Modern bacterial taxonomy is based on a polyphasic approach that combines phenotypic and genotypic characteristics, including 16S rRNA sequence similarity. However, the 95 % (for genus) and 98.7 % (for species) sequence similarity thresholds that are currently recommended to classify bacterial isolates were defined by comparison of a limited number of bacterial species, and may not apply to many genera that contain human-associated species. For each of 158 bacterial genera containing human-associated species, we computed pairwise sequence similarities between all species that have names with standing in nomenclature and then analysed the results, considering as abnormal any similarity value lower than 95 % or greater than 98.7 %. Many of the current bacterial species with validly published names do not respect the 95 and 98.7 % thresholds, with 57.1 % of species exhibiting 16S rRNA gene sequence similarity rates ≥98.7 %, and 60.1 % of genera containing species exhibiting a 16S rRNA gene sequence similarity rate <95 %. In only 17 of the 158 genera studied (10.8 %), all species respected the 95 and 98.7 % thresholds. As we need powerful and reliable taxonomical tools, and as potential new tools such as pan-genomics have not yet been fully evaluated for taxonomic purposes, we propose to use as thresholds, genus by genus, the minimum and maximum similarity values observed among species.

Anaerosalibacter massiliensis sp. nov. strain ND1(T) (= CSUR P762 = DSM 27308) is the type strain of A. massiliensis sp. nov., a new species within the genus Anaerosalibacter. This strain, the genome of which is described here, was isolated from the faecal flora of a 49-year-old healthy Brazilian man. Anaerosalibacter massiliensis is a Gram-positive, obligate anaerobic rod and member of the family Clostridiaceae. With the complete genome sequence and annotation, we describe here the features of this organism. The 3 197 911 bp long genome (one chromosome but no plasmid) contains 3271 protein-coding and 62 RNA genes, including six rRNA genes.