AME 21:151-159 (2000)  -  doi:10.3354/ame021151

ABSTRACT: Biofilms are a major nexus for biogeochemical transformations in inland waters. A defining feature of biofilms is an extracellular polysaccharide matrix. One of the proposed functions of the matrix is retention of extracellular enzymes. We investigated this function by following the kinetics of alkaline phosphatase (AP) and leucine aminopeptidase (LAP) in shaded and exposed limnetic biofilms developed on glass slides. Organic matter (OM) accumulation and chlorophyll content were also measured. Biofilm was scraped from the slides and partitioned in matric and particulate (ectocellular plus detrital bound) fractions. In addition to enzyme activity, the matric fraction was analyzed for carbohydrate and protein content. Over the May to October study period, matric Km values were significantly higher (by 30 to 50%) than particulate values for both enzymes in both treatments (n = 44). Vmax values were significantly higher in the particulate fraction for both enzymes in both treatments. Matric activity as a fraction of total activity averaged about 25% (3:1 ratio particulate: matric) for both enzymes, suggesting that the matrix was retaining enzymes. This was corroborated by principal component analysis which in general tied matric enzyme activity with matric carbohydrate and protein content and with OM accumulation and linked phosphatase activity to chlorophyll. There was no correlation between matric and particulate enzyme activities and both varied widely. During periods of seasonal turnover in dominant algal populations, matric activity exceeded particulate. Matric enzymes appear to be a significant community resource whose activity may affect the dynamics of biofilm communities.

KEY WORDS: Biofilm · Enzyme activity · Leucine Aminopeptidase · Phosphatase