6 mg/L. The PSB isolates also showed positive results for the production of indole acetic acid, ammonia, hydrogen-cyanide, and siderophore. The PSB inoculation significantly increased the shoot and root lengths, and fresh and dry weight of the millet seedlings. The study concluded that the PSB isolates from the millet rhizosphere in Lafia could enhance soil phosphorus availability and millet growth. The study recommended further research on the field application and optimization of the PSB inoculation.

Metagenomic assembled genomes indicated the potential application of hypersaline microbiome for plant growth promotion and stress alleviation in salinized soils.

The strategic implementation of metagenomic assembled genomes (MAGs) in exploring the properties and harnessing microorganisms from ecosystems like hypersaline niches has transformative potential in agriculture. This approach promises to redefine our comprehension of microbial diversity and its ecosystem roles. Recovery and decoding of MAGs unlock genetic resources, enabling the development of new solutions for agricultural challenges. Enhanced understanding of these microbial communities can lead to more efficient nutrient cycling, pest control, and soil health maintenance. Consequently, traditional agricultural practices can be improved, resulting in increased yields, reduced environmental impacts, and heightened sustainability. MAGs offer a promising avenue for sustainable agriculture, bridging the gap between cutting-edge genomics and practical field applications.

Screening of heavy metal-resistant rhizobial and non-rhizobial microflora isolated from Trifolium sp. growing in mining areas.

Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and development with several beneficial effects, especially in challenging environmental conditions, such as the presence of toxic contaminants. In this study, 49 isolates obtained from Trifolium sp. nodules growing on a Pb/Zn mine site were characterized for PGP traits including siderophores production, phosphate solubilization, extracellular enzymes production, and antifungal activity. The isolates were also screened for their ability to grow at increasing concentrations of NaCl and heavy metals, including lead, zinc, cobalt, copper, nickel, cadmium, and chromium. The findings of our study indicated that isolates Cupriavidus paucula RSCup01-RSCup08, Providencia rettgeri RSPro01, Pseudomonas putida RSPs01, Pseudomonas thivervalensis RSPs03-RSPs09, and Acinetobacter beijerinckii RSAci01 showed several key traits crucial for promoting plant growth, thus demonstrating the greatest potential. Most isolates displayed resistance to salt and heavy metals. Notably, Staphylococcus xylosus RSSta01, Pseudomonas sp. RSPs02, Micrococcus yunnanensis RSMicc01, and Kocuria dechangensis RSKoc01 demonstrated a significant capacity to grow at salt concentrations ranging from 10 to 20%, and isolates including Cupravidus paucula RSCup01-RSCup08 exhibited resistance to high levels of heavy metals, up to 1300 mg/L Pb++, 1200 mg/L Zn++, 1000 mg/L Ni++, 1000 mg/L Cd++, 500 mg/L Cu++, 400 mg/L Co++, and 50 mg/L CrVI+. Additionally, the analysis revealed that metal-resistant genes pbrA, czcD, and nccA were exclusively detected in the Cupriavidus paucula RSCup01 strain. The results of this study provide insights into the potential of plant growth-promoting rhizobacteria strains that might be used as inoculants to improve phytoremediation in heavy metal-contaminated soils.

Effectiveness of the Drought-tolerant Plant Growth Promoting Rhizobacteria (PGPR) that Supports Paddy Growth in Drought Condition

Drought stress is the primary constraint on plant-based food production, particularly paddy production. Several studies have examined plant resistance to heat and osmotic pressure. This study aimed to isolate bacteria with plant growth-promoting properties that could tolerate high temperatures and improve paddy growth during drought. Five isolates with a high optical density value (OD600) at 30% PEG 6000 (equivalent to -1.03MPa) and able to grow at high temperatures were identified based on the 16S rRNA gene sequences as Achromobacter spanius UKM UR10, Bacillus pumillus UKM UR11, Bacillus cereus UKM R66, and Bacillus altitudinis UKM RB11, which were isolated from the root, where as Bacillus sp. UKM S8 was isolated from rhizosphere soil. These isolates exhibited 1-amino cyclopropane-1-carboxylate (ACC) deaminase activities ranging between 1.01 and 1.12 mmol α-ketobutyrate mg-1 protein h-1, which degraded ACC to α-ketobutyrate and ammonia. Other plant growth promoters assessed include indole acetic acid (IAA; concentration between 9.69 and 13.15µg/ml) and phosphate solubilization (concentrations between 31.74 and 51.30 mg/l) production. Subsequently, the selected plant growth-promoting rhizobacteria (PGPR) were incorporated as a consortium and inoculated on paddy seeds, thus increasing total chlorophyll, proline, and soluble sugar content in paddy subjected to drought-stress conditions. Paddy yield components and performances, such as panicle number, spikelet number, dry grain weight, number of leaves, stalk length, and root length increased significantly. This isolated PGPR exhibits heat resistance, promotes plant growth, and can serve as an inoculant for paddy plants under drought conditions.

