8/12/2019 Plastic from the sun and CO2

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Plastic from the sun and CO 2

Few scientists disagree that the ever increasing level of CO2 in the earths atmosphere i shaving a debilitating effect on the global environment, most obviously though thegreenhouse effect. Brea throughs to ... further increases in atmospheric CO2 concentrationare vital. One promising field of research in this area focuses on the commercial fi!ing ofCO2 gas though the biological nprocess of photosynthesis.

One of the byproducts of this procces is polyhidro!ylbutylate "P#B$. %he main ingredient ofbiodegradable plastics. P#B is a cellular storage material synthesi&ed by bacteria. 'hene!tracted from cells and molded. %his subtance has the properties of a thermoplastic similarto polystyrene. (et it can be bro en down by microorganisms living the soil.

)ome P#B has been produced on a test basis by culturing bacteria in glucose media. *y

colleagues and i at the national intitute of bioscience and human technology "+ B#%$. On theother hand, are attempting to produce P#B directly from solar energy and CO2 usingCyanobacteria. Cyanobacteria or blue-green algae. re the most basic of organismic, butli e higher plants the are photosynthetic, meaning they fi! CO2, releasing o!ygen as abyproduct. From the bacteria A. eutrophus, which is nows to produce P#B from glucose.'e have isolated the gene that codes from the thee en&ymes used in P#B synthesis.

fter reproducing the gene in the bacteria escherichia coli, we introduced it into thecyanobacteria synechococcus. 'e then transfered the now transgenic cyanobacteriato aculture medium "compresing only inorganic salts li e phosphate and nitrate$ and left them togrow in the precense of light and air of 2 / to 0 / CO2. 'hen the nitrogen source in the

medium "nitrate$ was reduced. P#B accounted for around 0 / of the dry weight of therecombinant syanobacteria. %he picture above show cyanobacteria grown in the presence ofacetic acid. n the case. %he accumulation of phb "the large white granules$ rose to 21/.

Our goal is to produce a large yield of P#B from CO2 without the use of acetic acid.lthough the en&ymes from . eutophus that code for P#B synthesis are wor ing inside the

recombinant cyanobacteria, the sugars the cyanobacteria are producing by reducingatmospheric CO2 tend to be stored as cyanobacteria starch, which is their own cellularstorage material, rather that P#B. 'e will have to e!periment with growing conditions andnew gene manipulations to alter the recombinant cyanobacterias metabolism so that greater

uantities of P#B will be stored.

Future strategies

3ecently, we have isolated a strain of thermophilic cyanobacteria which accumulates largeamounts of P#B. 'hen cultured in light at 14 degrees celcius. %his strain rapidly multiplies.5oubling its cell numbers in appro!imately five hours. 'ithout any genitic manipulation ofaddition of acetic acid. %his strain accumulated over 24 / of its dry weight in P#B whenraised on medium that was low in nitrogen. 'e are currently investigating why this particularstrain stores so much P#B. 'e are also involved in preparatory wor for the future geneticmanipulation of thermophilic cyanobacteria.

8/12/2019 Plastic from the sun and CO2

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3eseachers are now traying to introduce the gene for P#B synthesis into higher plants, as amethod of producing biodegradable plastic though photosynthesis. %he benefits of usinghigher plants are manifold. %he most obvious being ease of cultivation. Only a limitednumber of large-scale microscopic algae culturing factories are currently in operating mainlyproducing health food products. #owever, productivity in this system is by no means low. nan e!ample of raising the spirulina algae in low latitude regions, an annual harvest of P#B ofappro!imately 67 grams "total dry cell waight$ per day per s uare meter has been reported.8nfortunately we dont have good data on production costs and cannot address the

uestion of what percentage of dry weight would have to be P#B to ma e such an operationprofitable. f however, a large-scale production system for microscopic algae was put on line

with the attendant goal of reducting CO2 level in the atmosphere. P#B would surely beplaced at the top of the list of useful byproducts.