- What we find the coolest from the work is that we find some of these Chlorobia strains to be abundant in different lakes and ponds in different continents. These bacteria live in the areas of the lakes that have no oxygen, below the first meters of oxygenated water. So, thinking about how ubiquitous strains of these bacteria can be in these different isolated environments is interesting. Does it disperse and migrate, how does it tolerate oxygen then? Or were they rather everywhere before Earth became oxygenated billions of years ago? Says Sarahi Garcia, assistant professor at Department of Ecology Environment and Plant Sciences (DEEP) at Stockholm University.

The photo shows lake Alinen Mustajarvi and the waterproof notebook where Sarahi Garcia took the temperature and oxygen profile notes, in a little boat used for sampling. Photo: Sarahi Garcia.

These green sulfur bacteria are real survivors and have evolved to endure tough conditions. They harvest light at extremely low intensities, in water depths were the least amount of light is available. It is the metabolic capacity and versatility they possess that enabled them to colonize dimly lit and oxygen-free lakes. They also have the capability to contribute to carbon budgets of lakes and at the same time contributing to sulfur, iron, hydrogen, and/or nitrogen cycling. This means they contribute to keep life in balance in the world.

- We speculate that they fixate carbon and exudate it to feed heterotopic bacteria as well, adds Sarahi Garcia.

The study also revealed which strains are the most abundant in nature, and the fact that they are different from cultivated Chlorobia, based on genetic divergence and presence of some genes of unknown function.

- There are a lot of unknowns and we still need to do more research to understand their physiology and role in biogeochemical cycles, says Sarahi Garcia.

Discover more about the research findings in the scientific publication: Freshwater Chlorobia Exhibit Metabolic Specialization among Cosmopolitan and Endemic Populations