Microorganisms tend to have a relatively fast rate of evolution. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation , transformation and transduction , even between widely divergent species.  This horizontal gene transfer , coupled with a high mutation rate and other means of transformation, allows microorganisms to swiftly evolve (via natural selection ) to survive in new environments and respond to environmental stresses . This rapid evolution is important in medicine, as it has led to the development of multidrug resistant pathogenic bacteria , superbugs , that are resistant to antibiotics . 
The study of the fate of persistent organic chemicals in the environment has revealed a large reservoir of enzymatic reactions with a large potential in preparative organic synthesis, which has already been exploited for a number of oxygenases on pilot and even on industrial scale. Novel catalysts can be obtained from metagenomic libraries and DNA sequence based approaches. Our increasing capabilities in adapting the catalysts to specific reactions and process requirements by rational and random mutagenesis broadens the scope for application in the fine chemical industry, but also in the field of biodegradation . In many cases, these catalysts need to be exploited in whole cell bioconversions or in fermentations , calling for system-wide approaches to understanding strain physiology and metabolism and rational approaches to the engineering of whole cells as they are increasingly put forward in the area of systems biotechnology and synthetic biology .