Researchers Engineer Bacteria To Produce Plastics

An anonymous reader quotes a report from Ars Technica: [A] team of Korean researchers [describe] how they've engineered a bacterial strain that can make a useful polymer starting with nothing but glucose as fuel. The system they developed is based on an enzyme that the bacteria use when they're facing unusual nutritional conditions, and it can be tweaked to make a wide range of polymers. The researchers focused on the system bacterial cells use for producing polyhydroxyalkanoates (PHAs). These chemicals are formed when the bacterial cells continue to have a good supply of carbon sources and energy, but they lack some other key nutrients needed to grow and divide. Under these circumstances, the cell will link together small molecules that contain a handful of carbons, forming a much larger polymer. When nutritional conditions improve, the cell can simply break down the polymer and use the individual molecules it contained.

The striking thing about this system is that it's not especially picky about the identity of the molecules it links into the polymer. So far, over 150 different small molecules have been found incorporated into PHAs. It appears that the enzyme that makes the polymer, PHA synthase, only cares about two things: whether the molecule can form an ester bond (PHAs are polyesters), and whether it can be linked to a molecule that's commonly used as an intermediate in the cell's biochemistry, Coenzyme A. Normally, PHA synthase forms links between molecules that run through an oxygen atom. But it's also possible to form a related chemical link that instead runs through a nitrogen atom, like those found on amino acids. There were no known enzymes, however, that catalyze these reactions. So, the researchers decided to test whether any existing enzymes could be induced to do something they don't normally do.

Overall, the system they develop is remarkably flexible, able to incorporate a huge range of chemicals into a polymer. This should allow them to tune the resulting plastic across a wide range of properties. And, considering the bonds were formed via enzyme, the resulting polymer will almost certainly be biodegradable. There are, however, some negatives. The process doesn't allow complete control over what gets incorporated into the polymer. You can bias it toward a specific mix of amino acids or other chemicals, but you can't entirely stop the enzyme from incorporating random chemicals from the cell's metabolism into the polymer at some level. There's also the issue of purifying the polymer from all the rest of the cell components before incorporating it into manufacturing. Production is also relatively slow compared to large-scale industrial production. The findings have been published in the journal Nature Chemical Biology.

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