Lethal factor is not required for Bacillus anthracis virulence in guinea pigs and rabbits

► We deleted the lef gene in the fully virulent Vollum strain. ► The mutation has no or little effect on the virulence in Guinea pigs. ► The mutation has limited effects on the virulence in rabbits. ► The mutant caused the death of 75%-50% of rabbits infected with spore doses higher than the WT LD50. ► The surviving rabbits were resistant to challenge with the wild type strain.