The significance of transparent exopolymeric particles (TEP) for microorganisms in Lake Pavin

Abstract

Transparent exopolymeric particles (TEP) consist of a matrix of colloidal fibrils and are produced from dissolved carbohydrate polymers exuded by phytoplankton and bacteria. These particles are involved in the formation of lake snow aggregates and are colonized by diverse microorganisms. Abundance, distribution, size spectra and bacterial colonization of TEP in Lake Pavin were studied and compared with data from other freshwater and marine systems. Abundance of TEP ranged from 105 to 106 particles L-1 and the majority of these particles contained attached bacteria. Bacterial density within TEP was related to temperature and decreased with particle size. TEP-associated bacteria were more important in the oligomesotrophic Lake Pavin than in the near-by eutrophic Lake Aydat, indicating that TEP are particularly important in environments with low nutrient loading. The community composition of particle-associated bacteria was different from that of free-living bacteria. In addition, we found that bacteria associated with TEP exhibit higher enzymatic activities than free-living cells in the surrounding water. Finally, the densities of heterotrophic nanoflagellates in Lake Pavin were more significantly related to the densities of TEP than to the densities of bacteria and the bacterial density within TEP. Based on comparisons with other freshwater and marine systems, we conclude that TEP are involved in the phytoplankton - primarily diatom - sedimentation processes and in the dynamics of bacteria and protozoa in the pelagic zone of aquatic ecosystems.