Whole genome sequence insight of two plant growth-promoting bacteria (B. subtilis BS87 and B. megaterium BM89) isolated and characterized from sugarcane rhizosphere depicting better crop yield potentiality.

Since sugarcane is a ratoon crop, genome analysis of plant growth-promoting bacteria that exist in its soil rhizosphere, can provide opportunity to better understand their characteristics and use of such bacteria in turn, may especially improve perennial crop productivity. In the present study, genome of two bacterial strains, one each of B. megaterium (BM89) and B. subtilis (BS87), isolated and reported earlier (Chandra et al., 2018), were sequenced and characterized. Though both strains have demonstrated plant growth promoting properties and enhanced in-vitro plant growth responses, functional annotation and analysis of genes indicated superiority of BS87 as it possessed more plant growth promotion attributable genes over BM89. Apart from some common genes, trehalose metabolism, glycine betaine production, peroxidases, super oxide dismutase, cold shock proteins and phenazine production associated genes were selectively identified in BS87 genome indicating better plant growth performances and survival potential under harsh environmental conditions. Genes for chitinase, d-cysteine desulfhydrase and γ-aminobutyric acid (GABA), as found in BM89, propose its selective utilization in defense and bio-control measures. Concomitant with better settlings' growth, scanning electron micrographs indicated these isolated and characterized bacteria exhibiting healthy colonization within root of sugarcane crop. Kegg pathways' assignment also revealed added pathways namely carbohydrate and amino acid metabolism attached to B. subtilis strain BS87, a preferable candidate for bio-fertilizer and its utilization to promote growth of both plant and ratoon crops of sugarcane usually experiencing harsh environmental conditions.

Transcriptional response of Bacillus megaterium FDU301 to PEG200-mediated arid stress.

BACKGROUND: For microorganisms on a paper surface, the lack of water is one of the most important stress factors. A strain of Bacillus megaterium FDU301 was isolated from plaques on a paper surface using culture medium with polyethylene glycol 200 (PEG200) to simulate an arid condition. Global transcriptomic analysis of B. megaterium FDU301 grown under normal and simulated arid conditions was performed via RNA-seq technology to identify genes involved in arid stress adaptation. RESULTS: The transcriptome of B. megaterium FDU301 grown in LB medium under arid (15% PEG200 (w/w)) and normal conditions were compared. A total of 2941 genes were differentially expressed, including 1422 genes upregulated and 1519 genes downregulated under arid conditions. Oxidative stress-responsive regulatory genes perR, fur, and tipA were significantly upregulated, along with DNA protecting protein (dps), and catalase (katE). Genes related to Fe2+ uptake (feoB), sporulation stage II (spoIIB, spoIIE, spoIIGA), small acid-soluble spore protein (sspD), and biosynthesis of compatible solute ectoine (ectB, ectA) were also highly expressed to various degrees. Oxidative phosphorylation-related genes (atpB, atpE, atpF, atpH, atpA, atpG, atpD, atpC) and glycolysis-related genes (pgk, tpiA, frmA) were significantly downregulated. CONCLUSION: This is the first report about transcriptomic analysis of a B. megaterium to explore the mechanism of arid resistance. Major changes in transcription were seen in the arid condition simulated by PEG200 (15%), with the most important one being genes related to oxidative stress. The results showed a complex mechanism for the bacteria to adapt to arid stress.

Isolation and characterization of plant growth-promoting rhizobacteria and their effects on the growth of Medicago sativa L. under salinity conditions.

