The anthrax toxin activator gene atxA is associated with CO2-enhanced non-toxin gene expression in Bacillus anthracis.
The Bacillus anthracis toxin genes, cya, lef, and pag, can be viewed as a regulon, in which transcription of all three genes is activated in trans by the same regulatory gene, atxA, in response to the same signal, CO2. In atxA+ strains, toxin gene expression is increased 5- to 20-fold in cells grown in 5% CO2 relative to cells grown in air. CO2-enhanced toxin gene transcription is not observed in atx4-null mutants. Here, we used two independent techniques to obtain evidence for additional CO2-induced atxA-regulated genes. First, total protein preparations from atxA4+ and atxA isolates grown in 5% CO2 and in air were examined by two-dimensional electrophoresis. Comparison of the resulting protein patterns indicated that synthesis of non-toxin proteins is influenced by growth in elevated CO2 and the toxin gene regulator, atxA. Second, we generated random transcriptional lacZ fusions in B. anthracis with transposon Tn917-LTV3. Transposon-insertion libraries were screened for mutants expressing CO2-enhanced atxA-dependent beta-galactosidase activity. DNA sequence analysis of transposon insertion sites in 17 mutants carrying CO2- and atxA-regulated fusions revealed 10 mutants carrying independent insertions on the 185-kb toxin plasmid pXO1 which did not map to the toxin genes. The tcr-lacZ fusion mutants (tcr for toxin coregulated) were Tox+, indicating that these genes may not be involved in anthrax toxin gene activation. Our data indicate a clear association of atxA with CO2-enhanced gene expression in B. anthracis and provide evidence that atxA regulates genes other than the structural genes for the anthrax toxin proteins.
Hoffmaster
A R
AR
Department of Microbiology and Molecular Genetics, Medical School, University of Texas-Houston, 77030, USA.
Koehler
T M
TM
D000942:Antigens, Bacterial; D001408:Bacillus anthracis / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000096:biosynthesis; D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D002245:Carbon Dioxide; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007763:Lac Operon; D008969:Molecular Sequence Data; D009154:Mutation; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014774:Virulence
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C030325:anthrax toxin; D002245:Carbon Dioxide