The genome, pangenome, and physiological analysis of Leclercia adecarboxylata (kcgeb_e1), a plant growth-promoting bacterium

Plant growth-promoting bacteria (PGPB) as biofertilizer plays an important role in agriculture practices. In this study, we isolated and identified plant-associated bacteria Leclercia adecarboxylata (kcgeb_e1) from the root region of the halophytic plant Sesuvium verrucosum. We tested its physiological activity and the effect of inoculation, with and without salt, on photosynthesis using Cajanus cajan. Further, we sequenced the whole genome of L. adecarboxylata (kcgeb_e1) and carried out pangenome analysis with 12 other genomes of the same species, which highlights unique genes enriched for pathways involved in abiotic stress tolerance (salinity, drought and heat) and carbohydrate transport. Moreover, gene families involved in abiotic stress tolerance, host adhesion, and transport were under positive selection (e.g., Aldo/keto reductase family, Hemagglutinin, Porin, and sugar transport). We observed a loss of ACC deaminase gene in this pangenome; however, this strain can still produce 1-aminocyclopropane-1-carboxylate (ACC), an enhancer of abiotic stress, which suggests that its homologue, d-cysteine sulfatase, has a bifunctional activity. In addition, this strain has Indole acetic acid (IAA) and phosphate solubilization activity. Combining these findings with the efficiency of colonizing the root surface of Solanum lycopersicum, this strain showed remarkable enhancement of photosynthesis, comparing control to inoculated plants. This increase in photosynthesis is consistent with an increase in sucrose under salt treatment, but not in glucose and fructose, which acts as a sensor in opposing the negative effect of salinity and promoting sustainable growth. Given all this, our study suggests that this PGPB can act as a biofertilizer for sustainable agriculture.

The Microbial Community Structure in the Rhizosphere of Theobroma cacao L. and Euterpe oleracea Mart. Is Influenced by Agriculture System in the Brazilian Amazon.

This study tested the hypothesis that cocoa monoculture (MS) and cocoa-açai agroforestry systems (AFS) may influence the microbial community structure and populations of plant growth-promoting bacteria (PGPR). Accordingly, the aim was to analyze the microbial community structure and PGPR populations in different agroecosystems in the Brazilian Amazon. To achieve this, the rhizosphere microbial community of cocoa and açai plants in both Amazonian seasons (dry and rainy) was analyzed using culture-dependent (PGPR screening) and -independent methods [PCR-DGGE based on rrs, alp, nifH gene, and intergenic region (ITS) of fungi]. Concerning PGPR screening, out of 48 isolated bacterial strains, 25% were capable of siderophore production, 29% of mineralized organic phosphate, 8% of inorganic phosphate solubilization, and 4% of indole acetic acid production. Moreover, 17% of isolates could inhibit the growth of various phytopathogenic fungi. Statistical analyses of DGGE fingerprints (p < 0.05) showed that bacterial and fungal community structures in the rhizosphere were influenced by the seasons, supporting the results of the physicochemical analysis of the environment. Furthermore, as hypothesized, microbial communities differed statistically when comparing the MS and AFS. These findings provide important insights into the influence of climate and cultivation systems on soil microbial communities to guide the development of sustainable agricultural practices.

