Fig 5.

Electron microscopy analysis of vegetative bacilli. (A) Scanning electron microscopy analysis of bacilli (WT, ltaS1 ltaS2 pJK4 [double mutant carrying the empty vector], and ltaS1 ltaS2 pltaS2 [complemented strain]) serially dehydrated and sputter coated with 80% platinum–20% palladium to 8 nm. Cells of wild-type and complemented mutant strains appear as rod-shaped bacilli, whereas the ltaS1 ltaS2 mutant bacilli remain tethered in long chains. Scale bar, 50 μm. (B) Thin-section transmission electron microscopy of the same cells as in panel A showing the irregular and deformed structure of the ltaS1 ltaS2 mutant compared to that of the WT and complemented strains. Scale bar, 200 nm. (C) Close-up of the cell envelope of thin-sectioned bacilli shown in panel B. The layers, from bottom to top, represent cytoplasm, membrane (thin darker line), envelope, and environmental milieu. Scale bar, 20 nm. (D) Measurement of the thickness of the cell envelope of bacilli. Measurements were performed using transmission electron micrographs as shown in panels B and C. Each dot represents one measurement.