Bacterial Variable Number Tandem Repeats

Repeated nucleotide sequences are less obvious in bacterial genomes but nevertheless are present, highly variable, and, in some cases, very important in biological processes. Variable number tandem repeat (VNTR) loci tend to be hypermutable through an insertion/deletion of short nucleotide repeat sequences. Great variation can be generated in this manner at mutation rates that are thousands, if not millions, of times faster than the rest of the genome. This variation not only has been used for high-resolution subtyping of bacterial pathogens but also can be involved in rapid phenotypic changes. Phase variation by pathogens to avoid host immune responses can be mediated by VNTR variation. Genomically localized hypermutability allows for selective rapid evolution, while avoiding secondary mutations that could lead to a genetic load upon the species.