Oligotrophic Marine Gammaproteobacteria Research Articles

Bacterioplankton Diversity and Distribution in Relation to Phytoplankton Community Structure in the Ross Sea Surface Waters.

Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. However, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here, we report data on the bacterial diversity in relation to phytoplankton community structure in the surface waters of the Ross Sea during the Austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay (TNB) coastal waters and the Ross Sea Open Waters (RSOWs), with a dominance of members belonging to the bacterial phyla Bacteroidetes and Proteobacteria. In the TNB coastal area, microbial communities were characterized by a higher abundance of sequences related to heterotrophic bacterial genera such as Polaribacter spp., together with higher phytoplankton biomass and higher relative abundance of diatoms. On the contrary, the phytoplankton biomass in the RSOW were lower, with relatively higher contribution of haptophytes and a higher abundance of sequences related to oligotrophic and mixothrophic bacterial groups like the Oligotrophic Marine Gammaproteobacteria (OMG) group and SAR11. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provide new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters, suggesting that specific rather than random interaction contribute to the organic matter cycling in the Southern Ocean.

Draft Genome Sequence of Strain LSUCC0112, a Gulf of Mexico Representative of the Oligotrophic Marine Gammaproteobacteria

Here, we present the draft genome sequence of strain LSUCC0112, a cultured representative from the Gulf of Mexico that is phylogenetically close to the OM182 clade within oligotrophic marine Gammaproteobacteria LSUCC0112 shows the potential for aerobic heterotrophy, glycogen synthesis, flagellar motility, and assimilatory sulfate reduction.

Expansion of Cultured Bacterial Diversity by Large-Scale Dilution-to-Extinction Culturing from a Single Seawater Sample.

High-throughput cultivation (HTC) based on a dilution-to-extinction method has been applied broadly to the cultivation of marine bacterial groups, which has often led to the repeated isolation of abundant lineages such as SAR11 and oligotrophic marine gammaproteobacteria (OMG). In this study, to expand the phylogenetic diversity of HTC isolates, we performed a large-scale HTC with a single surface seawater sample collected from the East Sea, the Western Pacific Ocean. Phylogenetic analyses of the 16S rRNA genes from 847 putative pure cultures demonstrated that some isolates were affiliated with not-yet-cultured clades, including the OPB35 and Puniceicoccaceae marine group of Verrucomicrobia and PS1 of Alphaproteobacteria. In addition, numerous strains were obtained from abundant clades, such as SAR11, marine Roseobacter clade, OMG (e.g., SAR92 and OM60), OM43, and SAR116, thereby increasing the size of available culture resources for representative marine bacterial groups. Comparison between the composition of HTC isolates and the bacterial community structure of the seawater sample used for HTC showed that diverse marine bacterial groups exhibited various growth capabilities under our HTC conditions. The growth response of many bacterial groups, however, was clearly different from that observed with conventional plating methods, as exemplified by numerous isolates of the SAR11 clade and Verrucomicrobia. This study showed that a large number of novel bacterial strains could be obtained by an extensive HTC from even a small number of samples.

A taxonomic framework for emerging groups of ecologically important marine gammaproteobacteria based on the reconstruction of evolutionary relationships using genome-scale data.

In recent years a large number of isolates were obtained from saline environments that are phylogenetically related to distinct clades of oligotrophic marine gammaproteobacteria, which were originally identified in seawater samples using cultivation independent methods and are characterized by high seasonal abundances in coastal environments. To date a sound taxonomic framework for the classification of these ecologically important isolates and related species in accordance with their evolutionary relationships is missing. In this study we demonstrate that a reliable allocation of members of the oligotrophic marine gammaproteobacteria (OMG) group and related species to higher taxonomic ranks is possible by phylogenetic analyses of whole proteomes but also of the RNA polymerase beta subunit, whereas phylogenetic reconstructions based on 16S rRNA genes alone resulted in unstable tree topologies with only insignificant bootstrap support. The identified clades could be correlated with distinct phenotypic traits illustrating an adaptation to common environmental factors in their evolutionary history. Genome wide gene-content analyses revealed the existence of two distinct ecological guilds within the analyzed lineage of marine gammaproteobacteria which can be distinguished by their trophic strategies. Based on our results a novel order within the class Gammaproteobacteria is proposed, which is designated Cellvibrionales ord. nov. and comprises the five novel families Cellvibrionaceae fam. nov., Halieaceae fam. nov., Microbulbiferaceae fam. nov., Porticoccaceae fam. nov., and Spongiibacteraceae fam. nov.

