Fungi and Algae Production of Ethylene Could be an Alternative source of Biobased Plastic Feedstock

Natural gas compounds such as ethylene and propylene are normally produced from natural gas liquids that are first isolated from petroleum refineries. The ethylene or propylene is then converted into plastic resins, which are the starting materials to produce common plastics such as polyethylene or polypropylene. The refineries that process natural gas liquids into ethylene or propylene are called steam cracking plants of which there are estimated to be over 40 in the US in states like Texas and Louisiana. As mentioned above, natural gas liquids must first be isolated from petroleum refineries and then delivered to the steam cracking plants. When the natural gas liquids are steam treated they break down into products like olefins, propylene and ethylene. Both propylene and ethylene produce plastics as mentioned above, however, ethylene is produced at a much higher percentage. Scientists in past decades have worked on methods to produce ethylene directly from alternative sources such as bacteria, fungi and even algae. Microbes and algae can also produce other manufacturing type gases such as hydrogen. Ethylene is also produced by plants but it is usually produced as a result of fruit ripening. Even certain common types of fungi can also produce ethylene. If ethylene is made by microorganisms in measurable amounts that are useful for the manufacture of products, they may be useful for the prodution of ethylene gas. It was found that around 25 % of fungi samples from over 200 varieties of fungi produced measurable amounts (~ 1 ppm or greater) of ethylene gas as a metabolic byproduct [ Ilag L. et al 1968 ]. Ethylene production has even been measured from soil samples containing bacteria or fungi, also in measurable quantities, mostly from fungi though [ Lynch 1972 ].

Even though many types of fungi, algae and microbes can produce ethylene in measurable quantities, it is prudent to just choose the species that can make ethylene in high quantities. Under natural conditions a fungi species can make over 100 ppm of ethylene gas [ Ilag et al 1968 ]. Just imagine what quantities could be produced from genetically engineered varieties. As with Hydrogen, microbes or algae can be genetically manipulated in order to produce ethylene in better amounts of more efficiently. Algae species such as Synechocytis have been genetically manipulated with ethylene response genes that may be similar to plant sources such as Arabidopsis [ Wilde et al 1997 ]. The amount of ethylene produced from algae such as this have then been monitored in heterotrophic conditions (minimal light). Similar growth conditions have been done with algae in order to produce hydrogen gas. In fact, algae can be grown in light or dark conditions in order to produce hydrogen. The idea of microbes, yeast and algae producing manufacturing gases such as ethylene and hydrogen is a novel concept and may be a realistic option dependent upon economics and engineering improvements. Microbes can even produce other valuable hydrocarbon based gases such as isoprene. Isoprene is usually a liquid based hydrocarbon but is also volatile under the right conditions. It is used to make products like rubber. In summary, gaseous sources of biomass from microbes may be logical alternative sources someday to help produce alternative products like plastics, with ethylene being a prime example.

REFERENCES

1. "Production of Ethylene by Fungi", Science vol 159 pg. 1357 - 1358, 1968, Ilag L., Curtis R.

2. "Identification of Substrates and Isolation of Microorganisms Responsible for Ethylene Production", Nature vol 240 pg 45-46, 1972, Lynch

3. SAME AS REFERENCE #1

4. FEBS Letters vol 406 issue 1-2, pg 89-92, 1997, Wilde A, Churin Y. Schubert H.

Photos taken from Web Album of Picasa

KEYWORDS: Fungi Production of Ethylene, Bioplastics, Polyethylene, Polypropylene, Ethylene Response Genes, Synechocystis, Isoprene, Rubber,
Algal and Microbial Hydrogen Production, Steam Cracking Plants, Hetereotrophic Fermentation

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PHB (Polyhydroxybutyrates) from Bioenergy Plants like Sugarcane & Corn

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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