Mineral Release Dynamics of Tricalcium Phosphate and Waste Muscovite by Mineral-Solubilizing Rhizobacteria Isolated from Indo-Gangetic Plain of India

Abstract

ABSTRACTThe aim of the present investigation was to evaluate the mineral release abilities of ten rhizobacterial strains isolated from rhizosphere of various crops growing in the Indo-Gangetic Plain (IGP) of India. Their abilities to solubilize inorganic phosphorus (P) and potassium (K) minerals from insoluble tricalcium phosphate (TCP) and waste muscovite (WM) revealed that rhizobacteria significantly solubilized different levels of inorganic P and fixed K, respectively. Some of the rhizobacterial stains have the ability to produce ammonia, indole-3-acetic acid (IAA), and hydrogen cyanide (HCN). The identification based on the 16S rDNA gene sequencing of selected mineral-solubilizing rhizobacteria (MSR) having greater potential to serve as bioagents were identified as Bacillus subtilis (BRHU01, BRHU03, and BHU20), Bacillus tequilensis (BRHU02), Bacillus licheniformis (BRHU04), Bacillus pumilus (BRHU05), Bacillus flexus (BHU02), Brevibacillus formosus (BHU16), Bacillus methylotrophicus (BHU29), and Bacillus amyloliquefaciens (BHU30). Interestingly, inorganic P and K solubilization by these strains belonging to genera Bacillus and Brevibacillus showed significant variations from 0.52 to 14.49 and from 1.62 to 8.60 µg mL−1, respectively. However, generally, pH values of culture media decreased from near neutral (6.43) to acidic (3.83) with increasing incubation period, and this was inversely correlated with quantities of K solubilized by these rhizobacterial strains. Meanwhile, the electrical conductivity (EC) of broth culture increased from 0.09 to 0.23 dS m−1 with increasing incubation period. Principal component analysis (PCA) of the MSR revealed three clusters, which exhibited high variance with respect to nutrient release. Taken together, these results suggest that Bacillus and Brevibacillus sp. identified in this study solubilized varying levels of inorganic P and fixed K from insoluble TCP and WM by acidolysis mechanisms.