Substantial activities of organic matter decomposition by deep-sea microbial communities

Heterotrophic microbial communities play an important role in the cycling of organic carbon in the ocean as they respire most of the dissolved organic matter (DOM) produced through primary productivity in surface waters. The DOM pool is mainly comprised of high-molecular weight biopolymers that require enzymatic transformation outside the cell prior to uptake by bacteria (secondary producers). Measurements of microbial enzyme activities in surface waters are quite common; however, information about activities of hydrolytic enzymes in the deep ocean are comparatively rare. This work presents potential hydrolysis rates of organic substrates (carbohydrates, peptides, organic phosphorous, i.e., major compounds of marine DOM) throughout the water column and in surface sediments in the north-eastern Pacific Ocean (Juan da Fuca Ridge). All of the substrates tested here were hydrolyzed at every depth from the surface ocean (50 m) to bottom waters (2650 m), albeit at different rates. Substantial organic matter break-down was found in deep waters and sediments, indicating the presence of a highly active heterotrophic microbial community in deep-sea environments fueled by organic matter from the surface. Ongoing work includes further characterization of microbial heterotrophic activities and the organisms carrying them out, helping to better understand elemental cycles in deep-sea environments.