Microbulbifer spongiae sp. nov., isolated from marine sponge Diacarnus erythraeanus.

Abstract

A novel bacterium, designated as MI-G^T, was isolated from marine sponge Diacarnus erythraeanus. Cells of strain MI-G^T are Gram-stain-negative, aerobic, and rod or coccoid-ovoid in shape. MI-G^T is able to grow at 10-40 °C (optimum, 28 °C), with 1.0-8.0% (w/v) NaCl (optimum, 4.0%), and at pH 5.5-9.0 (optimum, pH 8.0). The 16S rRNA gene sequence of strain MI-G^T shows 98.35, 97.32 and 97.25% similarity to those of Microbulbifer variabilis Ni-2088^T, Microbulbifer maritimus TF-17^T and Microbulbifer echini AM134^T, respectively. Phylogenetic analysis also exhibits that strain MI-G^T falls within a clade comprising members of the genus Microbulbifer (class Gammaproteobacteria). The genome size of strain MI-G^T is 4478124 bp with a G+C content of 54.51 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain MI-G^T and other type strains are 71.61-76.44% (ANIb), 83.27-84.36% (ANIm) and 13.4-18.7% (dDDH), respectively. These values are significantly lower than the recommended threshold values for bacterial species delineation. Percentage of conserved proteins and average amino acid identity values among the genomes of strain MI-G^T and other closely related species are 52.04-59.13% and 67.47-77.21%, respectively. The major cellular fatty acids of MI-G^T are composed of summed feature 8 (C_{18 : 1} ω7c or C_{18 : 1} ω6c), iso-C_{11 : 0} 3-OH, iso-C_{15 : 0}, C_{16 : 0}, and summed feature 9 (C_{17 : 1} iso ω9c or C_{16 : 0} 10-methyl). The polar lipids of MI-G^T mainly consist of phosphatidylethanolamine, phosphatidylglycerol, aminolipid, and two glycolipids. The major respiratory quinone is Q-8. Based on differential phenotypic and phylogenetic data, strain MI-G^T is considered to represent a novel species of genus Microbulbifer, for which the name Microbulbifer spongiae sp. nov. is proposed. The type strain is MI-G^T (=MCCC 1K07826^T=KCTC 8081^T).