OM43 is a clade of uncultured beta-proteobacteria that is commonly found in environmental nucleic acid sequences from productive coastal ocean ecosystems, and some freshwater environments, but is rarely detected in ocean gyres. Ecological studies associate OM43 with phytoplankton blooms, and evolutionary relationships indicate that they might be methylotrophs. Here we report on the genome sequence and metabolic properties of the first axenic isolate of the OM43 clade, strain HTCC2181, which was obtained using new procedures for culturing cells in natural seawater. We found that this strain is an obligate methylotroph that cannot oxidize methane but can use the oxidized C1 compounds methanol and formaldehyde as sources of carbon and energy. Its complete genome is 1304 428 bp in length, the smallest yet reported for a free-living cell. The HTCC2181 genome includes genes for xanthorhodopsin and retinal biosynthesis, an auxiliary system for producing transmembrane electrochemical potentials from light. The discovery that HTCC2181 is an extremely simple specialist in C1 metabolism suggests an unanticipated, important role for oxidized C1 compounds as substrates for bacterioplankton productivity in coastal ecosystems.

The abundance, genetic diversity, and crucial ecological and evolutionary roles of marine phages have prompted a large number of metagenomic studies. However, obtaining a thorough understanding of marine phages has been hampered by the low number of phage isolates infecting major bacterial groups other than cyanophages and pelagiphages. Therefore, there is an urgent requirement for the isolation of phages that infect abundant marine bacterial groups. In this study, we isolated and characterized HMO-2011, a phage infecting a bacterium of the SAR116 clade, one of the most abundant marine bacterial lineages. HMO-2011, which infects “ Candidatus Puniceispirillum marinum” strain IMCC1322, has an ∼55-kb dsDNA genome that harbors many genes with novel features rarely found in cultured organisms, including genes encoding a DNA polymerase with a partial DnaJ central domain and an atypical methanesulfonate monooxygenase. Furthermore, homologs of nearly all HMO-2011 genes were predominantly found in marine metagenomes rather than cultured organisms, suggesting the novelty of HMO-2011 and the prevalence of this phage type in the oceans. A significant number of the viral metagenome sequences obtained from the ocean surface were best assigned to the HMO-2011 genome. The number of reads assigned to HMO-2011 accounted for 10.3%–25.3% of the total reads assigned to viruses in seven viromes from the Pacific and Indian Oceans, making the HMO-2011 genome the most or second-most frequently assigned viral genome. Given its ability to infect the abundant SAR116 clade and its widespread distribution, Puniceispirillum phage HMO-2011 could be an important resource for marine virus research.

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The complete genome sequence of "Candidatus Puniceispirillum marinum" IMCC1322, the first cultured representative of the SAR116 clade in the Alphaproteobacteria, is reported here. The genome contains genes for proteorhodopsin, aerobic-type carbon monoxide dehydrogenase, dimethylsulfoniopropionate demethylase, and C 1 compound metabolism. The genome information proposes the SAR116 group to be metabolic generalists in ocean nutrient cycling.

Although the SAR11 clade of the Alphaproteobacteria represents the most abundant and ubiquitous bacterioplankton in the ocean, very few laboratories have successfully cultured SAR11 cells. All of the SAR11 strains isolated thus far have been retrieved from the Oregon coast and the Sargasso Sea. In this study, a modified dilution-to-extinction culturing with prolonged incubation at low temperature was applied in an effort to cultivate major bacterioplankton lineages in the East Sea, Western Pacific Ocean. Five to 10 cells were inoculated into each well of 48-well plates, followed by the incubation of the plates at 10 degrees C for 4, 8, 20, and 24 weeks. Among a total of 35 isolated strains, 18 strains assigned to the SAR11 clade were isolated after 8, 20, and 24 weeks of incubation, whereas no SAR11 cells were detected in the samples after 4 weeks of incubation. The SAR11 isolates, noticeably, comprised 64-82% of the total isolates from the plates incubated for 20 and 24 weeks. Extinction cultures belonging to the Roseobacter, OM43, and SAR92 clades were also cultivated. The results of this study suggest that long-term incubation at low temperatures might prove an alternative for the efficient cultivation of new variants of the members of the SAR11 clade.

