The glycerolipid and protein compositions of the outer and inner membranes of were studied. The wild-type strain Rm41 was shown to contain three phospholipids characteristic for most Gram-negative bacteria, phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol, this last compound being concentrated into the inner membrane. As in several bacteria interacting with plants, the presence of phosphatidylcholine, phosphatidyl--monomethylethanolamine and phosphatidyl--dimethylethanolamine was also demonstrated. Induction of the genes by luteolin did not affect the lipid composition and no difference in lipid composition was found between the wild-type strain and a number of Nodand Fixmutants tested. Protein analysis of the inner and outer membranes showed that they exhibit very different patterns with several bands specific for one or the other membrane. A Nodmutant carrying a large deletion in the symbiotic megaplasmid pRme41b showed differences in the protein patterns even before induction by luteolin, indicating that this megaplasmid codes for several membrane proteins. When the genes of strain Rm41 were induced by luteolin, two new bands at around 60 kDa and 44 kDa appeared in both the outer and the inner membranes. By using a strain overexpressing the genes and the technique of immunoblotting with antibodies against NodC, it was confirmed that the 44 kDa band corresponded to the NodC protein. This protein was not found in a C:: Tn mutant. This work represents the first step in the characterization of modifications induced by luteolin treatment at the membrane level.


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