Acetic Acid Inhibition of E. coli K011 during Fermentation by Brittany Oetter & Sara Walton

Research being done on forest bioproducts includes researching the efficiency and feasibility of using wood to produce ethanol. One of the three components of wood, hemicellulose, can be separated from the other two components and can then be fermented using bacteria such as Escherichia coli (E. coli). During fermentation, the bacteria convert the sugars of the hemicellulose into ethanol. However, this process may not be an effective way to produce fuel ethanol if it is an inefficient process. One problem is that certain compounds produced during the pretreatment of the hemicellulose before fermentation can inhibit the bacteria that are used in fermentation. One such degradation product is acetic acid, which may inhibit E. coli by penetrating the cell walls of the bacteria and making the cell cytoplasm acidic. This would make the process of using wood to produce ethanol by fermentation less efficient. One area for research involves investigating the use of genetically engineered strains of bacteria that might be more resistant to these degradation products.

This research will focus specifically on analyzing the effect of acetic acid on the fermentation of hemicellulose by E. coli K011, a recombinant strain of E. coli that is thought to be more resistant to the adverse effects of acetic acid. After growing this recombinant strain of E. coli it will be used to ferment sugars that have been extracted from wood chips. At first, a few fermentations will be done using pure sugars, and later the actual hemicellulose extracts will be used in the fermentations. This research will focus on finding out if fermentation done by this strain of recombinant E. coli is affected by the acetic acid in the same way that naturally occurring E. coli is. The goal will be to determine the extent to which acetic acid inhibits this strain of E. coli. The samples will be analyzed using HPLC (high performance liquid chromatography) to determine the amount of ethanol produced by the E. coli during fermentation and to examine how much of the sugars from the hemicellulose are converted into ethanol. The knowledge gained from this research could help determine the efficiency of using this fermentation process to produce ethanol from hemicellulose.

The inhibition of bacteria by degradation products of hemicellulose poses a problem to the idea of using biomass to produce ethanol. This particular research could help clarify this problem and help determine whether or not wood can become a practical resource for fuel ethanol production.

Brittany Oetter REU Interview 07/10/07

http://efolio.umeedu.maine.edu/~tvassiliev/FBRI/2007FBRI/Brittany.m4a