Award: OCE-1046098

One of the most exciting areas of discovery in marine ecology is the flow of nutrients and energy between components of the microbial community. This is because microbes comprise the base of marine food chains and productivity is controlled by nutrients and energy. A rationale for this project was to study the relationships between organisms that acquire the energy for growth by photosynthesis (photoautotrophs) and microbes that acquire energy from chemical reactions that release energy (chemoautotrophs). At first glance, those strategies might appear to be so different that the respective organisms would have little interactions. Indeed many chemoautotrophs are abundant in dark places where photosynthesis does not occur. However, one reaction producing energy that is harvested by microbes this the oxidation of ammonia to nitrite. That has a big impact on the photoautotrophs, which compete for the ammonia as a source of the nutrient, nitrogen. They can also use nitrite but must convert it back to ammonia - which requires energy! This project goal was to study the oxidation by ammonia, which is carried out in the ocean priomarily by a class of microbes called archaea, and determine what controls their rates. Moffett's specific contribution was to assess how the chemistry of seawater imposes specific challenges on the activity of these organisms. In particular, Moffett studied how key metals in seawater like copper (which are very scarce in the ocean) might affect the competition between archaea and photoautotrophs, like diatoms. The enzyme that oxidizes ammonia requires copper. Our work showed that much of the ocean is poised on the threshold of copper limitation for these ammonia oxidizers. Therefore, factors that control copper distribution in the ocean can influence these rates. Other biochemical reactions that need copper enzymes often have highly similar enzymes that can use other metals that might be more abundant. But ammonia oxidizers are stuck with coppper. Nevertheless, there are some places where copper is very scarce, yet these ammonia oxidizers are plentiful. The Arabian Sea is a great example. We surmise that they have figured out a way to acquire the copper they need even when it is 'hidden' in highly inert forms. For archaea that have mastered this trick, the copper is used by a whole suite of other biochemical functions as well. That complicates our interpretation since we can't apply a "one size fits all" model of the relationship between copper and ammonia oxidation. But it appears that copper plays a significant role in the structure of ammonia oxidizing communities. In many cases, addition of even trace quantities of copper to seawater results in a noticeable increase in ammonia oxidation rates. The work is closely integrated to the other activities of the project, especially the relationship between ammonia oxidation and ammonia concentration and light. These organisms are really good at acquiring the ammonia they need even when it is very scarce. That requires more copper. But they are very sensitive to damage by light. Much of that damage is caused by free radicals, which can be detoxified by enzymes - that require copper! So the challenges of acquiring scarce amounts of ammonia and copper in sunlit waters are great. Finally, the actual energy produced in the reaction is meager, so all of these complicated biochemical processes must be accomplished on a shoestring budget! Yet somehow these organisms prevail and prosper. Phytoplankton typically make do with the nitrite, having to give back the energy 'stolen' by the ammonia oxidizers to convert nitrite back to ammonia - the form required to make amino acids. Last Modified: 01/07/2016 Submitted by: James W Moffett