Tuberculosis bacterium is double-protected

Light and electron tomographic images of Mycobacterium bovis BCG. Top left: Several mycobacteria in the light microscope with about 1000 times magnification. Top right: Longitudinal section through a three-dimensionally reconstructed bacterial cell of 1.5 µm in length. The data were recorded in an electron microscope using the technique of cryo-electron tomography. The white bar indicates 100 nanometer or 0.1 micron. Bottom: 3-D structure of a section through the mycobacterial cell envelope. The structural details are color-coded. In yellow: the inner (left) and the outer (right) lipid bilayer. In blue: cell wall polymers that bind the mycolic acids. The cell envelope is 35 nanometers thick. Image: Christian Hoffmann/Harald Engelhardt, MPI of Biochemistry, Martinsried, Germany