Parvularcula Bermudensis Gen. Nov., Sp. Nov., a Marine Bacterium That Forms a Deep Branch in the Alpha-Proteobacteria

Two bacterial strains, HTCC2503T and HTCC2517, were isolated from the Bermuda Atlantic Time Series Station in the western Sargasso Sea, Atlantic Ocean, by new high-throughput culture methods that rely on dilution to extinction in very-low-nutrient media. Characterization of the two strains by polyphasic approaches revealed that they belonged to the same species. These isolates are gram-negative, strictly aerobic, chemoheterotrophic, slightly motile short rods with a single flagellum. The temperature, pH and NaCl concentration ranges for growth were 10-37 degrees C, 6.0-9.0 and 0.75-20% (w/v), respectively. Colonies on marine agar were very small (0.3-0.8 mm in diameter), yellowish-brown and very hard. Carotenoid pigments were synthesized but bacteriochlorophyll a was not. Several kinds of pentose, hexose, sugar alcohol, oligosaccharide and amino acid were utilized as sole carbon sources. Oxidase was produced, but catalase was not. All cellular fatty acids were even-numbered monounsaturated or saturated fatty acids and the major fatty acid was cis-7-octadecenoic acid (73.3%). The DNA G + C content of strain HTCC2503T was 60.8 mol%. Phylogenetic analyses of 16S rRNA gene sequences clearly indicated that the strains formed a distinct lineage, allied with activated sludge environmental clone H9, in the alpha-Proteobacteria. The clade containing strains HTCC2503T and HTCC2517 and clone H9 could not be phylogenetically associated with any of the six known orders of the alpha-Proteobacteria. From this polyphasic evidence, it is proposed that the novel strains should be classified as Parvularcula bermudensis gen. nov., sp. nov. The type strain is HTCC2503T (= ATCC BAA-594T = KCTC 12087T) and the reference strain is HTCC2517.