Development of a freeze substitution technique to examine the structure of Lactobacillus casei GR-1 grown in agar and under batch and chemostat culture conditions

A morphological examination was undertaken of Lactobacillus casei GR-1 by freeze substitution technique developed to prevent condensation upon fixation and to preserve extracellular material surrounding the cell wall. The strain was cultured for 24 h in 5% CO sub(2) at 37 degree C initially in brain heart infusion agar supplemented with 2% yeast extract, and the cells formed a short, electron-dense, tightly bound capsule observed under electron microscopy. The cell wall structure was resolved in most cases. The results indicate that nutrient conditions affect the morphology of Lactobacillus) and verify that the freeze substitution technique is a useful method to analyze the structure of bacterial cell surfaces.