Scientists already know that bacteria can create an electric current outside their own cell, known as extracellular electron transport. This has been demonstrated and analyzed in detail in some bacteria that specialize in the metabolism of metal salts. A team of researchers from Lund University and the National University of Ireland Galway has now studied extracellular electron transport in a completely different type of bacterium — the Gram-positive lactic acid bacterium Enterococcus faecalis.
Enterococcus faecalis, an opportunistic human pathogen found in the intestine of mammals. Image credit: Pete Wardell / CDC.
“Lactic acid bacteria, and many other bacteria, are probably capable of performing electrochemistry,” said Lund University’s Professor Lars Hederstedt, senior author of the study.
Professor Hederstedt and colleagues investigated what it takes for electrons from Enterococcus faecalis to be transported to an electrode.
“Our results show that enterococci placed at an electrode can give rise to an electric current created by the metabolism of the cell,” they said.
“The electrons are released when the bacterium breaks down sugar inside its cell.”
“The actual transmission of electrons to the electrode takes place with the help of what are known as quinone molecules inside the cell membrane.”
The results also show that a bacterium in its natural environment, i.e. together with other bacteria and fungi, may have properties that it otherwise lacks.
What happens is that two or more types of microorganisms intertwine their metabolic capacity to benefit the growth of one or both of the organisms.
This form of cooperation between microorganisms, known as synthrophy, may be linked to electron transport between the parties involved.
“Synthrophy provides a metabolic ability that the cells do not have on their own,” Professor Hederstedt said.
“For example, a certain chemical compound can be effectively broken down in nature only when two different types of bacteria occur together, but not individually.”
This phenomenon is of medical interest as enterococci are usually found in the intestine of both humans and animals.
Some species, such as Enterococcus faecalis, give rise to infections that are sometimes difficult to treat with antibiotics. Furthermore, the metabolism of these bacteria is associated with the onset of certain types of colon cancer.
“This research is also of interest in other areas. Detailed knowledge of electron transport between bacteria and electrodes is important in order to design and improve microbial electrochemical systems,” the scientists said.
“These systems have many areas of application apart from drug development, such as fuel cells in bioenergy production, waste water treatment plants and biosensors.”
The study was published recently online in the journal Biochemistry.
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Galina Pankratov et al. 2018. Extracellular Electron Transfer by the Gram-Positive Bacterium Enterococcus faecalis. Biochemistry 57 (30): 4597-4603; doi: 10.1021/acs.biochem.8b00600
