Electron microscope and autoradiographic study of ultrastructural aspects of competence and deoxyribonucleic acid absorption in Bacillus subtilis: ultrastructure of competent and noncompetent cells and cellular changes during development of competence.

By means of electron microscope autoradiography of component cultures of Bacillus subtilis exposed to [(3)H]thymidine-labeled transforming deoxyribonucleic acid competent and noncompetent cells can be distinguished. Competence is not limited to a specific phase of the cell division cycle. With serial section electron microscopy of competent and noncompetent cells, two types of mesosomal structures are observed: mesosomes connected to the plasma membrane only (plasma membrane mesosomes) and mesosomes which are additionally connected to the nuclear bodies (nuclear mesosomes). The two types show different cellular distributions. Especially the number of nuclear mesosomes is higher in competent than in noncompetent cells. This, and the observation that the increase and decrease of competence is correlated with both the number of cells carrying nuclear mesosomes and the number of nuclear mesosomes per cell, suggests that mesosomes are involved in the acquisition of competence.