Alkaliphilus serpentinus sp. nov. and Alkaliphilus pronyensis sp. nov., two novel anaerobic alkaliphilic species isolated from the serpentinite-hosted Prony Bay Hydrothermal Field (New Caledonia)

International audienceTwo novel anaerobic alkaliphilic strains, designated as LacT T and LacV T , were isolated from the Prony Bay Hydrothermal Field (PBHF, New Caledonia). Cells were motile, Gram-positive, terminal endosporeforming rods, displaying a straight to curved morphology during the exponential phase. Strains LacT T and LacV T were mesophilic (optimum 30°C), moderately alkaliphilic (optimum pH 8.2 and 8.7, respectively) and halotolerant (optimum 2% and 2.5% NaCl, respectively). Both strains were able to ferment yeast extract, peptone and casamino acids, but only strain LacT T could use sugars (glucose, maltose and sucrose). Both strains disproportionated crotonate into acetate and butyrate. Phylogenetic analysis revealed that strains LacT T and LacV T shared 96.4% 16S rRNA gene sequence identity and were most closely related to A. peptidifermentans Z-7036, A. namsaraevii X-07-2 and A. hydrothermalis FatMR1 (95.7%-96.3%). Their genome size was of 3.29 Mb for strain LacT T and 3.06 Mb for strain LacV T with a G + C content of 36.0 and 33.9 mol%, respectively. The ANI value between both strains was 73.2 %. Finally, strains LacT T (=DSM 100337 = JCM 30643) and LacV T (=DSM 100017 = JCM 30644) are proposed as two novel species of the genus Alkaliphilus, order Clostridiales, phylum Firmicutes, Alkaliphilus serpentinus sp. nov. and Alkaliphilus pronyensis sp. nov., respectively. The genomes of the three Alkaliphilus species isolated from PBHF were consistently detected in the PBHF chimney metagenomes, although at very low abundance, but not significantly in the metagenomes of other serpentinizing systems (marine or terrestrial) worldwide, suggesting they represent indigenous members of the PBHF microbial ecosystem