An international team of biologists led by Washington State University Professor Haluk Beyenal has discovered a new type of cooperative photosynthesis that could be used in microbial communities for waste treatment and energy production.

Photosynthetic bacteria account for nearly half of the world’s food production and carbon-based organic material.

Prof. Beyenal and his colleagues from the United States and China report today on the unique metabolic process seen for the first time in a pair of bacteria (Prosthecochloris aestuarii and Geobacter sulfurreducens) in the journal Nature Communications.

P. aestuarii, a green sulfur bacterium, was first isolated in 1970 by biologist Dr. Vladimir Gorlenko from hydrogen sulfide containing mud of the brackish lagoons Sasyk-Sivash and Sivash in Crimea, Ukraine.

Several years ago this microbe was found in samples collected from Hot Lake, a high salinity lake in northern Okanogan County near Oroville, Washington.

P. aestuarii is able to photosynthesize, using sunlight along with elemental sulfur or hydrogen sulfide to grow.

Prof. Beyenal and co-authors noticed that P. aestuarii tended to gather around a carbon electrode, an electricity conductor that they were operating in Hot Lake.

They isolated and grew P. aestuarii and determined that, similar to the way half of a battery works, the bacterium is able to grab electrons from a solid electrode and use them for photosynthesis.

The pink-colored Geobacter sulfurreducens, meanwhile, is known for its ability to convert waste organic matter to electricity in microbial fuel cells. The bacterium is also used in environmental cleanup.

G. sulfurreducens — like animals and humans – can’t photosynthesize. It consumes organic compounds, such as acetate, and ‘breathes’ out carbon dioxide.

The bacterium is known for its ability to donate electrons to a solid electrode. As it consumes acetate, it generates electrons, which can be collected as electricity.

The authors surmised that P. aestuarii and G. sulfurreducens might be able to help each other grow and put them together in the lab.

They found that P. aestuarii could accept electrons generated from G. sulfurreducens and use them in a new type of anaerobic photosynthesis never before seen.

Similar to how a battery or fuel cell works, the bacteria transfer electrons. They feed off each other to grow under conditions in which neither could grow independently.

From an ecological perspective, this new form of metabolism may play an important role in carbon cycling in oxygen free zones of poorly mixed freshwater lakes.

It may also present new possibilities for engineering microbial communities for waste treatment and bioenergy production.

“We think this could be a common bio-electrochemical process in nature,” Prof. Beyenal said.

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Phuc T. Ha et al. 2017. Syntrophic anaerobic photosynthesis via direct interspecies electron transfer. Nature Communications 8, article number: 13924; doi: 10.1038/ncomms13924