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. &#x0D; Keywords: Rhizospheric fungi, Phosphate solubilization, Dual culture plate, Plant growth parameters 

Biochemical Analysis and Characterization of Silver Nanoparticles Synthesized by the Endophytic Fungus Plectosphaerella oligotrophica S8A26 Associated with Anaphalis contorta

Endophytic fungi associated with medicinal plants produce compounds that have vast biological activities. Anaphalis contorta is a highly therapeutic plant that has been used in traditional medicine by various communities. In the present study, the endophytic fungus Plectosphaerella oligotrophica S8A26 was isolated from the stem part of A. contorta and assessed for its plant growth promotion abilities, and showed positive results for phosphate solubilization and ammonia production. The secondary metabolites were analyzed for the presence of seven biochemicals, which indicate the presence of flavonoids, phenols, saponins, and steroids. The total flavonoid content and total phenolic content were recorded to be 25.67 µg of QE/mg of EE and 5.06 µg of GAE/mg of EE, respectively. The isolate was allowed to synthesize silver nanoparticles and characterized using X-ray diffraction, Energy Dispersive X-ray, Particle size distribution, and Zeta potential. XRD analysis has shown the AgNPs are crystalline with an average size of 24.81 nm. EDX study reveals silver as the main component with 48.63%. Particle size distribution indicates that the majority of the particles occur in the size range of 65–70 nm. Zeta potential value of −31.8 mV shows that the AgNPs are stable. Studies like the biological activities of the endophyte as well as AgNPs, secondary metabolite profiling, and the isolation of bioactive compounds would constitute important future research.

Identification of Plant Growth-Promoting Rhizobacteria for the Development of Probiotic Consortia

 &#x0D; Soil infertility is one of the major challenges in agriculture. Although chemical fertilizers provide promising solution for crop growth in infertile soil, excessive application cause negative impacts on the natural systems such as soil and water. Moreover, these fertilizers can be converted into insoluble forms soon after application which often result in increasing the application frequency and the quantity. Hence, for decades plant growth-promoting rhizobacteria (PGPR) have been considered as an environmentally friendly alternative for chemical fertilizers. In this context, the present study was focused on the identification of candidate PGPRs for the development of probiotic packages for chilli (Capsicum annuum L.) which is one of the most widely grown and highly demanding vegetable crops in Sri Lanka. Rhizobacteria were isolated from the roots of healthy, young chilli plants grown in Angunakolapelessa, Sri Lanka and their rhizosphere soil. In total, 75 morphologically distinct strains were isolated, and they were inoculated into different nutrient media to screen their ability to solubilize insoluble mineral nutrient sources. Those media were National-Botanical-Research-Institute's phosphate agar [NBRIP-agar] with Ca3(PO4)2 as the P source, modified-Aleksandrov-agar containing mica as the K source and zinc-solubilizing-agar containing ZnCO3 as the Zn source. Further, bacteria were screened for N fixation in the nitrogen- fixing-bacteria (NfB) medium. Sixteen P-solubilizing-bacteria (PSB), 4 K-solubilizing-bacteria (KSB), 15 Zn-solubilizing-bacteria (ZnSB) and 10 N-fixing strains were identified. We noticed that all KSB strains also have the capacity to solubilize Ca3(PO4)2. All PSB strains, except CSTM10, can solubilize ZnCO3. The phosphate solubilizing index (PSI) was calculated to rank the P-solubilizing efficiency (PSE) of PSB. The highest PSI was found in CSTM40 and CSTM6. We further screened all mineral-solubilizing strains for the indole-3-acidic acid (IAA) production which is a PGP hormone. Cultures were induced for IAA production by supplementing the medium with 0.2% (w/v) tryptophan and IAA concentration was determined using the Salkowski's method. Nine strains were capable of producing IAA. The CSTM6 and CSTM21 showed the highest IAA production of&#x0D; 181.94 and 178.59 mg/L respectively. In conclusion, bacterial strains, CSTM6, CSTM14, CSTM21, CSTM24, CSTM40, CMTM1, CMTM2 and CSTM10 showed multiple PGP characteristics and they were selected as candidates for the developing probiotic consortia. They can be viewed as promising strains in sustainable agriculture since they perhaps can enhance the availability of mineral nutrients in soil and promote plant growth.&#x0D;  &#x0D; Keywords: Biofertilizer, Capsicum annuum, Plant growth-promoting rhizobacteria&#x0D;  &#x0D; Financial assistance from Indo-Sri Lanka Joint Research Programme 2019 funded by the State Ministry of Skill Development, Vocational Education, Research and Innovation, Sri Lanka is acknowledged.&#x0D;  

