Award: OCE-1924512

In the ocean’s "twilight zone," microscopic organisms play a critical role in the global nitrogen cycle. These bacteria act as natural recyclers, converting a chemical called nitrite into nitrate. To do this, they rely on specialized proteins called metalloenzymes, which require trace amounts of metals like iron, copper, and cobalt to function. This project set out to understand whether a scarcity of these essential metals, combined with naturally low-oxygen conditions in certain ocean zones, limits the growth and activity of these vital marine microorganisms.

Major Discoveries and Outcomes

Despite multi-year pandemic delays to planned ocean expeditions, the research team successfully pivoted to laboratory experiments and computer-based bioinformatic analysis before ultimately completing a 39-day research expedition to the Equatorial Pacific. Over the course of the project, the team uncovered multiple new findings that improve our understanding of the dark ocean:

• Iron Limits Nitrogen Recycling: During the culminating Equatorial Pacific expedition, the team conducted experiments proving their core hypothesis: the activity of nitrite-oxidizing bacteria in the ocean can be directly limited by the availability of iron. However, the distribution of iron limitation was patchy and not as wide-spread as initially hypothesized.
• Rethinking the Dark Carbon Cycle: In addition to recycling nitrogen, these microorganisms pull carbon out of the water to build their cells. By developing a novel chemical method to isolate the activity of specific microbes, the team disproved a long-standing assumption about the active carbon-fixing microbes in the deep ocean. They found that these nitrogen-recycling bacteria are actually only minor contributors to "dark carbon fixation," suggesting that other microbes are responsible for the high carbon uptake previously reported in the mesopelagic.
• Microbial Interdependence: The researchers revealed that these microbes do not act alone. They rely heavily on other members of the microbial community to survive, trading vitamins and organic carbon. When grown alongside other bacteria, or when forced to use alternative fuels (like formate), their demand for specific trace metals spikes dramatically.

Broader Impacts and Training

This award was instrumental in developing the next generation of oceanographic leaders. The project supported the hands-on training and mentorship of five early-career scientists. These researchers gained highly specialized skills in marine biology, chemistry, bioinformatics, and leading major research expeditions.

The team also engaged in public outreach, including lectures at the Santa Barbara Maritime Museum and teaching modules their Ocean Science Conference. Finally, all the genomic data, rate measurements, and chemical measurements developed during this award have been deposited into open-access public databases, providing invaluable resources to the global oceanographic and microbiological research communities.

 

 

Last Modified: 05/18/2026
Modified by: Alyson E Santoro