Francisella salimarina sp. nov., isolated from coastal seawater

Abstract

Four strains (SYSU SYW-1^T, SYW-2, SYW-3 and XLW-1) were isolated from seawater near the shore in Guangdong Province, China. Cells were Gram-stain-negative, aerobic, non-motile and non-spore-forming. Growth was observed at a temperature range of 16-40 °C (optimum, 32 °C), a pH range of 4-8 (optimum, pH 7) and in the presence of up to 10 % (w/v) NaCl. The major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine and an unidentified phospholipid. The respiratory quinone was ubiquinone 8 (UQ-8), and the predominant fatty acids were C_{18 : 0} 3-OH, C_{10 : 0}, C_{14 : 0} and C_{18 : 1}ω9<i>c</i>. Comparison of 16S rRNA gene and genome sequences confirmed that these strains represented a novel member of the genus <i>Francisella</i>, with less than 98.8 % 16S rRNA gene sequence similarity and less than 95 % genomic average nucleotide identity to recognized <i>Francisella</i> species. The phylogenetic tree based on 16S rRNA gene sequences and the protein-concatamer tree based on a concatenation of 28 protein marker sequences both indicated that the strains clustered with '<i>Francisella salina</i>' TX07-7308 and '<i>Francisella marina</i>' E95-16, but formed a distinct lineage group among the other members of the genus <i>Francisella</i>. The DNA G+C contents of the four strains were determined to be 32.9, 32.7, 32.9 and 32.9 %, respectively (genome). On the basis of phenotypic and genotypic features, the strains are considered to represent a novel species of the genus <i>Francisella</i>, for which the name <i>Francisella salimarina</i> sp. nov. is proposed. The type strain is SYSU SYW-1^T (=CGMCC 1.17031^T=NBRC 113781^T).