Bacteria of the genus Bacillus are widely used in agriculture due to their ability to synthesise IAA, but the metabolic pathways of IAA synthesis and the regulatory mechanisms of key genes remain unclear. In this study, the biochemical characteristics of Bacillus cereus, Bacillus subtilis and Bacillus safensis were detected. It was found that Bacillus subtilis has a higher indoles synthesis efficiency, Bacillus safensis has stronger salt tolerance and Bacillus cereus has more prominent alkali tolerance. Through whole-genome sequencing and comparative analysis, combined with the retrieval of key genes in the tryptophan metabolic pathway and the metabolic analysis of indole compounds, it is clarified that Bacillus cereus has three IAA synthesis pathways, namely TAM, IAM and IPyA; Bacillus subtilis contains IAM and IPyA pathways; and Bacillus safensis only has the IPyA pathway. This study offers new insights into Bacillus metabolism, high-quality strains for microbial agents, and matters for plant-growth bacteria application and agricultural sustainability.
Hou et al. (Wed,) studied this question.