Abstract
Clostridium thermosulfurogenes EM1 formed blebs, i.e., protrusions still in contact with the cytoplasmic membrane, that originated from the cytoplasmic membrane during growth in batch culture and continuous culture. They could be observed squeezed between the cell wall and cytoplasmic membrane in cells with seemingly intact wall layers (surface layer and peptidoglycan layer) as well as in cells with wall layers in different states of degradation caused by phosphate limitation or high dilution rates. Blebs were found to turn into membrane vesicles by constriction in cases when the cell wall was heavily degraded. Bleb and vesicle formation was also observed in the absence of substrates that induce alpha-amylase and pullulanase synthesis. No correlations existed between bleb formation and the presence of active enzyme. Similar blebs could also be observed in a number of other gram-positive bacteria not producing these enzymes, but they were not observed in gram-negative bacteria. For immunoelectron-microscopic localization of alpha-amylase and pullulanase in C. thermosulfurogenes EM1, two different antisera were applied. One was raised against the enzymes isolated from the culture fluid; the other was produced against a peptide synthesized, as a defined epitope, in analogy to the N-terminal amino acid sequence (21 amino acids) of the native extracellular alpha-amylase. By using these antisera, alpha-amylase and pullulanase were localized at the cell periphery in samples taken from continuous culture or batch culture. In samples prepared for electron microscopy by freeze substitution followed by ultrathin sectioning, blebs could be seen, and the immunolabel pinpointing alpha-amylase enzyme particles was seen not only randomly distributed in the cell periphery, but also lining the surface of the cytoplasmic membrane and the blebs. Cells exhibiting high or virtually no enzyme activity were labeled similarly with both antisera. This finding strongly suggests that alpha-amylase and pullulanase may occur in both active and inactive forms, depending on growth conditions.