Emerging techniques for metagenome screening

Biotechnologists are interested in metagenomics as a tool to obtain novel, industrially valuable genes without the difficulties associated with the isolation and cultivation of microbes from the environment. Although environmental metagenomes harbor a huge diversity of microbial genes, only a small portion of them are accessible by conventional screening techniques. This greatly limits the utility of metagenomic approaches, and efforts to broaden accessible genes are therefore essential to make metagenomics more useful and attractive. In this chapter, two techniques that we have recently developed to access previously inaccessible genes in metagenomes are introduced, namely, substrate-induced gene-expression screening (SIGEX) and preferential annealing and removal of abundant metagenome fragments (PARM). SIGEX introduces a new concept in metagenome screening that relies on gene-expression activities rather than nucleotide sequences and enzyme activities, while PARM removes numerically abundant, redundant gene fragments from metagenomes in order to increase the possibility of cloning scarce gene fragments and construct a library of greater genetic diversity. We anticipate that metagenomics will be further advanced by introducing these techniques as standard protocols.