ABSTRACT: Assessment of nutrient limitation in microbial populations in marine environments is an important topic. Existing methodologies generally demand long incubations in an experimental assay manipulating nutrients. We suggest a novel approach using the ratio between 2 ectoenzymatic activities, alkaline phosphatase (APA) and aminopeptidase (AMA), to evaluate nutrient limitation of microbial communities in situ. APA is used as an indication of P limitation and AMA of N limitation. The ratio bypasses the use of biomass estimations to calculate specific activities, which are error-prone and time-consuming. Our results from enrichment experiments have shown that the ratio APA:AMA increases in P-deficient treatments, and decreases after inorganic P addition. After P deficient nutrient addition (n treatments) the ratio APA:AMA increased to 90-230%, whereas following N+P balanced additions the ratio decreased to 30-70% of the initial value. These results demonstrate that this approach is easy, quick and gives a general insight into the nitrogen versus phosphorus nutrient balance of the communities without the need for biomass estimations or measurement of actual nutrient concentrations.

KEY WORDS: Alkaline phosphate · Aminopeptidase · N:P ratio · Microbial community

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Published in AME Vol. 23, No. 3 (2001) on February 28
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 2001