THE 16-KDA ALPHA-CRYSTALLIN (ACR) PROTEIN OF MYCOBACTERIUM-TUBERCULOSIS IS REQUIRED FOR GROWTH IN MACROPHAGES

Although the 16-kDa alpha-crystallin homologue of Mycobacterium tuberc ulosis (MTB) is the dominant protein produced by stationary phase cult ures in vitro, it is undetectable in logarithmically growing cultures. BS growing bacilli at defined oxygen concentrations, acr transcriptio n was shown to be strongly induced by mildly hypoxic conditions. Atr e xpression also was found to be induced during the course of in vitro i nfection of macrophages. The acr gene was replaced with a hygromycin r esistance cassette by allelic exchange in hITB H37Rv. The resulting De lta acr::hpt strain was shown to be equivalent to wild-type H37Rv in i n vitro growth rate and infectivity but was significantly impaired for growth in both mouse bone marrow derived macrophages and THP-1 cells. Lm addition to its proposed role in maintenance of long-term viabilit y during latent, asymptomatic infections, these results establish a ro le for the Acr protein in replication during initial MTB infection.