If you were to gather all the life forms from the ocean surface down to 200 meters deep, you’d notice that SAR11 bacteria, which are not visible to us, would constitute about 20% of the total biomass. These bacteria, known scientifically as Pelagibacterales, have adapted to flourish in marine areas that lack nutrients, playing a key role in nutrient cycles around the world. While their significance is acknowledged, the ways in which they affect our planet’s ecosystem have not been well understood until now. A new article has recently uncovered an essential aspect of these bacteria.
If you were to gather all the life forms from the ocean surface down to 200 meters deep, you’d notice that SAR11 bacteria, which are not visible to us, would constitute about 20% of the total biomass. These bacteria, known scientifically as Pelagibacterales, have adapted to flourish in marine areas that lack nutrients, playing a key role in nutrient cycles around the world. While their significance is acknowledged, the ways in which they affect our planet’s ecosystem have not been well understood.
Recently, a study published in Nature by scientists from the Okinawa Institute of Science and Technology (OIST) has shed light on an important aspect of these bacteria. “We were aware that SAR11 plays a crucial role in essential nutrient cycles like carbon and sulfur exchanges, but we didn’t grasp the complete picture,” stated Dr. Ben Clifton, the paper’s lead author. He added, “Now, by thoroughly mapping out the bacteria’s transport proteins, we have gained a clearer understanding of SAR11’s role in these cycles.” Senior author Professor Paola Laurino acknowledges that large-scale seawater sampling initiatives, such as the Tara Oceans project, provided the genomic data necessary for this breakthrough: “This data has enabled us to connect genomic information to the functions of proteins.”
Understanding the protein connections
Transport proteins are crucial for regulating the intake and output of nutrients within bacterial cells, significantly influencing their interactions with surrounding environments. This is particularly critical for SAR11 bacteria, whose nutrient uptake profoundly affects global nutrient cycles. However, studying these bacteria has been challenging due to their unique growth needs. To tackle this issue, the researchers modified E. coli bacteria to produce SAR11 transport proteins, making it easier to study them in a laboratory setting.
Investigating these genes within the SAR11 metagenome—the shared genetic material across all SAR11 species—required global data facilitated by vast genomic databases. The research team pinpointed genes related to key marine functions, including a specific protein that binds to DMSP, an important compound in the sulfur cycle and climate control. In total, they identified thirteen transport proteins, which manage the transport of DMSP, amino acids, glucose, and taurine, all playing essential roles in the environment.
Understanding global nutrient cycles
“Our experiments revealed distinct characteristics of transport proteins that allow SAR11 bacteria to survive in nutrient-scarce environments. Such insights could not have been gained solely by examining genomic data,” noted Dr. Clifton. However, the research on SAR11 is just beginning. After identifying the proteins that facilitate nutrient transport, the team is now investigating the metabolic pathways to comprehend how these nutrients are processed and utilized by the bacteria. They are also collaborating with the Weizmann Institute of Science to study how SAR11 engages with its surroundings before it takes up nutrients.
This study contributes to an emerging trend linking environmental DNA to protein functionality, opening doors to new insights on how microscopic organisms affect global processes. As Prof. Laurino expresses, “By connecting the broader view of marine diversity with the intricate details of protein biochemistry, we are laying the groundwork for further exploration into how bacterial proteins integrate into global nutrient cycles and the ways these bacteria are influenced by climate change and variations in ocean biodiversity.”
