Genetic and Physiological Studies of Bacillus anthracis Related to Development ofan Improved Vaccine

摘要

Most of our effort was spent on studies concerning the biology of the two B.anthracis plasmids, pXO1 which encodes toxin synthesis and pXO2 which encodes capsule synthesis. Analysis of Tn917 insertion mutants of pXO1 revealed several mutants that were altered in toxin production. In some instances, the altered phenotypes were the result of insertions within or deletions of one or more of the toxin structural genes. Analysis of another mutant, deficient in production of all three toxin components, led to the discovery and cloning of a gene, atxA, involved in trans-activation of toxin synthesis. Overproduction of toxin by another mutant suggested that Tn917 had inserted in a negative regulatory gene. Restriction analysis and physical mapping of pXO1 from several B. anthracis strains revealed an inversion of the toxin-encoding region of pXO1 from the Sterne strain. The inverted segment was found to be flanked by imperfect 1336-bp inverted repeats, each containing a sequence resembling a full or truncated IS150-like transposase gene. Comparison of Sterne and Weybridge A, which carry the inverted segment in opposite orientations, revealed no differences in phenotypes that could be associated with the inversion. Studies of insertion mutants of pXO2 suggested that some of the mutations are located in genes regulating synthesis of capsules. Among such mutants are those that overproduce capsular material, some that no longer require bicarbonate and CO2 for capsule synthesis, and some that have lost the ability to synthesize capsules. Capsule, Protective antigen, B. Anthracis, Plasmid pXO1, Transposon mutagenesis, Anthrax toxin, Plasmid pXO2, Regulatory genes.