Alkalibacterium subtropicum sp. nov., a slightly halophilic and alkaliphilic marine lactic acid bacterium isolated from decaying marine algae

Two novel strains of marine lactic acid bacteria, isolated from decaying marine algae collected from a subtropical area of Japan, are described. The isolates, designated O24-2T and O25-2, were Gram-positive, non-sporulating and non-motile. They lacked catalase and quinones. Under anaerobic cultivation conditions, lactate was produced from glucose with the production of formate, acetate and ethanol in a molar ratio of approximately 2 : 1 : 1. Under aerobic cultivation conditions, acetate and lactate were produced from carbohydrates and related compounds. The isolates were slightly halophilic, highly halotolerant and alkaliphilic. They were able to grow in 0–17.0 % (w/v) NaCl, with optimum growth of strains O24-2T and O25-2 at 1.0–3.0 and 1.0–2.0 % (w/v) NaCl, respectively. Growth of strain O24-2T was observed at pH 7.5–9.5, with optimum growth at pH 8.0–8.5. Comparative 16S rRNA gene sequence analysis revealed that the isolates occupied a phylogenetic position within the genus Alkalibacterium, showing highest similarity (99.6 %) to Alkalibacterium putridalgicola T129-2-1T. Although sequence similarity was high, the DNA–DNA relatedness value between strain O24-2T and A. putridalgicola T129-2-1T was 27 %, indicating that they are members of distinct species. The DNA G+C contents of O24-2T and O25-2 were 43.7 and 44.4 mol%, respectively, and DNA–DNA relatedness between the isolates was 89 %. The cell-wall peptidoglycan was type A4β, Orn-D-Asp. The major cellular fatty acid components were C14 : 0, C16 : 0 and C16 : 1ω9c. Based on phenotypic characteristics and genetic distinctiveness, the isolates were classified as representatives of a novel species within the genus Alkalibacterium, for which the name Alkalibacterium subtropicum sp. nov. is proposed; the type strain is O24-2T ( = DSM 23664T = NBRC 107172T).