Description of Hyphococcus formosus sp. nov. and Hyphococcus lacteus sp. nov., isolated from coastal sediment, and reclassification of Marinicaulis flavus as Hyphococcus luteus nom. nov. and Marinicaulis aureus as Hyphococcus aureus comb. nov.

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During a study on sediment bacterial diversity in coastal China, three bacterial strains, DH-69T, EH-24, and ECK-19T, were isolated from coastal sediments off Xiaoshi Island, Weihai. These strains were Gram-staining-negative, aerobic, and coccoid to rod-shaped with prosthecae and flagella. Comparison of the 16S rRNA gene showed that they shared the highest identity values with Hyphococcus flavus MCCC 1K03223T (96.2-97.6%), followed by Marinicaulis flavus SY-3-19T (95.2-96.8%) and Marinicaulis aureus HHTR114T (95.2-96.2%). Genome comparisons using average nucleotide identity (ANI) and average amino acid identity (AAI) suggested that the three novel strains and the three related strains belonged to the same genus, with strains DH-69T, EH-24, and ECK-19T identified as two distinct novel species. Pan-genome analysis revealed that 995 core genes were shared among 23 Hyphococcus genomes/MAGs. Secondary metabolites analysis identified a biosynthesis gene cluster for microsclerodermin, a potent antifungal peptide, in the novel strains. Moreover, these newly isolated strains were detected in various ecosystems, with a particular prevalence in marine environments, based on analysis of 500,048 amplicon datasets, underscoring their ecological preference. Based on polyphasic characterizations, strains DH-69T and EH-24 represent a novel species of the genus Hyphococcus, for which the name Hyphococcus formosus sp. nov. is proposed with the type strain DH-69T (= MCCC 1H00436T=KCTC 8010T). Strain ECK-19T represents another novel Hyphococcus species, for which the name Hyphococcus lacteus sp. nov. is proposed with the type strain ECK-19T (= MCCC 1H00435T=KCTC 8009T). Furthermore, Marinicaulis flavus and Marinicaulis aureus are proposed to be reclassified as Hyphococcus luteus nom. nov. and Hyphococcus aureus comb. nov., respectively, accompanied by an emended description of the genus Hyphococcus.