Abstract
Blautia, a genus established in 2008, is a relevantly abundant taxonomic group present in the microbiome of human and other mammalian gastrointestinal (GI) tracts. Several described (or proposed) Blautia species are available at this date. However, despite the increasing level of knowledge about Blautia, its diversity is still poorly understood. The increasing availability of Blautia genomic sequences in the public databases opens the possibility to study this genus from a genomic perspective. Here we report the pangenome analysis and the phylogenomic study of 225 Blautia genomes available in RefSeq. We found 33 different potential species at the genomic level, 17 of them previously undescribed; we also confirmed by genomic standards the status of 4 previously proposed new Blautia species. Comparative genomic analyses suggest that the Blautia pangenome is open, with a relatively small core genome (∼ 700–800 gene families). Utilizing a set of representative genomes, we performed a gene family gain/loss model for the genus, showing that despite terminal nodes suffered more massive gene gain events than internal nodes (i.e., predicted ancestors), some ancestors were predicted to have gained an important number of gene families, some of them associated with the possible acquisition of metabolic abilities. Gene loss events remained lower than gain events in most cases. General aspects regarding pangenome composition and gene gain/loss events are discussed, as well as the proposition of changes in the taxonomic assignment of B. coccoidesTY and the proposition of a new species, “B. pseudococcoides.”
Highlights
Blautia, a taxonomic genus placed in the Lachnospiraceae family of the Firmicutes phylum, was initially described in 2008, from the reclassification of former Ruminococcus species isolated from stool samples (Liu et al, 2008)
We present a pangenome analysis with a phylogenomic focus of a set of non-redundant Blautia genomes, in order to offer a first picture of the genomic diversity across the members of the Blautia genus, as well as to study the phylogenomic relationship among the lineages of Blautia
Considering the aforementioned criterion, we found a set of 33 genomic species clusters from the Blautia dataset (Table 1 and Supplementary Table 4); twelve of those genomic species groups include one sequenced type strain: B. argi, B. brookingsii, B. faecicola, B. hansenii, B. hominis, B. hydrogenotrophica, B. luti, B. massiliensis, B. obeum, B. faecis, B. caecimuris and B. wexlerae
Summary
A taxonomic genus placed in the Lachnospiraceae family of the Firmicutes phylum, was initially described in 2008, from the reclassification of former Ruminococcus species isolated from stool samples (Liu et al, 2008) Members of this genus are obligately anaerobic, nonsporulating, coccobacillus-shaped Gram-positive microorganisms with the ability to ferment different carbohydrates. Some members had been proved to have more specific roles, as for example, B. hydrogenotrophica, a hydrogen consumer capable of establishing cross-feeding relationships with other members of the gut microbiota (Plichta et al, 2016) Microbes from this genus were associated with changes in diet, showing increased abundance under whole grain consumption (Martínez et al, 2013), or under a low-fat diet (Wan et al, 2019). This diversity of (positive or negative) associations may reflect a previously unknown diversity among members of the genus, remaining to be discovered
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