VARIABILITY IN ECTOHYDROLYTIC ENZYME-ACTIVITIES OF PELAGIC MARINE-BACTERIA AND ITS SIGNIFICANCE FOR SUBSTRATE PROCESSING IN THE SEA

Microbial utilization of polymeric and particulate organic matter in a quatic environments depends on the activities of hydrolytic ectoenzyme s present in the periplasm or bound to bacterial surfaces. Numerous st udies have quantified this activity and shown that it is an ubiquitous phenotype of bacterial populations in oceans and lakes. However, litt le is known about the distribution of this activity among the differen t species that constitute the bacterial community in natural assemblag es. We examined whether marine bacteria isolated from several types of particles and from the surrounding seawater exhibit different pattern s of hydrolytic enzyme activities. We screened 44 marine isolates for the presence of enzymatic activity measured as the hydrolysis of fluor ogenic substrates. Isolates were obtained from Southern California Eig ht (USA) seawater after size fractionation to concentrate unattached o r particle-attached bacteria. Isolates were also obtained from larvace an houses and aggregates produced in laboratory microcosms which had b een enriched with nutrients to create phytoplankton blooms. The activi ties of the following enzymes were assayed: protease, beta-glucosidase , alpha-glucosidase, alkaline phosphatase, lipase and chitinase. Cell- specific activities of all enzymes varied over a broad range (4 to 381 0 amol cell(-1) h(-1) for protease; 0 to 35 amol cell(-1) h(-1) for be ta-glucosidase; 0 to 8 amol cell(-1) h(-1) for alpha-glucosidase; 0.7 to 410 amol cell(-1) h(-1) for alkaline phosphatase; 0.2 to 584 amol c ell(-1) h(-1) for lipase; 0 to 559 amol cell(-1) h(-1) for chitinase) suggesting shifts in the dominant species of bacteria could strongly i nfluence the rates and patterns of polymer and particle hydrolysis in seawater. Some isolates had a single dominant activity, which varied a mong isolates. This suggests 'specialization' for different types of p olymeric substrates in different species. However, no distinct differe nces in enzyme activity profiles were found between isolates collected from various types of particles versus those from the surrounding wat er.