Comparative genome analysis of commensal segmented filamentous bacteria (SFB) from turkey and murine hosts reveals distinct metabolic features

Abstract

\n Background: Segmented filamentous bacteria (SFB) are intestinal commensal microorganisms that have been demonstrated to induce the innate and adaptive immune responses in mouse and rat hosts. SFB are Gram-positive, spore-forming bacteria that fail to grow in vitro due to unique metabolic requirements. Recently, SFB have been implicated in improved health and growth outcomes in commercial turkey flocks. To assess the nature of SFB in turkeys and how they may differ from mammalian-associated SFB, the genome of turkey-associated SFB was compared with six representative genomes from murine hosts using an in silico approach.Results: The SFB-turkey genome is 1.6 Mb in length with a G+C content of 26.14%, and contains 1,604 coding sequences (CDS). Comparative genome analyses revealed that all the seven SFB strain possesses a shared set of metabolic deficiencies and auxotrophies, specifically the inability of all the SFB strains to synthesize most of the amino acids, nucleotides and cofactors, emphasizing the importance of metabolite acquisition from the host intestinal environment. Among the seven SFB genomes, the SFB-turkey genome is the largest and contains the highest number of predicted CDS. The SFB-turkey genome possesses cellular metabolism genes that are absent in the rodent SFB strains including catabolic pathways for sucrose, stachyose, raffinose and other complex glycans. Other unique genes associated with SFB-turkey genome is loci for the biosynthesis of biotin, and degradation enzymes to recycle primary bile acids, both of which may play an important role to help turkey associated SFB survive and secure mutualism with its avian host. Conclusions: Comparative genomic analysis of seven SFB genomes revealed that each of the strains have a core set of metabolic capabilities and deficiencies that make these bacteria challenging to culture ex vivo. When compared to the murine-associated strains, turkey-associated SFB serves as a phylogenetic outgroup and a unique member among all the sequenced strains of SFB. This turkey-associated SFB strain is the first reported non-mammalian SFB genome, and highlights the impact of host specificity on the evolution of metabolic capabilities.