Plant growth-promoting rhizobacteria are a group of free-living bacteria that colonize plant rhizosphere and benefit plant root growth, thereby increasing host plant to cope with salinity induced stress. The aim of this study was to (1) isolate and characterize auxin-producing bacteria showing a high plant growth-promoting (PGP) potential, and (2) evaluate the PGP effects on the growth of Medicago sativa L under salinity stress (130 mM NaCl). Of thirteen isolates, Bacillus megaterium NRCB001 (NRCB001), B. subtilis subsp. subtilis NRCB002 (NRCB002) and B. subtilis NRCB003 (NRCB003) had the ability to produce auxin, which ranged from 47.53 to 154.38 µg ml-1. The three auxin-producing bacterial strains were shown multiple PGP traits, such as producing siderophore and NH3, showing ACC deaminase activity, solubilize phosphate and potassium. Furthermore, NRCB001, NRCB002, and NRCB003 could survive in LB medium containing 1750 mM NaCl. The three auxin-producing with salinity tolerance strains were selected for further analyses. In greenhouse experiments, when inoculated with NRCB001, NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 24.1%, 23.1% and 38.5% respectively, compared with those of non-inoculated control seedlings under normal growth condition. When inoculated with NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 96.9 and 71.6% respectively, compared with those of non-inoculated control seedlings under 130 mM NaCl condition. Our results indicated that NRCB002 and NRCB003 having PGP traits are promising candidate strains to develop biofertilizers, especially used under salinity stress conditions.

Impacts of plant growth promoters and plant growth regulators on rainfed agriculture.

Demand for agricultural crop continues to escalate in response to increasing population and damage of prime cropland for cultivation. Research interest is diverted to utilize soils with marginal plant production. Moisture stress has negative impact on crop growth and productivity. The plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGR) are vital for plant developmental process under moisture stress. The current study was carried out to investigate the effect of PGPR and PGRs (Salicylic acid and Putrescine) on the physiological activities of chickpea grown in sandy soil. The bacterial isolates were characterized based on biochemical characters including Gram-staining, P-solubilisation, antibacterial and antifungal activities and catalases and oxidases activities and were also screened for the production of indole-3-acetic acid (IAA), hydrogen cyanide (HCN) and ammonia (NH3). The bacterial strains were identified as Bacillus subtilis, Bacillus thuringiensis and Bacillus megaterium based on the results of 16S-rRNA gene sequencing. Chickpea seeds of two varieties (Punjab Noor-2009 and 93127) differing in sensitivity to drought were soaked for 3 h before sowing in fresh grown cultures of isolates. Both the PGRs were applied (150 mg/L), as foliar spray on 20 days old seedlings of chickpea. Moisture stress significantly reduced the physiological parameters but the inoculation of PGPR and PGR treatment effectively ameliorated the adverse effects of moisture stress. The result showed that chickpea plants treated with PGPR and PGR significantly enhanced the chlorophyll, protein and sugar contents. Shoot and root fresh (81%) and dry weights (77%) were also enhanced significantly in the treated plants. Leaf proline content, lipid peroxidation and antioxidant enzymes (CAT, APOX, POD and SOD) were increased in reaction to drought stress but decreased due to PGPR. The plant height (61%), grain weight (41%), number of nodules (78%) and pod (88%), plant yield (76%), pod weight (53%) and total biomass (54%) were higher in PGPR and PGR treated chickpea plants grown in sandy soil. It is concluded from the present study that the integrative use of PGPR and PGRs is a promising method and eco-friendly strategy for increasing drought tolerance in crop plants.

Heavy metal-immobilizing bacteria increase the biomass and reduce the Cd and Pb uptake by pakchoi (Brassica chinensis L.) in heavy metal-contaminated soil.

Microbial immobilization is a novel and environmentally friendly technology that uses microbes to reduce metal availability in soil and accumulation of heavy metals in plants. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of pakchoi in Cd- and Pb-contaminated farmland and investigated their effects on Cd and Pb accumulation in pakchoi and the underlying mechanisms. The results showed that two urease-producing bacteria, Bacillus megaterium N3 and Serratia liquefaciens H12, were identified by screening. They had higher ability to produce urease (57.5 ms cm-1 min-1 OD600-1 and 76.4 ms cm-1 min-1 OD600-1, respectively). The two strains allowed for the immobilization of Cd and Pb by extracellular adsorption, bioprecipitation, and increasing the pH (from 6.94 to 7.05-7.09), NH4+ content (69.1%-127%), and NH4+/NO3- ratio (from 1.37 to 1.67-2.11), thereby reducing the DTPA-extractable Cd (35.3%-58.8%) and Pb (37.8%-62.2%) contents in the pakchoi rhizosphere soils and the Cd (76.5%-79.7%) and Pb (76.3%-83.5%) contents in the leaves (edible tissue) of pakchoi. The strains were highly resistant to heavy metal toxicity; produced IAA, siderophores and abscisic acid; and increased the NH4+/NO3- ratio, which might be related to the two strains protectiing pakchoi against the toxic effect of Cd and Pb and increasing pakchoi biomass. Thus, the results were supposed to strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Comparative study on the biodegradation of chlorpyrifos-methyl by Bacillus megaterium CM-Z19 and Pseudomonas syringae CM-Z6.

