AUTHOR=Zhou Qian , Li Guanqiao , Cui Yinshan , Xiang Jingshu , Zhu Shu , Li Shijun , Huang Jingyu , Wang Yafang , Liu Ying , Zhou Li 

TITLE=Genomic characterization of Bacillus cereus isolated from food poisoning cases revealed the mechanism of toxin production

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1238799

DOI=10.3389/fmicb.2023.1238799

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p><italic>Bacillus cereus</italic> is a ubiquitous opportunistic human pathogen that causes food intoxications worldwide. However, the genomic characteristics and pathogenic mechanisms of <italic>B. cereus</italic> are still unclear.</p></sec><sec><title>Methods</title><p>Here, we isolated and purified nine strains of <italic>B. cereus</italic> (<italic>LY01-LY09</italic>) that caused vomiting, diarrhea and other symptoms from four foodborne outbreaks happened in Guizhou Province in southwest China from June to September 2021. After colony observation, Gram staining, microscopic examination and biochemical test, they were identified as <italic>B. cereus</italic>. The genomic characteristics, phylogenetic relationships and virulence factors of the isolated strains were analyzed at the genome level. Genome sequencing, comparative genomic analysis, secondary metabolite analysis and quantitative PCR were utilized to give a thorough exploration of the strains.</p></sec><sec><title>Results</title><p>We obtained the genome maps of <italic>LY01-LY09</italic> and found that <italic>LY01-LY09</italic> had a complex interspecific relationship with B. anthracis and <italic>B. thuringiensis</italic>. We also observed a contraction of gene families in <italic>LY01-LY09</italic>, and the contracted families were mainly associated with prophage, which contributed to the species diversity of <italic>B. cereus</italic>. The <italic>Hsp20</italic> gene family underwent a rapid evolution in <italic>LY01-LY09</italic>, which facilitated the adaptation of the strains to adverse environmental conditions. Moreover, the <italic>LY01-LY09</italic> strains exhibited a higher copy number in the non-ribosomal polypeptide synthetase (NRPS) genes and carried the complete cereulide synthetase (<italic>ces</italic>) gene cluster sequences. Considering that the <italic>NRPS</italic> system is a classical regulatory mechanism for emetic toxin synthesis, we hypothesized that <italic>LY01-LY09</italic> could synthesize emetic toxins through the regulation of <italic>ces</italic> gene clusters by the <italic>NRPS</italic> system.</p></sec><sec><title>Discussion</title><p>These findings are important for further investigation into the evolutionary relationship between <italic>B. cereus</italic> and their related species, as well as the underlying mechanisms governing the synthesis and secretion of bacterial toxins.</p></sec>