Biocatalysts are extensively used in the industrial production of bulk chemicals and pharmaceuticals and over 300 processes have been implemented. In the vast majority of processes, enzymes of microbial origin are used as the microbial kingdom represents a huge – and still only partially explored – reservoir for biocatalysts with desired properties. Furthermore, the metagenome approach facilitates the discovery of novel enzymes from microbial sources and hence the number of potentially useful biocatalysts increased exponentially in the past decade.
In contrast, enzymes from animal tissues are less preferred as these often occur as mixture of isoenzymes differing in substrate specificity and product safety (i.e. virus infections), which often restricts their industrial use. Another important source of biocatalysts are plant enzymes. Very often an enzyme does not meet the requirements for a large-scale application and its properties have to be optimized. This usually includes not only the selectivity but also process-related aspects such as long-term stability at certain temperatures or pH-values and activity in the presence of high substrate concentrations to achieve highest productivity.
Beside rather classical strategies such as immobilization, additives or process engineering, molecular biology techniques nowadays represent probably the most important methodology to tailor-design the enzyme for a given process. Two different strategies are used: rational protein design and directed (molecular) evolution, which are increasingly applied in a synergistic manner. Recent advances have mainly focused on applying directed evolution to enzymes, especially important for organic synthesis, such as monooxygenases, ketoreductases, lipases or aldolases in order to improve their activity, enantioselectivity, and stability. The combination of directed evolution and rational protein design using computational tools is becoming increasingly important in order to explore enzyme sequence-space and to create improved or novel enzymes. These developments should allow to further expand the application of microbial enzymes in industry.