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2 Polish Journal of Environmental Studies

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Protozoans prefer large and metabolically active bacteria

100%

Koton-Czarnecka M. , Chrost R. J.

Polish Journal of Environmental Studies

2003

tom 12

nr 3

The aim of our studies was to verify the hypothesis that heterotrophic nanoflagellates (HNF) prefer large and metabolically active bacterial cells, and avoid small and inactive bacteria. Determined grazing rates on bacteria differing in sizes and metabolic activity and observed changes in bacterioplankton structure in samples with and without bacterial grazers indicated that HNF prefer large (but not too large) and actively metabolizing bacterial cells. Bacterial size fraction between 0.4 and 0.8 μm represented the majority of all grazed bacteria, i.e. 61.6±6.9 %. Grazing rates on live bacteria were 1.83 times greater than grazing rates on dead bacteria. This preferential protozoan feeding strongly affects composition and activity of bacterial communities in aquatic environments.

Measurement of protozoan grazing on bacteria by means of [3H-thymidine]-labeled natural assemblages of lake bacteria

100%

Koton-Czarnecka M. , Chrost R. J.

2002

tom 11

nr 4

Protozoan grazing on bacteria transfers significant amounts of organic carbon to higher trophic levels in aquatic ecosystems. Therefore, the determination of protozoan grazing rates on bacteria is necessary for estimating the efficiency of microbial loops in organic matter utilization and transformation. Currently, a variety of methods are available to measure protozoan grazing on bacteria but most of them result in serious physical perturbations of the examined samples. We describe an assay for protozoan grazing on bacteria by means of [3H-methyl]thymidine-labelled natural bacterial assemblages as a food tracer for protozoans. Using this method we determined the protozoan grazing rates on bacteria in ten Mazurian lakes in April and July, 2000. We compared the grazing rates with bacterial biomass production and the trophic state index of studied lakes.