Researchers discover metabolic processes of microbes

By SHIRLEY MARINO | April 11, 2019

A research team at Washington University in St. Louis has been working on understanding the metabolic processes of a strain of Rhodopseudomonas palustris. This microbe is commonly found in swine waste lagoons, earthworm droppings and pond water. 

The team led by Arpita Bose, an assistant professor of biology, and Michael Guzman, a PhD candidate, previously discovered the process by which R. palustris consumes electrons from conductive materials such as rust, through a process known as extracellular electron uptake.

“R. palustris strains can be found in wild and exotic places like a rusty bridge in Woods Hole, Massachusetts where TIE-1 was isolated from,” Bose said in a press release. “Really, you can find these organisms everywhere. This suggests that extracellular electron uptake might be very common.”

The team’s latest research, built on their previous accomplishments, discovered the process by which R.palustris deposits the electrons it consumes from electricity. Bose elaborated on the importance of this discovery.

“It clearly shows for the first time how this activity — the ability for the organism to eat electricity — is connected to carbon dioxide fixation.”

The researchers observed the deposit of electrons on membrane proteins of the organism that play important roles during the process of photosynthesis. They also discovered its link to carbon dioxide through the inhibition of the microbe’s ability to fix carbon dioxide; this almost completely limited its ability to consume electrons.

“It really wants to fix carbon dioxide using this system,” Bose said. “If you take it away — this innate ability — it just doesn’t want to take up electrons at all.”

Bose further explained this process by assimilating it to that of a rechargeable battery. She explained that R.palustris is able to do this by reducing carbon dioxide in order to discharge its redox pool and then taking electrons in again.

Bose’s lab is now using this information to attempt to create bioplastics and biofuels. They believe this will open up new pathways through which to achieve interaction with electrodes in the environment. 

“For a long time, people have known that microbes can interact with analogues of electrodes in the environment — that is, minerals that are also charged,” Guzman said. “But no one really appreciated how this process could also be done by photoautotrophs, such as these types of organisms that fix their own carbon and use light to make energy. This research fills a poorly understood gap in the field.”

They are not the only ones interested in this discovery as the Department of Energy and the Department of Defense have showed interest in the potential to use this for sustainable energy storage efforts.

Nonetheless, there are still challenges to overcome. One such challenge is the fact that R.palustris is an anaerobe. This means the microbe thrives in environments which lack oxygen. However, this organism has the versatility that others lack, making overcoming this challenge somewhat less difficult.

Regardless of this challenge, Bose hopes that their lab’s discovery will have a positive impact on future research on sustainable energy.

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