Only One of the Five Ralstonia solanacearum Long-Chain 3-Ketoacyl-Acyl Carrier Protein Synthase Homologues Functions in Fatty Acid Synthesis

Ralstonia solanacearum , a major phytopathogenic bacterium, causes a bacterial wilt disease in diverse plants. Although fatty acid analyses of total membranes ofR. solanacearum showed that they contain primarily palmitic (C16:0 ), palmitoleic (C16:1 ) andcis -vaccenic (C18:1 ) acids, little is known regardingR. solanacearum fatty acid synthesis. TheR. solanacearum GMI1000 genome is unusual in that it contains four genes (fabF1 ,fabF2 ,fabF3 , andfabF4 ) annotated as encoding 3-ketoacyl-acyl carrier protein synthase II homologues and one gene (fabB ) annotated as encoding 3-ketoacyl-acyl carrier protein synthase I. We have analyzed this puzzling apparent redundancy and found that only one of these genes,fabF1 , encoded a long-chain 3-ketoacyl-acyl carrier protein synthase, whereas the other homologues did not play roles inR. solanacearum fatty acid synthesis. Mutant strains lackingfabF1 are nonviable, and thus, FabF1 is essential forR. solanacearum fatty acid biosynthesis. Moreover,R. solanacearum FabF1 has the activities of both 3-ketoacyl-acyl carrier protein synthase II and 3-ketoacyl-acyl carrier protein synthase I.