The strains CM-Z19 and CM-Z6, which are capable of highly degrading chlorpyrifos-methyl, were isolated from soil. They were identified as Bacillus megaterium CM-Z19 and Pseudomonas syringae CM-Z6, respectively, based on the 16S rRNA and an analysis of their morphological, physiological and biochemical characteristics. The strain CM-Z19 showed 92.6% degradation of chlorpyrifos-methyl (100 mg/L) within 5 days of incubation, and the strain CM-Z6 was 99.1% under the same conditions. In addition, the degradation characteristics of the two strains were compared and studied, and the results showed that the strain CM-Z19 had higher phosphoesterase activity and ability to degrade the organophosphorus pesticide than did the strain CM-Z6. However, the strain CM-Z19 could not degrade its first hydrolysis metabolite 3,5,6-trichloro-2-pyridinol (TCP) and could not completely degrade chlorpyrifos-methyl. The strain CM-Z6 could effectively degrade TCP and could degrade chlorpyrifos-methyl more quickly than strain CM-Z19.

Complete genome sequence of Bacillus megaterium JX285 isolated from Camellia oleifera rhizosphere.

Bacillus megaterium strain JX285, isolated from rhizosphere red soil sample, can solubilize inorganic phosphorus, which increases the amount of available phosphorus and promotes plant growth. To investigate the mechanisms underlying phosphate solubilization, we sequenced the entire genome of B. megaterium strain JX285 (CGMCC 1.1621), which comprises a circular chromosome of 5,066,463 bp and seven plasmids of 167,030, 128,297, 60,905, 134,795, 9,598, 37,455, and 6332 bp, respectively. The whole genome sequence includes 5948 protein-coding genes, 124 tRNAs, and 29 rRNAs, and has been deposited at Genbank/EMBL/DDBJ with accession numbers CP018874-CP018881. We detected genes associated with organic acid production, which may be vital for phosphate conversion. Furthermore, phosphatase-encoding genes were also detected. The information embedded in the genome will assist in studying the mechanisms of phosphate solubilization. In conclusion, analysis of the JX285 genome will further our knowledge regarding this strain and may contribute to its biotechnological application.

Characterization of Two Self-Sufficient Monooxygenases, CYP102A15 and CYP102A170, as Long-Chain Fatty Acid Hydroxylases.

Self-sufficient P450s, due to their fused nature, are the most effective tools for electron transfer to activate C-H bonds. They catalyze the oxygenation of fatty acids at different omega positions. Here, two new, self-sufficient cytochrome P450s, named CYP102A15 and CYP102A170, from polar Bacillus sp. PAMC 25034 and Paenibacillus sp. PAMC 22724, respectively, were cloned and expressed in E. coli. The genes are homologues of CYP102A1 from Bacillus megaterium. They catalyzed the hydroxylation of both saturated and unsaturated fatty acids ranging in length from C12-C20, with a moderately diverse profile compared to other members of the CYP102A subfamily. CYP102A15 exhibited the highest activity toward linoleic acid with Km 15.3 µM, and CYP102A170 showed higher activity toward myristic acid with Km 17.4 µM. CYP10A170 also hydroxylated the Eicosapentaenoic acid at ω-1 position only. Various kinetic parameters of both monooxygenases were also determined.

Multiplex and quantitative PCR targeting SCAR markers for strain-level detection and quantification of biofertilizers.

