Turning up the heat
A news article via my favorite daily blog, io9.com, which details a report from the scientific journal Nature. Researchers at the University of California, Berkeley, and at the University of Maryland have recently characterized a novel extremophile isolated from a hot spring in Nevada. The organism is a member of domain Archaea, which was isolated from a 94 °C geothermal pool using an enrichment isolation technique to isolate organisms able to degrade cellulose.
In enrichment isolation, a mixture of organisms are grown under conditions which favor the growth of desired microorganisms. Previous work had identified an archaeon, Desulfurococcus fermentans, which had the ability to grow on filter paper at elevated temperature, however there are no other examples of prokaryotes that produce cellulose-degrading enzymes that are effective at higher temperatures. The authors of this study hypothesized that a mixture of hyperthermophilic microorganisms might be able to collectively break down pulverized plant material, and set out to isolate a mixture by growing geothermal pool samples in a liquid medium containing pulverized grass as the primary carbon and energy source at 90 °C. After three weeks, the culture was transferred to medium containing strips of filter paper as the sole carbon source, and allowed to grow until the filter paper was visibly degraded.
Once a suitably enriched culture was obtained, the DNA sequence of the mixture of microorganisms was obtained. Because the DNA sequence represents the sequence of several species of organisms, the resultant sequence is referred to as a metagenome, and is a very useful way to quickly look at a molecular level at a complex system of living organisms. The DNA sequence was then analyzed for all gene sequences, and genes similar in sequence to known cellulases were identified. Candidate genes were then cloned, inserted into carrier DNA molecules, and used to transform E. coli strains. The transformed E. coli strains then produced proteins encoded by the DNA from the hyperthermophilic microorganisms. The “made in E. coli” proteins were then analyzed for their ability to break down cellulose at elevated temperatures. One candidate protein was designated EBI-244, and was found to be able to break down cellulose at very high temperatures, with an optimal activity of 109 °C and was very resistant to denaturation by a variety of means including strong detergents and high salt conditions.
This report represents a very important finding in biotechnology and industry, and could significantly affect the world’s dependence on fossil fuels. Currently, ethanol is produced via the process of fermentation of corn, and the utility/economic impact of ethanol as a gasoline supplement is currently controversial. Yeast are only able to ferment simple sugars such as glucose to produce ethanol, and the starches found in the corn kernels must first be broken down by the activity of bacteria which must later be eliminated to prevent the further breakdown of the sugars and consequent reduction in the efficiency of the process. However, since the only part of the corn plant which can be used in this process are the starch-rich corn kernels, the majority of the plant is primarily made of cellulose, which is unusable in this process for the production of fuel.
This is where this report becomes useful: cellulose represents the largest portion of plant material, and is chemically very difficult to break down on an industrial scale. If it were not for the action of microbial degradation of cellulose, plant material would continually accumulate in the environment. Cellulose-degrading microorganisms are therefore essential for recycling of organic material in the biosphere, and these organisms can be harnessed in industrial settings to break down the non-starch portion of plant material for the production of ethanol. This process however has been prone to spoilage and contamination, and is therefore not very efficient.
The introduction of a heat stable process will have several advantages over existing methods for breaking down cellulose. First, enzymatic processes occur more quickly at elevated temperatures, which will allow the more rapid production of monosaccharides for fermentation by yeasts. Second, this report details the breakdown of cellulose using a purified enzyme produced using recombinant DNA methods, which means that only the desired enzymatic breakdown of cellulose to glucose will be occurring without the competing reactions found in a living cell. Third, these reactions can now occur at a temperature that will be resistant to contamination by other microorganisms from the surrounding environment, unless other hyperthermophiles were able to gain access to the industrial bioreactors. Fourth, bioreactors are not limited to starch-rich corn as their initial starting material; any excess plant material can be used as a source of cellulose, including even recycled paper. Look forward to filling your car with your old BIO230 lab report instead of gas early next year!
Posted on July 17, 2011, in Microbes in the News, Strange but True, Uncategorized and tagged Archaea, Ethanol, University of California Berkeley, University of Maryland College Park. Bookmark the permalink. Comments Off.