Metaproteomics reveals the major microbial players and their biogeochemical functions in a productive coastal system in the northern South China Sea.

We study the metaproteome of the GF/F-prefiltered fraction of a microbial community from Shantou coast summer surface waters using a shotgun proteomic approach. Spectra attributed to the marine Roseobacter clade (MRC), the oligotrophic marine Gammaproteobacteria (OMG) group and Flavobacteria dominated in the microbial community, accounting for 21.0%, 23.2% and 12.7% of all of the detected spectra, respectively, whereas the SAR 92 clade accounted for 50% of the OMG group. The abundance of TonB-dependent receptors (TBDRs) was detected and the majority of TBDRs were attributed to the OMG, whereas a large number of ABC transporters matched to the MRC, which suggests niche separation in the microbial community. Expression of proteorhodopsin and RagB/SusD from Flavobacteria facilitates their attachment and growth on algal-derived organic matter. Taurine and glycine betaine appear to be an important source of carbon and nitrogen for the Rhodobacteraceae and SAR11 cluster. The detection of carbon monoxide dehydrogenase, formate dehydrogenase, O-acetylhomoserine sulfhydrylase and sulfur oxidation protein from the MRC demonstrated that members of the MRC play important roles in coastal ocean biogeochemical cycles. This study provides the first insight into functional processes occurring in microbial communities in coastal waters in the South China Sea.

Metagenomic and geochemical characterization of pockmarked sediments overlaying the Troll petroleum reservoir in the North Sea.

BackgroundPockmarks (depressions in the seabed) have been discovered throughout the world’s oceans and are often related to hydrocarbon seepage. Although high concentrations of pockmarks are present in the seabed overlaying the Troll oil and gas reservoir in the northern North Sea, geological surveys have not detected hydrocarbon seepage in this area at the present time. In this study we have used metagenomics to characterize the prokaryotic communities inhabiting the surface sediments in the Troll area in relation to geochemical parameters, particularly related to hydrocarbon presence. We also investigated the possibility of increased potential for methane oxidation related to the pockmarks. Five metagenomes from pockmarks and plain seabed sediments were sequenced by pyrosequencing (Roche/454) technology. In addition, two metagenomes from seabed sediments geologically unlikely to be influenced by hydrocarbon seepage (the Oslofjord) were included. The taxonomic distribution and metabolic potential of the metagenomes were analyzed by multivariate analysis and statistical comparisons to reveal variation within and between the two sampling areas.ResultsThe main difference identified between the two sampling areas was an overabundance of predominantly autotrophic nitrifiers, especially Nitrosopumilus, and oligotrophic marine Gammaproteobacteria in the Troll metagenomes compared to the Oslofjord. Increased potential for degradation of hydrocarbons, especially aromatic hydrocarbons, was detected in two of the Troll samples: one pockmark sample and one from the plain seabed. Although presence of methanotrophic organisms was indicated in all samples, no overabundance in pockmark samples compared to the Oslofjord samples supports no, or only low level, methane seepage in the Troll pockmarks at the present time.ConclusionsGiven the relatively low content of total organic carbon and great depths of hydrocarbon containing sediments in the Troll area, it is possible that at least part of the carbon source available for the predominantly autotrophic nitrifiers thriving in this area originates from sequential prokaryotic degradation and oxidation of hydrocarbons to CO2. By turning CO2 back into organic carbon this subcommunity could play an important environmental role in these dark oligotrophic sediments. The oxidation of ammonia to nitrite and nitrate in this process could further increase the supply of terminal electron acceptors for hydrocarbon degradation.

Predicted Protein Subcellular Localization in Dominant Surface Ocean Bacterioplankton

Bacteria consume dissolved organic matter (DOM) through hydrolysis, transport and intracellular metabolism, and these activities occur in distinct subcellular localizations. Bacterial protein subcellular localizations for several major marine bacterial groups were predicted using genomic, metagenomic and metatranscriptomic data sets following modification of MetaP software for use with partial gene sequences. The most distinct pattern of subcellular localization was found for Bacteroidetes, whose genomes were substantially enriched with outer membrane and extracellular proteins but depleted of inner membrane proteins compared with five other taxa (SAR11, Roseobacter, Synechococcus, Prochlorococcus, oligotrophic marine Gammaproteobacteria). When subcellular localization patterns were compared between genes and transcripts, three taxa had expression biased toward proteins localized to cell locations outside of the cytosol (SAR11, Roseobacter, and Synechococcus), as expected based on the importance of carbon and nutrient acquisition in an oligotrophic ocean, but two taxa did not (oligotrophic marine Gammaproteobacteria and Bacteroidetes). Diel variations in the fraction and putative gene functions of transcripts encoding inner membrane and periplasmic proteins compared to cytoplasmic proteins suggest a close coupling of photosynthetic extracellular release and bacterial consumption, providing insights into interactions between phytoplankton, bacteria, and DOM.

Genome Sequence of Strain IMCC1989, a Novel Member of the Marine Gammaproteobacteria

Strain IMCC1989 is a novel member of the oligotrophic marine Gammaproteobacteria (OMG) group and is closely related with a symbiont group of the genera Teredinibacter and "Candidatus Endobugula." Here we present the genome sequence of strain IMCC1989, which was isolated from the Yellow Sea by using dilution-to-extinction culturing.

Environmental proteomics of microbial plankton in a highly productive coastal upwelling system

Metaproteomics is one of a suite of new approaches providing insights into the activities of microorganisms in natural environments. Proteins, the final products of gene expression, indicate cellular priorities, taking into account both transcriptional and posttranscriptional control mechanisms that control adaptive responses. Here, we report the proteomic composition of the < 1.2 μm fraction of a microbial community from Oregon coast summer surface waters, detected with two-dimensional liquid chromatography coupled with electrospray tandem mass spectrometry. Spectra corresponding to proteins involved in protein folding and biosynthesis, transport, and viral capsid structure were the most frequently detected. A total of 36% of all the detected proteins were best matches to the SAR11 clade, and other abundant coastal microbial clades were also well represented, including the Roseobacter clade (17%), oligotrophic marine gammaproteobacteria group (6%), OM43 clade (1%). Viral origins were attributed to 2.5% of proteins. In contrast to oligotrophic waters, phosphate transporters were not highly detected in this nutrient-rich system. However, transporters for amino acids, taurine, polyamines and glutamine synthetase were among the most highly detected proteins, supporting predictions that carbon and nitrogen are more limiting than phosphate in this environment. Intriguingly, one of the highly detected proteins was methanol dehydrogenase originating from the OM43 clade, providing further support for recent reports that the metabolism of one-carbon compounds by these streamlined methylotrophs might be an important feature of coastal ocean biogeochemistry.

Improved group-specific PCR primers for denaturing gradient gel electrophoresis analysis of the genetic diversity of complex microbial communities

Phylum- and class-specific PCR primers were tested for the production of clone libraries and for denaturing gradient gel electrophoresis (DGGE) analysis of complex bacterial communities. Primers were designed to specifically amplify 16S rRNA gene fragments of the phyla Bacteroidetes, Planctomycetes and Firmicutes, of three classes of the phylum Proteobacteria, the Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria, and of the Cyanobacteria (including chloroplast 16S rRNA genes). The specificity of the seven primer pairs was tested by producing clone libraries from environmental DNA samples from mesotrophic (Norwegian coastal) and oligotrophic (Northern Atlantic Gyre) environments. Five of the seven primer pairs specifically amplified target 16S rRNA gene sequences. Exceptions were the Betaproteobacteria- and Firmicutes-specific primers, which were relatively successful with coastal water mesocosm samples but less so with the Northern Atlantic Gyre sample. Phylogenetic analysis of sequences from the Gammaproteobacteria clone library revealed that the coastal sample yielded a number of clones that clustered within clades that belong to the oligotrophic marine Gammaproteobacteria (OMG) group, indicating that this group is not confined exclusively to the oligotrophic environment. Comparison of the bacterial diversity of the environmental DNA sample from the coastal and the open ocean using a two- or three-step nested PCR-DGGE process revealed significant differences in the bacterial communities. The application of the group-specific primers provides a higher resolution genetic fingerprinting approach than existing DGGE primer sets.

