Electron transport between species discovered in deep-sea research

By Marilyn Malara  |  Sept. 19, 2015 at 2:37 PM
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PASADENA, Calif., Sept. 19 (UPI) -- Researchers at the California Institute of Technology have discovered two microbial species capable of sharing the energy needed to consume methane through electron transfer without direct contact.

Researchers say it is the first time interspecies electron transport, or the external passing of electrons from one type of cell to another, has been discovered among microorganisms in a natural setting.

The research, detailed in the latest issue of Nature, was led by Professor of Geobiology Victoria Orphan, whose lab has studied the relationship between these two species in deep-sea methane seeps for the last two decades.

A species of bacteria and a species of archaea work together in syntrophy to consume large quantities of methane, which discharges from the ocean floor.

Methane, or CH4, is a greenhouse gas and -- when released into ocean water and air in large quantities -- a primary contributor to climate change.

In order to complete their research on location at the bottom of the ocean, scientists used research submersible Alvin to collect samples of the microbes from seep sediments to be returned to the lab for testing. The team incorporated fluorescent DNA stains to note the two specific microbes and study their proximity in various bacterial communities.

To find whether the microorganisms' proximity had an effect on their ability to work together to absorb methane, researchers used a "tracer" to measure activity. Then, they measured the clusters of microbes using a specialized instrument called a nanoscale secondary ion mass spectrometry (nanoSIMS).

The results surprised researchers, because cell locations did not influence their consumption of methane.

"Since this is a syntrophic relationship, we would have thought the cells at the interface -- where the bacteria are directly contacting the archaea -- would be more active, but we don't really see an obvious trend," Orphan said in a press release. "What is really notable is that there are cells that are many cell lengths away from their nearest partner that are still active."

After further research incorporating the work of co-authors Shawn McGlynn and Chris Kempes, results suggested electrons were naturally capable of traveling longer distances between cells than previously thought.

"Chris came up with a generalized model for the methane-oxidizing syntrophy based on direct electron transfer, and these models results were a better match to our empirical data," said Orphan. "This pointed to the possibility that these archaea were directly transferring electrons derived from methan to the outside of the cell, and those electrons were being passed to the bacteria directly."

"It's really one of the first examples of direct interspecies electron transfer occurring between uncultured microorganisms in the environment. Our hunch is that this is going to be more common than is currently recognized," she said.

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