By analyzing the gains and losses in genes from phytoplankton samples collected from all major ocean regions, researchers at the University of California at Irvine have created the most nuanced, highest resolution map yet to show where these photosynthetic organisms thrive or are forced to adapt. to limited amounts of key nutrients nitrogen, phosphorus and iron.
As part of the new Bio-GO-SHIP initiative, UCI scientists carried out eight deployments to six different research vessels, spending 228 days at sea in the Atlantic, Pacific and Indian Oceans. They generated nearly 1,000 ocean metagenomes from 930 locations around the world, with an average distance between collection points of 26.5 kilometers (about 16.5 miles).
In a study published today in Science, UCI researchers explain how they used a wealth of information embedded in microbial genes – particularly of the phytoplankton species Prochlorococcus – as a biosensor of ocean health and productivity. Oceanographers working in this field are keenly interested in understanding how these organisms adapt to “nutritional stress,” which is the struggle to find or use the essential substances they need to grow and reproduce.
“Phytoplankton are fundamental to the marine food web, and they are responsible for almost half of the global carbon dioxide uptake on an ongoing basis, so the health and distribution of these organisms is very important,” said said co-lead author Adam Martiny, UCI Professor of Earth System Science. “The knowledge gained from these trips will help climatologists make more robust predictions about the role of phytoplankton in regulating carbon stocks in the atmosphere and the ocean.”
Since microbial phytoplankton live in large populations and have rapid life cycles, researchers suggest that changes in community composition and genomic content can provide an early warning of environmental transformations and do so much more quickly than ‘by simply analyzing the physics and chemistry of the oceans.
“The limitation of nitrogen, phosphorus and iron in many ocean surface regions is almost impossible to detect through chemical analysis of water samples; the amounts of these elements are just too low, ”said lead author Lucas Ustick, UCI graduate student in ecology and evolutionary biology. . “But quantifying changes in the Prochlorococcus genes involved in the absorption of major nutrients, and their combinations, provides a strong indicator of the geography of nutritional stress.”
The authors pointed out that all genomes of Prochlorococcus include a certain gene that allows phytoplankton to directly assimilate inorganic phosphate freely available in seawater. But when this compound is scarce, phytoplankton adapts by gaining a gene. which allows cells to absorb dissolved organic phosphorus, which can be detected in their genome.
The researchers also looked at many other examples of genetic adaptations for different levels of phosphorus, iron, and nitrogen in the environment to see what kinds of compromises phytoplankton continually make. The result was a global map of nutritional stress. The researchers were also able to identify regions where phytoplankton undergo co-stress involving two or more elements, one of which is almost always nitrogen.
The team’s work revealed that the North Atlantic Ocean, the Mediterranean Sea and the Red Sea were regions under high phosphorous stress. Nitrogen stress-adapted genotypes are prevalent in so-called oligotrophic regions where nutrients are low and oxygen is high, and research sampling results suggest widespread adaptation to iron stress.
Analysis of phytoplankton genotypes confirmed known biogeographic patterns of nutritional stress estimated by different techniques, but it also revealed previously unknown regions of nutritional stress and co-stress. The researchers had a limited understanding of nutritional stress in the Indian Ocean prior to their metagenomic analysis, but their work has filled many blanks. They now know that the Arabian Sea upwelling region is an area under some iron stress, and they have detected phosphorus stress associated with southerly ocean currents, among many other findings.
Yet, they say, there is always more to learn.
“Our work highlights gaps in our measurements of high latitude environments, in most of the Pacific Oceans, and in deeper water ecosystems,” said co-first author Alyse Larkin, UCI postdoctoral researcher in systems science earthly. “The progress we have made on our recent expeditions inspires us to travel the entire planet.”
This project was funded by the National Science Foundation, NASA, and the National Institutes of Health. Other UCI researchers included Melissa Brock, graduate student in Ecology and Evolutionary Biology; Keith Moore, professor of Earth System Science; Nathan Garcia, Earth System Science Project Scientist; Catherine Garcia, holder of a graduate doctorate. studying earth system science; Jenna Lee, UCI undergraduate graduate student and Nicola Wiseman, Earth system science graduate student.