Distinct morphological changes in the ultrastructure of Sarcina ventriculi were observed when cells were grown in medium of constant composition at pH extremes of 3.0 and 8.0. Transmission electron microscopy revealed that at low pH (less than or equal to 3.0) the cells formed regular packets and cell division was uniform. When the pH was increased (to greater than or equal to 7.0), the cells became larger and cell division resulted in irregular cells that varied in shape and size. Sporulation occurred at high pH (i.e., greater than or equal to 8.0). The sporulation cycle followed the conventional sequence of development for refractile endospores, with the appearance of a cortex and multiple wall layers. The spores were resistant to oxygen, lysozyme, or heating at 90 degrees C for 15 min. Spores germinated within the pH range of 4.6 to 7.0.
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