Potential plant growth promoting traits and bioacidulation of rock phosphate by thiosulfate oxidizing bacteria isolated from crop plants

Thiosulfate oxidizing bacteria isolated from crop plants were tested for their traits related to plant growth promotion and their ability to solubilize Morocco rock phosphate (RP) through oxidation of thiosulfate to sulfuric acid. All the tested strains grew in Nfb medium (except Dyella ginsengisoli) and possessed beta-1,3 glucanase activity (except Burkholderia kururiensis). Of the fourteen tested strains, 2 were found positive for siderophore production, 3 each for phytohormones (IAA), and salicylic acid production. Based on qualitative and quantitative assays, 5 strains were found to efficiently solubilize tri-calcium phosphate in Pikovskaya's medium. Nine strains exhibited ACC (1-aminocyclopropane-1-carboxylate) deaminase activity. In gnotobiotic experiments, Pandoraea sputorum ATSB28 which possessed the lowest ACC deaminase (0.44 nM of alpha-Keto butyrate formed min(-1) mg of protein(-1)) activity increased the primary root length of canola by 166%. Inoculation of Pandoraea sp. strain ATSB30 in mixture containing RP and thiosulfate significantly enhanced the water extractable-P (1147 mu g P g RP-1) and bicarbonate extractable-P (1144 mu g P g RP-1) on day 45. Glucose amendment resulted in increased RP solubilization as compared to glucose unamended treatments. Thiosulfate oxidizing bacteria tested in this study possessed at least one or more plant growth promoting traits apart from thiosulfate oxidation and solubilized the RP.