Physiological basis of the low calcium response in Yersinia pestis.
It is established that duplication in vitro of that amount of Ca2+ (2.5 mM) and Mg2+ (1.5 mM) present in blood permits vegetative growth of Yersinia pestis with repression of virulence factors encoded by the Lcr plasmid (Lcr+); similar simulation of intracellular fluid (no Ca2+ and 20 mM Mg2+) promotes bacteriostasis with induction of these virulence determinants. However, proliferation of yersiniae in mice occurs primarily within necrotic focal lesions (supplied by Ca(2+)-deficient host cell cytoplasm) within visceral organs rather than in Ca(2+)-sufficient blood. The present study addressed this enigma by defining conditions necessary for achieving vegetative growth of Lcr+ yersiniae at 37 degrees C in simulated intracellular fluid. Maximum optical densities were increased by substitution of K+ for Na+ and elimination of Cl-; the combination of Na+ plus L-glutamate was selectively toxic to Lcr+ cells. This phenomenon was attributed in part to the absence of aspartase in Y. pestis (a lesion known to facilitate massive accumulation of L-aspartate via transamination of the oxalacetate pool by L-glutamate). Replacement of L-glutamate by exogenous L-aspartate or alpha-ketoglutarate reversed this toxicity by favoring retention of oxalacetate. Proliferation of Lcr+ cells in a medium containing K+ and L-aspartate but lacking added Ca2+ and Na+ was markedly enhanced by increasing the concentration of fermentable carbohydrate. Accordingly, in the worst-case scenario (i.e., added Na+, Cl-, and L-glutamate), Lcr+ yersiniae underwent restriction of growth after one doubling, and in the best-case scenario (i.e., added K+ and L-aspartate), the organisms completed more than five doublings, thereby achieving full-scale growth. Both of these Ca(2+)-deficient media promoted maximum induction of Mg(2+)-induced V antigen, a virulence factor encoded by the Lcr plasmid.
Department of Microbiology, Michigan State University, East Lansing 48824.
J M
JM
Fowler
R R
RR
Brubaker
D000942:Antigens, Bacterial / Q000096:biosynthesis*; D002118:Calcium / Q000494:pharmacology*; D050260:Carbohydrate Metabolism; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000494:pharmacology; D010071:Oxaloacetates / Q000494:pharmacology; D010957:Plasmids / Q000276:immunology*; D052899:Pore Forming Cytotoxic Proteins; D012964:Sodium / Q000494:pharmacology; D014774:Virulence / Q000235:genetics; D015010:Yersinia pestis / Q000187:drug effects / Q000254:growth & development / Q000276:immunology*
D000942:Antigens, Bacterial; D003470:Culture Media; C043908:LcrV protein, Yersinia; D010071:Oxaloacetates; D052899:Pore Forming Cytotoxic Proteins; D018698:Glutamic Acid; D012964:Sodium; D002118:Calcium