Differential Expression of Borrelia burgdorferiProteins during Growth In Vitro

ABSTRACTIn an earlier paper we described the transcriptionally regulated differential levels of expression of two lipoproteins of Borrelia burgdorferi, P35 and P7.5, during growth of the spirochetes in culture from logarithmic phase to stationary phase (K. J. Indest, R. Ramamoorthy, M. Solé, R. D. Gilmore, B. J. B. Johnson, and M. T. Philipp, Infect. Immun. 65:1165–1171, 1997). Here we further assess this phenomenon by investigating whether the expression of other antigens of B. burgdorferi, including some well-characterized ones, are also regulated in a growth-phase-dependent manner in vitro. These studies revealed 13 additional antigens, including OspC, BmpD, and GroEL, that were upregulated 2- to 66-fold and a 28-kDa protein that was downregulated 2- to 10-fold, during the interval between the logarithmic- and stationary-growth phases. Unlike with these in vitro-regulated proteins, the levels of expression of OspA, OspB, P72, flagellin, and BmpA remained unchanged throughout growth of the spirochetes in culture. Furthermore, ospAB, bmpAB,groEL, and flaall exhibited similar mRNA profiles, which is consistent with the constitutive expression of these genes. By contrast, the mRNA and protein profiles of ospCand bmpDindicated regulated expression of these genes. While bmpDexhibited a spike in mRNA expression in early stationary phase, ospCmaintained a relatively higher level of mRNA throughout culture. These findings demonstrate that there are additional genes besides P7.5and P35whose regulated expression can be investigated in vitro and which may thus serve as models to facilitate the study of regulatory mechanisms in an organism that cycles between an arthropod and a vertebrate host.