Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 3 2010 10.5194/bg-7-1007-2010 http://www.biogeosciences.net/7/1007/2010/ http://www.biogeosciences.net/7/1007/2010/bg-7-1007-2010.html http://www.biogeosciences.net/7/1007/2010/bg-7-1007-2010.pdf 1007 1015 2010-03-15 Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation K. Ziervogel ziervoge@email.unc.edu A. D. Steen C. Arnosti Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapman Hall, CB#3300, Chapel Hill, NC 27599-3300, USA now at: Center for Geomicrobiology, University of Århus, Ny Munkgade 1540, 0800 Århus C, Denmark Marine snow aggregates are heavily colonized by heterotrophic microorganisms that express high levels of hydrolytic activities, making aggregates hotspots for carbon remineralization in the ocean. To assess how aggregate formation influences the ability of seawater microbial communities to access organic carbon, we compared hydrolysis rates of six polysaccharides in coastal seawater after aggregates had been formed (via incubation on a roller table) with hydrolysis rates in seawater from the same site that had not incubated on a roller table (referred to as whole seawater). Hydrolysis rates in the aggregates themselves were up to three orders of magnitude higher on a volume basis than in whole seawater. The enhancement of enzyme activity in aggregates relative to whole seawater differed by substrate, suggesting that the enhancement was under cellular control, rather than due to factors such as lysis or grazing. A comparison of hydrolysis rates in whole seawater with those in aggregate-free seawater, i.e. the fraction of water from the roller bottles that did not contain aggregates, demonstrated a nuanced microbial response to aggregate formation. Activities of laminarinase and xylanase enzymes in aggregate-free seawater were higher than in whole seawater, while activities of chondroitin, fucoidan, and arabinogalactan hydrolyzing enzymes were lower than in whole seawater. These data suggest that aggregate formation enhanced production of laminarinase and xylanase enzymes, and the enhancement also affected the surrounding seawater. Decreased activities of chondroitin, fucoidan, and arabinoglactan-hydrolyzing enzymes in aggregate-free seawaters relative to whole seawater are likely due to shifts in enzyme production by the aggregate-associated community, coupled with the effects of enzyme degradation. Enhanced activities of laminarin- and xylan-hydrolyzing enzymes in aggregate-free seawater were due at least in part to cell-free enzymes. Measurements of enzyme lifetime using commercial enzymes suggest that hydrolytic cell-free enzymes may be active over timescales of days to weeks. 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