Biofertilizers are the eco-friendly bio-input being used to sustain the agriculture by reducing the chemical inputs and improving the soil health. Quality is the major concern of biofertilizer technology which often leads to poor performance in the field and thereby loses the farmers' faith. To authenticate the strain as well as its presumed cell load of a commercial product, sequence characterized amplified region (SCAR) markers were developed for three biofertilizer strains viz., Azospirillum brasilense (Sp7), Bacillus megaterium (Pb1) and Azotobacter chroococcum (Ac1). We evaluated the feasibility of multiplex-PCR and quantitative real-time PCR for SCAR marker-based quality assessment of the product as well as the persistence of the strains during crop growth. We showed that multiplex PCR can concurrently discriminate the strains based on the amplicons' size and detects up to 104 cells per g or per ml of carrier-based or liquid formulation of biofertilizer, respectively. The detection limit of quantitative PCR targeting SCAR markers is 103 cells per g or ml of biofertilizer. Both the PCR methods detected and quantified them in the maize rhizosphere. Hence SCAR marker-based quality assessment would be a sensitive tool to monitor the biofertilizer production as well as its persistence in the inoculated crop rhizosphere.

Novel phosphate-solubilising bacteria isolated from sewage sludge and the mechanism of phosphate solubilisation.

A great amount of insoluble phosphate in agricultural soils is not available for crops. Three strains of bacteria (Bacillus megaterium YLYP1, Pseudomonas prosekii YLYP6 and Pseudomonas sp. YLYP29) isolated from activated sludge and soil could efficiently solubilise tricalcium phosphate. In particular, the novel strain P. prosekii YLYP6 produced 716 mg L-1 of available phosphate within 6 days under the optimal culture conditions [20 °C, pH 7.9, inoculum size of 0.5% (v:v)] determined by response surface methodology. P. prosekii YLYP6 demonstrated efficient phosphate solubilisation in response to broad variations in pH (5-9) and temperature (15-35 °C). The phosphate solubilisation curves of the strains fit well with a first-order kinetic model (R2 > 0.939), with a half-life of 1.51-5.94 d for 5.0 g L-1 calcium phosphate. Continuous culture experiments combined with scanning electron microscopic observations and gas chromatography-mass spectrometry analysis revealed that 2,3-dimethylfumaric acid, gluconic and N-butyl-tert-butylamine that were produced by P. prosekii YLYP6 were responsible for phosphate solubilisation by supplying H+ ions and organic anions. Efficient phosphate solubilisation in actual soil by P. prosekii YLYP6 demonstrated the strong application potential to reduce the use of chemical P fertilisers and the resulting agricultural nonpoint pollution.

Electrochemical Surface-Enhanced Raman Spectroscopy as a Platform for Bacterial Detection and Identification.

The field of bacterial screening is in need of a rapid, easy to use, sensitive, and selective platform for bacterial detection and identification. Current methods of bacterial identification lack time efficiency, resulting in problems for many sectors of society. Surface-enhanced Raman spectroscopy (SERS) has been investigated as a possible candidate for bacterial screening due to its demonstrated ability to detect biological molecules with a high degree of sensitivity. However, the field of bacterial screening using SERS is currently facing limitations such as signal irreproducibility, weak spectra, and difficulty differentiating between strains based on the SERS spectra of bacteria alone. The current study reports on the first ever use of electrochemical surface-enhanced Raman spectroscopy (EC-SERS) for bacterial screening. The results of this study demonstrate the ability of EC-SERS to greatly improve upon the SERS performance for the detection of Gram-positive and Gram-negative bacteria both in terms of improved peak intensities and spectral richness. EC-SERS shows great promise in its ability to advance SERS-based bacterial screening and could potentially be used for more efficient species discrimination at the point-of-need (PON).

Characterization of Bacillus megaterium, Bacillus pumilus, and Paenibacillus polymyxa isolated from a Pinot noir wine from Western Washington State.

This report provides the first confirmed evidence of Bacillus-like bacteria present in a wine from Washington State. These bacteria were isolated from a 2013 Pinot noir wine whose aroma was sensorially described as being 'dirty' or 'pond scum.' Based on physiological traits and genetic sequencing, three bacterial isolates were identified as Bacillus megaterium (strain NHO-1), Bacillus pumilus (strain NHO-2), and Paenibacillus polymyxa (strain NHO-3). These bacteria grew in synthetic media of low pH (pH 3.5) while some survived ethanol concentrations up to 15% v/v. However, none tolerated molecular SO2 concentrations ≥0.4 mg/l. Growth of strains NHO-1 and NHO-3 in a Merlot grape juice resulted in increases of titratable and volatile acidities while decreases in titratable acidity were noted for NHO-2.

