One of the largest fluxes of carbon in most of the ecosystems is that from the detritus to microorganisms. Microbial ectoenzymes play a basic role in the degradation of detritus. However, the role of ectoenzymes in dependence of the detritus composition has not been studied. In a microcosm experiment we have followed the development of nine ectoenzymatic activities and hydrolytic bacteria during the degradation of four sources of detritus (macrophytes, algae, leaves and chitin). Throughout the degradation of algae and macrophytes, a succession of ectoenzymatic activities could be observed. This succession started with the hydrolysis of oligosaccharides and starch (high α-glucosidase, β-glucosidase, exocellulase and amylase activities), and was followed by the hydrolysis of plant structural polysaccharides (endocellulase and endoxylanase activities). Such a succession was neither found in the enrichments with leaves, with lower peaks of activity, nor of chitin. This latter was characterized by a high chitinolytic activity and the highest alkaline phosphatase/peptidase ratio. Along the experiment, the number of hydrolytic colonies (amylolytic, cellulolytic, xylanolytic, chitinolytic) varied between 2-52 % of the total CFUs, amylolytic colonies generally being the most abundant (up to 35 % of total CPUs). For 20 isolates, their ability to hydrolyze starch, cellulose, xylane and chitin when offered as single carbon source was checked. Of the isolates, 55 % could use more than one polymer. Very likely, the ability to hydrolyze several carbon sources offers these bacteria the possibility to shift or even express simultaneously various enzymes. During the process of microbial decomposition of detritus shown here, characterized by changes in the available molecules, bacteria with the ability to hydrolyze several carbohydrates would have an advantage to persist in the system in contrast to bacteria that could only hydrolyze one of the tested polymers. In aquatic environments exposed to changing inputs of organic matter such as the littoral zones, bacteria with multiple hydrolytic potential would very likely show a better adaptation

The study was supported by the joint research project “Cycling of organic matter in Lake Constance”

15 pages, 6 figures, 1 table

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