Effect of soil nutrient management and land configuration on rhizospheric microbial diversity under cotton (Gossypium spp.)-wheat (Triticum aestivum) cropping system in semi-arid region

Microbial diversities in the vicinity of root rhizosphere play a crucial role in promoting plant and soil ecosystem health and productivity. They have great potential as key indicators of soil health in agro-ecosystems enhancing the availability of nutrients. Therefore, a study was carried out during 2019–20 and 2020–21 at research farm of Chaudhary Charan Singh Haryana Agricultural University, Hisar, Haryana to investigate the rhizospheric microbial diversities under cotton (Gossypium spp.)-wheat (Triticum aestivum L.) cropping system as affected by land configuration and nutrient management. Experiment consisted of 5 nutrient treatments replicated thrice and two land configurations, viz. raised bed (RB) and flatbed (FB) planned in factorial randomized block design (RBD). The results of experiment under RB revealed that farmyard manure (FYM) and FYM with biofertilizer and cow urine formulation (FYM + Org) showed the highest bacterial, fungal, phosphate solubilizing bacteria, azotobacter and actinomycetes population (6.92 to 7.51, 24.63 to 26.80, 7.61 to 7.68, 8.74 to 9.15,7.27 to 7.66 cfu/g soil, respectively). The decrease in microbial diversity was observed under inorganic fertilizer application through soil test crop response approach with targeted yield of 5.5 and 2.8 mg/ha (STCR5.5/2.8) and 6.0 and 3.2 mg/ha (STCR6.0/3.2) and control for cotton and wheat, respectively. Higher microbial population and soil organic carbon was found in RB compared to FB. The STCR5.5/2.8 and STCR6.0/3.2 recorded highest cotton and wheat yield followed by FYM and FYM+Org and least in control under cotton-wheat system. Thus, the study suggests that RB planting with an addition of manures along with biofertilizer and cow urine formulation could be a sustainable and feasible practice through enhanced microbial population raising soil fertility leading to increase the crop yields under semi-arid regions.

Isolation and characterization of PGPR obtained from different arsenic-contaminated soil samples and their effect on photosynthetic characters of maize grown under arsenic stress.

Contamination of the environment due to speedup of anthropogenic activities has become a serious threat to modern humanity. Among the contaminants, the new emerging concern is the heavy metal (HM) contamination in the environment. Because the persistence and harmfulness of heavy metals affect the ecosystem and the health of plants, animals, and humans, they are the most toxic substances in the environment. Among them, Arsenic (As) emerged as major environmental constraint leading to enormous negative effects on the plant, animal, and human health. Even in minute quantity, As is known to cause various critical diseases in humans and toxicity in plants. Research was performed to observe the capability of plant growth-promoting strains of bacteria in enhancing Zea mays (L.) growth in arsenic polluted soil. Total 30 bacterial strains were isolated from the polluted soils, screened for plant growth promotion potential and arsenic tolerance. Eighteen isolates showed resistance to different levels of sodium arsenate (ranging from 0 to 50 mM) in agar plate using LB media. Of 18 isolates, 83.3% produced IAA, methyl red, and hydrogen cyanide; 55.5% exhibited catalase activity; 61.1% showed siderophore production; 88.8% showed phosphate solubilization; and 44.4% showed oxidase, Voges proskauer activity, and KOH solubility. The most efficient isolates SR3, SD5, and MD3 with significant arsenic tolerance and plant growth-promoting (PGP) activity were examined via sequencing of amplified 16S rRNA gene. Isolates of bacteria, i.e., SR3, SD5, and MD3, showing multiple PGP-traits were identified as Bacillus pumilus (NCBI accession number: OR459628), Paenibacillus faecalis (NCBI accession number: OR461560), and Pseudochrobactrum asaccharolyticum (NCBI accession number: OR458922), respectively. Maize seeds treated with these PGPR strains were grown in pots contaminated with 50 ppm and 100 ppm sodium arsenate. Compared to untreated arsenic stressed plants, bacterial inoculation P. asaccharolyticum (MD3) resulted 20.54%, 18.55%, 33.45%, 45.08%, and 48.55% improvement of photosynthetic pigments (carotenoid content, chlorophyll content, stomatal conductance (gs), substomatal CO2, and photosynthetic rate), respectively. Principal component analysis explained that first two components were more than 96% of the variability for each tested parameter. The results indicate that in comparison to other isolates, P. asaccharolyticum isolate can be used as efficient agent for improving maize growth under arsenic polluted soil.

