Two recently reported bacterial strains that were identified as the dominant caproate-producing bacteria in pit clay, were further characterized to determine their phylogeny and taxonomy. The two strains, designated as LBM19010T and JNU-WLY1368, were short rod-shaped, Gram-stain-positive, non-motile and strictly anaerobic. Analysis of the 16S rRNA gene sequences revealed that strains LBM19010T and JNU-WLY1368 shared a 16S rRNA gene sequence similarity of 99.93 % and belonged to a recent proposed genus Caproicibacterium in the family Oscillospiraceae. The proposed type strain, LBM19010T, showed the highest 16S rRNA gene sequence similarity to Caproicibacterium amylolyticum LBM18003T (96.34%), followed by Caproiciproducens galactitolivorans JCM 30532T (94.14 %). The pairwise average nucleotide identity and average amino acid identity values between strains LBM19010T and LBM18003T were 74.84 and 76.18 %, respectively. Growth of strain LBM19010T occurred at pH 4.5-7.5 (optimum, pH 5.0-5.5), 20-40 °C (optimum, 35 °C) and with 0-1 % (w/v) NaCl (optimum, 0 %). Strains LBM19010T and JNU-WLY1368 were both able to ferment several hexoses, disaccharides, starch and lactate but not pentoses. Caproate and butyrate were the major end-products from glucose. The predominant cellular fatty acids (>10 %) of strain LBM19010T were C16 : 0 (56.3 %), C14 : 0 DMA (19.5 %) and C14 : 0 (14.9 %). The identified polar lipids of strain LBM19010T were diphosphatidylglycerol, phosphatidylglycerol, three unidentified phospholipids and nine unidentified glycolipids. Based on phylogenetic, phenotypic and chemotaxonomic evidence, strains LBM19010T and JNU-WLY1368 belong to a novel species of the genus Caproicibacterium, for which the name Caproicibacterium lactatifermentans sp. nov. is proposed. The type strain is LBM19010T (=GDMCC 1.1627T=JCM 33782T).
Keywords: Caproicibacterium lactatifermentans; Oscillospiraceae; caproate; pit clay; strong aroma-type liquor.