Characterization of Polyhydroxyalkanoate Produced by Bacillus megaterium VB89 Isolated from Nisargruna Biogas Plant.

Polyhydroxyalkanoates (PHAs) are naturally occurring biodegradable polymers that can curb the extensive use of polypropylene based plastics. In contrast to chemically synthesized polypropylene plastics, PHAs are biodegradable and thus environmentally safe. PHAs have attracted much attention as biocompatible and biodegradable thermoplastics. The present study involves isolation of bacteria from different environments capable of synthesizing PHAs. The bacterium producing highest yield of PHA (0.672 ± 0.041 g/L) was identified as Bacillus megaterium VB89 by biochemical and molecular techniques such as 16S rDNA sequence analysis. Strain VB89 produced polyhydroxybutyrate (PHB) as revealed by FTIR and NMR. This PHB had an average molecular weight of 2.89 × 105 Da and a polydispersity index of 2.37. Thermal properties of the PHB included a glass transition temperature of 13.97 °C, a melting temperature of 181.74 °C, and a decomposition temperature of 234 °C. All these properties indicated that VB89 produced PHB of high purity and good thermal stability.

Isolation, Identification, and Optimization of Culture Conditions of a Bioflocculant-Producing Bacterium Bacillus megaterium SP1 and Its Application in Aquaculture Wastewater Treatment.

A bioflocculant-producing bacterium, Bacillus megaterium SP1, was isolated from biofloc in pond water and identified by using both 16S rDNA sequencing analysis and a Biolog GEN III MicroStation System. The optimal carbon and nitrogen sources for Bacillus megaterium SP1 were 20 g L-1 of glucose and 0.5 g L-1 of beef extract at 30°C and pH 7. The bioflocculant produced by strain SP1 under optimal culture conditions was applied into aquaculture wastewater treatment. The removal rates of chemical oxygen demand (COD), total ammonia nitrogen (TAN), and suspended solids (SS) in aquaculture wastewater reached 64, 63.61, and 83.8%, respectively. The volume of biofloc (FV) increased from 4.93 to 25.97 mL L-1. The addition of Bacillus megaterium SP1 in aquaculture wastewater could effectively improve aquaculture water quality, promote the formation of biofloc, and then form an efficient and healthy aquaculture model based on biofloc technology.

Magnetic Trapping of Bacteria at Low Magnetic Fields.

A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells.

Bacillus megaterium SF185 induces stress pathways and affects the cell cycle distribution of human intestinal epithelial cells.

The interaction between the enteric microbiota and intestinal cells often involves signal molecules that affect both microbial behaviour and host responses. Examples of such signal molecules are the molecules secreted by bacteria that induce quorum sensing mechanisms in the producing microorganism and signal transduction pathways in the host cells. The pentapeptide competence and sporulation factor (CSF) of Bacillus subtilis is a well characterized quorum sensing factor that controls competence and spore formation in the producing bacterium and induces cytoprotective heat shock proteins in intestinal epithelial cells. We analysed several Bacillus strains isolated from human ileal biopsies of healthy volunteers and observed that some of them were unable to produce CSF but still able to act in a CSF-like fashion on model intestinal epithelial cells. One of those strains belonging to the Bacillus megaterium species secreted at least two factors with effects on intestinal HT29 cells: a peptide smaller than 3 kDa able to induce heat shock protein 27 (hsp27) and p38-MAPK, and a larger molecule able to induce protein kinase B (PKB/Akt) with a pro-proliferative effect.

Identification of Bacillus megaterium and Microbacterium liquefaciens genes involved in metal resistance and metal removal.

