2023-05-18 11:45:41
In the sea, countless plant-like microorganisms form an invisible floating forest. Drifting, these tiny organisms use sunlight to absorb carbon dioxide (CO2) from the atmosphere. Collectively, these photosynthesizing plankton, or phytoplankton, absorb almost as much CO2 as the world’s terrestrial forests. Cyanobacteria of the genus Prochlorococcus, emerald-colored floating microbes that make up the most abundant phytoplankton in the oceans today, contribute a sizeable fraction of the phytoplankton’s collective capacity to sequester carbon.
But the genus Prochlorococcus did not always inhabit the high seas. Everything points to their evolutionary ancestors residing exclusively near the coast, where nutrients were abundant and where they could form community microbial mats on the seabed, structures that provide greater protection to the microbes integrated into it. So how did the descendants of these coastal dwellers end up becoming today’s powerful deep-sea photosynthesizers?
Giovanna Capovilla’s team, from the Massachusetts Institute of Technology (MIT) in the United States, believes that the key was an improvised vehicle. In a new study, Capovilla and her colleagues suggest that perhaps the ancestors of the genus Prochlorococcus acquired the ability to latch onto chitin bits, broken-down fragments of animals’ exoskeletons. The microbes adhered to the bits of chitin that came across them and thus, carried by the current, these chitin particles served the microorganisms as rafts that transported them out to sea. These chitin rafts probably also provided essential nutrients, which allowed the microbes to survive during the voyage.
The new study suggests that the coastal ancestors of Prochlorococcus colonized the oceans by living on chitin particles that served as rafts to transport them out to sea. In that sense, their adventure was similar to those of human sailors of bygone ages who made perilous voyages into the unknown, reaching lands where they had never been before. (Drawing: Jose-Luis Olivares / MIT. CC BY-NC-ND 3.0)
Thus, generation after generation, microbes were given the opportunity to develop new abilities to adapt to life on the high seas. Over time, they must have evolved to a point where they stopped relying on chitin rafts and could begin to live like the creatures that today float on the high seas without needing to be on shore.
If bacteria of the genus Prochlorococcus and other photosynthetic organisms had not colonized the ocean, we would be looking at a very different planet, as Rogier Braakman of MIT and a co-author of the study warns. “Being able to attach to these rafts of chitin was what allowed them to establish themselves in a whole new and vast part of the planet’s biosphere, and to do so in a way that changed the Earth forever.”
The study is titled “Chitin utilization by marine picocyanobacteria and the evolution of a planktonic lifestyle”. And it has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS). (Source: NCYT de Amazings)
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