Supply of acetyl-CoA to N₂-fixing bacteroids: insights from the mutational and proteomic analyses of <em>Sinorhizobium meliloti</em>

Rhizobia represent a diverse group of gram-negative bacteria capable fixing atmospheric nitrogen in symbiosis with leguminous plants. Mechanisms symbiotic efficiency are important to study not only reveal the “fine tuning” host–symbiont supra-organismal genetic system emergence, but also develop agriculture minimal environmental risks. In this paper we demonstrate that among seven genes whose inactivation by Tn5 insertions results an increased rhizobia (Sinorhizobium meliloti) alfalfa (Eff++ phenotype), six involved metabolism small molecules. One them (SMc04399) encodes for acetate-CoA transferase catalyzing formation acetyl-CoA from acyl-CoA. Since is required operation Krebs cycle, providing ATP N2 fixation, suggest significant portion coenzyme utilized bacteroids provided plant cell supporting energy-consuming nitrogenase reaction. Proteomic data analysis allow us lability enzymatic pathways which production and catabolism should be modified obtain Eff++ phenotype. This phenotype was developed after NoeB protein host-specific nodulation characterized elevated wild type S. meliloti bacteroids, suggesting multifunctional role noeB operation.