As Einstein said, “Everything is energy and that’s all there is to it.” That’s exactly what scientists uncovered when studying microbes in the human gut.
At a time when governments are trying to discover renewable, clean sources of energy, the solution may be closer than most people think! Following a gut feeling, researchers discovered a microbial species that can generate electricity useful as a source for microbial fuel cells.
On Wednesday, the journal Nature, published findings from a University of California research team that discovered electron-generating bacteria found in the human gut capable of creating electricity. Light et al. showed that the gram-positive bacterium, Listeria monocytogenes, is able to make energy through extracellular electron transfer (EET) in the gut.
Listeria monocytogenes
By By Elizabeth White
EET is a process similar to the electron transfer pathway found in respiration. However, in EET, electrons are transferred to a final acceptor on the exterior of the cell, not the interior. The mechanism of EET is well known for gram-negative microbes, such as Shewanella oneidensis. Residing in an environment rich in minerals, S. oneidensis uses EET to transport electrons to an acceptor outside of the cell, creating accessible energy. By mutating L. monocytogenes, Light et. al identified key proteins in the EET transport pathway, but not the terminal electron acceptor.
Why was this exciting news? L. monocytogenes employs a simpler EET pathway using fewer electron transfer steps than gram-negative bacteria, opening up a new avenue to create potentially more effective microbial fuel cells. However, it’s important to note that the EET pathway isn’t vital for the survival of L. monocytogenes; it is simply more efficient in producing energy when the bacteria is in a nutrient-rich environment. Thus, I think that despite the existence of a simpler EET pathway for gram-positive bacteria, scientists would be wise to not give up on researching the gram-negative EET pathway since the conditions in which gram-positive bacteria use EET may be constrained to certain environments. In addition, researchers have not yet determined which EET pathway, gram-negative or gram-positive, results in the creation of more energy, which is another reason for study into both EET pathways to continue.
Genomic studies by Light et. al, have identified a multitude of gram-positive bacteria with the potential of having EET proteins, indicating that the EET pathway of electrical production is evolutionarily and environmentally diverse, and may be present in currently undiscovered microbes. There may be a wide range of microbes waiting to be investigated to discover answers to my questions and make efficient microbial fuel cells.
Schematic of a microbial fuel cell. Microbes facilitate the oxidation of fuel in order to drive a current. By Bretschger O, Osterstock JB, Pinchak WE, Ishii S, Nelson KE
Discovering the EET mechanism of gram-positive bacterium, L. monocytogenes, has opened up the possibility of creating another form of microbial fuel cells. Unfortunately, I think the replacement of gram-positive bacteria in microbial fuel cells over gram-negative bacteria will continue to be unfeasible until the terminal electron acceptor in the EET pathway is identified along with the factors that affect the expression of the EET pathway in gram-positive bacteria.
-Teresa Howard
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