Functional metagenomics for enzyme discovery: challenges to efficient screening.

Metagenomics has emerged as an alternative approach to conventional microbial screening that allows exhaustive screening of microbial genomes in their natural environments. Despite the potential usefulness of this approach, functional analysis of the metagenome is often problematic because of insufficient and biased expression of the cloned genes in Escherichia coli. This review highlights recent studies on the screening of metagenomic libraries and discusses some possible solutions for overcoming the expression problem in function-based screening.