Tricalcium phosphate solubilisation by new endophyte Bacillus methylotrophicus CKAM isolated from apple root endosphere and its plant growth-promoting activities

Abstract

Bacillus methylotrophicus CKAM obtained from root endosphere of healthy apple trees was selected on the basis of higher P-solubilisation (687 mg/L), nitrogenase activity (237.6 ηmole C2H4 h−1mg−1 protein), IAA (34 µg/mL), siderophore unit (96.4 %) and antifungal activity against F. oxysporum (88.22 %), Phytophthora sp. (70.00 %), D. necatrix (61.73 %), S. rolfsii (44.54 %) and P. aphanidermatum (62.56 %). We investigated the ability of isolate CKAM to solubilise insoluble P via two possible mechanisms: proton excretion by ammonium assimilation and organic acid production. There were no clear differences in pH and P-solubilisation between glucose–ammonium and glucose–nitrate media. P-solubilisation was significantly promoted with glucose compared with fructose. HPLC study showed that isolate CKAM produced mainly gluconic and oxalic acids with small amounts of 2-ketogluconic, formic acids. During the culture, the pH was reduced with increase in gluconic acid concentration and was inversely correlated with soluble P concentration. Analysis of antifungal compounds involved in their antagonistic activity showed that isolate CKAM produced chitinase, proteases, pectinase and the antibiotic lipopeptides surfactin, fengycin and iturin A. It was notable that isolate CKAM exhibited highest protection against S. rolfsii (58 %) followed by F. oxysporum (54.5 %), D. necatrix (52.7 %), P. aphanidermatum (36.3 %) and Phytophthora sp. (21.8 %) in biocontrol trials using the pathosystem tomato. Remarkable increase was observed in seed germination (27.07 %), shoot length (42.33 %) root length (52.6 %), shoot dry weight (62.01 %) and root dry weight (45.7 %) of tomato under net house condition. Isolate CKAM possessed traits related to plant growth promotion, therefore, could be a potential candidate for the development of biofertiliser or biocontrol agent.