SAR11 Bacteria’s Role in Carbon Cycling and Climate Solutions
Paola Laurino
Okinawa Institute of Science and Technology, Japan
Winning article: The ultra-high affinity transport proteins of ubiquitous marine bacteria (Nature, 2024)
“Ocean microbes hold the key to both marine health and climate solutions.”
Marine SAR11 bacteria, the most abundant microbes on Earth, constitute approximately 18% of oceanic biomass and play a pivotal role in global biogeochemical cycles. Over the past two decades, their significance in marine ecosystems has become increasingly apparent, particularly in the uptake of dissolved organic matter (DOM) and the cycling of carbon and essential nutrients. These microorganisms are not only fundamental to ocean health but also hold immense potential for addressing climate change. In our manuscript, we present a comprehensive structural and biochemical study integrating multiomics analysis (combining data from genomics, proteomics, and other biological fields) of transport proteins in a SAR11 bacterium, revealing novel insights into their ecological and planetary-scale impacts.
Our research identifies a novel high-affinity, broad-specificity transporter prevalent across SAR11 ecotypes, which targets C4/C5 dicarboxylates. This discovery resolves a long-standing uncertainty about the carbon sources fueling SAR11’s remarkable abundance and efficiency in nutrient-poor ocean environments. Additionally, we demonstrate that SAR11 transport proteins exhibit unprecedented binding affinities in the picomolar (pM) range, explaining their extraordinary nutrient uptake efficiencies. These molecular adaptations link SAR11’s biochemical mechanisms to their broader ecological role, shedding light on their influence on carbon cycling and nutrient dynamics in marine ecosystems.
Figure 1: An example of a transport protein in a SAR11 bacterium and its distribution in samples of the ocean from across the world. Because of their abundance, these transport proteins are widely distributed throughout the ocean and have a global impact on the uptake of organic matter in the ocean. Credit: Clifton et al. Created with Biorender.com
Our findings have profound implications for marine conservation, policy, and industrial applications. By monitoring nutrient levels and genomic shifts in SAR11 bacteria, particularly changes in their substrate-binding proteins (SBPs), governments can better predict changes in marine organism populations. SAR11’s sensitivity to the nutrient levels in their environment allows researchers to monitor their genomic shifts, particularly in their substrate-binding proteins (SBPs) and nutrient levels, to better predict changes in marine organism populations. This, in turn, can inform plans for the preservation of marine biodiversity. By understanding how SAR11 processes carbon, policymakers can design strategies to enhance natural carbon sequestration processes in marine ecosystems, such as protecting habitats that support SAR11 populations.
The high-affinity transport proteins identified in SAR11 bacteria also offer exciting opportunities for industrial applications. These proteins could be adapted for bioengineering solutions in carbon capture, wastewater treatment, and nutrient recycling, contributing to sustainability across various sectors. For instance, leveraging SAR11’s nutrient uptake mechanisms could enhance bioremediation efforts, improving water quality and reducing pollution in aquatic ecosystems.
SAR11 bacteria are foundational to the health and resilience of marine ecosystems, which are critical components of the Earth’s biosphere. By proactively monitoring genomic adaptations in SAR11, we can track their responses to novel nutrients and pollutants, gaining a deeper understanding of how these changes enable them to colonize new ocean regions. Expanding SAR11 distribution contributes to biosphere integrity and amplifies SAR11’s role as a critical carbon sink, bolstering the ocean’s ability to sequester carbon and mitigate climate change. To safeguard planetary boundaries, particularly biosphere integrity, it is crucial to leverage this knowledge to drive policies and practices that protect and enhance SAR11 populations. By ensuring their optimal function, we can prevent the destabilization of marine ecosystems and maintain the resilience of our oceans in the face of ongoing environmental change.
Figure 2: Paola Laurino’s co-authors on Japan’s winning research paper. From left to right: Ben E Clifton (Lead Author), Colin J Jackson, Gen-Ichiro Uechi, and Uria Alcolombri.