Role of Purine Biosynthesis in Bacillus anthracis Pathogenesis and Virulence

Abstract

Bacillus anthracis, the etiological agent of anthrax, is a spore-forming, Gram-positive bacterium and a category A biothreat agent. Screening of a library of transposon-mutagenized B. anthracis spores identified a mutant displaying an altered phenotype that harbored a mutated gene encoding the purine biosynthetic enzyme PurH. PurH is a bifunctional protein that catalyzes the final steps in the biosynthesis of the purine IMP. We constructed and characterized defined purH mutants of the virulent B. anthracis Ames strain. The virulence of the purH mutants was assessed in guinea pigs, mice, and rabbits. The spores of the purH mutants were as virulent as wild-type spores in mouse intranasal and rabbit subcutaneous infection models but were partially attenuated in a mouse intraperitoneal model. In contrast, the purH mutant spores were highly attenuated in guinea pigs regardless of the administration route. The reduced virulence in guinea pigs was not due solely to a germination defect, since both bacilli and toxins were detected in vivo, suggesting that the significant attenuation was associated with a growth defect in vivo. We hypothesize that an intact purine biosynthetic pathway is required for the virulence of B. anthracis in guinea pigs.

CovRS-Regulated Transcriptome Analysis of a Hypervirulent M23 Strain of Group A Streptococcus pyogenes Provides New Insights into Virulence Determinants

“…The higher requirements of purine biosynthesis by CovS Ϫ may reflect the limited concentration of purines in the THY medium or may represent clones naturally selected by the hypervirulent CovS Ϫ strain during host infection. An active purine biosynthesis pathway was also identified in other intracellular pathogens, such as Listeria monocytogenes (51) and Bacillus anthracis (52), due to limited concentration of purines in host cells. Two genes involved in glutamine biosynthesis, glnA and glnR, were also highly activated in M23ND/CovS Ϫ at LP growth.…”

Helicobacter pylori Relies Primarily on the Purine Salvage Pathway for Purine Nucleotide Biosynthesis

“…Often, numerous purine nucleotide biosynthesis genes are found in the same operons, allowing them to be controlled by a single, regulatory mechanism (34)(35)(36). Regulators for purine nucleotide biosynthesis and salvage pathways are abundant; regulatory promoter-binding proteins (33,34) and riboswitches (4,43) are utilized for many of these genes in most other bacteria.…”

“…Genes comprising either pathway often are found in operons (34)(35)(36) and are often regulated by the same regulatory promoterbinding proteins (33,34) or riboswitches (4,43), generating feedback loops that allow the organism to alternate between the two synthesis pathways while maintaining adequate purine nucleotide pools. Additionally, the allosteric regulation of nucleotide pools has also been shown in key enzymes in both purine (60,61) and pyrimidine (59) nucleotide biosynthesis, indicating enzyme activity also may add an additional means of regulation.…”

“…Studies specific to enzymes found in the de novo purine synthesis pathway have shown that absence of key enzymes in the pathway can directly affect growth rates and virulence in Bacillus anthracis (35), Y. pestis (9), S. Typhimurium (48), and Streptococcus pneumoniae (56). Similarly, the purine salvage pathway has also been investigated in numerous organisms (42,55).…”

Novel Role for the yceGH Tellurite Resistance Genes in the Pathogenesis of Bacillus anthracis

“…Sequencing of the B. anthracis genome identified a number of genes that share homologies to known virulence factors of other pathogens (3). Subsequently, studies have coupled targeted mutagenesis with rodent infection models to identify chromosomal virulence genes, including the dltABCD operon for lipoteichoic acid modification (4), the asbAB siderophore (5), the ABC transporter mntA (6), the nitric oxide synthase nos (7), the ClpXP protease (8), the purine biosynthesis gene purH (9), and the stress resistance gene hrtA (10).…”