Dynamic modeling of microbial metabolism, at the individual enzymatic reaction level, is becoming increasingly feasible and fruitful. This seminar will present two problems of interest. The first example is a recently completed modeling effort in optimizing a newly engineered microbe for fermenting pentose sugars to ethanol. The non-linear enzymatic reaction rate expressions are incorporated into the dynamic model to address large perturbations to the metabolism caused by additional enzymatic activities and predict accurately the impact of changing the enzyme concentrations on the overall fermentative capability. The second example is in understanding or modeling the spontaneous metabolic oscillations, which occur over a finite range of conditions in yeast continuous cultures. This problem is of current research interest, in which I seek active collaboration with applied mathematicians to model the yeast metabolism in more detail to include most of the known enzymatic reactions involved as well as the genetic regulatory mechanisms that control the levels of different enzymes.