Microbial life in sedimentary biofilms the challenge to microbial ecologists

Modification and decomposition processes of material in sedirnents are dominated by microorganisms. Through microbial colonization, cells become immobilized at particle surfaces and embedded in an organic matrix of extracellular polysaccharides. The development of complex sedimentary biofilms is the net result of transport and exchange processes between the biofilm and surrounding water, and modification and transformation processes of matter within the biofilm. This article illustrates aspects of microbial life in sedimentary biofilms: microbial colonization of particles, key functions of extracellular polysaccharides, spatial heterogeneity of microbial distribution and activity, and distribution and availability of organic carbon. Examination of our present knowledge indicates that micro-scale measurements rather than investigations in the bulk sediment are required, that much more attention has to be paid to the fact that microorganisms condition specific features of their environment rather than simply reacting to the environment, and that availability instead of concentration of carbon has to be measured. To obtain a better insight into the function of sedimentary biofilrns, traditional approaches have to be modified.