Bacterial populations and processes involved in acetate and propionate consumption in anoxic brackish sediment

Bacterial populations and pathways involved in acetate and propionate consumption were studied in anoxic brackish sediment from the Grosser Jasmunder Bodden, German Baltic Sea. Uptake of acetate and propionate from the porewater was studied using stable carbon isotope-labeled compounds. Labeled acetate was not produced as an intermediate during propionate uptake experiments, and propionate consumption was not affected by the addition of acetate. In parallel, incorporation of labeled acetate and propionate into phospholipid-derived Fatty acids (PLFA) was studied to indicate bacterial populations involved in the consumption of these substrates. The C-13-acetate label was mainly recovered in even-numbered PLFA (16:1 omega 7c, 16:0 and 18:1 omega 7c). In contrast, primarily odd-numbered PLFA (a15:0, 15:0, 17:1 omega6 and 17:0) and the even-numbered i16:0 were labeled after incubation with C-13-propionate. Although single PLFA labeled with propionate are commonly found in sulfate reducers, the complete PLFA-labeling pattern does not resemble any of the know strains. However, the acetate-labeling pattern is similar to Desuflotomaculum acetoxidans and Desulfofrigus spp., two acetate-consuming, sulfate reducers. In conclusion, our data suggest that acetate and propionate were predominantly consumed by different, specialized groups of sulfate-reducing bacteria. [KEYWORDS: sulfate-reducing bacteria, acetate, propionate, sediment, phospholipid-derived fatty acid, C-13 labeling]

Distribution and activity of microorganisms in the sea Proceedings

SIGLEAvailable from TIB Hannover: ZB 3231(8) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Is there competition among ciliates and nematodes?

Bergtold M, Gunther V, Traunspurger W. Is there competition among ciliates and nematodes? FRESHWATER BIOLOGY. 2005;50(8):1351-1359.1. Biotic interaction between the ciliate Cyclidium glaucoma and the nematode Caenorhabditis elegans was investigated by manipulating the densities of the organisms in microcosms with and without sediment. 2. After 11 days the abundance of ciliates, nematodes and bacteria as well as extracellular enzyme activity were determined. Ciliates had a negative effect on nematode abundance in microcosms without sediment and in microcosms with sandy sediment, whereas in muddy sediment the effect was less distinctive. An effect of nematodes on ciliates was not observed. 3. The common resource bacteria were not affected negatively by the activity of the grazers. Overall grazer biomass increased with the addition of sediment to the microcosms, suggesting a rise of the carrying capacity in the experimental system. Especially in muddy sediment the abundance of bacteria and extracellular enzyme activity was higher compared to the microcosms without sediment. 4. The results of the experiment suggest a strong interspecific competition between nematodes and ciliates, where nematodes are, at least temporary, strongly affected