Dimethylsulfoniopropionate Turnover Is Linked to the Composition and Dynamics of the Bacterioplankton Assemblage during a Microcosm Phytoplankton Bloom

Processing of the phytoplankton-derived organic sulfur compound dimethylsulfoniopropionate (DMSP) by bacteria was studied in seawater microcosms in the coastal Gulf of Mexico (Alabama). Modest phytoplankton blooms (peak chlorophyll a [Chl a] concentrations of approximately 2.5 microg liter(-1)) were induced in nutrient-enriched microcosms, while phytoplankton biomass remained low in unamended controls (Chl a concentrations of approximately 0.34 microg liter(-1)). Particulate DMSP concentrations reached 96 nM in the enriched microcosms but remained approximately 14 nM in the controls. Bacterial biomass production increased in parallel with the increase in particulate DMSP, and nutrient limitation bioassays in the initial water showed that enrichment with DMSP or glucose caused a similar stimulation of bacterial growth. Concomitantly, increased bacterial consumption rate constants of dissolved DMSP (up to 20 day(-1)) and dimethylsulfide (DMS) (up to 6.5 day(-1)) were observed. Nevertheless, higher DMSP S assimilation efficiencies and higher contribution of DMSP to bacterial S demand were found in the controls compared to the enriched microcosms. This indicated that marine bacterioplankton may rely more on DMSP as a source of S under oligotrophic conditions than under the senescence phase of phytoplankton blooms. Phylogenetic analysis of the bacterial assemblages in all microcosms showed that the DMSP-rich algal bloom favored the occurrence of various Roseobacter members, flavobacteria (Bacteroidetes phylum), and oligotrophic marine Gammaproteobacteria. Our observations suggest that the composition of the bacterial assemblage and the relative contribution of DMSP to the overall dissolved organic sulfur/organic matter pool control how efficiently bacteria assimilate DMSP S and thereby potentially divert it from DMS production.

Cultivation and growth characteristics of a diverse group of oligotrophic marine Gammaproteobacteria.

Forty-four novel strains of Gammaproteobacteria were cultivated from coastal and pelagic regions of the Pacific Ocean using high-throughput culturing methods that rely on dilution to extinction in very low nutrient media. Phylogenetic analysis showed that the isolates fell into five rRNA clades, all of which contained rRNA gene sequences reported previously from seawater environmental gene clone libraries (SAR92, OM60, OM182, BD1-7, and KI89A). Bootstrap analyses of phylogenetic reliability did not support collapsing these five clades into a single clade, and they were therefore named the oligotrophic marine Gammaproteobacteria (OMG) group. Twelve cultures chosen to represent the five clades were successively purified in liquid culture, and their growth characteristics were determined at different temperatures and dissolved organic carbon concentrations. The isolates in the OMG group were physiologically diverse heterotrophs, and their physiological properties generally followed their phylogenetic relationships. None of the isolates in the OMG group formed colonies on low- or high-nutrient agar upon their first isolation from seawater, while 7 of 12 isolates that were propagated for laboratory testing eventually produced colonies on 1/10 R2A agar. The isolates grew relatively slowly in natural seawater media (1.23 to 2.63 day(-1)), and none of them grew in high-nutrient media (>351 mg of C liter(-1)). The isolates were psychro- to mesophilic and obligately oligotrophic; many of them were of ultramicrobial size (<0.1 micro m(3)). This cultivation study revealed that sporadically detected Gammaproteobacteria gene clones from seawater are part of a phylogenetically diverse constellation of organisms mainly composed of oligotrophic and ultramicrobial lineages that are culturable under specific cultivation conditions.