Screening for Biocatalysts

The first step in the set-up of a viable biocatalytic method or process is the identification of a suitable biocatalyst showing the desired selectivity/specificity, optimal performance and sufficient stability under process conditions. Such biocatalysts may be microbial, plant or animal cells or enzymes derived thereof. 

By reviewing literature, it becomes obvious that three main screening strategies have been followed, so far  

A third approach, related to approach 2, is the search for novel enzymes catalyzing difficult reaction types, where no indications or knowledge on their existence is yet available. Typical examples for this approach from the last decade are the discovery and investigation of enzymes catalyzing Baeyer-Villiger oxidations [53] or Diels-Alder-type reactions [74]. 

Speculations on the number of species living on earth indicate that the major part (i.e. about 95%) of the microbial world still remains to be discovered and studied (Table 4.) 

Class of organisms Described species Total number of estimated species High Low Working figure % of known species Accuracy 

The use of microorganisms or commercially available enzymes to perfonn biotransformations is well established. Numerous routes have been developed to prepare chiral fine chemicals with enzymes from all classes, often in combination with chemical methods, and it is clear that many of the major phannaceutical companies are investing heavily in this type of research and development. With approaches such as dynamic kinetic resolution, pathway engineering, and screening for biocatalysts showing such promise, many new biotransformations will undoubtedly be discovered to develop novel, green bioprocesses in the future. 

Martineau, W. in Chiral Chemicals, The Freedonia Group Cleveland, OH, 1996. 

Rollieim, P. in The Enzyme Industry Specialty and Medical Applications, Business Communications Company Norwalk, CT, 1994. 

in Industrial Enzymology, Godfrey, T., West, S., Eds Macmillan Press Ltd London, 1996 p. 155. 

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Wahler D, Reymond JL. High-throughput screening for biocatalysts. Curr. Opin. Biotechnol. 2001 12 535-544. 

The present congress will offer interesting contributions to increasing the efficiency of screenings for biocatalysts with the use of modem, physical, biochemical or molecular biological methods. 

Improved methods of screening for biocatalysts should be quicker, more accurate, selective and more easily automated. The emphasis should be on rational, direct screening procedures rather than indirect or random methods. Such rational direct methods could involve six steps ... 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

D. Wahler and J.E. Reymond Novel Methods for Biocatalyst Screening. Curr. Opin. Chem. Biol. 5, 152 (2001). 

Cheetam, P.S. (1987) Screening for novel biocatalysts. Enzyme Microb. Technol., 9, 194-213. 

J.-M. Sonet, Screening for novel biocatalysts from biodiversity, Bioforum Int. 2001, 5, 232-234. 

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