Molecular diversity in Bacillus anthracis

Molecular typing of Bacillus anthracis is has been extremely difficult due to the lack of polymorphic DNA markers. We have identified nine novel varia ble number tandemly repeated loci from previously known amplified fragment length polymorphism markers or from the DNA sequence. In combination with t he previously known vrrA locus, these markers provide discrimination power to genetically characterize B. anthracis isolates. The variable number tand em repeat (VNTR) loci are found in both gene coding (genic) and non-coding (non-genic) regions, The genic differences are 'in frame' and result in add itions or deletion of amino acids to the predicted proteins. Due the rarity of molecular differences, the VNTR changes represent a significant portion of the genetic variation found within B. anthracis. This variation could r epresent an important adaptive mechanism. Marker similarity and differences among diverse isolates have identified seven major diversity groups that m ay represent the only world-wide B. anthracis clones. The lineages reconstr ucted using these data may reflect the dispersal and evolution of this path ogen.