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Aquatic Microbial Ecology

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AME 65:159-168 (2011)  -  DOI:

The direct role of enzyme hydrolysis on ammonium regeneration rates in estuarine sediments

Afonso C. Souza1, Tamara K. Pease2, Wayne S. Gardner1,*

1The University of Texas at Austin, Marine Sciences Institute, 750 Channel View Drive, Port Aransas, Texas 78373, USA
2The University of Texas at Brownsville, Chemistry and Environmental Science, 80 Fort Brown Brownsville, Texas 78520, USA

ABSTRACT: Benthic ammonium (NH4+) regeneration in coastal marine sediments has a fundamental role in nitrogen (N) cycling and N supply to primary producers. Nitrogen regeneration involves benthic microbial mineralization of organic-N, which, in turn, depends on protein hydrolysis. These processes were examined in Aransas Bay (Texas, USA) sediments by monitoring NH4+ evolution as a function of enzyme activity in controlled sediment slurries. Casein and tannic acid were added to evaluate the direct role of aminopeptidase on NH4+ production and the effects of a polyphenolic enzyme inhibitor, respectively. Casein additions increased the NH4+ concentration from 19 ± 0.3 to 737 ± 150 µM in 120 h, a final concentration 4.3-fold higher than that of control samples and 2.9-fold higher than that of samples with casein and tannic added together. Lower NH4+ concentration in samples with tannic acid indicated that inhibiting aminopeptidase activity reduced NH4+ production rates. The concentration of the regenerated NH4+ related directly to aminopeptidase activity in controls (r = 0.86, p < 0.01), casein-enriched (r = 0.89, p < 0.01), and casein plus polyphenol treatments (r = 0.71, p < 0.01) over the first 72 h. The results demonstrate the importance of aminopeptidase in regenerating NH4+ in sediments and provide insights about mechanisms of enzyme hydrolysis and NH4+ fluxes in estuarine sediments.

KEY WORDS: Leucine-aminopeptidase · Extracellular enzymes · Ammonium regeneration · Marine sediments

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Cite this article as: Souza AC, Pease TK, Gardner WS (2011) The direct role of enzyme hydrolysis on ammonium regeneration rates in estuarine sediments. Aquat Microb Ecol 65:159-168.

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