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Appl Environ Microbiol. 1991 May; 57(5): 1306-1312
Copyright © 1991, American Society for Microbiology. All Rights Reserved.

5'-Nucleotidase Activity in a Eutrophic Lake and an Oligotrophic Lake

James B. Cotner Jr.^,* and Robert G. Wetzel

Department of Biology, University of Michigan, Ann Arbor, Michigan 48109

ABSTRACT

Differences in enzymatic hydrolysis of dissolved organic phosphorus and subsequent phosphorus uptake were compared by using dual-labeled (-³²P and 2-³H) ATP in oligotrophic Lake Michigan and a moderately eutrophic lake in southeastern Michigan. More than 50% of the phosphate that was hydrolyzed was immediately taken up into bacterium-sized particles in the eutrophic lake and at a near-shore site in Lake Michigan. Less than 50% of the hydrolyzed phosphate was taken up into bacterium-sized particles at an offshore site in Lake Michigan. It is hypothesized that differences in size-fractionated uptake were the result of greater phosphorus utilization capacity in bacteria in habitats where loading of organic carbon is greater. Substantial isotope dilution of labeled phosphate uptake by unlabeled phosphate occurred, which implied that the phosphate was hydrolyzed extracellularly in both systems. Comparable nucleotidase activities were measured in the eutrophic lake and Lake Michigan, but the significance of the phosphate regenerated relative to particulate phosphorus pools was an order of magnitude greater in Lake Michigan. Seventy percent of the nucleotidase activity was inhibited by 100 µM phosphate in the eutrophic lake, which suggests that most hydrolysis was by phosphatase. Therefore, nucleotidase activity may be more important to phosphorus regeneration in oligotrophic habitats than phosphatase activity.

^* Corresponding author.

Present address: National Oceanic and Atmospheric Administration/Great Lakes Environmental Research Laboratory, 2205 Commonwealth Boulevard, Ann Arbor, MI 48105.

Present address: Department of Biology, University of Alabama, Tuscaloosa, AL 35487.