Expression of acid-stable proteins and modified lipopolysaccharide of Yersinia pestis in acidic growth medium.

Growth medium simulating the phagolysosomal environment in which Yersinia pestis resides during its intracellular growth in vivo was made by acidification of Ca2+-deficient medium. When used for cultivation of Y. pestis EV-76 (pLCR+;pPst+;pFra+) and its isogenic derivatives--KM-217 (pLCR+;pPst-;pFra-) and KM-218 (pLCR-;Ppst-; pFra-)--this medium permitted survival and proliferation of viable bacteria without any growth restriction. Moreover, a correlation between the pH of growth medium and bacterial yield was established. Acidification completely inhibited fibrinolytic (pla protease) activity (PAA) of Y. pestis carrying pPst and allowed synthesis of specific outer-membrane proteins (Yops) without any degradation by the pla protease. Comparison of whole-cell lysates of the strains tested in PAAG-SDS showed that, in addition to previously described Yops, Y. pestis synthesised new acidic proteins which appeared only under acidic conditions and were encoded by pLCR or chromosomally. Some changes in O-specific polysaccharide chains of Y. pestis LPS that were dependent on cultivation temperature and pH of the medium were also demonstrated.