Microbial Communities Thrive by Transferring Electrons

The Science

Photosynthetic bacteria are major primary producers on Earth, using sunlight to convert inorganic compounds in the environment into more complex organic compounds that fuel all living systems on the planet. A team of researchers recently discovered a new microbial metabolic process called syntrophic anaerobic photosynthesis, which could represent an important, widespread form of carbon metabolism in oxygen-depleted zones of poorly mixed freshwater lakes.

The Impact

The discovery of syntrophic anaerobic photosynthesis reveals new possibilities for bioengineering microbial communities for use in waste treatment and bioenergy production.

Summary

Almost all life on Earth relies directly or indirectly on primary production—the conversion of inorganic compounds in the environment into organic compounds that store chemical energy and fuel the activity of organisms. Nearly half of global primary productivity occurs through photosynthetic carbon dioxide (CO₂) fixation by sulfur bacteria and cyanobacteria. In oxygen-depleted environments, photosynthetic bacteria use inorganic compounds such as water, hydrogen gas, and hydrogen sulfide to provide electrons needed to convert CO₂ into organic compounds. These organic compounds also make their way into the food web, where they support the growth of heterotrophs—organisms that cannot manufacture their own food. A recent study revealed a new metabolic process, called syntrophic anaerobic photosynthesis, in which photosynthetic and heterotrophic bacteria cooperate to support one another’s growth in oxygen-depleted environments. Researchers from Washington State University, Pacific Northwest National Laboratory (PNNL), China University of Geoscience, and Southern Illinois University made this discovery using the Quanta scanning electron microscope and the FEI Tecnai T-12 cryo-transmission electron microscope at the Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy Office of Science user facility. Their analysis revealed that a heterotrophic bacterial species, Geobacter sulfurreducens, directly transfers electrons to a photosynthetic bacterial species, Prosthecochloris aestuarii, which uses electrons to fix CO₂ into cell material. At the same time, donating electrons allows G. sulfurreducens to support its own metabolic needs by converting acetate into CO₂ and water. This potentially widespread, symbiotic form of metabolism, which links anaerobic photosynthesis directly to anaerobic respiration, could be harnessed to develop new strategies for waste treatment and bioenergy production.

Principal Investigator(s)

Haluk Beyenal
Washington State University
[email protected]

Alice Dohnalkova
EMSL
[email protected]

Funding

This work was supported by the U.S. Department of Energy (DOE), Office of Biological and Environmental Research, Genomic Science program and is a contribution of the PNNL Foundational Scientific Focus Area (FSFA). A portion of this work was conducted at EMSL, a DOE Office of Science user facility.

References

P. T. Ha, S. R. Lindemann, L. Shi, A. C. Dohnalkova, J. K. Fredrickson, M. T. Madigan, and H. Beyenal, “Syntrophic anaerobic photosynthesis via direct interspecies electron transfer.” Nature Communications 8 (2017). DOI:10.1038/ncomms13924.