Faecalibacterium langellae sp. nov. isolated from human faeces

The genus <i>Faecalibacterium</i> 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 <i>rpoA</i> gene sequences revealed that the two strains belong to the genus <i>Faecalibacterium</i>. 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 <i>Faecalibacterium taiwanense</i> HLW78^T, indicating that CNCM I-4540 should be classified as <i>F. taiwanense</i>. In contrast, CNCM I-4541 did not exhibit ANI or dDDH values above the species threshold for any known species within the genus <i>Faecalibacterium</i>. These findings indicate that CNCM I-4541 represents a novel species within the genus <i>Faecalibacterium</i>, for which the name <i>Faecalibacterium langellae</i> sp. nov. is proposed. The type strain is CNCM I-4541^T (=CIP 112513^T=JCM 39552^T).