Heterotrophic microbes consume much of the organic matter (OM) produced in the ocean. Although a considerable part of OM degradation occurs at depth, the effects of hydrostatic pressure on OM degradation in the deep ocean are seldom measured. We investigated the effect of deep ocean pressures on the activities of extracellular enzymes that heterotrophic microbes use to degrade high molecular weight (HMW) organic matter. To distinguish pressure effects on extracellular enzymes released from microbes from the effects on the microbes themselves, we first stimulated enzyme production via HMW OM addition to seawater. Freely released enzymes were isolated by filtration. The free enzymes as well as microbe-containing seawater were then incubated at pressures characteristic of the surface and deep ocean, and activities of peptidases, glucosidase, and chitinase enzymes were measured. For most incubations, activities at high pressure were 30% or more of activities at atmospheric pressure. Pressure enhancement as well as pressure inhibition was evident for both the free enzymes and bulk communities. Free enzymes showed comparatively more consistent pressure effects across sites compared to the bulk communities. These data suggest that despite partial pressure inhibition of enzymes and organisms of the upper ocean, they can still contribute to organic matter degradation at considerable depth. Our data also suggest that pressure effects on enzymes vary by type and class, likely due in part to pressure sensitivities of the enzyme-producing members of the active microbial community.Heterotrophic microbes consume much of the organic matter (OM) produced in the ocean. Although a considerable part of OM degradation occurs at depth, the effects of hydrostatic pressure on OM degradation in the deep ocean are seldom measured. We investigated the effect of deep ocean pressures on the activities of extracellular enzymes that heterotrophic microbes use to degrade high molecular weight (HMW) organic matter. To distinguish pressure effects on extracellular enzymes released from microbes from the effects on the microbes themselves, we first stimulated enzyme production via HMW OM addition to seawater. Freely released enzymes were isolated by filtration. The free enzymes as well as microbe-containing seawater were then incubated at pressures characteristic of the surface and deep ocean, and activities of peptidases, glucosidase, and chitinase enzymes were measured. For most incubations, activities at high pressure were 30% or more of activities at atmospheric pressure. Pressure enhancement as well as pressure inhibition was evident for both the free enzymes and bulk communities. Free enzymes showed comparatively more consistent pressure effects across sites compared to the bulk communities. These data suggest that despite partial pressure inhibition of enzymes and organisms of the upper ocean, they can still contribute to organic matter degradation at considerable depth. Our data also suggest that pressure effects on enzymes vary by type and class, likely due in part to pressure sensitivities of the enzyme-producing members of the active microbial community.

Primary Presenter: Stephanie Caddell, University of North Carolina at Chapel Hill (smc2002@ad.unc.edu)

Authors:

Carol Arnosti, University of North Carolina at Chapel Hill  (arnosti@email.unc.edu)

Ronnie Glud, University of Southern Denmark, Department of Biology, Odense, Denmark; Tokyo University of Marine Science and Technology, Department of Ocean and Environmental Sciences, Tokyo, Japan  (rnglud@biology.sdu.dk)

John Paul Balmonte, University of Southern Denmark, Odense M, Denmark  (jpbalmonte@biology.sdu.dk)