Cell Division and Photosynthetic Apparatus Construction in the Cell Envelope Deficient ‘Phofil’ Mutant of Rhodopseudomonas sphaeroides

Summary: The ‘Phofil’ mutant of Rhodopseudomonas sphaeroides showed a disturbed adaptation with respect to a change from aerobic to photosynthetic conditions. The mutation was a pleiotropic one: firstly, the cells formed multinucleate filaments with occasional septa, and secondly, they integrated only a fraction of the synthetized pigments. The phenotypes appeared in photosynthetic conditions during a period of unbalanced growth (unadapted state) followed by balanced exponential growth where the phenotypes were corrected (adapted state). Ultraviolet light irradiation or exposure to low temperature, but not partial or total depigmentation, caused adapted cells to return to the unadapted state. Except for those associated with pigments, no appreciable defect in the polypeptide composition of the cell envelope was detected by SDS—polyacrylamide gel electrophoresis. However, the protein/phospholipid ratio of the envelope fraction was approximately 50% higher, in the mutant than in the parent. These findings, and others described in the text, suggested the existence of defects in the cell wall and in the inner membrane.