POTENTIAL ACTIVITIES OF EXTRACELLULAR ENZYMES IN THE DEEP SUBSURFACE SEDIMENTS OF THE BALTIC SEA BASIN

Heterotrophic microorganisms in sediments produce extracellular enzymes in order to hydrolyze organic macromolecules so that they can be brought inside the cell and used for energy and growth. Extracellular enzymes therefore potentially act as mediators for the fate of organic carbon in sediments. The Baltic Sea Basin presents an excellent opportunity for studying extracellular enzymes and organic carbon degradation because it is a primarily depositional environment with high potential for organic carbon preservation. Using core samples obtained from IODP Expedition 347, the potential activities of multiple carbon degrading enzymes in the deep subsurface of the Baltic Sea Basin were measured using small substrate proxies containing the fluorescent compounds 4-methylumbelliferone (MUB) or 7-amino-4-methylcoumarin (AMC). Here we report the potential maximum hydrolysis rates (V_max) for the following enzymes in the Baltic Sea subsurface: phosphomonoesterase, β-D-xylosidase, β-D-glucanase, N-acetyl-β-D-glucosaminidase, β-glucosidase, α-glucosidase, leucyl aminopeptidase, arginyl aminopeptidase, prolyl aminopeptidase, ornithyl aminopeptidase, gingipain and clostripain. This work helps to clarify the controls on sedimentary organic matter, and its fate in the marine subsurface. It also provides new insight into the mechanisms and even the limits of microbial life in subsurface ecosystems like the Baltic Sea Basin.