摘要:

Flow velocity required to erode a bed of acid‐washed sand is increased by intergranular adhesion resulting from growth of the benthic marine bacteriumAl‐teromonas atlantica.In general, we find that either pure exopolymer alone or exopolymer generated during in situ growth increases erosion resistance of fine quartz sand. Moreover, the degree of erosion resistance increases in proportion to the concentration of exopolymer‐component uronic acids, which in turn is dependent on relative nitrogen content of peptone‐based growth media. Specifically, we observe that approximately 100 nmol of exopolymer or 1.5 nmol of component uronic acids generated by in situ bacterial growth under nitrogen‐rich conditions per gram of dry sediment can effectively double seawater‐flume flow velocity required for initiation of transport of otherwise noncohesive, 125–177 μm quartz grains. This maximal effect corresponds to an estimated adhesive force that exceeds submerged particle weight by an order of magnitude and exceeds particle‐specific uronic acids weight by seven orders of magnitude. Rapid analysis by gas chromatography/mass spectrometry of purified exopolymer obtained fromA. atlanticacultures shows it to be a polysaccharide containing approximately 20% uronic acids by weight. Maximal exopolymer and component uronic acid concentrations generated in these experiments are an order of magnitude less than values previously reported for estuarine sediments. These results are the first to correlate specific exopolymer components with sediment erosion resistance and further demonstrate the importance of microbial exudates in sediment binding believed to occur in a wide range of marine environments.

ISSN:0149-0451    

DOI:10.1080/01490459009377874

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The composition of carbon and oxygen stable isotopes was determined for calcite associated with the freshwater cyanobacteriaHomoeothrix Crustacea, Phormidium incrustatum,andRivularia haematitesand the green algaGongrosira incrustansin a UK travertine‐depositing stream. The δ13C values ofRivulariacalcites deposited in summer were significantly higher than those deposited during winter. This was interpreted as the result of photosynthetic activity within colonies.

ISSN:0149-0451    

DOI:10.1080/01490459009377875

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We used methane‐production measurements of slurried peat to study controls of methane production in six contrasting Appalachian wetland sites. The sites differed widely in plant‐community composition and in rates of methane production, which varied from 3 μmol/L/day in slurried‐peat samples from a shrub‐dominated bog to 216 μmol/L/day in peat from a spruce‐forested wetland. Three controlling factors of methane production were examined: organic‐chemical components of the peat (e.g., hot‐water soluble, sulfuric acid soluble, sulfuric acid insoluble), concentrations of dissolved organic carbon, and rates of sulfate reduction. Peats from shrub‐dominated sites contained mostly acid‐insoluble organic matter, which was presumably recalcitrant to microbial decomposition. In contrast, peats from moss‐and sedge‐dominated sites contained mostly acid‐soluble organic matter, which was presumably labile. Differences of organic‐chemical components of the peat could explain about 50% of the variation in rates of methane production among samples from the sites. Rates of sulfate reduction in peat samples were relatively high (5–397 μmol/L/day), despite low in situ concentrations of dissolved sulfate (<250 μmol/L), but sulfate reduction was not well correlated with rates of methane production, nor were concentrations of dissolved organic carbon. Amendments of methanol and trimethylamine to peat samples from any individual site did not stimulate rates of methane production. In general but not always, glucose, hydrogen, and acetate amendments stimulated rates of methane production. Sulfate amendments that stimulated sulfate reduction also inhibited methane production by 90%; however, reversal of the inhibition was achieved by acetate and hydrogen amendments. Control of methane production in these organic‐rich wetlands is related more to organic‐chemical components of the peat than to the activity of coincident sulfate‐reducing bacteria.

ISSN:0149-0451    

DOI:10.1080/01490459009377876

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Apatite formation from organic matter (ribonucleic acid) and calcium carbonate (cuttlebone) requires intervention of microorganisms. We have attempted to characterize this mineral formation process by locating the alkaline phosphatase and the crystals formed. Alkaline phosphatase, which is important for the liberation of the necessary components, was localized in the periplasmic space ofProvidencia rettgeriin the same manner as inEscherichia coli.Accordingly, the release of inorganic phosphate and the formation of apatite may occur at this site. However, electron microscope observations revealed the presence of extracellular apatite; moreover, apatite particles that were formed with or without bacteria (with alkaline phosphatase from hydrolyzed ribonucleic acid as phosphorus source) were closely similar in size and appearance. The formation of apatite can thus be qualified as biologically induced mineralization. Nevertheless, a bacterial cell can also act as a nucleator for apatite crystallization, but this would appear exceptional.

ISSN:0149-0451    

DOI:10.1080/01490459009377877

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490459009377878

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490459009377879

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490459009377873

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor