Plant-Associated Representatives of the <em>Bacillus cereus</em> Group Harbor a Rich Biosynthetic Potential of Antimicrobial Compounds and are Efficient in Suppressing Plant Pathogens

Abstract

Seventeen bacterial strains able to suppress plant pathogens have been isolated from healthy Vietnamese crop plants, and taxonomically assigned as members of the Bacillus cereus group. In order to prove their potential as biocontrol agents, we performed a comprehensive analysis which included whole genome sequencing of selected strains, and mining for genes and gene clusters involved in the synthesis of endo- and exotoxins, and secondary metabolites, such as antimicrobial peptides (AMPs). Kurstakin, thumolycin, and other AMPs were detected and characterized by different mass spectrometric methods, such as MALDI-TOF-MS, and LIFT-MALDI-TOF/TOF fragment analysis. Based on their whole genome sequences, the plant-associated isolates were assigned to the following species and subspecies: B. cereus subsp. cereus (6), B. cereus subsp. bombysepticus (5), Bacillus tropicus (2), and Bacillus pacificus. Three isolates represented novel genomospecies. Genes encoding entomopathogenic crystal and vegetative proteins were detected in B. cereus subsp. bombysepticus TK1. In vitro assays revealed that many plant-associated isolates enhanced plant growth and suppressed plant pathogens. Our findings indicated that plant-associated representatives of the B. cereus group are a rich source of putative antimicrobial compounds with potential in sustainable agriculture. However, the presence of virulence genes might restrict their application as biologicals in agriculture.