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

Abstract

Microbial utlllzatlon of polymenc and particulate organic matter in aquatlc environments depends on the activltles of hydrolytic ectoenzymes present in the periplasm or bound to bactenal sur faces Numerous studles have quantified this activity and shown that it is a n ubiquitous phenotype of bactenal populatlons In oceans and lakes However llttle IS known about the distribution of this activity among the dlfferent species that constitute the bacterial community In natural assemblages We examined whether manne bactena isolated from several types of particles and from the surrounding seawater exhibit dlfferent patterns of hydrolytic enzyme activities We screened 44 m a n n e 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 bactena Isolates were also obtained from larvacean houses and aggregates produced in laboratory nlicrocosms whlch had been ennched with nutnents to create phytoplankton blooms The aclvlties of the following enzymes were assayed protease, P-glucos~dase, a-glucosidase alkahne phosphatase lipase and chitinase Cell-speciflc activities of all enzymes vaned over a broad range (4 to 3810 amol cell-' h-' for protease 0 to 35 am01 cell-' h-' for P-glucosldase 0 to 8 am01 cell-' h ' for a-glucosidase 0 7 to 410 amol cell-' h-' for alkahne phosphatase 0 2 to 584 am01 cell-' h ' for lipase 0 to 559 am01 cell ' h I for chitinase) suggesting shifts in the dominant species of bactena could strongly influence the rates and patterns of polymer and particle hydrolysis in seawater Some isolates had a single dominant activlty whlch vaned among isolates This suggests specialization for dlfferent types of polyrnenc substrates in d~fferent species However no distinct differences In enzyme activlty profiles were found between isolates collected from vanous types of particles versus those from the surr o u n d ~n g water KEY WORDS: Ectoenzyme .Marine bactena .