Investigation of factors influencing spore germination of Paenibacillus polymyxa ACCC10252 and SQR-21.

Bioorganic fertilizer containing Paenibacillus polymyxa SQR-21 showed very good antagonistic activity against Fusarium oxysporum. To optimize the role of P. polymyxa SQR-21 in bioorganic fertilizer, we conducted a study of spore germination under various conditions. In this study, L-asparagine, glucose, fructose and K(+) (AGFK), and sugars (glucose, fructose, sucrose, and lactose) plus L-alanine were evaluated to determine their ability to induce spore germination of two strains; P. polymyxa ACCC10252 and SQR-21. Spore germination was measured as a decrease in optical density at 600 nm. The effect of heat activation and germination temperature were important for germination of spores of both strains on AGFK in Tris-HCl. L-Alanine alone showed a slight increase in spore germination; however, fructose plus L-alanine significantly induced spore germination, and the maximum spore germination rate was observed with 10 mmol l(-1) L-alanine in the presence of 1 mmol l(-1) fructose in phosphate-buffered saline (PBS). In contrast, fructose plus L-alanine hardly induced spore germination in Tris-HCl; however, in addition of 10 mmol l(-1) NaCl into Tris-HCl, the percentages of OD(600) fall were increased by 19.6% and 24.3% for ACCC10252 and SQR-21, respectively. AGFK-induced spore germination was much more strict to germination temperature than that induced by fructose plus L-alanine. For both strains, fructose plus L-alanine-induced spore germination was not sensitive to pH. The results in this study can help to predict the effect of environmental factors and nutrients on spore germination diversity, which will be beneficial for bioorganic fertilizer storage and transportation to improve the P. polymyxa efficacy as biological control agent.