Friday 18 March 2016

Will eat your pet for free

The North Pacific Gyre [prev] is one of humankind's largest, ugliest and most recent creations. Eeee when I were a lad only 50 years ago chemists knew all about PET: it was invented/patented in 1941.  PET = polyethylene terephthalate. It was one of the polymers that launched the tawdry, cheap-and-cheerful Age of Plastic. Plastic brought huge utility to the Third World where it appeared in a rainbow of jugs and basins, buckets and bowls that could store food and fetch water and be easily kept clean. PET is a chemist's dream; they can make the stuff in two different condensation reactions
one expelling methanol and one expelling water from the input monomers. It is a thermoplastic: it liquefies with increased temperature. And temperature changes up and down have crucial effects on the properties of the final polymer.  Rigid, strong, infinitely durable soda bottles and cuddly warm fleece blankets are the same stuff chemically. The difference is in the temperature at which the polymerisation takes place and more importantly the speed with which the product is cooled down.
The PET bottle, formed when the plastic is rapidly cooled to an amorphous clear, rigid solid, was patented by Nicholas Wyeth in 1973. Wyeth was an engineer employed by DuPont and thought up a disposable plastic bottle that would replace glass for Coke Pepsi DrPepper sales.  After rejecting various forms of polypropylene as unable to withstand the pressure of carbonated liquids, he experimented with PET until he had developed a product that has been used in its billions. He retired a few years later so PET bottles was his last hurrah.  Wyeth?  Any relation to Andrew Wyeth the painter? Yes = brother. So I'd rather show a picture of The Brother's most iconic painting Christina's World than a billion Coke bottles.  Their father N.C. Wyeth was also an illustrator and artist not without talent.

The strength of PET is what makes it a) useful and b) indestructible.  The cost of each item is so low that manufacturers and users can afford to throw it away when empty. That's part of the reason why you pay €1 for a bottle of water (that costs 0.1c) and some mystical ingredients and a lot of sugar or aspartame to make it palatable. Whatever, a fraction of the bottles finish up in water-course and get washed out to sea where they bob about forever. If the bottle gets crushed by an idiot shark, the fragments continue to float - another advantage of PET is its low density, light weight and minimal shipping costs. Boyan Slat has floated a mechanical solution to sweeping up the fragments of our wastefulness. If you missed that boat, you can get aboard and contribute to SeaVax on Avaaz.

Another potentially useful player in the clean up process hit the blogosphere earlier in the month. Ideonella sakaiensis is a betaproteobacteria which reverses the condensation reaction that forms PET by using a pair of enzymes to ease apart the so-hard-to-break chemical bonds. We've met 'betas' before in the not-very-nice Neisseria "clap" gonorrhoeae and  Neisseria "head-banger" meningitidisI. sakaiensis was isolated by a team of Japanese microbiologists just outside a plastic recycling facility and made a huge international splash:
Une bactérie mangeuse de plastique!
бактерий, которые бы смогли «поедать» ПЭТ!
una bacteria capaz de comerse un plástico muy común!
Plastik-fressende Bakterien!
I. sakaiensis was the most successful bacteria at breaking down a thin film of PET working at 30oC. That is a regime utterly different from the cold wet salty environment of the North Pacific Gyre but knowing that the capable enzymes exist is a huge first step in scaling up a solution to the plastic dump problem. The problem with mechanical solutions to sweeping-up plastic is that the particles are so small that plankton [on which the entire oceanic ecosystem depends] become by-catch. For a bacterial predator the small size is, if anything, an advantage because it exposes more surface area to attack.  As you do, because you can nowadays, the Japanese team sequenced the genome of their star PET degrader and identified two orphan genes ISF6_4831 and ISF6_0224 which code for the enzymes that do the work. 4831 and 0224 are genomic locations, so the genes are a long way from each other but also apparently a long way from any similar genes in other betaproteobacteria - they appear to have come from nowhere.  Oh oh, I feel an undergraduate research project coming on to see where I. sakaiensis acquired it's ability to exploit a novel food-source.

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