Fifteen years ago, AtxA was isolated as a toxin gene activator and five years 
later it was shown to be a Bacillus anthracis master regulator. AtxA controls 
the expression of more than a hundred genes belonging to all genetic elements, 
the chromosome and both virulence plasmids, including those encoding the major 
virulence factors. AtxA can activate or repress gene expression. The mechanism 
by which AtxA exerts its control is unknown; it is indirect on some genes but 
may be direct on others. The expression of many AtxA-controlled genes is induced 
by the presence of bicarbonate/CO(2). AtxA links the metabolic state and 
virulence gene expression.