Immense amounts of genetic information are contained within microbial genomes. As the number of completely sequenced microbial genornes is increasing, functional and comparative genomic techniques will be employed for sequence analysis and gene characterization. Sequence comparison and expression profiling by DNA microarrays can determine phylogenetic relationships and identify genes while bacterial artificial chromosomes (BACs) allow the study of entire biochemical pathways and permit the expression of bacterial genes in a foreign host. (C) 2002 Elsevier Science B.V. All rights reserved.