The use of PHAs (Polyhydroxyalkoanates) also known as PHBs (Polyhydroxybutyrates - are a subset of PHAs) used as a bioplastic material may become more of a reality due to the drastic drop in prices that are payed per pound of the material. PHBs are becoming competitive with another bioplastic material called PLA (Polylactic acid). In fact, the price per pound of each material has dropped by more than four times their former price within the last 5 years. Both materials can be produced from a variety of sources, which may explain its drop in price, but they are mostly obtained from the fermentation of certain types of bacteria. For example, PLA contains Lactic Acid, which is a common byproduct of Lactic Acid Bacteria. The development of the biofuel industry may be another reason the price of such materials have dropped so drastically. Like ethanol, large amounts of Lactic Acid can be produced from the ensilage of corn stover products. Now, the use of genetic engineering may provide more quantities of the other bioplastic material, PHBs, from the leaves of sugarcane or possibly corn plants too. Researchers from the University of Queensland & BSES have been able to produce dozens of genetic varieties of sugarcane plants that contain PHBs in the leaves of the plants [ 1. EPOBIO Workshop Two 2007 ]. Genes that are able to produce PHBs in bacteria such as R. Eutropha are transplanted into plants such as sugarcane, where the material accumulates in the leaves as the plant matures. Other agricultural plants have also been experimented with transgenically using these type of genes such as flax, corn, alfalfa and others [ 2. Daniell & Chase 2004 ]. Corn and sugarcane are two of the main types of energy crops used to produce ethanol in both North and South America. The unused portions of the plant could be harvested into a resulting PHB material. Since these plants are grown in large quantities
to provide biofuels, large quantities of PHBs could be produced simultaneously.
Experiments have also been done with sugar beet plants too. Sugar beets are the other main source of our raw sugar or sucrose supply, and grows in various places across the United States. These type of agricultural residues could be utilized for this purpose. In the future, the conversion of plant crop residues into further chemicals and fuels should be more widespread not only in the United States but across the world. As these renewable resources are utilized, more sensible policies should be developed outlining the more practical usage of crop residues. Probably the most prevalent and common residue will most likely be corn stover. It already has other practical uses such as ensilage for feed and chemicals. It has also been commonly used as fodder (ie fertilizer) for the next growing season. Competition of corn stover use most likely will happen. Corn leaves could also be targeted to produce amounts of PHBs, but other uses such as further ethanol production may be more practical. Scientists at various universities have also genetically bred corn plants to breakdown cellulose into sugars that can be used in future ethanol or other chemical fermentations. Since the same genes that produce PHBs in plants are originally taken from bacteria, microbial cultivation in bioreactors may be a more favorable and practical method in producing PHBs. However, since large amounts of corn and sugarcane are cultivated, it makes sense to utilize the leaf residues for further products. Not enough information is known by the author to know whether it is practical to cultivate other types of plants for PHB harvesting. This should be an area for qualified plant biologists and scientists who work with specific species to decide.
REFERENCES
1. "Sugarcane as a Biofactory - Products from Plants from crops and forests to zero-waste biorefiniries", EPOBIO Workshop 2 - May 2007 by SIIB - Sugar Industry Innovation through Biotechnology
2. "Molecular Biology & Biotechnology of Plant Organelles and Chloroplasts : Chloroplasts & Mitochondria", [2004], Daniell H., Chase C.,
Photos taken from Picassa Web Album
KEYWORDS: Polyhydroxybutyrates, PHB, Polyhydroxyalkoanates, PHA, Poly lactic acid, PLA, Bioplastics, Energy Crops, Sugarcane, Corn Stover, Genetic Engineering, Genetically Modified Plants
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