A USC-led research team discovered the unique role that a light-capturing marine microbe plays in regulating Earth’s climate. The team consisted of scientists from California, China, the UK, and Spain. The results of their study were published this week in Science Advances.
Laura Gómez-Consarnau led the research team and is an assistant professor of biology at the USC Dornsife College of Letters, Arts and Sciences. In a press release from USC regarding the nature of the study, she explained that "oceans are important for climate change because they play a key role in the carbon cycle. Understanding how that works, and the marine organisms involved, helps us refine our climate models to predict climate in the future."
Their research focused on rhodopsins—microbes with light-sensitive proteins that trap sunlight similar to how the human eye gathers light. When organic matter is scarce, rhodopsins use sunlight to create energizing adenosine triphosphate. Prior to the discovery of rhodopsins about 20 years ago, it was thought that ocean sunlight was only metabolized by chlorophylls in algae and bacteria. However, although rhodopsins use sunlight to create energy, they don’t absorb CO2 in the way that marine algae do.
Previous research estimated that rhodopsins represent 80% of marine bacteria. A 2014 study discovered that bacteria containing rhodopsin were much more abundant than previously thought. Additionally, they discovered that rhodopsins were concentrated in nutrient-poor waters in which they trap more sunlight that algae. The existence of low-nutrient zones throughout the global ocean is expected to increase with rising ocean temperatures. As a result, rhodopsins will be able to utilize sunlight and thrive in the absence of nutrients whereas algae will be limited. The effects of this shift will have cascading impacts on climate regulation, resulting in less carbon sequestering in the ocean.
Gómez-Consarnau explained that “with fewer nutrients near the surface, algae will have limited photosynthesis, and the rhodopsin process will be more abundant.” As a result of this shift, “the ocean won't be able to absorb as much carbon as it does today. So more CO2 gas may remain in the atmosphere, and the planet may warm faster."