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 O24-2(T) 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 O24-2(T) and O25-2 at 1.0-3.0 and 1.0-2.0% (w/v) NaCl, respectively. Growth of strain O24-2(T) 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 T129-2-1(T). Although sequence similarity was high, the DNA-DNA relatedness value between strain O24-2(T) and A. putridalgicola T129-2-1(T) was 27%, indicating that they are members of distinct species. The DNA G+C contents of O24-2(T) 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 C(14:0), C(16:0) and C(16:1)ω9c. 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 O24-2(T) (=DSM 23664(T)=NBRC 107172(T)).