Life at the oxic-anoxic interface: microbial activities and adaptations

Molecular oxygen is one of the most important reactants in biogeochemical c ycles. Due to its low solubility in water, the consumption of oxygen lends to the development of oxic-anoxic interfaces, which separate aerobic from a naerobic processes in virtually all environments, ranging in scale from oce anic sediments to the fecal pellets of a small soil invertebrate. Three cas e studies were selected to illustrate the basic situation and the specific characteristics of oxic-anoxic interfaces. sediments. the rhizosphere of aq uatic plants? and the intestinal tract of insects. Each system is governed by the same general principles, but striking differences arise from: e.g., the nature of the major microbial activities and the mechanisms controlling metabolite fluxes. Also scale and dimensional differences as well as the c onsequences of temporal fluctuations are of fundamental importance. Recent developments in microbial ecology, which often combine traditional and mode rn approaches. have significantly further ed our understanding of the speci fic microniches and the metabolic and behavioral adaptations of microorgani sms to life at the oxic-anoxic interface. New concepts help to define the t argets of future studies: the spatial organization of microbial populations , their microenvironments and in situ activities, and the functional intera ctions within structured microbial communities. (C) 2000 Federation of Euro pean Microbiological Societies. Published by Elsevier Science B.V. All righ ts reserved.