Metabolic control of dissolved organic matter dynamics

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Although dissolved organic matter (DOM) represents the largest reservoir of organic carbon in seawater and plays critical roles in material cycling within the oceans, little is known about mechanisms by which DOM dynamics is controlled in seawater. In this project, we focused on interactions between DOM and microbes in marine environments and evaluated the factors that affect bacterial degradation of DOM.A novel approach was developed to determine the degradation rate constant of dissolved proteins (an important component of DOM) by using radiolabeled bacterial proteins and peptidoglycan. The newly developed method allowed us to follow microbial respiration (degradation) of proteins and other biopolymers in natural seawater. Results demonstrated that the proteins associated with other biopolymers such as phospholipid are much less easily degradable than the proteins freely dissolved. These results are consistent with recent findings that bacterial membrane proteins and cell wall material largely accumulate in oceanic waters and suggest that the steric protection of HMW-DOM is an important mechanism by which DOM accumulates in seawater. Our data have important implications for understanding DOM turnover and modeling DOM dynamics in the oceans.