Bourgogne Agathe, Drysdale Melissa, Hilsenbeck Susan G, Peterson Scott N, Koehler Theresa M
Department of Microbiology and Molecular Genetics, The University of Texas-Houston Health Science Center, 77030, USA.
Infect Immun. 2003 May;71(5):2736-43. doi: 10.1128/IAI.71.5.2736-2743.2003.
Control of anthrax toxin and capsule synthesis, the two major virulence factors of Bacillus anthracis, has been associated with two regulatory genes, atxA and acpA, located on virulence plasmids pXO1 and pXO2, respectively. We used transcriptional profiling to determine whether atxA and/or acpA control genes other than those already described and to investigate functional similarities of the regulators. Transcription was assessed in a pXO1(+) pXO2(+) parent strain and in isogenic mutants in which one or both regulatory genes were deleted. We determined that in addition to the toxin and capsule genes, atxA controls expression of numerous other genes on both plasmids and the chromosome. Generally, plasmid-encoded genes were more highly regulated than chromosomal genes, and both positive and negative effects were observed. Certain atxA-regulated genes were affected synergistically in an atxA acpA mutant. Yet overall, acpA appears to be a minor regulator with fewer targets than atxA. In contrast to previous reports of acpA function in attenuated strains, acpA had a minimal influence on capsule gene transcription and capsule synthesis in a genetically complete strain. Surprisingly, acpA expression was positively affected by atxA, although atxA-activated capsule gene transcription is not acpA dependent. The newly discovered atxA-regulated targets include genes predicted to encode secreted proteins and proteins with roles in transcriptional regulation and signaling. Regulation of chromosomal genes by atxA is particularly intriguing, given that many of the target genes have homologues in other Bacillus species that lack atxA homologues. Given the global effect of atxA on gene expression in B. anthracis, previous assumptions regarding reduced virulence of strains harboring single plasmids must be reassessed and the potential roles of newly identified atxA-regulated genes should be investigated.
炭疽芽孢杆菌的两个主要毒力因子——炭疽毒素和荚膜合成的调控与两个分别位于毒力质粒pXO1和pXO2上的调控基因atxA和acpA有关。我们利用转录谱分析来确定atxA和/或acpA是否调控除已描述基因之外的其他基因，并研究这些调控因子的功能相似性。在pXO1(+) pXO2(+)亲本菌株以及缺失一个或两个调控基因的同基因突变体中评估转录情况。我们确定，除了毒素和荚膜基因外，atxA还调控两个质粒和染色体上的许多其他基因的表达。一般来说，质粒编码的基因比染色体基因受到更高程度的调控，并且观察到了正向和负向两种影响。某些受atxA调控的基因在atxA acpA突变体中受到协同影响。然而总体而言，acpA似乎是一个次要的调控因子，其靶标比atxA少。与之前关于acpA在减毒株中功能的报道相反，acpA对基因完全型菌株中的荚膜基因转录和荚膜合成影响极小。令人惊讶的是，acpA的表达受到atxA的正向影响，尽管atxA激活的荚膜基因转录并不依赖于acpA。新发现的受atxA调控的靶标包括预测编码分泌蛋白以及在转录调控和信号传导中起作用的蛋白的基因。atxA对炭疽芽孢杆菌染色体基因的调控尤其引人关注，因为许多靶基因在缺乏atxA同源物的其他芽孢杆菌属物种中有同源物。鉴于atxA对炭疽芽孢杆菌基因表达的全局影响，必须重新评估之前关于携带单个质粒菌株毒力降低的假设，并且应该研究新鉴定的受atxA调控基因的潜在作用。