Common Bacillus mitigate tomato verticillium wilt and bacterial specks when combined with an essential oil extract

This study was conducted to evaluate the effect of growth promoting rhizobacteria (PGPR) alone and in combination with an essential oil (EO) extracted from Tetraclinis articulata (Vahl) Masters in protecting tomato plants against verticillium wilt and bacterial speck diseases. Three strains, identified as Bacillus toyonensis EI, Bacillus thuringiensis ES and Bacillus thuringiensis RA, possess in vitro PGPR activity such as the production of indole acetic acid and ammonia, and the solubilization of phosphates. In planta, they significantly increased the stem length, number of leaflets, leaf area, and root biomass. EO and the three strains, alone or in combination, were able to enhance photosynthetic parameters such as net photosynthesis and transpiration rate. They also significantly reduced leaf alteration (LA) index, stunting index (SI) and browning index (BI) caused by Verticillium dahliae kleb. In tomato. Reduction of LAI ranged from 25% to 37%, and it enhanced to more than 60% when plants were treated with EO combined with B. thuringiensis SE or with B. toyonensis EI, indicating a synergistic effect. Moreover, EO as well as the three Bacillus strains were also able to enhance tomato resistance against bacterial speck disease caused by Pseudomonas syringae pv. tomato. The average number of lesions was significantly reduced by the application of EO and the three strains, reaching 94% with combination of EO with B. thuringiensis RA. Bacterial population analyses showed that plants with reduced symptoms exhibited significantly lower bacterial concentrations. In tomato plants inoculated with V. dahliae results showed that EO as well as three strains were able to enhance H2O2 accumulation, at the late stage of infection, which might lead to reduce disease. However, within the pathosystem tomato/P. syringe pv. tomato, H2O2 accumulation was highly enhanced by the pathogen and inhibited after combined treatment.

Halotolerant and plant growth-promoting endophytic fungus Aspergillus terreus CR7 alleviates salt stress and exhibits genoprotective effect in Vigna radiata.

Soil salinity is one of the major environmental stresses that results in reduction of cultivable land and decreased productivity. In the present study, halotolerant and plant growth-promoting endophytic fungi were isolated from Catharanthus roseus, and their effect in mitigating salt stress in Vigna radiata was evaluated. An isolate CR7, identified to be Aspergillus terreus, showing plant growth promotion activities, viz. IAA production (23.43 ± 0.79 μg/ml), phosphate solubilization (133.63 ± 6.40 μg/ml), ACC deaminase activity (86.36 ± 2.70 μmol α-ketobutyrate/h/mg protein) etc. and ability to grow at 15% NaCl was selected for further in vivo studies. Colonization of CR7 was carried out in V. radiata which was subjected to different concentrations of salt (150, 200, and 250 mM NaCl). Under salt stress, A. terreus CR7 inoculated plants showed substantially improved root and shoot length, biomass, chlorophyll content, relative water content, phenolics, protein content, and DPPH scavenging activity. Endogenous IAA level was enhanced by 5.28-fold in treated plants at maximum salt stress. Inoculation of A. terreus CR7 affected oxidative stress parameters, exhibiting an increase in catalase and superoxide dismutase and reduction in proline, electrolyte leakage, and malondialdehyde content. Fluorescent microscopic analysis of roots revealed improved cell viability and decreased levels of glutathione and hydrogen peroxide under salt stress in treated plants. The isolate A. terreus CR7 also protected against DNA damage induced by salt stress which was evaluated using comet assay. A decrease in DNA tail length, tail moment, and olive tail moment to the extent of 19.87%, 19.76%, and 24.81%, respectively, was observed in A. terreus CR7-colonized plants under salt stress. It can be concluded that A. terreus CR7 can be exploited for alleviating the impact of salt stress in crop plants.

Whole genome sequencing and characterization of Pantoea agglomerans DBM 3797, endophyte, isolated from fresh hop (Humulus lupulus L.).

