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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 53 (2005), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Exopolymeric substances (EPS) isolated from a pure culture of the marine bacterium Marinobacter sp. and the marine diatom Skeletonema costatum (axenic) were partially purified, chemically characterized and used as dissolved organic matter (DOM) for the production of macroaggregates. The role of organic particles such as transparent exopolymeric particles (TEP) and Coomassie stained particles (CSP) in the production of macroaggregates was experimentally assessed. Three experimental rolling tanks containing sterile medium with: (1) EPS, (2) EPS + live diatom cells and (3) EPS + killed bacteria, and three control tanks without any added EPS were used for macroaggregate production. Changes in abundance and average size of macroaggregates were monitored using image analysis, whereas TEP and CSP were enumerated microscopically. In the presence of microbial EPS, macroaggregates of a size of 23–35 mm2 were produced. Aggregate size and abundance considerably varied with both time and source of EPS. No correlation was observed for macroaggregate size and abundance with either TEP or CSP. One-way ANOVA demonstrated significant differences in the variance of particle abundance and size in tanks having only EPS or EPS in combination with live diatom cells. Our data suggest that production of macroaggregates was influenced by polymer chemistry and surface properties of colliding particles, whereas TEP and CSP concentrations were influenced by molecular weight of EPS and the presence of growing cells. Interestingly, macroaggregates were formed in the near absence of TEP and CSP, highlighting the role of other unknown processes in the transformation of DOM to particulate organic matter (POM) in aquatic environments.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 54 (2005), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Bacteria of the phyla Proteobacteria and Bacteroidetes are known to be the most prominent heterotrophic organisms in marine surface waters. In order to investigate the occurrence of these phyla in a coastal environment, the tidal flat ecosystem German Wadden Sea, we analyzed a clone library of PCR-amplified and sequenced 16S rRNA gene fragments and isolated 46 new strains affiliated with these phyla from the water column with various polymers and complex media as substrates. The phylogenetic affiliation of these strains was analyzed on the basis of sequenced 16S rRNA gene fragments. Subsequently, a comprehensive phylogenetic analysis of Proteobacteria and Bacteroidetes including available sequences from oxic habitats of earlier studies of this ecosystem was performed. Sequences of the earlier studies were derived from isolation approaches and from denaturing gradient gel electrophoresis (DGGE) analyses of environmental samples and high dilution steps of MPN (most probable number) cultures. The majority of the 265 sequences included in this analysis affiliated with α-Proteobacteria (45.3%), γ-Proteobacteria (31.7%), and Bacteroidetes (16.2%). Almost 7% belong to the δ-Proteobacteria and several of these clones affiliated with the Myxococcales, a group comprising obligate aerobic organisms. Within the α- and γ-Proteobacteria specific clusters were identified including isolates from high dilution steps of dilution cultures and/or clones from the clone library or DGGE gels, implying a high abundance of some of these organisms. Within the γ-Proteobacteria a new cluster is proposed, which consists of marine surface-attached organisms. This SAMMIC (Surface Attached Marine MICrobes) cluster comprises only uncultured phylotypes and exhibits a global distribution. Overall, the analysis indicates that Proteobacteria and Bacteroidetes of the Wadden Sea have a surprisingly high diversity, presumably a result of the signature of this ecosystem as a melting pot at the land–sea interface and comprising a great habitat variety.
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  • 3
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Marine aggregates are densely colonized by bacteria, and inter-specific interactions such as inhibition are important for colonization by aggregate-associated bacteria and thus affect the turnover of organic matter in the sea. In order to study antagonistic activities we carried out inhibition tests with 51 isolates obtained exclusively from aggregates of the German Wadden Sea. 16S rRNA gene sequences of all isolates revealed that 35% of the isolates affiliated with the Flavobacteria/Sphingobacteria group, 24% and 16% with α- and γ-Proteobacteria, respectively, 16% with the Bacillus/Clostridium group, and 10% with Actinobacteria. The relatively high percentage of Gram-positive bacteria may be related to specific features of the Wadden Sea environment. After 11 days of incubation using Burkholder agar diffusion assays the percentage of inhibitory isolates was 54.1% and this decreased to 20.7% after 20 days of incubation but it did not decline for members of the Bacillus/Clostridium group. Inhibitory activity was expressed in strain-specific patterns even though some isolates were closely related according to their 16S rRNA gene sequences. Antagonistic activity was lowest for Flavobacteria/Sphingobacteria (35%) and highest for Actinobacteria (80%). We further examined whether growth of isolates was affected when they were placed on lawns of certain other isolates. In parallel with lowest percentage of inhibitory isolates, highest growth occurred on lawns of the Flavobacteria/Sphingobacteria group whereas it was lowest on lawns of Actinobacteria and the Bacillus/Clostridium group. The high inhibitory activity of both groups of Gram-positive bacteria fits well with data from chemical screening using matrix-assisted laser desorption ionization time of flight mass spectrometry. Hence, inhibitory activity greatly influences inter-specific interactions and may impact microbial degradation and remineralization of particulate organic matter in aquatic environments.
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2008. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 53 (2008): 21-38, doi:10.3354/ame01230.
    Description: We now have a relatively good idea of how bulk microbial processes shape the cycling of organic matter and nutrients in the sea. The advent of the molecular biology era in microbial ecology has resulted in advanced knowledge about the diversity of marine microorganisms, suggesting that we might have reached a high level of understanding of carbon fluxes in the oceans. However, it is becoming increasingly clear that there are large gaps in the understanding of the role of bacteria in regulating carbon fluxes. These gaps may result from methodological as well as conceptual limitations. For example, should bacterial production be measured in the light? Can bacterial production conversion factors be predicted, and how are they affected by loss of tracers through respiration? Is it true that respiration is relatively constant compared to production? How can accurate measures of bacterial growth efficiency be obtained? In this paper, we discuss whether such questions could (or should) be addressed. Ongoing genome analyses are rapidly widening our understanding of possible metabolic pathways and cellular adaptations used by marine bacteria in their quest for resources and struggle for survival (e.g. utilization of light, acquisition of nutrients, predator avoidance, etc.). Further, analyses of the identity of bacteria using molecular markers (e.g. subgroups of Bacteria and Archaea) combined with activity tracers might bring knowledge to a higher level. Since bacterial growth (and thereby consumption of DOC and inorganic nutrients) is likely regulated differently in different bacteria, it will be critical to learn about the life strategies of the key bacterial species to achieve a comprehensive understanding of bacterial regulation of C fluxes. Finally, some processes known to occur in the microbial food web are hardly ever characterized and are not represented in current food web models. We discuss these issues and offer specific comments and advice for future research agendas.
    Description: Our work was supported by the following grants: NSF grant 0217282 (H.D.), Spanish MEC grant MODIVUS (J.M.G.), the Swedish Science Council (J.P.), the IEO time-series RADIALES programme (X.A.G.M.), the Earth and Life Science Division of the Dutch Science Foundation, ARCHIMEDES project, #835.20.023 (G.J.H.).
    Keywords: Carbon flux ; Microbial ecology ; Ocean ; Bacteria ; Protists ; Light ; Genomics ; Chemoautotrophy ; Models
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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