Faecalibacterium langellae sp. nov. isolated from human faeces.

The genus Faecalibacterium is one of the major butyrate-producing bacteria in the human gut. Due to its production of beneficial metabolites and reduced populations in diseased patients, it is regarded as a potential biomarker of healthy gut microbiota. Strains Collection Nationale de Cultures de Microorganismes (CNCM) I-4540 and CNCM I-4541 were isolated from faeces of a healthy elderly and a healthy adult respectively. In this study, we conducted a taxonomic analysis of these strains. Phylogenetic analyses based on 16S rRNA gene and rpoA gene sequences revealed that the two strains belong to the genus Faecalibacterium. A core gene phylogenetic tree further supported their phylogenetic placement. CNCM I-4540 shared an average nucleotide identity (ANI) value of 96.7% and a digital DNA-DNA hybridization (dDDH) value of 74.3% with Faecalibacterium taiwanense HLW78^T, indicating that CNCM I-4540 should be classified as F. taiwanense. In contrast, CNCM I-4541 did not exhibit ANI or dDDH values above the species threshold for any known species within the genus Faecalibacterium. These findings indicate that CNCM I-4541 represents a novel species within the genus Faecalibacterium, for which the name Faecalibacterium langellae sp. nov. is proposed. The type strain is CNCM I-4541^T (=CIP 112513^T=JCM 39552^T).