This paper brings new information about the genome and phenotypic characteristics of Pantoea agglomerans strain DBM 3797, isolated from fresh Czech hop (Humulus lupulus) in the Saaz hop-growing region. Although P. agglomerans strains are frequently isolated from different materials, there are not usually thoroughly characterized even if they have versatile metabolism and those isolated from plants may have a considerable potential for application in agriculture as a support culture for plant growth. P. agglomerans DBM 3797 was cultured under aerobic and anaerobic conditions, its metabolites were analyzed by HPLC and it was tested for plant growth promotion abilities, such as phosphate solubilization, siderophore and indol-3-acetic acid productions. In addition, genomic DNA was extracted, sequenced and de novo assembly was performed. Further, genome annotation, pan-genome analysis and selected genome analyses, such as CRISPR arrays detection, antibiotic resistance and secondary metabolite genes identification were carried out. The typical appearance characteristics of the strain include the formation of symplasmata in submerged liquid culture and the formation of pale yellow colonies on agar. The genetic information of the strain (in total 4.8 Mb) is divided between a chromosome and two plasmids. The strain lacks any CRISPR-Cas system but is equipped with four restriction-modification systems. The phenotypic analysis focused on growth under both aerobic and anaerobic conditions, as well as traits associated with plant growth promotion. At both levels (genomic and phenotypic), the production of siderophores, indoleacetic acid-derived growth promoters, gluconic acid, and enzyme activities related to the degradation of complex organic compounds were found. Extracellular gluconic acid production under aerobic conditions (up to 8 g/l) is probably the result of glucose oxidation by the membrane-bound pyrroloquinoline quinone-dependent enzyme glucose dehydrogenase. The strain has a number of properties potentially beneficial to the hop plant and its closest relatives include the strains also isolated from the aerial parts of plants, yet its safety profile needs to be addressed in follow-up research.

Cultural techniques capture diverse phosphate-solubilizing bacteria in rock phosphate-enriched habitats.

Phosphorus (P) deficiency is a common problem in croplands where phosphate-based fertilizers are regularly used to maintain bioavailable P for plants. However, due to their limited mobility in the soil, there has been an increased interest in microorganisms that can convert insoluble P into a bioavailable form, and their use to develop phosphate-solubilizing bioinoculants as an alternative to the conventional use of P fertilizers. In this study, we proposed two independent experiments and explored two entirely different habitats to trap phosphate-solubilizing bacteria (PSBs). In the first experiment, PSBs were isolated from the rhizoplane of native plant species grown in a rock-phosphate (RP) mining area. A subset of 24 bacterial isolates from 210 rhizoplane morphotypes was selected for the inorganic phosphate solubilizing activities using tricalcium phosphate (TCP) as the sole P source. In the second experiment, we proposed an innovative experimental setup to select mycohyphospheric bacteria associated to arbuscular mycorrhizal fungal hyphae, indigenous of soils where agronomic plant have been grown and trapped in membrane bag filled with RP. A subset of 25 bacterial isolates from 44 mycohyphospheric morphotypes was tested for P solubilizing activities. These two bacterial subsets were then screened for additional plant growth-promoting (PGP) traits, and 16S rDNA sequencing was performed for their identification. Overall, the two isolation experiments resulted in diverse phylogenetic affiliations of the PSB collection, showing only 4 genera (24%) and 5 species (17%) shared between the two communities, thus underlining the value of the two protocols, including the innovative mycohyphospheric isolate selection method, for selecting a greater biodiversity of cultivable PSB. All the rhizoplane and mycohyphospheric PSB were positive for ammonia production. Indol-3-acetic acid (IAA) production was observed for 13 and 20 isolates, respectively among rhizoplane and mycohyphospheric PSB, ranging, respectively, from 32.52 to 330.27 μg mL-1 and from 41.4 to 963.9 μg mL-1. Only five rhizoplane and 12 mycohyphospheric isolates were positively screened for N2 fixation. Four rhizoplane PSB were identified as siderophore producers, while none of the mycohyphospheric isolates were. The phenotype of one PSB rhizoplane isolate, assigned to Pseudomonas, showed four additive PGP activities. Some bacterial strains belonging to the dominant genera Bacillus and Pseudomonas could be considered potential candidates for further formulation of biofertilizer in order to develop bioinoculant consortia that promote plant P nutrition and growth in RP-enriched soils.

