One of the smallest and most powerful organisms on the planet are plant-like bacteria known to marine biologists as Prochlorococcus. These green microbes are less than a micron in diameter and their populations are scattered throughout the upper ocean layers, where a teaspoon of seawater can host millions of microorganisms.
Prochlorococcus It grows through the process of photosynthesis, using sunlight to convert carbon dioxide in the atmosphere into organic carbon molecules. Microbes are responsible for 5% of the world’s photosynthetic activity, and scientists have hypothesized that photosynthesis is a microbial transport strategy to obtain the carbon it needs for growth.
But a new Massachusetts Institute of Technology study in natural microbiology Today he found it Prochlorococcus It relies on other carbon delivery strategies, more than previously thought.
Organisms that use a combination of strategies to conserve carbon are known as mixotrophs. Most marine plankton are plants that feed on mixtures. and while Prochlorococcus Known for occasionally engaging in mixed diets, scientists have speculated that microbes live primarily through a photosynthetic lifestyle.
A new MIT study shows that, in fact, Prochlorococcus Perhaps more combinations than he would have allowed. A microbe can obtain a third of its carbon through a second strategy: consuming the dissolved remains of another dead microbe.
The new estimates could have implications for climate models, as microbes are a major force in capturing and “fixing” carbon in the Earth’s atmosphere and oceans.
“If we want to predict what will happen to carbon fixation in different climates or predict where Prochlorococcus We will live or we will not live in the future, we may not do it well if we lose the processes that account for a third of the population’s carbon supply. ”, Planetary Sciences (EAPS), Department of Civil and Environmental Engineering.
The study co-author is MIT first and postdoctoral author Zhen Wu, along with collaborators from the University of Haifa, the Leibniz Institute for Baltic Sea Research, the Leibniz Institute for Freshwater Ecology and Inland Fisheries and the University of Potsdam.
Plankton persists
Where is it Prochlorococcus First discovered in the Sargasso Sea in 1986 by MIT Professor Sally “Benny” Chisholm and others, these microbes have been observed in all oceans of the world, inhabiting the sunlit upper layers from the surface to about 160 meters. Within this range, light levels vary and microbes have developed numerous ways to represent photosynthetic carbon even in low-light areas.
These organisms have also developed a way to consume organic compounds including glucose and certain amino acids, which can help microbes survive for limited periods of time in dark ocean areas. But living on organic compounds is like eating only junk food, and there is evidence Prochlorococcus This will die after a week in areas where photosynthesis is not an option.
However, researchers including Daniel Scheer of the University of Haifa, co-author of the new study, looked at a healthy population of Prochlorococcus which continues deep into sunlit areas, where light intensity must be very low to support populations. This suggests that microbes must transition to a non-magnetic phototrophic lifestyle to consume other sources of organic carbon.
“It seems at least a little Prochlorococcus They use the organic carbon found in mixed feeds, “Tills said.” That begs the question: how much?
What light cannot explain
In their new research paper, Wu, Sher and their colleagues try to measure the amount of carbon you emit Prochlorococcus It is consumed by processes other than photosynthesis.
The team first looked at measurements made by Scheer’s team, which took samples from the ocean at various depths in the Mediterranean and measured phytoplankton concentrations, including Prochlorococcuscombined with the intensity of light and the accompanying nitrogen concentration, rich essential nutrients are available in the deep layers of the ocean and can be absorbed by plankton to form proteins.
Wu and Follows used this data and similar information from the Pacific Ocean, along with previous research from the Chisholm lab, which determined the rate of photosynthesis that Prochlorococcus This can be done at a certain light intensity.
“We have transformed this light intensity profile into a potential rate of growth: how fast the population is Prochlorococcus It can grow if it gets all of its carbon through photosynthesis and light is the limiting factor, ”Atebus explains.
The team then compared these calculated rates to growth rates previously observed in the Pacific Ocean by several other research groups.
“These data suggest that, below a certain depth, there is a lot of growth that cannot be explained by photosynthesis,” Falls said. “Some other processes have to work to make up for the difference in carbon supply.”
The researchers concluded that in the deepest and darkest areas of the ocean, Prochlorococcus The population is able to survive and thrive by switching to a mixed diet, including consuming organic carbon from the tailings. In particular, microbes can perform osmosis, a process in which an organism passively absorbs organic carbon molecules by osmosis.
Judging by how quickly the microbes grew under a sunlit area, the team calculated that Prochlorococcus He receives a third of his carbohydrate diet through a mixed feeding strategy.
“It’s like moving from a specialist to a generalist lifestyle,” says Foles. “If I only eat pizza, if I am 20 miles from a pizzeria I am in trouble, while if I also eat a hamburger I can go to the nearest McDonald’s. People think Prochlorococcus As specialists, they do one thing (photosynthesis) very well. But it turns out they may have a more general lifestyle than we previously thought. “
Chisholm, who has both Literally The book is written figuratively ProchlorococcusThe group’s findings say it “broadens the range of conditions under which populations can not only survive but thrive. This study is changing the way we think about roles. Prochlorococcus in the microbial food web.
This research was supported in part by the Israel Science Foundation, the US National Science Foundation, and the Simmons Foundation.
