17-27: Metabolomic analysis of Spathaspora passalidarum under varying oxygen and carbon conditions

Spathaspora passalidarum, a native xylose fermenting yeast found in association with wood boring beetles, provides an interesting model for the study of intracellular responses during pentose fermentation. It exhibits a specific fermentation rate that is up to three times higher on xylose than on glucose.  Additionally, S. passalidarum is capable of co-fermenting glucose and xylose, suggesting that this organism possesses a weak glucose repression mechanism and a strong glucose/xylose transport system. These unique characteristics of S. passalidarum provide an ideal opportunity for metabolomics to advance the bioconversion of hemicellulosic materials.

Understanding metabolic flux during fermentation is an important challenge in identifying factors that limit efficient ethanol production. Metabolite profiling has long been a useful tool for identifying bottlenecks, however obtaining meaningful data in sufficient replicates can be arduous and the results are often limited in scope. Metabolomics is a rapidly developing field, and HPLC-MS/MS provides a powerful tool to efficiently identify and quantitate a large number of metabolites simultaneously. 

We have used this approach to simultaneously determine the concentrations of more than 40 intracellular metabolites during the cultivation of S. passalidarum on glucose or xylose under aerobic and oxygen limiting conditions.  Metabolites were analyzed during early growth phase and oxygen limited fermentation in order to better define the differences between the growth and ethanol production.  The metabolite levels exhibited during fermentation on glucose and xylose reflect the higher fermentation rates observed with xylose and suggest a regulatory mechanism.