Comparative Transcriptional Study of the Putative Mannose Donor Biosynthesis Genes in Virulent Mycobacterium tuberculosis and Attenuated Mycobacterium bovis BCG Strains
ABSTRACTMycobacterium tuberculosiscontains mannosylated cell wall components which are important in macrophage recognition and response. The building block for the mannosyl constituents of these components is GDP-mannose, which is synthesized through a series of enzymes involved in the mannose donor biosynthesis pathway. Nothing is known about the expression levels of the genes encoding these enzymes during the course of infection. To generate transcriptional profiles for the mannose donor biosynthesis genes from virulentM. tuberculosisand attenuatedMycobacterium bovisBCG, bacteria were grown in broth culture and within human macrophages. Our results with broth-grown bacteria show that there are differences in expression of the selected genes betweenM. tuberculosisand BCG, with increased expression ofmanCinM. tuberculosisandmanAin BCG during stationary-phase growth. Results forM. tuberculosisextracted from within macrophages show thatwhiB2is highly expressed andmanBandmanCare moderately expressed during infection.Rv3256c,Rv3258c, andppm1have high expression levels early and decreased expression as the infection progresses. Results with BCG show that, as inM. tuberculosis,whiB2is highly expressed throughout infection, whereas there is either low expression or little change in expression of the remaining genes studied. Overall, our results show that there is differential regulation of expression of several genes in the mannose donor biosynthesis pathway ofM. tuberculosisand BCG grown in broth and within macrophages, raising the possibility that the level of mannose donors may vary during the course of infection and thereby impact the biosynthesis of mannose-containing cell wall molecules.