Alteromonas algae sp. nov. and Alteromonas ulvae sp. nov., isolated from the seaweed Ulva prolifera dominating green tides in the Yellow Sea

Strains A079 T and A081 T were isolated from the floating seaweed Ulva prolifera , which is the dominant species of the world’s largest green tides in the Yellow Sea. Both strains were Gram-stain-negative, aerobic and motile via a single polar flagellum. The major fatty acids of the two strains were C 16:0 , C 17:1 ω8c, C 18:1 ω7c and summed feature 3 (C 16:1 ω7c and/or C 16:1 ω6c). Cells of the strain A079 T were oval or short rod-shaped. Cells of the strain A081 T were rod-shaped. A079 T grew at 10–37 °C, pH 6.0–10.0 and 1–12% (w/v) NaCl. A081 T grew at 10–40 °C, pH 6.0–11.0 and 1–12% (w/v) NaCl. Phylogenetic analyses based on 16S rRNA genes and whole-genome sequences revealed that strains A079 T and A081 T belong to the genus Alteromonas . The average nucleotide identity and digital DNA–DNA hybridization values between strains A079 T , A081 T and related Alteromonas species ranged from 68.98 to 88.75% and 20.40 to 36.40%, respectively. Comparative genomic analysis discovered that A079 T possessed a unique RiPP-like (TP-1161) cluster. Strain A089 T exhibited the potential to utilize ulvan, and an acyl-homoserine lactone synthesis gene cluster was predicted in the strain. These findings reveal possible mechanisms for phycosphere adaptation. Phenotypic, chemotaxonomic, phylogenetic and genomic evidence support that strains A079 T and A081 T represent two novel species of the genus Alteromonas , for which the names Alteromonas algae sp. nov. (type strain A079 T =MCCC 1K09912 T =KCTC 18157 T ) and Alteromonas ulvae sp. nov. (type strain A081 T =MCCC 1K09913 T =KCTC 18158 T ) are proposed.