AME 10:223-230 (1996)  -  doi:10.3354/ame010223

Variability in ectohydrolytic enzyme activities of pelagic marine bacteria and its significance for substrate processing in the sea

Martinez J, Smith DC, Steward GF, Azam F

Microbial utilization of polymeric and particulate organic matter in aquatic environments depends on the activities of hydrolytic ectoenzymes present in the periplasm or bound to bacterial surfaces. Numerous studies have quantified this activity and shown that it is an ubiquitous phenotype of bacterial populations in oceans and lakes. However, little is known about the distribution of this activity among the different species that constitute the bacterial community in natural assemblages. We examined whether marine bacteria isolated from several types of particles and from the surrounding seawater exhibit different patterns of hydrolytic enzyme activities. We screened 44 marine isolates for the presence of enzymatic activity measured as the hydrolysis of fluorogenic substrates. Isolates were obtained from Southern California Bight (USA) seawater after size fractionation to concentrate unattached or particle-attached bacteria. Isolates were also obtained from larvacean houses and aggregates produced in laboratory microcosms which had been enriched with nutrients to create phytoplankton blooms. The activities 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 3810 amol cell-1 h-1 for protease; 0 to 35 amol cell-1 h-1 for beta-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 cell-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 influence the rates and patterns of polymer and particle hydrolysis in seawater. Some isolates had a single dominant activity, which varied among isolates. This suggests 'specialization' for different types of polymeric substrates in different species. However, no distinct differences in enzyme activity profiles were found between isolates collected from various types of particles versus those from the surrounding water.

Ectoenzyme . Marine bacteria . Organic matter decomposition

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