How our green technology may rest on bacterial skills

By Colin Barras You may think that it is only human ingenuity that can lead us to a greener, cleaner future. But if we are to develop technologies that significantly reduce our impact on the planet, the humble bacteria may deserve as much recognition as any human engineers. With many of the most advanced sustainable technologies still a long way from being viable on a large scale it is still unclear which approaches will succeed. But in areas from biofuels to fuel cells technologies based on the smarts of bacteria have the potential to win out. The huge diversity of the bacterial portion of the biosphere is providing researchers with all kinds of tools and techniques. Experiments with bacteria have provided some of the clearest views yet of evolution in action. That is good new for engineers as much as it is for evolutionists, because many bacteria have already evolved to live off the pollution created by humans. In 2008, Kevin O’Connor‘s team at University College Dublin, Ireland, was trying to find a way to convert cheap PET plastic bottles into something more valuable, because despite their ubiquity these bottles are rarely worth recycling commercially. Cost-effective industrial processes that could “upcycle” PET were hard to find and so the team decided to try a bacterial approach. Although none were known that could perform a useful conversion, the researchers trusted that natural selection would have found a way. They went on the hunt for bacteria that had evolved to digest plastic bottles. Sure enough, the team found strains of Pseudomonas soil bacteria near a PET bottle processing plant that feed on PET, and convert it into a more valuable polymer, PHA. Each bacterium gorges on PET to the point that it becomes 24% PHA plastic by volume. Further selection in the lab should produce an even more efficient bottle-eating bug. As well as eating our waste, bacteria can provide our fuel. More than a decade ago Eugene Premuzic at Brookhaven National Laboratory in Upton, New York, was prospecting for and found bacteria able to clean the sulphur and nitrogen from crude oil. He demonstrated that bacteria could provide a way to meet tightening restrictions on fuel quality in the US and EU designed to reduce smog and acid rain. Bacteria are also helping with the development of the cleaner successors to oil. Genetically engineered bacteria can ferment cellulose from plant waste to produce ethanol, Lee Lynd of Dartmouth College in Hanover, New Hampshire, has shown. It is also possible to pick the pockets of bacteria for their chemical skills. Last year a team from Michigan State University in East Lansing used genes from cow stomach bacteria to create a corn variety that digests its own cellulose after harvesting, facilitating the production of ethanol. Earlier this year a UK team showed that bacteria could even be used to produce hydrogen from water. This could potentially solving the key problem of the expense of generating the gas, which is holding back dreams of a hydrogen economy. A decade ago, an enzyme that produces hydrogen from hydrogen ions in the environment was isolated from a bacterium that extracts energy from sulphur compounds. Fraser Armstrong and Erwin Reisner at the University of Oxford attached it to light-activated nanoparticles to create a light-powered, hydrogen-producing dust. In the right chemical environment the dust absorbs light energy which allows the enzyme to convert hydrogen ions from water molecules into hydrogen gas. Although much work is still needed to improve the efficiency, results are “promising” according to Armstrong. Bacteria may also help address another weakness of the hydrogen economy – the fact that fuel cells that make electricity from the gas rely on expensive platinum catalysts. The role of the precious metal could be performed by bacterial enzymes that are as active as platinum catalysts but more selective for hydrogen, Kylie Vincent at the University of Oxford told New Scientist in 2006. They could make fuel cells more compact into the bargain. “With platinum electrodes, a special membrane has to be used to keep the two fuels separate, or you would get no power at all. If you have very specific catalysts like enzymes, you don’t need a membrane.” But the enzymes are not without their own faults and at the moment they cost more than platinum. However, the price of enzyme-catalysed cells is more likely to drop than that of a precious metal subject to growing demand. Hydrogen fuel cells can power transport like cars, trucks or boats, but less-power-hungry machines could use fuel cells that rely on bacteria alone. Microbial fuel cells that harvest electrons from colonies of living bacteria were first developed in 2004, in the form of a cell that produces power from sewage. Since then they have been used to power seafloor sensors listening for turtles, and versions using bacteria that grow electrical connections among themselves have also been developed to boost a fuel cell’s power. Bioinspired technology drawing on “engineering” found in the natural world is increasingly common. But while octopus robots might make better headlines, lowly bacteria are already contributing to an unrivalled range and depth of technologies. More on these topics:
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