Genome-based reclassification of Parabacteroides chartae as a later heterotypic synonym of Macellibacteroides fermentans.

Abstract

Strain PK034 was isolated from a municipal wastewater treatment plant in Stillwater, OK, USA. A comparison of 16S rRNA gene sequences revealed ≥99.4% sequence similarity to the type strains of Macellibacteroides fermentans (isolated from an up-flow anaerobic filter) and Parabacteroides chartae (isolated from wastewater from a paper mill), suggesting their close relatedness and the possibility of these strains belonging to the same species. The genus Macellibacteroides currently contains a single species, while the genus Parabacteroides currently contains 13 species. Phylogenetic analysis using the 16S rRNA gene, whole-genome phylogenomic analysis and overall genomic-based relatedness indices indicated that PK034 and the type strains of M. fermentans and P. chartae shared average nucleotide identity and digital DNA-DNA hybridization values >95% and >70%, which are the currently accepted thresholds for species-level delineation. Furthermore, such analysis also placed PK034 and the type strains of M. fermentans and P. chartae as a distinct branch within the Tannerellaceae family of the Bacteroidales order, clustering separately from all other species of the genus Parabacteroides. Comparison of phenotypic and physiological traits revealed a high level of shared characteristics and physiological optima between all isolates. Thus, it is proposed that P. chartae NS31-3^T has been erroneously classified as a member of the genus Parabacteroides, that strains PK034, M. fermentans and P. chartae constitute the same species and that P. chartae Tan et al. 2012 should be taken as a later heterotypic synonym of M. fermentans Jabari et al. 2012.