The effect of combination of root exudates substances on stimulation of Bacillus spores' germination.

Root exudates play a crucial role in the rhizosphere by influencing the growth and activity of plant growth-promoting rhizobacteria (PGPR), such as Bacillus velezensis. Previous studies have shown that most Bacillus spores can germinate in the rhizosphere while remain dormant in the soil. Understanding the relationship between specific components of root exudates and spore germination could provide valuable insights into how plants alter the ratio of spores in the rhizosphere through root exudates. In this study, we observed that Bacillus spore germination was induced by root exudates from maize (Fengtian) and two cucumber varieties (9930 and Jinchun 4). Maize root exudates induced spore germination at a significantly higher rate compared to cucumber exudates. We identified L-valine, β-alanine, xylose, glucose, and asparagine as key germination-inducing compounds in the exudates. Notably, when these compounds were combined, spore germination rates increased to over 80 %. We found that the maize-specific root exudate asparagine significantly enhanced the spore germination inducing ability of other germinants even at low concentrations. Furthermore, our results indicate that the GerA receptor specifically recognizes amino acids, while GerB and GerK work cooperatively to sense sugars and amides. These findings provide new insights into plant-microbe interactions and could inform the development of more effective Bacillus-based biofertilizers, improving their application in sustainable agriculture.