Isolation and genome analysis of Winogradskyella algicola sp. nov., the dominant bacterial species associated with the green alga Dunaliella tertiolecta

Microalgae and bacteria are known to be closely associated in diverse environments. To isolate dominant bacterial species associated with a green alga, Dunaliella tertiolecta, a photoreactor culture of the microalga was investigated using culture-based and culture-independent approaches. The bacterial community structure of the algal culture showed that the most abundant bacterial species under the culture conditions was related to the genus Winogradskyella. The closely related amplicon sequences, showing ≥ 99.5% 16S rRNA gene sequence similarity to one of the isolates, designated IMCC-33238ᵀ, constituted > 49% of the bacterial community and was therefore regarded as the most dominant species in the algal culture. Strain IMCC33238ᵀ was characterized by Gramstaining-negative and orange-colored rods. Phylogenetic analyses of the 16S rRNA genes as well as whole genome sequences revealed that strain IMCC33238ᵀ belonged to Winogradskyella and shared more than 97.2% 16S rRNA gene sequence similarity with Winogradskyella species. The strain contained iso-C₁₅:₁ G, iso-C₁₅:₀, iso-C₁₅:₀ 3-OH, and summed feature 3 (C₁₆:₁ω6c and/or C₁₆:₁ω7c) as major fatty acids and MK-6 as the predominant quinone. The polar lipids found in strain IMCC33238ᵀ were phosphatidylethanolamine, two unidentified aminolipids, and three unidentified lipids. The genome of strain IMCC33238ᵀ was 3.37 Mbp in size with 33.9 mol% G + C content and proteorhodopsin. Many genes encoding folate and vitamin production are considered to play an important role in the bacteria-algae interaction. On the basis of phylogenetic and phenotypic characteristics, strain IMCC33238ᵀ represents a novel species in the genus Winogradskyella, for which the name Winogradskyella algicola sp. nov. is proposed. The type strain is IMCC33238ᵀ (= KACC 21192T = NBRC 113704ᵀ).