Erythrobacter litoralis has been known as a bacteriochlorophyll a-containing, aerobic, anoxygenic, phototrophic bacterium. Here we announce the complete genome sequence of E. litoralis HTCC2594, which is devoid of phototrophic potential. E. litoralis HTCC2594, isolated by dilution-to-extinction culturing from seawater, could not carry out aerobic anoxygenic phototrophy and lacked genes for bacteriochlorophyll a biosynthesis and photosynthetic reaction center proteins.

We investigated coliphages from various fecal sources, including humans and animals, for microbial source tracking in South Korea. Both somatic and F ؉ -specific coliphages were isolated from 43 fecal samples from farms, wild animal habitats, and human wastewater plants. Somatic coliphages were more prevalent and abundant than F ؉ coliphages in all of the tested fecal samples. We further characterized 311 F ؉ coliphage isolates using RNase sensitivity assays, PCR and reverse transcription-PCR, and nucleic acid sequencing. Phylogenetic analyses were performed based on the partial nucleic acid sequences of 311 F ؉ coliphages from various sources. F ؉ RNA coliphages were most prevalent among geese (95%) and were least prevalent in cows (5%). Among the genogroups of F ؉ RNA coliphages, most F ؉ coliphages isolated from animal fecal sources belonged to either group I or group IV, and most from human wastewater sources were in group II or III. Some of the group I coliphages were present in both human and animal source samples. F ؉ RNA coliphages isolated from various sources were divided into two main clusters. All F ؉ RNA coliphages isolated from human wastewater were grouped with Q␤-like phages, while phages isolated from most animal sources were grouped with MS2-like phages. UniFrac significance statistical analyses revealed significant differences between human and animal bacteriophages. In the principal coordinate analysis (PCoA), F ؉ RNA coliphages isolated from human waste were distinctively separate from those isolated from other animal sources. However, F ؉ DNA coliphages were not significantly different or separate in the PCoA. These results demonstrate that proper analysis of F ؉ RNA coliphages can effectively distinguish fecal sources.

Two facultatively anaerobic mesophilic bacteria, strains MEBiC 07026T and MEBiC 08903T, were isolated from two different tidal flat sediments and both strains showed approximately 92.2 % 16S rRNA gene sequence similarity with [Cytophaga] fermentans DSM 9555T. 16S rRNA gene sequence similarity between the two new isolates was 97.5 % but levels of DNA–DNA relatedness between the two were 31.3–31.8 %. Phylogenetic analysis revealed that the two isolates and [Cytophaga] fermentans DSM 9555T were affiliated with the family Marinilabiliaceae in the class Bacteroidia . The dominant fatty acids of strains MEBiC 07026T, MEBiC 08903T and [Cytophaga] fermentans DSM 9555T were branched-type or hydroxylated C15 : 0, but [Cytophaga] fermentans DSM 9555T contained a higher proportion of anteiso-branched fatty acids. The two new isolates contained a markedly higher proportion of monounsaturated fatty acids than other members of the family Marinilabiliaceae . The major respiratory quinone of the strains was MK-7. Strains MEBiC07026T and MEBiC08903T utilized a wide range of carboxylic acids whereas [Cytophaga] fermentans DSM 9555T utilized carbohydrates rather than carboxylic acids. The DNA G+C content of the novel strains was about 44 mol% but that of [Cytophaga] fermentans DSM 9555T revealed from the genome sequence was 37.6 mol%. Based on evidence from this polyphasic taxonomic study, a novel genus, Carboxylicivirga gen. nov., is proposed in the family Marinilabiliaceae with two novel species, Carboxylicivirga mesophila sp. nov. with type strain MEBiC 07026T ( = KCCM 42978T = JCM 18290T) and Carboxylicivirga taeanensis sp. nov. with type strain MEBiC 08903T ( = KCCM 43024T = JCM 19490T). Additionally, [Cytophaga] fermentans DSM 9555T ( = ATCC 19072T) is reclassified as Saccharicrinis fermentans gen. nov., comb. nov.