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No phosphatidylcholine (PC) was detected in themembrane of Rhodobacter sphaeroides pmtA mutant (PmtA1)lacking phosphatidylethanolamine (PE) N-methyltransferase,whereas PE in the mutant was increased up to the mole %comparable to the combined level of PE and PC of wild type.Neither the fatty acid composition nor the fluidity of membranewas altered by pmtA mutation. Consistently, aerobic andwild type. However, PmtA1 showed an extended lag phase (15 h)after the growth transition from aerobic to photoheterotrophicconditions, indicating the PC requirement for the efficientformation of intracytoplasmic membrane (ICM). Interestingly,the B800-850 complex of PmtA1 was decreased more thantwofold in comparison with wild type, whereas the level of theB875 complex comprising the fixed photosynthetic unit wasnot changed. Since puc expression is not affected by pmtAof the B800-850 complex in the ICM of R. sphaeroides.