Solubilization of potassium-bearing minerals by a wildtype strain of Bacillus edaphicus and its mutants and increased potassium uptake by wheat

Two potassium (K)-bearing minerals, Nanjing feldspar and Suzhou illite, were used to investigate K mobilization by the wild-type strain NBT of Bacillus edaphicus, also labeled MPs(+), selected for high activity in mobilizing potassium from minerals, and by four of its UV + LiCl mutants, MPs(++), MPs(+)1, MPs(+)2, and MPs(-). In liquid cultures, the five bacterial strains showed better growth on Suzhou illite than on Nanjing feldspar. Suzhou illite was the better potassium source for the growth of the wild type and the MPs(++), MPs(+)1, and MPs(+)2 mutants. Solubilization of K from its sources by the wild-type NBT and the MPs(++) mutant resulted mostly from the action of organic acids and capsular polysaccharides. Oxalic acid seemed to be a more active agent for the solubilization of Nanjing feldspar. Oxalic and tartaric acids were likely involved in the solubilization of Suzhou illite. The MPs(-) mutant did not produce any organic acid or capsular polysaccharide when grown on the above two K sources. In a pot experiment, wheat (Triticum aestivum L.) 'Yangmai-158' was grown in a yellow-brown soil that had low available K. After inoculation with bacterial strains, B. edaphicus NBT and its four mutants, MPs(++), MPs(+)1, MPs(+)2, and MPs(-) (in separate tests), the root growth and shoot growth of wheat were significantly increased by B. edaphicus NBT and the mutants MPs(+) and MPs(+)1. Bacterial inoculation also resulted in significantly higher N, P, and K contents of plant components. The bacteria were able to survive in the wheat rhizosphere soils after root inoculation.