Muricauda okinawensis sp. Nov. and Muricauda yonaguniensis sp. Nov., Two Marine Bacteria Isolated from the Sediment Core near Hydrothermal Fields of Southern Okinawa Trough

Two strains, 81s02(T) and 334s03(T), were isolated from the sediment core near the hydrothermal field of southern Okinawa Trough. The cells of both strains were observed to be rod-shaped, non-gliding, Gram-staining negative, yellow-pigmented, facultatively anaerobic, catalase and oxidase positive, and showing optimum growth at 30 °C and pH 7.5. The strains 81s02(T) and 334s03(T) were able to tolerate up to 10% and 9% (w/v) NaCl concentration, respectively. Based on phylogenomic analysis, the average nucleotide identity (ANI) and the digital DNA-DNA hybridization (dDDH) values between the two strains and the nearest phylogenetic neighbors of the genus Muricauda were in range of 78.0–86.3% and 21.5–33.9%, respectively. The strains 81s02(T) and 334s03(T) shared 98.1% 16S rRNA gene sequence similarity to each other but were identified as two distinct species based on 81.4–81.5% ANIb, 85.5–85.6% ANIm and 25.4% dDDH values calculated using whole genome sequences. The strains 81s02(T) and 334s03(T) shared the highest 16S rRNA gene sequence similarity to M. lutimaris SMK-108(T) (98.7%) and M. aurea BC31-1-A7(T) (98.8%), respectively. The major fatty acid of strains 81s02(T) and 334s03(T) were identified similarly as iso-C(15:0), iso-C(17:0) 3-OH and iso-C(15:1) G, and the major polar lipids of the both strains consisted of phosphatidylethanolamine and two unidentified lipids. The strains contained MK-6 as their predominant menaquinone. The genomic G+C contents of strains 81s02(T) and 334s03(T) were determined to be 41.6 and 41.9 mol%, respectively. Based on the phylogenetic and phenotypic characteristics, both strains are considered to represent two novel species of the genus Muricauda, and the names Muricauda okinawensis sp. nov. and Muricauda yonaguniensis sp. nov. are proposed for strains 81s02(T) (=KCTC 92889(T) = MCCC 1K08502(T)) and 334s03(T) (=KCTC 92890(T) = MCCC 1K08503(T)).