More Proof of Outer Membrane Cytochrome Role in Electron Transfer

Apr 19, 2010
Photomicrographs of Shewanella oneidensis MR-1 wild-type cells (blue) cultured aerobically on Fe(III)-citrate plates. Epifluorescence micrographs demonstrate specific labeling of the cell surface with antibodies against (A) MtrC or (B) OmcA (green).

(PhysOrg.com) -- Another step toward improving understanding of electron exchange between microbes and minerals has been documented in the January 2010 issue of Geobiology. Bacteria such as the metal-reducing Shewanella oneidensis MR-1 exchange electrons with minerals in soil, sediment, and subsurface material. These interactions impact processes such as the reduction and stabilization of contaminants in groundwater.

Researchers from Pacific Northwest National Laboratory, the University of Wisconsin, Milwaukee, and the University of Guelph recently discovered that outer-membrane cytochromes MtrC and OmcA of S oneidensis MR-1 are key to reducing and transforming ferrihydrite, a widespread mineral that controls the mobility of metals in the environment. Their work is part of ongoing research to understand this most basic earth-life interaction that is fundamental to environmental contaminant migration, water quality, and and trace metal availability.

Microbe-mineral interactions are central to biogeochemistry and the fundamental element cycling processes that shape earth's geology. One of the grand challenges of geomicrobiology is to understand the processes driving the reductive transformations at the microbe-mineral interface. This has proven to be exceptionally difficult, as reactions at the interface are most likely regulated by biological adhesion mechanisms and chemical reactions. Multiple mechanisms have been proposed for extracellular electron transfer to solids by bacteria such as Shewanella, but the pathways are poorly understood, and few quantitative relationships have been established.

Using a suite of microscopic, spectroscopic, and biochemical techniques at the Department of Energy's EMSL, the scientists analyzed purified recombinant proteins and investigated genetic mutants unable to produce the outer-membrane cytochromes. They demonstrated that both cytochromes undergo rapid electron exchange with ferrihydrite in vitro, with MtrC displaying faster transfer rates than OmcA.

Immunomicroscopy with cytochrome-specific antibodies revealed that MtrC co-localizes with iron solids on the cell surface, while OmcA is distributed more diffusely over the cell surface. In the absence of both MtrC and OmcA, the cells' ability to reduce ferrihydrite was significantly hindered, and no mineral transformation products were detected. Collectively, these results highlight the importance of the outer-membrane cytochromes in reducing and transforming ferrihydrite and support a role for direct electron transfer from the outer-membrane cytochromes at the to the mineral.

Explore further: Researchers successfully clone adult human stem cells

More information: Reardon CL, A Dohnalkova, P Nachimuthu, DW Kennedy, D Saffarini, BW Arey, L Shi, Z Wang, DA Moore, JS McLean, DM Moyles, MJ Marshall, JM Zachara, JK Fredrickson, and AS Beliaev. 2010. "Role of Outer-Membrane Cytochromes MtrC and OmcA in the Biomineralization of Ferrihydrite by Shewanella oneidensis MR-1." Geobiology 8(1):56-68. doi:10.1111/j.1472-4669.2009.00226.x

Related Stories

Progress Toward a Biological Fuel Cell?

Dec 30, 2008

(PhysOrg.com) -- Biological fuel cells use enzymes or whole microorganisms as biocatalysts for the direct conversion of chemical energy to electrical energy. One type of microbial fuel cell uses anodes (positive electrodes) ...

The Efficacy of Bacteria

Jan 12, 2010

(PhysOrg.com) -- Marching to their own drummer. That's what bacteria from different environments do when turning toxic, mobile selenium into a less dangerous, non-mobile form, according to a study led by Dr. ...

Recommended for you

Researchers successfully clone adult human stem cells

Apr 18, 2014

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Researchers develop new model of cellular movement

Apr 18, 2014

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

For resetting circadian rhythms, neural cooperation is key

Apr 17, 2014

Fruit flies are pretty predictable when it comes to scheduling their days, with peaks of activity at dawn and dusk and rest times in between. Now, researchers reporting in the Cell Press journal Cell Reports on April 17th h ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

brant
not rated yet Apr 19, 2010
Isnt electron transfer the same as current flow?

It seems as though everything is electric.

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.