Bacterial Life in the Plußsee: General Remarks on Aquatic Microbial Ecology

Abstract

Until recently it was thought that heterotrophic bacteria in aquatic ecosystems played only a trivial role in organic fluxes and in the functioning of the ecosystem. It was commonly accepted that phytoplankton primary production was utilized predominantly by herbivores (mainly zooplankton) and passed on to the organisms that comprise the grazing food chain. Even in recently published, widely distributed books on limnology, bacteria are still treated as only remineralizers and/or decomposers of organic matter in the energy and organic matter fluxes throughout a lake ecosystem (Wetzel 1983, Cole 1988, Schwoerbel 1987, Sommer 1989, Lampert and Sommer 1993). Very little attention has been directed to further implications of bacterial dynamics for the trophic relationships between these microorganisms and higher trophic levels and the functioning of the lake ecosystem. This notion has changed significantly during the last decade with results from new methods of measuring bacterial production, biomass and activity of bacteria, and their in situ growth rates. In an ecosystem context, these new findings portray bacteria as a very dynamic metabolic and trophic component representing a major pathway for organic matter and energy flux in the aquatic food web (Sherr and Sherr 1988, Ducklow and Carlson 1992, Simon et al. 1992, Chróst 1992).