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| Titel |
Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation |
| VerfasserIn |
K. Ziervogel, A. D. Steen, C. Arnosti |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 3 ; Nr. 7, no. 3 (2010-03-15), S.1007-1015 |
| Datensatznummer |
250004589
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| Publikation (Nr.) |
 copernicus.org/bg-7-1007-2010.pdf |
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| Zusammenfassung |
| 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.
Considering water residence times of up to 10 days in the investigation area
(Apalachicola Bay), enzymes released from aggregates may be active over
timescales long enough to affect carbon cycling in the Bay as well as in the
adjacent Gulf of Mexico. Aggregate formation may thus be an important
mechanism shaping the spectrum of enzymes active in the ocean, stimulating
production of cell-free enzymes and leading to spatial and temporal
decoupling of enzyme activity from the microorganisms that produced them. |
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