Selection versus Screening in Directed Evolution

Efficient high-throughput assays for assessing activity, stereoselectivity, and thermostability of enzymes constitute essential components of directed evolution. The terms ‘screening’ and ‘selection’ are sometimes used interchangeably, albeit in a confusing manner. Screening means the measurement of a given enzyme property such as activity and/or enantioselectivity by an automated analytical technique such as UV/vis spectroscopy, fluorescence, multiplex mass spectrometry (MS), robotic gas chromatography (GC), or HPLC. Genetic selection, on the other hand, involves an experimental platform in which the host organism has a growth and survival advantage because it harbors an enzyme or mutants thereof with a desired catalytic profile. The advent of directed evolution of stereoselective enzymes included the first medium-throughput ee-assay and sparked research directed toward developing further and more efficient medium- and high-throughput ee-screening systems. The optimal choice of a selection or screening system depends upon the particular goal of a directed evolution project.