Final answer:
Bacillus anthracis has two principal virulence factors that are encoded on two plasmids: pX01, which encodes a three-part toxin, and pX02, which encodes a capsular polysaccharide.
Step-by-step explanation:
The two principal virulence factors of Bacillus anthracis, the pathogen responsible for anthrax, are coded on two large plasmids, pX01 and pX02. The plasmid pX01 encodes a three-part toxin that suppresses the host immune system. Meanwhile, the plasmid pX02 encodes a capsular polysaccharide that helps the bacterium evade the host's immune system. These two virulence factors contribute significantly to the bacterium's ability to cause severe and potentially lethal infections.
Genome sequencing has shown that while B. anthracis is genetically similar to its cousin Bacillus cereus, these two plasmids are what grant B. anthracis its high virulence. B. cereus lacks these plasmids and hence these specific virulence factors, which is why it is associated with less severe symptoms, such as food poisoning.