Bacillus megaterium MNSH1-9K-1 and Microbacterium liquefaciens MNSH2-PHGII-2, 2 nickel- and vanadium-resistant bacteria from mine tailings located in Guanajuato, Mexico, are shown to have the ability to remove 33.1% and 17.8% of Ni, respectively, and 50.8% and 14.0% of V, respectively, from spent petrochemical catalysts containing 428 ± 30 mg·kg(-1) Ni and 2165 ± 77 mg·kg(-1) V. In these strains, several Ni resistance determinants were detected by conventional PCR. The nccA (nickel-cobalt-cadmium resistance) was found for the first time in B. megaterium. In M. liquefaciens, the above gene as well as the czcD gene (cobalt-zinc-cadmium resistance) and a high-affinity nickel transporter were detected for the first time. This study characterizes the resistance of M. liquefaciens and B. megaterium to Ni through the expression of genes conferring metal resistance.

Expression Analysis of Ni- and V-Associated Resistance Genes in a Bacillus megaterium Strain Isolated from a Mining Site.

Bacillus megaterium strain MNSH1-9K-1 was isolated from a mining site in Guanajuato, Mexico. This B. megaterium strain presented the ability to remove Ni and V from a spent catalyst. Also, its associated metal resistance genes nccA, hant, VAN2, and smtAB were previously identified by a PCR approach. The present study reports for the first time, in B. megaterium, the changes in the expression of the genes nccA (Ni-Co-Cd resistance); hant (high-affinity nickel transporter); smtAB, a metal-binding protein gene; and VAN2 (V resistance) after exposure to 200 ppm of Ni and 200 ppm of V during the stationary phase of the microorganism in PHGII liquid media. The data presented here may contribute to the knowledge of the genes involved in the Ni and V resistances of B. megaterium, and the possible pathways implicated in the Ni-V removal processes, which may be potentiated for the biological treatment of high metal content residues.

Isolation and identification of Bacillus megaterium YB3 from an effluent contaminated site efficiently degrades pyrene.

Industrial effluents contaminated sites may serve as repositories of ecologically adapted efficient pyrene degrading bacteria. In the present study, six bacterial isolates from industrial effluents were purified using serial enrichment technique and their pyrene degrading potential on pyrene supplemented mineral salt medium was assessed. 16S rRNA sequence analysis showed that they belong to four bacterial genera, namely Acinetobacter, Bacillus, Microbacterium, and Ochrobactrum. Among these isolates, Bacillus megaterium YB3 showed considerably good growth and was further evaluated for its pyrene-degrading efficiency. B. megaterium YB3 could degrade 72.44% of 500 mg L(-1) pyrene within 7 days. GC-MS analysis of ethyl acetate extracted fractions detected two relatively less toxic metabolic intermediates of the pyrene degradation pathway. B. megaterium YB3 also tested positive for catechol 1, 2-dioxygenase and aromatic-ring-hydroxylating dioxygenase indole-indigo conversion assays. Considering the ability and efficiency of B. megaterium YB3 to degrade high pyrene content, the strain can be used as a tool to develop bioremediation technologies for the effective biodegradation of pyrene and possibly other PAHs in the environment.

Rock inhabiting potassium solubilizing bacteria from Kerala, India: characterization and possibility in chemical K fertilizer substitution.

The role of rock inhabiting bacteria in potassium (K) solubilization from feldspar and their application in crop nutrition through substitution of fertilizer K was explored through the isolation of 36 different bacteria from rocks of a major hill station at Ponmudi in Thiruvananthapuram, Kerala, India. A comprehensive characterization of K solubilization from feldspar was achieved with these isolates which indicated that the K solubilizing efficiency increases with decrease in pH and increase in viscosity and viable cell count. Based on the level of K solubilization, two potent isolates were selected and identified as Bacillus subtilis ANctcri3 and Bacillus megaterium ANctcri7. Exopolysaccharide production, scanning electron microscopic and fourier transform infrared spectroscopic studies with these efficient strains conclusively depicted the role of low pH, increase in viscosity, and bacterial attachment in K solubilization. They were also found to be efficient in phosphorus (P) solubilization, indole acetic acid production as well as tolerant to wide range of physiological conditions. Moreover, the applicability of K containing rock powder as a carrier for K solubilizing bacteria was demonstrated. A field level evaluation on the yield of a high K demanding tuberous vegetable crop, elephant foot yam (Amorphophallus paeoniifolius (dennst.) nicolson) established the possibility of substituting chemical K fertilizer with these biofertilizer candidates successfully.