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Abstract

Using a novel multi-cell continuous flow assembly, we studied the dynamic interactions between high-molecular weight substrate consumption, fermentation, and terminal metabolism by microbial communities in anaerobic marine sediments. This system allowed partial physical separation of individual steps in the remineralization of high-molecular weight organic matter: degradation of high-molecular weight polysaccharides, net formation of volatile fatty acids, and net sulfate reduction. Time series experiments yielded insight into time scales of extracellular enzyme production as well as the onset of terminal metabolism. These data also allowed us to assess the rate dependence of individual steps in organic carbon degradation. The major accumulated product of hydrolysis and fermentation was acetate, followed by lactate and formate. The rate of the initial exoenzymatic hydrolysis of polysaccharides was an order of magnitude faster than fermentation and sulfate reduction rates, and suggested a scenario whereby dissolved organic carbon could at least temporarily accumulate in pore waters. The lag in the consumption of hydrolyzed products by sulfate-reducing bacteria may reflect the differential response of the microbial community to increased substrate availability.