Monday, August 5, 2013

Just what is in Compost anyway?

Sometimes the convergence of a number of seemingly unrelated topics results in a very interesting scientific story. For example, when the topic of composting comes up, the idea of biofuel is not normally entertained at the same time. Likewise, “Who done it” is a phrase most often associated with an Alfred Hitchcock movie or an Agatha Christie novel rather than a scientific paper. Yet a collaboration between researchers at the U.S, Department of Energy (DOE) the Joint BioEnergy Institute (JBEI) and the Environmental Molecular Sciences Laboratory (EMSL) is trying to solve a “Who done it” mystery in regards to what works best to generate fermentable sugars for biofuel production by looking at compost.

For a number of reasons, advanced biofuel research has focused on the use of lignocellulosic material in lieu of using grain based starches as a source of fermentable sugars. Unfortunately the conversion of cellulosic material to fermentable sugars is much more difficult than grains yet the commercialization of biofuel production from lingocellulosic biomass is contingent on the development of cost-competitive ways to extract fermentable sugars. Towards that end scientists have looked at optimizing the enzymatic steps of digestion of lignocellulosic material. Composting, which is the natural digestion of organic material by a mixture of bacteria and fungi, takes advantage of millions of years of evolutionary optimization of organisms. By dissecting what organisms and enzymes are in a complex mixture such as that responsible for digestion of compost, one can ascertain the best combination to use for man-made applications.

It’s long been known that a mixture of bacteria and fungi work in concert to degrade cellulosic material, but the specific roles of various species has been unknown. Applying a combination of metagenomic and metaproteomic techniques on a compost-derived consortium of thermophilic bacterium adapted to grow on switchgrass the individual microbial species most active in digesting switchgrass, were identified. Interestingly, while the species Thermus thermophilus and Rhodothermus marinus were found to be the most abundant, the strains Gemmatimonadetes and Paenibacillus actually provided the lion’s share of deconstructive enzyme activity. The bacteria and enzymes identified as being important can then be used in an optimized cocktail for commercial conversion of biomass to fermentable sugars.

So the next time you add food scraps, yard waste or leaves to your compost pile, keep in mind that the same organisms that break down this waste to provide nutrients for your garden might also help reduce our dependence on fossil fuels for transportation. So as the adage says; "Don’t treat your compost like dirt."


By: BioTek Instruments, Paul Held PhD, Laboratory Manager

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