Small change: Keeping pace with microevolution

Bacterial genomes are increasingly viewed in terms of the integration of accessory and dispensable genetic elements into a conserved genomic core. This duality provides both the evolutionary stability that is required for the maintenance of essential functions and the flexibility that is needed for rapid exploitation of new niches. This review focuses on combining genome sequencing, microarray and multilocus sequence data to explore microevolutionary divergence in single species and genera.