My lab studies the obligate intracellular pathogen, Rickettsia prowazekii . Rickettsiae are transmitted by arthropods and are the cause of diseases such as epidemic typhus and Rocky Mountain spotted fever. These fascinating organisms exist in the cytoplasm of the host cell, unbound by any host cell-derived membrane structures. As a result, R. prowazekii has evolved into the quintessential metabolic scavenger; many large/charged metabolites available in the rich milieu of eukaryotic cytosol are transported, not synthesized. My laboratory is interested in examining the interplay between transport of host cell metabolites and endogenous biosynthetic pathways to determine how these obligate intracellular pathogens fulfill their metabolic requirements. Will this give us a glimpse into how growth in cytosol has directed the evolution of this small genome organism (only 834 putative open reading frames!)? This is the ultimate philosophical question! Rickettsial fatty acid and phospholipid biosyntheses are ideal model systems to dissect this balance between transport and synthesis. Rickettsiae appear to have evolved a previously unidentified mechanism for malonyl-CoA synthesis, the first committed step in fatty acid synthesis that differs from mechanisms currently described  in  the  literature AND rickettsiae  possess  a  transport  system  for  the

substrate for this enzyme, acetyl-CoA. A similar balance exists for rickettsial glycerol-3-phosphate (G3P) synthesis a critical precursor of phospholipids. Rickettsiae possess a protein annotated as a G3P dehydrogenase which converts dihydroxyacetone phosphate (DHAP) to G3P, required for phospholipid synthesis. The presence of this enzyme seems strikingly out-of-place considering that rickettsiae DO NOT possess glycolytic or gluconeogenic pathways to produce DHAP. We have determined that rickettsiae transport DHAP from the host. We are currently identifying and characterizing this system.

In addition to studies of Rickettisae physiology, we are interested in elucidating mechanisms of gene regulation in this organism. The entire DNA sequence of R. prowazekii is known and at least 13 open reading frames (ORFs) have been annotated as regulatory gene products. This poorly understood aspect of gene regulation in rickettsiae may be critical to pathogenesis. My group is interested in identifying the target genes of these regulatory networks and determining their relative contributions to Rickettsial pathogenesis. In particular, we are interested in the study of two-component response regulators and elucidation of the regulons of genes under their control.

Recent Publications:

Alexeyev, M.F., R.A.W. Roberts, R.M. Daugherty, J.P. Audia, and H.H. Winkler. 2004. Cysteine-scanning mutagenesis and thiol modification of the Rickettsia prowazekii ATP/ADP Translocase: evidence that TM I and II, but not III, are structural components of the aqueous ATP translocation channel. Biochemistry. 43(22): 6995-7002.

Daughtery, R.M., N. Linka, J.P. Audia, C. Urbany, H.E. Neuhaus, and H.H. Winkler. 2004. The nucleotide transporter of Caedibacter caryophilus exhibits an extended substrate spectrum compared to the analogous ATP/ADP Translocase of Rickettsia prowazekii. J. Bacteriol. 186(10): 3262-3265.

Winkler, H.H., R. M. Daugherty, and J.P. Audia. 2003. Cysteine-scanning mutagenesis and thiol modification of the Rickettsia prowazekii ATP/ADP translocase: Evidence TM VIII faces an aqueous channel. Biochemistry. 42(43): 12562-12569.

Audia J. P., Foster J. W. 2003. Acid Shock Accumulation of Sigma S in Salmonella enterica Involves Increased Translation, Not Regulated Degradation. J. Mol. Microbiol. Biotechnol. 5(1): 17-28.

Bang, I. S., J. P. Audia, Y. K. Park, and J. W. Foster. 2002. Autoinduction of the ompR response regulator by acid shock and control of the Salmonella enterica acid tolerance response. Mol. Microbiol. 44: 1235-50.

Audia, J. P., C. C. Webb and J. W. Foster. 2001. Breaking through the acid barrier: an orchestrated response to proton stress by enteric bacteria. Int. J. Med. Microbiol. 291:1-10.

Mukhopadhyay, S., J. P. Audia, and H. E. Schellhorn. 2000. BarA, a probable two-component regulator, is required for transcriptional induction of the conserved alternative sigma factor RpoS in Escherichia coli. Mol. Microbiol. 37: 371-81.

Moreno, M*., J. P. Audia*, C. Webb, S. Bearson and J. W. Foster. 2000 Regulation of Sigma S degradation in Salmonella enterica var Typhimurium: in vivo interactions between Sigma S, the response regulator MviA/RssB, and ClpX. J. Mol. Microbiol Biotech. 2:245-254. (*these authors were listed as equal contributors to this work).

Chang, L., L. Wei, J. P. Audia, R. A. Morton, and H. E. Schellhorn. 1999. Expression of the Escherichia coli NRZ nitrate reductase is highly growth phase dependent and is controlled by RpoS, the alternative vegetative sigma factor. Mol. Microbiol. 34: 756-66.

Schellhorn, H. E., J. P. Audia, L. Wei, and L. Chang. 1998. Identification of conserved, RpoS-dependent stationary-phase genes of Escherichia coli. J. Bacteriol. 180: 6283-91.

Links

American Society for Rickettsiology Homepage (http://www.cas.umt.edu/rickettsiology/)

RicBase Rickettsia Genome Database (http://igs-server.cnrs-mrs.fr/mgdb/Rickettsia/)

NCBI BLAST Homepage (http://www.ncbi.nlm.nih.gov/BLAST/)

KEGG Encyclopedia (http://www.genome.ad.jp/kegg/kegg2.html)

Canadian Broadcasting Corporation Homepage (http://www.cbc.ca/)