1 Biotechnology of Microbial Enzymes. © 2017 Elsevier Inc. All rights reserved. 2017 Chapter 1 Useful Microbial Enzymes— An Introduction Sergio Sanchez 1 and Arnold L. Demain 2 1 Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México (UNAM), Mexico City, Mexico 2 Research Institute for Scientists Emeriti (RISE), Drew University, Madison, NJ, United States 1.1 THE ENZYMES: A CLASS OF USEFUL BIOCHEMICALS According to the International Union of Biochemistry (IUB), and based on their nature of reaction, enzymes are divided into six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. The use of enzymes in industrial processes has been of crucial importance since they can eliminate the use of high temperatures, extreme pH values, organic solvents, and at the same time, offer high substrate specificity, low toxicity, product purity, reduced environmental impact, and ease of termination of activity. Microorganisms constitute the major source of enzymes as they produce high concentrations of extracellular enzymes. Screening for the best enzymes is simple, allowing the examination of thousands of cultures in a short period of time. Microorganisms used for enzyme production include around 50 GRAS bacteria and fungi. Bacteria are mainly represented by Bacillus subtilis, Bacillus licheniformis, and various Streptomyces species. Fungi are usually represented by Aspergillus, Mucor, and Rhizopus. Microorganisms can be cultured in large quantities in a rel2atively short period by established methods of fermentation. Microbial enzyme production is economical on a large scale due to inexpensive culture media and short fermentation cycles. There are more than 3000 different enzymes known but only 5% are com- mercially used (Binod et al., 2013). Over 500 commercial products are made using enzymes (Johannes and Zhao, 2006). In regard to the total enzyme mar- ket, its global figures depend on the consulted source. In one case, the market reached $5.1 billion in 2009 and is predicted to rise 6.45 per annum to grasp $6.9 billion in 2017 (The Freedonia Group, Inc., 2014). In a second report, it was estimated to be $3.3 billion in 2010 and to reach $4.4 billion by DOI: http://dx.doi.org/10.1016/B978-0-12-803725-6.00001-7