Updating the metagenomics toolbox.

Metagenomics--the application of the genomics suit of technologies to uncultivated microorganisms--is coming of age. Sophisticated technologies are being developed and adapted to this promising genetic resource to make increasing use of the seemingly boundless molecular and functional diversity. Particular progress has been made in the areas of randomly proliferating limited-source DNA, massively parallel sequencing without cloning, isolating specific target sequences from highly complex template mixtures, high-throughput assay systems targeting metabolic pathways, artificial transcriptional regulators activating reporter genes to indicate enzymatic substrate conversion and cDNA cloning from extracted mRNA to directly clone actively expressed genes from a microbial consortium. However, challenges still lie ahead. Most prominently, the efficient heterologous expression of a plethora of potentially interesting enzymes from unknown source organisms is not readily achieved.