Bacillus cereus group species: Genetics, Physiology, and Host Interactions

Bacillus anthracis, a Gram-positive spore-forming soil bacterium and member of the Bacillus cereus group species, is distinguished by its ability to cause anthrax in mammals. Depending upon the route of entry, infection with spores can result in cutaneous disease, which is readily treatable with antibiotics, or systemic disease, which is often fatal. The continuing worldwide incidence of anthrax in animal populations, risk of human infection associated with animal outbreaks, and potential for use of B. anthracis as a biological weapon, warrant continued investigation of this organism and its virulence mechanisms.

Virulence of B. anthracis is associated with synthesis of the anthrax toxin proteins, protective antigen, lethal factor, and edema factor, and an antiphagocytic capsule composed of poly-D-glutamic acid. Our work focuses on the genetic basis for expression of the structural genes for the toxin proteins, pagA, lef, and cya, the capsule biosynthesis operon, capBCAD, and other genes with a known or suspected role in virulence. The toxin genes are located on pXO1 (182-kb), while the capsule genes are found on pXO2 (93-kb).

The model for virulence gene regulation in B. anthracis is of growing complexity and includes numerous trans-acting regulators. The most critical and far-reaching regulator is atxA, a pXO1 gene that appears to be unique to the species. atxA is essential for expression of all toxin genes, contributes to control of the capsule operon, and affects expression of numerous chromosomal genes. We are establishing the molecular functions and epistatic relationships of atxA and other regulators. Using a mouse model for inhalation anthrax, we are evaluating gene expression and development in vivo, including spatial and temporal measurements of germination and dissemination.

In related studies, we are examining the relatedness of B. anthracis to the closely-related, but less harmful species, B. cereus and B. thuringiensis. The three species are very similar physiologically and genetically, yet they cause vastly different diseases. With certain important exceptions, key differences in gene expression, as opposed to genetic content, may result in the differing pathogenesis associated with these species.

We are also interested in the B. anthracis lifecycle outside of the mammalian host. We are studying B. anthracis germination and multiplication in the soil, particularly in association with the plant rhizosphere. These investigations have implications for genetic exchange between B. anthracis and other soil organisms and for detection of the bacterium in the environment.

SELECTED PUBLICATIONS:

Drysdale M, Olson G, Koehler TM, Lipscomb MF, and Lyons CR (2007). Murine innate immune response to virulent toxigenic and nontoxigenic mutants of Bacillus anthracis. Infect. Immun. 75:1757-1764. [abstract]

Hadjifrangiskou M, Chen Y, and Koehler TM (2007). The alternative sigma factor sH is required for toxin gene expression in Bacillus anthracis. J. Bacteriol. 189:1874-1883. [abstract]

Ross CL, Koehler TM (2006). plcR/papR-independent expression of Anthrolysin O by Bacillus anthracis. J. Bacteriol. 188:7823-7829. [abstract]

Heninger S, Drysdale M, Lovchik J, Hutt J, Lipscomb MF, Koehler TM, Lyons CR (2006). Toxin-deficient mutants of Bacillus anthracis are lethal in a murine model for pulmonary anthrax. Infect. Immun. 74:6067-6074. [abstract]

Hu H, Sa Q, Koehler TM, Aronson AI, Zhou D (2006). Inactivation of Bacillus anthracis spores in murine primary macrophages. Cell. Microbiol. 8:1634-1642. [abstract]

Saile E, Koehler TM (2006). Bacillus anthracis multiplication, persistence, and genetic exchange in the rhizosphere of grass plants. Appl Environ Microbiol 72:3168. [abstract]

Drysdale M, Bourgogne, A, Koehler TM (2005). Transcriptional analysis of the Bacillus anthracis capsule regulators. J Bacteriol 187:5108. [abstract]

Drysdale M, Heninger S, Hutt J, Chen Y, Lyons CR, Koehler TM (2005). Capsule synthesis by Bacillus anthracis is required for dissemination in murine inhalation anthrax. EMBO J. 24:221. [abstract]

Xu Y, Lian X, Chen Y, Koehler TM, Hook M (2004). Identification and biochemical characterization of two novel collagen binding MSCRAMMs of Bacillus anthracis. J. Biol. Chem. 279:51760. [abstract]

Chen Y, Tenover F,4 Koehler TM (2004). ß-lactamase gene expression in a penicillin-resistant Bacillus anthracis strain. Antimicrob. Agents Chemother. 48:4873. [abstract]

Tinsley E, Naqvi A, Bourgogne A, Koehler TM, Khan SA (2004). Isolation of a minireplicon of plasmid pXO2 of Bacillus anthracis and characterization of the plasmid-encoded RepS replication protein. J Bacteriol 186:2717.[abstract]

Drysdale M, Bourgogne A, Hilsenbeck SG, Koehler TM (2004). atxA controls Bacillus anthracis capsule synthesis via acpA and a newly-discovered regulator, acpB. J Bacteriol 186:307.[abstract]

Bourgogne A, Drysdale M, Hilsenbeck SG, Peterson SN, Koehler TM (2003) Global effects of virulence gene regulators in a Bacillus anthracis strain with both virulence plasmids. Infect Immun 71:2736 [abstract]

Chen Y, Succi J, Tenover FC, Koehler TM (2003) ß-lactamase genes of the penicillin-susceptible Bacillus anthracis Sterne strain. J Bacteriol 185:823 [abstract]

Read TD, ..., Friedlander AM, Koehler TM, Hanna PC, Kolsto AB, Fraser CM (2003) The genome sequence of Bacillus anthracis Ames and comparison to closely related bacteria. Nature 423:81 [abstract]

Shannon JG, Ross CL, Koehler TM, Rest RF (2003) Characterization of anthrolysin O, the Bacillus anthracis cholesterol-dependent cytolysin. Infect Immun 71:3183 [abstract]

Materon IC, Queenan AM, Koehler TM, Bush K, Palzkill T (2003) Biochemical characterization of ß-lactamases Bla1 and Bla2 from Bacillus anthracis. Antimicrob Agents Chemother 47:2040 [abstract]

[compete list of publications on PubMed]

Postdoctoral Research Fellow positions
• Position available to study B. anthracis-host interactions, including virulence mechanisms and host-induced gene expression. Strong consideration will be given to applicants with experience in molecular genetics, microscopy, cell culture and animal models.
• Position available to study regulation of virulence gene expression in B. anthracis and related species. Strong consideration will be given to applicants with experience in molecular genetics, protein structure/function and bioinformatics.

A recent Ph.D. in microbiology or a related area is required. All applicants must be able to comply with Select Agent regulations and pass Department of Justice security risk assessment. Send CV, description of research experience, and names/tele./e-mail of three referees to Terri Koehler