image: Niu Y. et al. Fig. 1: Scheme of the synthetic process of the gene- and nano-engineered E. coli cell
Building on similar past work, researchers created a new bacterial strain that gobbles up sewage even faster and generates a more powerful electric current.
A genetically- and nano-engineered form of a common bacterium can gobble up carbon-containing compounds like those found in sewage and generate impressive amounts of electricity in the process, according to a new study.
The approach is the latest in a series of efforts to harness the power of microbes to marry the goals of generating renewable electricity and sustainably cleaning up wastewater.
“Microbial fuel cells (MFCs) are an emerging technology that could degrade contaminants and produce electricity simultaneously with the assistance of microorganisms,” researchers from Henan Normal University in Xinxiang, China write in the journal Nature Sustainability. “However, key challenges remain for their practical implementation:” namely, existing ways to catalyze this process tend to be expensive or sluggish.
Enter Escherichia coli, one of the world’s most well-studied species of bacteria, which normally lives in the guts of humans and other animals. In the new study, the researchers first used genetic engineering to supercharge E. coli’s production of cytochrome c. Cytochrome c is a protein found in the cell membrane that is involved in cellular energy balance, catalyzing oxidation and reduction reactions – reactions that in turn are the key to electricity generation in microbial fuel cells. So that takes care of the sluggish part.
Then, the researchers used nanoengineering techniques to coat the bacteria with particles of polypyrrole, an electricity conducting polymer, like rolling a microscopic fritter in even tinier breadcrumbs.
Finally, they constructed battery-like fuel cells using commercially available platinum carbon for the negative electrode and the souped-up E. coli at the positive electrode. (The polypyrrole “breadcrumbs” help the bacteria stick to the electrode, enhancing the transfer of electricity in the fuel cell.) The power output is “comparable to those of high-performance biofuel cells reported to date,” the researchers report.
The genetically- and nano-engineered E. coli gobble up carbon-containing organic compounds in sewage faster than other types of bacteria that have been used in microbial fuel cell experiments in the past. They also create a more powerful electric current than either standard E. coli or engineered E. coli without the nano-coating.
The nanocoating has no effect on the viability or reproduction of the bacteria, so E. coli can keep on generating electricity as long as their food source holds out. In the current study, “the microbial catalysts have an outstanding lifetime of more than 80 [hours] with little current attenuation,” the researchers report.
The bacteria had consumed all the nutrients in their medium by 100 hours into the experiment, but “the power generation performance rapidly recovered to the original value” as soon as the food source was topped up again. In the real world, of course, the supply of nutrient-laden wastewater is more or less endlessly renewable.
“This study not only provides a new direction towards the design of sustainable microbial catalysts but also suggests a feasible technology for wastewater treatment and energy production,” the researchers write.
Source: Niu Y. et al. “Sustainable power generation from sewage with engineered microorganisms as electrocatalysts.” Nature Sustainability 2024
Sustainable power generation from sewage with engineered microorganisms as electrocatalysts
Nature Sustainability (2024)
Microbial fuel cells (MFCs) are an emerging technology that could degrade contaminants and produce electricity simultaneously with the assistance of microorganisms. However, key challenges remain for their practical implementation, including the lack of efficient and cost-effective catalysts at the cathode. Here we take advantage of a sustainable cathode biocatalyst to construct a high-performance MFC that allows fast treatment of sewage and competitive power output. Our catalyst design is built on the Escherichia coli cell, which, upon coupled gene and nano engineering, shows excellent oxygen reduction reaction activity (current density of 3.32 mA cm−2 and onset potential of 0.63 V versus the reversible hydrogen electrode) and accelerates the depollution of organic matter in sewage sludge. Remarkably, glucose consumption reaches a level as high as 19.4 mM in 100 h with a maximum power density of 334 μW cm−2. Combined characterizations and theoretical calculations reveal that the enabling chemistry is the unique configuration of the iron centre of intermembranous cytochrome c in cells. Our study not only opens a new path for the rational design of electrocatalysts but also suggests the feasibility of addressing environmental issues using MFCs.
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