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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