Borrelia burgdorferi proteins whose expression is similarly affected by culture temperature and pH

Previously we had demonstrated the upregulation in the expression of severa l proteins, including the lipoproteins OspC and P35, of Borrelia burgdorfer i in the stationary growth phase. Since the expression of OspC is also know n to be affected by culture temperature and,pH, we examined the effects of both variables on the expression of the remaining stationary-phase-upregula ted proteins. Our study revealed that the expression of each of the remaini ng stationary-phase-upregulated proteins, P35 included, was also influenced by culture temperature; these proteins were selectively expressed at 34 de greesC but not at 24 degreesC. Significantly, the expression of a majority of these proteins was also affected by culture pH, since they were abundant ly expressed at pH 7.0 (resembling the tick midgut pH of 6.8 during feeding ) but only sparsely at pH 8.0 (a condition closer to that of the unfed tick midgut pH of 7.4). We propose that this group of B. burgdorferi proteins, which in culture is selectively expressed under conditions of 34 degreesC a nd pH 7.0, may be induced in the tick midgut during the feeding event. Furt hermore, the differential and coordinate expression of these proteins under different environmental conditions suggests that the encoding genes may be coregulated.