 The methodology of metagenomics can be described as a four step process, consisting of: 1) the collection of environmental samples, 2) the isolation of microbial DNA from these samples, 3a) the direct analysis of the DNA or 3b) the creation of a genomic DNA library by fragmentation and insertion of the sampled DNA into suitable vectors (for instance plasmids that can be propagated in laboratory bacterial strains). These genomic libraries can then be used to 4a) sequence or 4b) perform a functional screen of the sampled genomic DNA. As the distinction between steps 4a) and 4b) already implies, metagenomics can be divided into a sequence- and a function-based approach (Gabor 2007; Sleator et al. 2008). In the former the collected DNA is sequenced so that potential genes present in the sample can be identified and, if feasible, the genomes of all the microbes that were present in the sample can be reconstituted.