Final answer:
The two principal virulence factors of Bacillus anthracis are its toxins and capsule, encoded on plasmids pX01 and pX02, leading to the bacterium's lethal virulence and immune evasion.
Step-by-step explanation:
The two principal virulence factors of Bacillus anthracis, the bacterium responsible for anthrax, are its toxins and capsule. These virulence factors are encoded on two large plasmids: pX01 and pX02. The plasmid pX01 is responsible for producing a three-part toxin that suppresses the host's immune system, while plasmid pX02 encodes for a capsular polysaccharide that protects the bacterium from the host immune system. Other bacterial pathogens produce distinct virulence factors, but for B. anthracis, it's the combination of these plasmids that confers its lethal virulence and capacity for immune evasion.