Photobacterium
aquae sp. nov., isolated from a recirculating mariculture system
A Gram-staining-negative, heterotrophic, facultatively anaerobic bacterium, designated AE6T, was isolated from a grouper (Epinephelus malabaricas) culture tank in a recirculating mariculture system located in Tianjin, China. Strain AE6T was able to grow at 15–40 °C (optimum, 30–35 °C), at pH 5.5–10.0 (optimum, pH 7.0–7.5) and in the presence of 0.5–7 % (w/v) NaCl (optimum, 2–3 %). It contained Q-8 as the predominant respiratory quinone, phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) as the major polar lipids and C16 : 1ω7c/C16 : 1ω6c (40.4 %), C18 : 1ω7c (15.5 %) and C16 : 0 (13.5 %) as the predominant cellular fatty acids. The genomic DNA G+C content was 47.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain AE6T belonged to the genus Photobacterium (94.2–96.8 % of 16S rRNA gene sequence similarity) and formed a distinct phylogenetic lineage within the genus and exhibited the highest sequence similarity to Photobacterium aphoticum CECT 7614T (96.8 %). Multilocus sequence analysis (MLSA) using four loci (gyrB, rpoA, pyrH and recA) also revealed that strain AE6T was phylogenetically related to the genus Photobacterium . Based on the phylogenetic, chemotaxonomic and phenotypic evidence, strain AE6T is considered to represent a novel species of the genus Photobacterium , for which the name Photobacterium aquae sp. nov. is proposed. The type strain is AE6T ( = CGMCC 1.12159T = JCM 18480T).