Award: OCE-2241720

Below, we describe the project outcomes in terms of intellectual merit, and broader impact.

Organic matter in the ocean, as is the case for organic matter on land, is recycled by organisms that consume, transform, and regenerate it as carbon dioxide and nutrients. In the ocean, much of this recycling activity is carried out by bacteria, which are active throughout the entire ocean, from the surface to water depths exceeding 5000 m. A major difference between carbon recycling on land and in the ocean is the high pressure conditions to which bacteria are subject at depth, since water is very heavy.  The water pressure at 5000 meters, for example, is approximately five hundred times higher than it is at the surface of the ocean. These high-pressure conditions in the ocean’s depths are likely to affect the manner in which bacteria process organic matter, but because of the difficulty of investigating these bacteria and the processes they carry out under high pressure conditions, comparatively few previous studies on these topics are available. 

Our project aimed to help fill this knowledge gap. We focused on the initial step of organic matter recycling, in which bacteria use enzymes to cut up large organic matter to smaller pieces. We focused on bacteria using two different methods to recycle large organic matter: some bacteria (sharing bacteria) excrete enzymes outside the cell, and use them to chop up organic matter outside the cell to sizes that they can take up, potentially sharing some of the small pieces produced by enzymes with other bacteria. Other bacteria (selfish bacteria) can cut up and transport organic matter into the cell without producing pieces that are shared with other bacteria. An essential part of this project was our collaboration with colleagues in Denmark and Germany, who have specialized instruments that enabled us to study both types of bacteria and their enzymes under high pressure conditions.

We found that most enzymes produced by sharing bacteria that live in the surface ocean do not function effectively at high pressure, whereas more of the enzymes produced by sharing bacteria collected at deeper depths functioned more effectively under high pressure. The selfish bacteria, however, seemed to manage well under all the pressure conditions that we tested: even selfish bacteria from the surface ocean could function effectively under high pressure. As part of this work, we tested at sea an instrument built by our Danish colleagues, and found that samples collected and incubated in the deep ocean clearly showed active selfish bacteria. These results help us better understand the conditions under which specific types of organic matter can be recycled in the ocean, and the bacteria that may be responsible. In the future, detailed study of selfish bacteria may help reveal the specific characteristics of these bacteria that let them function well also under high pressure conditions. The enzymes of sharing bacteria from the deep ocean could also be studied further. Successful use of the Danish sampler means that it could also be used to carry out other investigations of bacterial processes in the deep ocean.

Broader impacts of the project included participation of two undergraduates who worked on the project for several years, joining us in the lab and at sea.  Both of these undergraduates presented their research results at conferences. One is a co-author on a published scientific paper, the other is a co-author on a manuscript that we are currently writing. One postdoc was supported by the project. As part of the project, the postdoc carried out original research with our collaborators in Denmark and in Germany; two of his papers are already published, and a third is in preparation. The postdoc also visited several middle-school classes and talked about his research. Results from the project were presented in four invited talks and six conference presentations; they were also discussed in oceanography classes taught at the university.

 

 

Last Modified: 06/12/2026
Modified by: Carol Arnosti