Matric and particulate phosphatase and aminopeptidase activity in limneticbiofilms

Biofilms are a major nexus for biogeochemical transformations in inland wat ers. A defining feature of biofilms is an extracellular polysaccharide matr ix. One of the proposed functions of the matrix is retention of extracellul ar enzymes. We investigated this function by following the kinetics of alka line phosphatase (AP) and leucine aminopeptidase (LAP) in shaded and expose d limnetic biofilms developed on glass slides. Organic matter (OM) accumula tion and chlorophyll content were also measured. Biofilm was scraped from t he slides and partitioned in matric and particulate (ectocellular plus detr ital 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 K-m values were significantly higher (by 30 to 50%) th an particulate values for both enzymes in both treatments (n = 44). V-max v alues were significantly higher in the particulate fraction for both enzyme s in both treatments. Matric activity as a fraction of total activity avera ged 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 phosp hatase activity to chlorophyll. There was no correlation between matric and particulate enzyme activities and both varied widely. During periods of se asonal turnover in dominant algal populations, matric activity exceeded par ticulate. Matric enzymes appear to be a significant community resource whos e activity may affect the dynamics of biofilm communities.