Isolation and characterization of Rhodovulum strictum sp. nov. and some other purple nonsulfur bacteria from colored blooms in tidal and seawater pools

Abstract

Several strains of phototrophic purple nonsulfur bacteria were isolated from colored blooms occurring in tidal and seawater pools in Japan. All of these isolates had ovoid to rod-shaped cells that were motile by means of single polar flagella and contained vesicular intracytoplasmic membranes together with bacteriochlorophyll a and carotenoids of the spheroidene series. They produced ubiquinone 10 as the major quinone and contained straight-chain fatty acids, with C18:1 predominating. They were mesophilic, halophilic, and photoheterotrophic, utilized sulfide and thiosulfate as electron donors for phototrophic growth, and photoassimilated a wide variety of organic compounds as carbon sources. Our results suggested that all of these isolates are members of the recently described genus Rhodovulum. The isolates were classified into four groups (designated groups I through IV) on the basis of phenotypic and genotypic data. The group I isolates, which were the most abundant purple nonsulfur bacteria recovered from the blooms, grew in the presence of NaCl concentrations ranging from 0.5 to 3.0% (optimum NaCl concentration, 0.8%) and at pH values ranging from 7.5 to 9.0 (optimum pH, 8.0 to 8.5). On the basis of these unique physiological traits, together with genotypic and phylogenetic data, we propose that the group I isolates should be classified as members of a new species, Rhodovulum strictum. The group II isolates were identified definitely as Rhodovulum sulfidophilum, and the group III and IV isolates were phenotypically most similar to R. sulfidophilum and Rhodovulum adriaticum, respectively, but could be differentiated from these species by DNA-DNA pairing data.