|Tracking Microbial Metabolism in Marine DOM|
When you walk into a biologist’s office or lab, you will likely see a large wall-poster of all the chemical reactions within 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 if we could make such a reaction map for a “super-organism” such as the ocean. Instead of individual compounds connected by reaction pathways, the poster 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 diversity and systems biology literature (Gasol et al., 2008; Raes and Bork, 2008) and the notions of “ecological functioning units” and synergistic chemical interactions are supported by new field and laboratory data (Grossart and Simon, 2007; Hofle et al., 2008; Morris et al., 2008; Teira et al., 2008). However, this view will remain incomplete if we focus only on descriptions of the microbes in the oceans. To complete the map, we must identify the compounds that serve as the currency for these interactions, those that are traded between organisms for nutrition or communication as well as those that are exuded in chemical defense.
At this moment, we know very little about the molecular-level composition and dynamics of this important DOM pool as it pertains to different organisms and growth conditions (e.g., light, nutrients). Protein annotations of microbial transporters focus on the dynamics of small molecules such as glucose, glycine-betaine, and individual amino acids. However, most DOM has been shown to be high-molecular weight and unavailable to these transporters. Thus, our current measurements of DOM and its composition are at odds with our understanding of microbial physiology and DOM utilization. With new analytical techniques like ultrahigh resolution mass spectrometry and new information from the genome sequences of important marine microbes, our field is poised to address this conundrum and to identify novel DOM compounds that serve as the basis of interactions of microorganisms in aquatic environments.
Funding: WHOI Director of Research (2009-10); NSF Chemical Oceanography (2009-12; OCE-0928424); Gordon and Betty Moore Foundation (2012-2015) Personnel: Krista Longnecker (Research associate/ lab manager), Huixiang Xie (sabbatical visitor), Winn Johnson (JP student), Melissa Kido Soule (LC/MS method development), Crystal Breier (lab technician).
Publications: Longnecker, K. et al. submitted (Sept 2012) Limnology & Oceanography.
Kujawinski, E. B., et al Submitted (Oct 2012). Proceedings of the National Academy of Sciences, USA.;
E. B. Kujawinski. 2011. Ann. Rev. Mar. Sci.