Zwitterionic membrane lipids phosphatidylethanolamine and phosphatidylcholine affect transcription and physiology of Sinorhizobium meliloti in different ways
Dr. Otto Geiger, Centro de Ciencias Genómicas, Universidad Nacional Autόnoma de México, Cuernavaca, Morelos, México
Sinorhizobium meliloti contains the negatively charged phosphatidylglycerol and cardiolipin as well as the zwitterionic phosphatidylethanolamine (PE) and phosphatidylcholine (PC) as major membrane phospholipids. In previous studies we had isolated S. meliloti mutants that lack PE or PC. Transcript profiles of mutants unable to form PE or PC are distinct; they differ from each other and they are different from the wild type. For example, a PE-deficient mutant of S. meliloti shows an increase of transcripts that might be required for the degradation of C1 compounds and a decrease of transcripts that might be required for iron uptake or for the catabolism of myo-inositol. In contrast, a PC-deficient mutant of S. meliloti shows an increase of transcripts that encode a possible lytic transglycosylase or enzymes required for succinoglucan biosynthesis and a decrease of transcripts that are required for flagellum formation. Changes similar to those in the PC-deficient mutant are observed when S. meliloti wild type is exposed to acidic conditions of growth. Growth of the PC-deficient mutant is especially sensitive to acidity and we suggest that a PC-deficient membrane in S. meliloti is more fluid and therefore more permeable for protons. Also, some mutants altered in the ExoR/ExoS/ChvI regulatory system resemble the PC-deficient mutant in their transcript profile and we suggest that the lack of PC in the sinorhizobial membrane is sensed and transmitted by the ExoR/ExoS/ChvI regulatory system.