Desempenho de remineralizadores inoculados com microrganismos como fonte de potássio e outros nutrientes

ABSTRACT The consumption of potassium (K) fertilizers in Brazilian agriculture exceeds the national production of this input by more than ten times, indicating the need for alternatives to reduce imports of these products. The objective of this study was to evaluate the performance of the remineralizing rocks phonolite and olivine melilitite as sources of K and other nutrients, as well as the effects of inoculation with Bacillus subtilis and Bacillus megaterium on the solubilization of these rocks in the soil. A greenhouse experiment was conducted using a randomized block design, with four replications, in a factorial arrangement consisting of three K sources (potassium chloride, phonolite, and olivine melilitite), three rates (150, 300, and 600 kg ha-1 K2O), with and without inoculant, and two controls without K (one with and one without inoculant). The experimental units consisted of pots containing 3 kg of soil and a strawberry plant grown for eight months. The treatment with olivine melilitite inoculated with rhizobacteria favored phosphate solubilization when applied the highest rate. Olivine melilitite remineralizer, alone or inoculated with rhizobacteria, increased K+ and Ca2+ contents in the soil when applied at the intermediate and highest rates (300 and 600 kg ha-1 K2O), highlighting this remineralizer as an alternative potassium source for plants.

PRODUCTION OF ORGANIC ACID AND SOLUBILIZATION OF INORGANIC PHOSPHATE BY A BACTERIUM ISOLATED FROM CONTAMINATED SOIL

Many agricultural soils have significant phosphorus (P) reserves, much of which builds up because of frequent P fertilizer applications. However, roughly 95 to 99% of soil phosphorus is found as insoluble phosphates and is therefore unavailable for plant uptake. The current investigation characterized a bacterial strain that was obtained from contaminated soil and showed the ability to solubilize insoluble inorganic phosphates. An efficient phosphate-solubilizing bacterium was isolated in polluted soil in Mumbai. The phosphate solubilization index of this isolate was assessed using tribasic calcium phosphate-supplemented Pikovskaya’s (PVK) medium. After growing under constant agitation for seven days, the medium pH decreased from 7.0 to 3.5 units. Based on the colony morphology, microscopic analysis, and MALDI-TOF sequencing, the bacterial isolate was identified as Klebsiella pneumoniae. Phosphate solubilization was linked to a pH drop caused by bacterial growth in a medium with glucose as a carbon source. The secretion of organic acids by these phosphate-solubilizing bacteria is responsible for their ability to solubilize inorganic phosphate. GC-MS analysis revealed the presence of carbamic acid, dodecanoic acid, tetra decanoic acid, and trifluoroacetic acid in the culture supernatant. The amount of phosphate solubilized by the bacterium was determined by phosphomolybdate assay and was found to be 667.0 ug/ml which was much higher than the control bacterium S. aureus which was 131.0 ug/ml. To the best of our knowledge, this is the first report mentioning the isolation of phosphate solubilizing bacterium from polluted soil in Mumbai.

Exploring rhizobacteria of wild sugarcane (Saccharum spontaneum L.) and their plant growth promoting potential

In this study, the rhizospheric soil of wild sugarcane from three different salt-affected soils of the eastern Indo-Gangetic Plains was sampled. Rhizospheric bacteria from S. spontaneum were isolated and they were characterized for growth-promoting traits with molecular identification. A total of 49 isolates were isolated from three S. spontaneum rhizosphere soils from different places. These isolates were shown to have differential tolerance to NaCl concentrations up to 2000 mM. Owing to their host habitat and poor nutrient availability, these bacteria were found to have excellent tolerance to high NaCl concentrations along with having multiple plant growth traits. Apart from salt tolerance, these isolates were screened for EPS production, phosphate solubilization, zinc solubilization, siderophore production and ammonia production and based on multiple plant growth-promoting traits, twenty isolates were taken for molecular identification and further in vivo screening. These twenty S. spontaneum rhizospheric microbes belonged to the classes Gammaproteobacteria, Firmicutes (Bacilli) and Actinomycetia, representing six genera and 15 species. In vivo growth promotion studies indicated that some of these isolates could improve germination and growth in rice seedlings. The results of this study signify the possibility of utilizing wild crop microbiomes to nurture cultivated crops under adverse growing conditions.