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Plastic from bacteria – now in algae!

The views expressed are those of the author and are not necessarily those of Scientific American.

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Bacteria are capable of producing a wide range of exciting and important materials, and one of the most unusual is probably bacterial plastics. Used by the bacteria as an energy store, these bioplastics are of particular interest as not only could they be a non-oil-based form of plastic but they are also biodegradable. At the moment, they are still far more expensive than conventional plastics, but researchers are working on finding ways to make bacterial bioplastic a more viable alternative to synthetic plastics.

Commercial plastics are formed from long repeating carbon-based chains formed from simple chemical units. The plastic polyethylene for example is formed of many repeating ethylene units:

In polytetrafluoroethylene all the hydrogens are replaced by fluorines.

These long chain polymers are usually derived from oil, because oil contains a large number of long hydrocarbons. However long carbon molecules are also  good for energy storage, and are usually seen in nature in the form of starch or cellulose. Some bacteria, rather than using starch, instead use a long-chain carbon storage molecule that is very similar to plastic. These are stored inside the bacteria as small granules, surrounded by the enzymes that create them.

A granule of stored bioplastic within a bacteria, surrounded by the bacterial membrane. Image from reference 2.

While bacteria are great at making exciting molecules they are not always the best candidates for industrial scale production. Bacterial bioplastics are a good idea but for large-scale production the genes that produce these plastics would have to be moved into either more industrial strains of bacteria, yeast, or algae. Algae are an interesting choice, because not only do they have to capacity to produce a large amount of the plastic product, they also live off sunlight, and can be produced and harvested in large quantities. As oil is currently far cheaper than any natural plastics alternative, any move to decrease the  price of bioplastics would increase it’s attractiveness for both the public and  research investors.

Reference 1, below, details experimental work to do just that; transfer the genes that bacteria use for making plastic into an algae host. Large scale  gene-moving doesn’t always work, but in this case the algae managed to produce plastics in up to 10% of the algal dry weight after only ten days. Not only could these plastics be extracted successfully, they could also be seen forming as granules within the algae, which must have been incredibly exciting for the researchers to watch!

Phaeodactylum tricornutum - the algae used in this experiment. Image from wikimedia commons credit below.

The best thing about this experiment is that this represents what I would see as quite a rough transfer of DNA. The genes were moved over wholescale, in their original bacterial form. I suspect an increase in product could be obtained by adapting the DNA for the algae. While DNA is a universal molecule, different organisms prefer slightly different code, so optimisation of the DNA, and even adjustment of the flux of upstream precursor pathways, could go a long way to increasing the yield of bioplastic in algae.

Picture credit: Image courtesy of Alessandra de Martino and Chris Bowler, Stazione Zoologica and Ecole Normale Supérieure.

Ref 1 =Hempel F, Bozarth AS, Lindenkamp N, Klingl A, Zauner S, Linne U, Steinbuchel A, & Maier UG (2011). Microalgae as bioreactors for bioplastic production. Microbial cell factories, 10 (1) PMID: 22004563

Ref 2 = Rehm BH (2003). Polyester synthases: natural catalysts for plastics. The Biochemical journal, 376 (Pt 1), 15-33 PMID: 12954080

S.E. Gould About the Author: A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. Follow on Twitter @labratting.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. duggerdm 10:38 am 10/26/2011

    As a biochemist the author should be aware that algae requires far more than “sunshine” to produce anything. She should also be aware of several mass balance analysis studies (U of K’s in particular – ref. below) that show that algae and other proposed biofuel plants have a negative mass balance because at the very large commercial scale required, the are dependent on NPK fertilizers – like 95% (direct and indirect) of global food production.

    She should also be aware of the confluence of the peak petroleum, peak phosphate impacts on our food production capability – as the seven billionth person is born on the planet this week. Recent phosphate reserve estimates show that we could could deplete the remain phosphate deposits in as little as 50 years – and that doesn’t count new NPK (phosphate demands from India, China, Africa and Indonesia and other parts of the developing world) nor the two to three fold demand increase in NPK that a major biofuel industry might create.

    Given the relatively short window of opportunity before our food production capabilities are seriously and irreparably diminished, our species has to solve it’s it’s interlinked and simultaneous energy, food production, sustainable population and climate change problems – tripling the use of NPK/phosphates for fuel, or even plastics as we experience these declining food production resources (peak petroleum and peak phosphates) would seem to be at best willfully ignorant and worst suicidal.

    Suggested reading:

    - The Rational Optimist – a book by Matt Ridley

    Link to this
  2. 2. S.E. Gould in reply to S.E. Gould 11:02 am 10/26/2011


    Thanks for your comment! The economic and biochemical realities of algal production of natural substances is a fascinating topic, and one that deserves a whole host of blog posts, or even a book of its own. This post is only a brief glimpse at recent research in bioplastics; focusing on the scientific interest of synthetic gene manipulation rather than the economic merits of bacterial bioplastics. As a synthetic biologist I do tend to spend more time getting excited about new developments that considering their large-scale and wider implications.

    Although algae do use more than “sunshine” to generate biomass (if they did it would be nothing short of miraculous!) the use of photosynthesis does provide them with a distinct advantage over bacteria, which require an additional carbon source as well as the nitrogen and phosphate requirements that you pointed out. I tend to err on the side of more simplistic explanations on this blog, as I would not like to loose the wider reader base by getting bogged down in biochemical detail.

    Your links look very comprehensive and useful for this topic, I would encourage anyone with an interest in the economics of natural products, and the phosphate and nitrogen load of algae production to take a look at them.

    Link to this
  3. 3. agapakis 11:53 am 10/26/2011

    It is definitely really hard to balance the cool technical aspects of genes and polymers with the economic, environmental, and social considerations (especially in the kind of concise and well-written posts that you specialize in!), but as a fellow synthetic biologist that’s what I find most exciting and important about the field. When talking about applied projects like producing plastics and replacing petroleum products the whole point is to be able to offer a truly sustainable alternative, and the issues of resources and land use are as central as issues of enzymes and macromolecules. It’s a big challenge and there’s no good solution yet, so there’s of course still room for short and fascinating posts about bioplastics with thought-provoking and discussion-starting comment threads!

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