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Aquatic Microbial Ecology

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AME 84:127-140 (2020)  -  DOI:

Quantification of small-scale heterogeneity in aquatic aminopeptidase activity

Brian M. Gaas1,2,*, James W. Ammerman1,3,4

1Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901, USA
2Present address: Department of Environment, Government of Yukon, Whitehorse, Yukon Y1A 4Y9, Canada
3Present address: Long Island Sound Study, Stamford Government Center, Stamford, CT 06904, USA
4Present address: School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794, USA
*Corresponding author:

ABSTRACT: Leucine aminopeptidase (LAP) is one of the enzymes involved in the hydrolysis of peptides, and is sometimes used to indicate potential nitrogen limitation in microbes. Small-scale variability has the potential to confound interpretation of underlying patterns in LAP activity in time or space. An automated flow-injection analysis instrument was used to address the small-scale variability of LAP activity within contiguous regions of the Hudson River plume (New Jersey, USA). LAP activity had a coefficient of variation (CV) of ca. 0.5 with occasional values above 1.0. The mean CVs for other biological parameters—chlorophyll fluorescence and nitrate concentration—were similar, and were much lower for salinity. LAP activity changed by an average of 35 nmol l-1 h-1 at different salinities, and variations in LAP activity were higher crossing region boundaries than within a region. Differences in LAP activity were ±100 nmol l-1 h-1 between sequential samples spaced <10 m apart. Variogram analysis indicated an inherent spatial variability of 52 nmol l-1 h-1 throughout the study area. Large changes in LAP activity were often associated with small changes in salinity and chlorophyll fluorescence, and were sensitive to the sampling frequency. This study concludes that LAP measurements in a sample could realistically be expected to range from zero to twice the average, and changes between areas or times should be at least 2-fold to have some degree of confidence that apparent patterns (or lack thereof) in activity are real.

KEY WORDS: Aminopeptidase · Ectoenzyme activity · Variability · Coefficient of variation · Automated methods · River plume

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Cite this article as: Gaas BM, Ammerman JW (2020) Quantification of small-scale heterogeneity in aquatic aminopeptidase activity. Aquat Microb Ecol 84:127-140.

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