S34: Rational design of chemically-defined microbial fermentation media: a balanced approach

We have developed a rational approach to microbial media design based on two orthogonal determinations of cellular requirements for macronutrients and key micronutrients.  First, we measured component uptake per unit biomass when each component was provided in excess in high cell density fermentations (Method 1).  Second, we supplied each component in varying amounts as the limiting nutrient with all other nutrients supplied in excess.  The slope of the resulting plot of component concentration vs. biomass yield gave a second estimate for the component requirement (Method 2).  Interestingly the requirements determined by the two methods were in almost complete disagreement, except for phosphate.   For the remaining components studied we believe the discrepancy is due to one of two phenomena: 

1. Method 1 > Method 2:  This could occur if a particular component is taken up in excess of its actual requirement when supplied in excess.  We saw this response with Iron, where the actual nutrient requirement is given by Method 2.
2. Method 2 > Method 1:  This could occur if the component uptake is reliant on a transporter with a low substrate affinity.  We saw this response with Mg, Ca, K, and Zn.  Here the actual requirement is given by Method 1, but the minimum required concentration is given by Method 2.

Using this approach we formulated an improved fermentation media in which all major mineral components were reduced from 30%-100% compared to the standard media, resulting in demonstrable improvements to fermentation and recovery yields at pilot and commercial scale.