Properties of a Biocatalyst

Every bioprocess starts with the best possible cell factory. A better performing cell will allow for less capital, lower variable cost for the fermentation, and a simpler recovery process as the product will be more concentrated. More than one property makes for a good cell factory and none of the commonly used cell factories have all the needed attributes. Case-by-case development of a biocatalyst is still the norm, even though a platform for a given organism would help accelerate process development. Described below are elements from a process point of view to consider in choosing a biocatalyst for a bioprocess. 

Microorganisms have been isolated which can perform at a wide range of pH or temperature (Zambare et al., 2011), use synthesis gas as a carbon source (KOpke et al.. 

FIGURE 6.2 Theoretical maximum yield of isoprene from glucose (soM Rue), and oxygen consumed per mol of isoprene made (dotted Une), as a function of the ratio of the two 

2 Variable Cost Although several factors impact direct or variable cost, the cost of carbon to feed cell factories is often more than 50% of the total direct 

Production of an enzyme by a bacterial or a fungal strain is more complicated since a protein is composed of 20 amino acids as building blocks. Theoretical protein mass yield on glucose is then best estimated from the stoichiometry of the building blocks and is close to 50%, according to Equation 6.1, based on the elemental composition (Nielsen et al., 2002)  

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Robustness Other properties of a biocatalyst can also have a very significant impact on the bioprocess. For example, substrate and product tolerances are important considerations (Nicolaou et al., 2010). Tolerance can be improved by strain evolution (Miller et al., 2009) or by targeted genetic modification (Zingaro and Papoutsakis, 2013). 

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