 In the functional approach the fragments of DNA that are stored in the library are used in what is often called a ‘functional screen’. To perform such a screen the researchers introduce the library plasmids into specific bacterial strains which then read and express any protein-coding sequence that might be present on the fragments, thereby producing the protein(s) the fragment codes  for.[24]  The key to a functional screen is to create conditions in which only those bacteria that express a protein with the function of interest can be singled out (for instance by making sure that only those cells survive). Once the cells are singled out the library plasmid they contain can be recovered and sequenced allowing the researcher to identify the protein(s) encoded by that fragment. Functional metagenomics is often used to identify novel microbial proteins that can be used in biotechnological and pharmaceutical contexts and it is not surprising that metagenomics was and still is of great interest to the biotechnological sector (Streit &amp; Schmitz 2004; Lorenz &amp; Eck 2005; Culligan et al. 2014; Ekkers et al. 2012).