Biomedical subjects

Kevin L Vergin

Publications and source records attributed to Kevin L Vergin.

5 recordsLinked to original sources

PubMed2005

Proteorhodopsin in the ubiquitous marine bacterium SAR11.

Proteorhodopsins are light-dependent proton pumps that are predicted to have an important role in the ecology of the oceans by supplying energy for microbial metabolism. Proteorhodopsin genes were first discovered through the cloning and sequencing of large genomic DNA fragments from seawater. They were later shown to be widely distributed, phylogenetically diverse, and active in the oceans. Proteorhodopsin genes have not been found in cultured bacteria, and on the basis of environmental sequence data, it has not yet been possible to reconstruct the genomes of uncultured bacterial strains that have proteorhodopsin genes. Although the metabolic effect of proteorhodopsins is uncertain, they are thought to function in cells for which the primary mode of metabolism is the heterotrophic assimilation of dissolved organic carbon. Here we report that SAR11 strain HTCC1062 ('Pelagibacter ubique'), the first cultivated member of the extraordinarily abundant SAR11 clade, expresses a proteorhodopsin gene when cultured in autoclaved seawater and in its natural environment, the ocean. The Pelagibacter proteorhodopsin functions as a light-dependent proton pump. The gene is expressed by cells grown in either diurnal light or in darkness, and there is no difference between the growth rates or cell yields of cultures grown in light or darkness.

Alphaproteobacteria↗

PubMed2005

Genome streamlining in a cosmopolitan oceanic bacterium.

The SAR11 clade consists of very small, heterotrophic marine alpha-proteobacteria that are found throughout the oceans, where they account for about 25% of all microbial cells. Pelagibacter ubique, the first cultured member of this clade, has the smallest genome and encodes the smallest number of predicted open reading frames known for a free-living microorganism. In contrast to parasitic bacteria and archaea with small genomes, P. ubique has complete biosynthetic pathways for all 20 amino acids and all but a few cofactors. P. ubique has no pseudogenes, introns, transposons, extrachromosomal elements, or inteins; few paralogs; and the shortest intergenic spacers yet observed for any cell.

Alphaproteobacteria↗

PubMed2004

Lentisphaera araneosa gen. nov., sp. nov, a transparent exopolymer producing marine bacterium, and the description of a novel bacterial phylum, Lentisphaerae.

Two phylogenetically distinct marine strains producing transparent exopolymers (TEP), designated HTCC2155(T) and HTCC2160, were cultivated from Oregon coast seawater by dilution to extinction in a high throughput culturing format. When cultured in low-nutrient seawater media, these strains copiously produced Alcian Blue-stainable viscous TEP. Growing cells were attached to each other by the TEP in a three dimensional network. Polymerase chain reaction employing 16S rDNA primers specific for the novel isolates indicated that they are indigenous to the water column of the Atlantic and Pacific oceans. The abundance of the isolates as determined by 16S rRNA dot blots, however, indicated that they are less than 1% of the total bacterial community. In phylogenetic analyses, the strains consistently formed a new phylum-level lineage within the domain Bacteria, together with members of the candidate phylum VadinBE97, which consists of Victivallis, the first cultured genus in the candidate phylum, and 16S rRNA gene clones from DNA extracted from marine or anaerobic terrestrial habitats. Five putative subgroups were delineated within this phylum-level lineage, including a marine group and an anaerobic group. The isolates are Gram negative, strictly aerobic, chemoheterotrophic, and facultatively oligotrophic sphere-shaped bacteria. The DNA G+C content of strain HTCC2155(T) was 48.3 mol% and the genome size was 2.9 mb. It is proposed from these observations that the strains be placed into a new genus and a new species named Lentisphaera araneosa (type strain HTCC2155(T) = ATCC BAA-859(T) = KCTC 12141(T)) gen. nov., sp. nov., the cultured marine representative of the Lentisphaerae phyl. nov., and the phylum be divided into two novel orders named the Lentisphaerales ord. nov. and the Victivallales ord. nov.

Bacteria↗

PubMed2002

Cultivation of the ubiquitous SAR11 marine bacterioplankton clade.

The alpha-proteobacterial lineage that contains SAR11 and related ribosomal RNA gene clones was among the first groups of organisms to be identified when cultivation-independent approaches based on rRNA gene cloning and sequencing were applied to survey microbial diversity in natural ecosystems. This group accounts for 26% of all ribosomal RNA genes that have been identified in sea water and has been found in nearly every pelagic marine bacterioplankton community studied by these methods. The SAR11 clade represents a pervasive problem in microbiology: despite its ubiquity, it has defied cultivation efforts. Genetic evidence suggests that diverse uncultivated microbial taxa dominate most natural ecosystems, which has prompted widespread efforts to elucidate the geochemical activities of these organisms without the benefit of cultures for study. Here we report the isolation of representatives of the SAR11 clade. Eighteen cultures were initially obtained by means of high-throughput procedures for isolating cell cultures through the dilution of natural microbial communities into very low nutrient media. Eleven of these cultures have been successfully passaged and cryopreserved for future study. The volume of these cells, about 0.01 micro m(3), places them among the smallest free-living cells in culture.

Alphaproteobacteria↗

PubMedDate not supplied

SAR11 clade dominates ocean surface bacterioplankton communities.

The most abundant class of bacterial ribosomal RNA genes detected in seawater DNA by gene cloning belongs to SAR11-an alpha-proteobacterial clade. Other than indications of their prevalence in seawater, little is known about these organisms. Here we report quantitative measurements of the cellular abundance of the SAR11 clade in northwestern Sargasso Sea waters to 3,000 m and in Oregon coastal surface waters. On average, the SAR11 clade accounts for a third of the cells present in surface waters and nearly a fifth of the cells present in the mesopelagic zone. In some regions, members of the SAR11 clade represent as much as 50% of the total surface microbial community and 25% of the subeuphotic microbial community. By extrapolation, we estimate that globally there are 2.4 x 10(28) SAR11 cells in the oceans, half of which are located in the euphotic zone. Although the biogeochemical role of the SAR11 clade remains uncertain, these data support the conclusion that this microbial group is among the most successful organisms on Earth.

Alphaproteobacteria↗