Polyphasic and phylogenomic reevaluation of Zhongshania and Marortus with the description of Zhongshania aquatica sp. nov.

Advancing our understanding of microbial diversity and taxonomy in Korean coast, this study focuses on two intriguing bacterial genera, Marortus and Zhongshania, revealing significant insights through morphological and genomic analyses. The type strain, BJYM1 (= KCTC 92326 = NBRC 115677) was isolated from seawater in Tongyeong, South Korea. BJYM1 was characterized as a Gram-negative aerobic strain with a rod shape and a single polar flagellum. Optimal growth conditions for BJYM1 were identified as 30 °C, pH 6.5, and 0-2% (w/v) NaCl on MA medium. Based on 16S rRNA gene sequence analysis, strain BJYM1 formed a clade with Z. aquimaris CAU 1632, followed by M. luteolus ZX-21 and Z. marina DSW25-10. The phylogenetic relationships of these four strains were also confirmed by genome-based and MALDI-TOF analyses. Strains Z. marina DSW25-10, Z. aquimaris CAU 1632, and BJYM1 possessed a single polar flagellum. The genome of strain BJYM1 had a size of 4.5 Mb with a DNA G + C content of 48.2 mol%. The major respiratory quinone was ubiquinone-8 (Q-8). Major polar lipids included phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and diphosphatidylglycerol (DPG). The major fatty acid was C. Digital DNA-DNA hybridization values between reference strains were notably lower than 70%, with ANI values ​​ranging from 73.31 to 78.57% and AAI values ​​ranging from 75.91 to 83.01%. However, Z. marina DSW25-10 and M. luteolus ZX-21 exhibited dDDH values greater than 70%, as well as ANI and AAI values exceeding 95%. KEGG analysis revealed distinct metabolic pathways between two groups: Group 1 (Z. antarctica DSM 25701, Z. aliphaticivorans SM-2) had high cytochrome c oxidase and transporter: phosphonate pathway activities, while Group 2 (Z. marina DSW25-10, Z. aquimaris CAU 1632, M. luteolus ZX-21, BJYM1) exhibited Sec-SRP, chemotaxis, sulfide oxidation, and sulfur assimilation. BJYM1 displayed unique pathways, including the Cobalt transporter CorA, starch/glycogen synthesis, starch/glycogen degradation, and ferrous iron transporter FeoB. Through comprehensive physiological, phenotypic, and phylogenetic analyses, strain BJYM1 was identified as a new species within the genus Zhongshania, named Zhongshania aquatica sp. nov.