In vivo Bacillus anthracis gene expression requires PagR as an intermediate effector of the AtxA signalling cascade.
ABSTRACT Transcription of the major Bacillus anthracis virulence genes is triggered by CO2, a signal mimicking the host environment. A 182-kb plasmid, pXO1, carries the anthrax toxin genes and the genes responsible for their regulation of transcription, namely atxA and, pagR, the second gene of the pag operon. AtxA has major effects on the physiology of B. anthracis. It coordinates the transcription activation of the toxin genes with that of the capsule biosynthetic enzyme operon, located on the second virulence plasmid, pXO2. In rich medium, B. anthracis synthesises alternatively two S-layer proteins (Sap and EA1). An exponential phase "Sap-layer" is subsequently replaced by a stationary phase "EA1-layer". S-layer gene transcription is controlled by alternative sigma factors and by Sap acting as a transcriptional repressor of eag. Furthermore, in vitro in presence of CO2 and in vivo, AtxA is part of the sap and eag regulatory network. Only eag is significantly expressed in these conditions and this is due to AtxA activating eag and repressing sap transcription. PagR, and not AtxA itself, is the direct effector of this regulation by binding to sap and eag promoter regions. Therefore, PagR mediates the effect of AtxA on eag and sap and is the most downstream element of a signalling cascade initiated by AtxA. Taken together, these results indicate that the B. anthracis transcriptional regulator AtxA is controlling the synthesis of the three toxin components and of the surface elements (capsule and S-layer). Thus, AtxA is a master regulator that coordinates the response to host signals by orchestrating positive and negative controls over genes located on all genetic elements.
Article: Comparative transcriptional profiling of Bacillus cereus sensu lato strains during growth in CO2-bicarbonate and aerobic atmospheres.[show abstract] [hide abstract]
ABSTRACT: Bacillus species are spore-forming bacteria that are ubiquitous in the environment and display a range of virulent and avirulent phenotypes. This range is particularly evident in the Bacillus cereus sensu lato group; where closely related strains cause anthrax, food-borne illnesses, and pneumonia, but can also be non-pathogenic. Although much of this phenotypic range can be attributed to the presence or absence of a few key virulence factors, there are other virulence-associated loci that are conserved throughout the B. cereus group, and we hypothesized that these genes may be regulated differently in pathogenic and non-pathogenic strains. Here we report transcriptional profiles of three closely related but phenotypically unique members of the Bacillus cereus group--a pneumonia-causing B. cereus strain (G9241), an attenuated strain of B. anthracis (Sterne 34F(2)), and an avirulent B. cereus strain (10987)--during exponential growth in two distinct atmospheric environments: 14% CO(2)/bicarbonate and ambient air. We show that the disease-causing Bacillus strains undergo more distinctive transcriptional changes between the two environments, and that the expression of plasmid-encoded virulence genes was increased exclusively in the CO(2) environment. We observed a core of conserved metabolic genes that were differentially expressed in all three strains in both conditions. Additionally, the expression profiles of putative virulence genes in G9241 suggest that this strain, unlike Bacillus anthracis, may regulate gene expression with both PlcR and AtxA transcriptional regulators, each acting in a different environment. We have shown that homologous and even identical genes within the genomes of three closely related members of the B. cereus sensu lato group are in some instances regulated very differently, and that these differences can have important implications for virulence. This study provides insights into the evolution of the B. cereus group, and highlights the importance of looking beyond differences in gene content in comparative genomics studies.PLoS ONE 02/2009; 4(3):e4904. · 4.09 Impact Factor
Article: Cryptococcus neoformans senses CO2 through the carbonic anhydrase Can2 and the adenylyl cyclase Cac1.[show abstract] [hide abstract]
ABSTRACT: Cryptococcus neoformans, a fungal pathogen of humans, causes fatal meningitis in immunocompromised patients. Its virulence is mainly determined by the elaboration of a polysaccharide capsule surrounding its cell wall. During its life, C. neoformans is confronted with and responds to dramatic variations in CO2 concentrations; one important morphological change triggered by the shift from its natural habitat (0.033% CO2) to infected hosts (5% CO2) is the induction of capsule biosynthesis. In cells, CO2 is hydrated to bicarbonate in a spontaneous reaction that is accelerated by carbonic anhydrases. Here we show that C. neoformans contains two beta-class carbonic anhydrases, Can1 and Can2. We further demonstrate that CAN2, but not CAN1, is abundantly expressed and essential for the growth of C. neoformans in its natural environment, where CO2 concentrations are limiting. Structural studies reveal that Can2 forms a homodimer in solution. Our data reveal Can2 to be the main carbonic anhydrase and suggest a physiological role for bicarbonate during C. neoformans growth. Bicarbonate directly activates the C. neoformans Cac1 adenylyl cyclase required for capsule synthesis. We show that this specific activation is optimal at physiological pH.Eukaryotic Cell 02/2006; 5(1):103-11. · 3.60 Impact Factor
Article: Contribution of ExsFA and ExsFB proteins to the localization of BclA on the spore surface and to the stability of the bacillus anthracis exosporium.[show abstract] [hide abstract]
ABSTRACT: Spores of Bacillus anthracis, the etiological agent of anthrax, and the closely related species Bacillus cereus and Bacillus thuringiensis, possess an exosporium, which is the outermost structure surrounding the mature spore. It consists of a paracrystalline basal layer and a hair-like outer layer. To date, the structural contribution of only one exosporium component, the collagen-like glycoprotein BclA, has been described. It is the structural component of the hair-like filaments. Here, we describe two other proteins, ExsFA and ExsFB, which are probably organized in multimeric complexes with other exosporium components, including BclA. Single and double exsF deletion mutants were constructed and analyzed. We found that inactivation of exsF genes affects the BclA content of spores. BclA is produced by all mutants. However, it is partially and totally released after mother cell lysis of the DeltaexsFA and DeltaexsFA DeltaexsFB mutant strains, respectively. Electron microscopy revealed that the exsF mutant spores have defective exosporia. The DeltaexsFA and DeltaexsFA DeltaexsFB spore surfaces are partially and totally devoid of filaments, respectively. Moreover, for all mutants, the crystalline basal layer appeared unstable. This instability revealed the presence of two distinct crystalline arrays that are sloughed off from the spore surface. These results indicate that ExsF proteins are required for the proper localization of BclA on the spore surface and for the stability of the exosporium crystalline layers.Journal of Bacteriology 09/2005; 187(15):5122-8. · 3.83 Impact Factor