Genomic mechanisms underlying the adaptation of Anaerobutyricum species to the human host

The Anaerobutyricum genus, comprising Anaerobutyricum hallii and Anaerobutyricum soehngenii , is prevalent in the human gut microbiota and produces short-chain fatty acids (SCFAs) that influence host metabolism and inflammation. However, systematic genomic studies on this genus are limited. In this study, we conducted a comprehensive genomic analysis of 84 Anaerobutyricum genomes, based on the average nucleotide identity (ANI), average amino acid identity (AAI) and core genes phylogenetic tree analysis, we clustered the Anaerobutyricum genus to Anaerobutyricum spp. , Anaerobutyricum hallii and Anaerobutyricum soehngenii . Specifically, Anaerobutyricum hallii and Anaerobutyricum soehngenii are specific to human hosts, possessing longer genomes and lower GC content. They contain more integrative and conjugative elements (ICEs), which genetically encoded dltA , mbtB and dhbE genes that responds for the biosynthesis of siderophore group nonribosomal peptides, which might contribute to its colonization. In addition, ICEs in Anaerobutyricum hallii and Anaerobutyricum soehngenii could also pose a risk for antibiotic resistance gene transfer. Our study advances the understanding the of Anaerobutyricum 's and host adaptability, highlighting the importance of genomic analysis in refining taxonomic boundaries and assessing the safety of using these bacteria as probiotics. • We redefined the Anaerobutyricum genus into distinct groups. • Anaerobutyricum hallii and Anaerobutyricum soehngenii exhibit human-host specificity. • Hallii and A. soehngenii exhibit longer genomes, lower GC content and more ICEs. • ICEs harbor genes potentially contributing to bacterial colonization and adaptation. • Genomic analysis refines taxonomic boundaries and assesses safety for probiotics.