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Carbon sources for the production of PHAs

An attractive feature of the microbial PHAs is the ability to produce them using renewable carbon sources. The plastic materials widely in use today are synthesised from fossil fuels such as petroleum and natural gas. PHAs on the other hand can be produced using renewable carbon sources such as sugars and plant oils, which is an indirect way of utilizing the atmospheric CO2 as the carbon source. Various waste materials such as whey [14, 15], molasses [16, 17, 18]and starch [19, 20] are also being considered as potential carbon sources for PHA production. The carbon source available to a microorganism is one of the factors (others being the PHA synthase substrate specificity and the types of biochemical pathways available) that determine the type of PHAs produced. For industrial scale production, the carbon source significantly contributes to the final cost. This makes the carbon source one of the most important component in the production of PHA and is therefore a prime target for potential cost reduction.

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From top left: Oil palm fruit bunch, Crude palm kernel
oil, A 10-L Infors bioreactor, Purified PHA Bottom: Facial
oil blotting films made from 100% PHA

A recombinant strain of R. eutropha PHB-4 (a PHA-negative mutant), harboring the PHA synthase gene from Aeromonas caviae, could produce a random copolymer of 3HB and 3-hydroxyhexanoate (3HHx) from plant oils such as olive oil, palm oil and corn oil. The P[3HB-co-3HHx] content was approximately 80% of the dry cell weight and the 3HHx mole fraction was 4-5 mol% regardless of the structure of the triglycerides fed [21]. The results demonstrate that inexpensive renewable plant oils are excellent carbon sources for the efficient production of PHA.