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.