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Date: 2015-10-07; view: 387.

Scriprt 7. Synthetic biology

Unit 4. Bacteria

Genetically engineered bacteria can be used to attack other bacterial species.

Biofilms are a problem in medicine. When bacteria gang up to form the continuous sheets that bear this name they are far harder to kill with antibiotics than when they just float around as individual cells. Biofilms on devices such as implants are thus difficult to shift, and those growing on the surfaces of human organs are frequently lethal. But Matthew Chang, a biochemical engineer at Nanyang Technological University in Singapore, has worked out a new way to attack them. His weapon is a different type of bacterium, which he has genetically engineered into a finely honed anti-biofilm missile.

The starting point for this new piece of biotechnology is a common gut bacterium called Escherichia coli. Though this species is best known to the wider world for causing food poisoning, most strains of it are benign, and it is one of the work-horses of genetics.

The story began in 2011 when Dr. Chang worked out how to program E. coli to release destructive antimicrobial peptides when they came into contact with another bacterium, Pseudomonas aentginosa. This species, which is common in hospitals, likes to form biofilms and is a frequent cause of sepsis.

To deal with this film-forming propensity, Dr Chang did a second bit of genetic tinkering. He armed his modified E. coli with an enzyme called DNase I. Curiously, a lot of the chemical links holding individual P. aeruginosa bacteria together in a biofilm are made of DNA, a molecule more familiar as the material of genes. DNase 1 attacks DNA, and thus acts to break the film up.

That worked too, but it was still not enough to create a useful medical agent because the modified E. coli did not seek out their targets. So, as he has just reported in Synthetic Biology, Dr Chang has now done a third piece of engineering by changing his bugs' food-detection system to react to the signalling molecules that P. aentginosa release when they are seeking to link up with their neighbours.

Laboratory tests suggest these triply armed E. coli kill P. aernginosa biofilms six times as effectively as the version armed only with antimicrobial peptides and DNase I. This is not yet a deployable medicine, but it is a novel and intriguing approach. And it is one that might easily be used against other biofilm-forming species, by changing which signaling molecules the engineered E. coli are sensitive to. (From The Economist. October 12, 2013)