THE IMPACT OF MICROBIAL METABOLISM ON MARINE DISSOLVED ORGANIC MATTER

Abstract Microbes mediate global biogeochemical cycles through their metabolism, and all metabolic processes begin with the interaction between the microbial cell wall or membrane and the external environment. For all heterotrophs and many autotrophs, critical growth substrates and factors are present within the dilute and heterogeneous mixture of compounds that constitutes dissolved organic matter (DOM). In short, the microbe--molecule interaction is one of the fundamental reactions within the global carbon cycle. Here, I summarize recent findings from studies that examine DOM--microbe interactions from either the DOM perspective (organic geochemistry) or the microbe perspective (microbial ecology). Gaps in our knowledge are highlighted and future integrative research directions are proposed. Key Words dissolved organic matter, microorganisms, metabolomics, ABC transporters OVERVIEW When you walk into a biologist’s (or biochemist’s) office, you will likely see a large poster of all the chemical reactions that occur in a cell’s metabolism. Perhaps, like me, you will be struck by the sheer complexity of the pathways, the interdependence of all the reaction arrows, and the critical role played by each reaction in the life of the cell. Now imagine a reaction map for a “superorganism ” such as the ocean. Instead of individual compounds connected by reaction pathways, the map would show organisms connected by chemical compounds that pass through the dissolved organic matter (DOM) pool. Averaged over large spatial and temporal scales, these individual organisms and chemical interactions would culminate in the observed global elemental cycles. This view of the marine ecosystem is ascending in the microbial ecology literature (Azam & Worden 2004, Gasol et al. 2008, Raes & Bork 2008), and the notions of ecological functioning units and synergisti