Pan-genome analysis of Bacillus for microbiome profiling.

Recent advances in high-throughput sequencing technology allow for in-depth studies on microbial genomes and their communities. While multiple strains of the same species could display genomic variations with different gene contents in diverse habitats and hosts, the essential functions for a specific species are conserved as core genes that are shared among strains. We have comprehensively analyzed 238 strains of five different Bacillus species to identify the properties of core and strain-specific genes. Core and strain-specific genes in each Bacillus species show significant differences in their functions and genomic signatures. Using the core genes defined in this study, we have precisely identified the Bacillus species that exist in food microbiomes. Without resorting to culture-based whole genome sequencing, an unexpectedly large portion of the core genes, 98.22% of core genes in B. amyloliquefaciens and 97.77% of B. subtilis, were reconstructed from the microbiome. We have performed a pan-genome analysis on the core gene data of multiple Bacillus species to investigate the Bacillus species in food microbiome. Our findings provide a comprehensive genetic landscape of the Bacillus species, which is also consistent with previous studies on a limited number of strains and species. Analysis based on comprehensive core genes should thus serve as a powerful profiling tool to better understand major constituents in fermented food microbiomes.