RESUMO
Heterotrophic bacteria isolated from water samples taken from Hiroshima Bay, Japan, and referred to as Alexandrium (Dinophyceae) cyst formation-promoting bacteria, were assigned to the Roseobacter-Sulfitobacter-Silicibacter group within the alpha-Proteobacteria on the basis of nearly complete 16S rRNA gene sequences. Phylogenetic analyses showed that two strains, CFPB-A9T and CFPB-A5, are closely related to each other and that their closest relative was Jannaschia helgolandensis (95.9 % sequence similarity). These strains were Gram-negative, motile, obligately aerobic rods that required sodium ions and 2-7 % sea salts for growth and did not produce bacteriochlorophyll a. Their optimal growth temperature was 25-30 degrees C. The strains had Q-10 as the dominant respiratory quinone. Primary cellular fatty acid in both strains was 18 : 1omega7c. The DNA G + C contents of strains CFPB-A9T and CFPB-A5 were 59.1 and 59.2 mol%, respectively. Based on physiological, biological, chemotaxonomic and phylogenetic data, the strains are considered to represent a novel species, Jannaschia cystaugens sp. nov., with type strain CFPB-A9T (= LMG 22015T = NBRC 100362T).
Assuntos
Rhodobacteraceae/classificação , Rhodobacteraceae/isolamento & purificação , Água do Mar/microbiologia , Bacterioclorofila A/análise , Composição de Bases , DNA Bacteriano/química , DNA Bacteriano/isolamento & purificação , DNA Ribossômico/química , DNA Ribossômico/isolamento & purificação , Ácidos Graxos/análise , Genes de RNAr , Japão , Microscopia Eletrônica , Dados de Sequência Molecular , Movimento , Filogenia , Quinonas/análise , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Rhodobacteraceae/fisiologia , Rhodobacteraceae/ultraestrutura , Sais , Análise de Sequência de DNA , Temperatura , Microbiologia da ÁguaRESUMO
A total of 31 bacterial isolates that have potential Alexandrium cyst formation-promoting activity (Alex-CFPB) were isolated from Hiroshima Bay (Japan), which is characterized by seasonal blooms of the toxic dinoflagellate Alexandrium tamarense. The population structure of Alex-CFPB was analyzed by means of restriction fragment length polymorphism analysis of the 16S rRNA genes (16S rDNA). Fourteen ribotypes, A to N, were observed among the 31 isolates of Alex-CFPB by using four restriction enzymes, MboI, HhaI, RsaI and BstUI. Among them, seven isolates, which were obtained from the seawater samples taken during the peak and termination periods of the A. tamarense bloom in 1998, belonged to ribotype A. This result suggests that bacterial strains of ribotype A may be dominant in the Alex-CFPB assemblages during these periods. The partial 16S rDNA-based phylogenetic tree of 10 ribotypes studied showed that nine of them fell into the Rhodobacter group of the alpha subclass of the Proteobacteria: Eight of nine ribotypes of the Rhodobacter group fell into the lineage of the Roseobacter subgroup, and one fell into the Rhodobacter subgroup. The non-Rhodobacter group type fell into the Marinobacterium-Neptunomonas-Pseudomonas group of the gamma-Proteobacteria: Isolates of Alex-CFPB ribotypes A and C do not have clear growth-promoting activities but have strong cyst formation-promoting activities (CFPAs) under our laboratory conditions. These results show that the Alex-CFPB assemblage may consist of various bacteria that belong mainly to the Roseobacter group and have strong CFPAs. These results suggest that not only the Alexandrium cyst formation-inhibiting bacteria (Alex-CFIB) reported previously but also Alex-CFPB, especially bacteria of ribotype A, may play significant roles in the process of encystment and bloom dynamics of Alexandrium in the natural environment.