Unique microbial photosynthesis discovered

Researchers at Washington State University have discovered a new type of cooperative photosynthesis that could be used in engineering microbial communities for waste treatment and bioenergy production.

Prosthecochloris aestaurii, a green-tinged, plant-like microbe, comes from the extreme environment of Hot Lake, a high salinity lake in northern Okanogan County near Oroville, Wash. Discovered and identified a few years ago by researchers at the U.S. Department of Energy's Pacific Northwest National Laboratory and Southern Illinois University, the bacterium is able to photosynthesize, using sunlight along with elemental sulfur or hydrogen sulfide to grow.

The researchers noticed that P. aestuarii tended to gather around a carbon electrode, an electricity conductor that they were operating in Hot Lake. The researchers 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 researchers 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.

For further details see:

Phuc T. Ha, Stephen R. Lindemann, Liang Shi, Alice C. Dohnalkova, James K. Fredrickson, Michael T. Madigan, Haluk Beyenal. Syntrophic anaerobic photosynthesis via direct interspecies electron transfer. Nature Communications, 2017; 8: 13924 DOI:10.1038/NCOMMS13924

Posted by Dr. Tim Sandle