Submitted to: Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/23/2007
Publication Date: 5/20/2007
Citation: Roberts, D.P., Mckenna, L.F., Lohrke, S.M., Rehner, S.A., De Souza, J.T. 2007. Pyruvate dehydrogenase activity is important for colonization of seeds and roots by enterobacter cloacae. Soil Biology and Biochemistry. 39:2150-2159. Interpretive Summary: Soilborne plant pathogens cause diseases that result in major economic losses to farmers in the United States. Biological control measures for these diseases need to be developed due to environmental problems associated with existing chemical controls. However, little is known regarding the genetic and biochemical means by which biological control agents grow on seeds and roots of plants and suppress pathogens that infect these seeds and roots. Colonization of roots and other plant parts is thought to be important for biological control. In this study we demonstrated that the aceF gene of the biological control bacterium Enterobacter cloacae was important for colonization of seeds and roots of diverse crop plants by this bacterium. This gene encodes the dihydrolipoamide acetyltransferase subunit of the pyruvate dehydrogenase enzyme complex. This enzyme complex is critical for growth on carbohydrates, amino acids and other organic acids released by seeds and roots by E. cloacae. This information will be useful to scientists devising strategies to improve biological control through enhancement of growth of biological control agents on cucumber roots.
Technical Abstract: Enterobacter cloacae shows promise for suppression of damping-off of cucumber and other crops caused by Pythium ultimum. Enterobacter cloacae M43 is a transposon mutant of E. cloacae 501R3 that was significantly impaired in colonization of seeds and roots of diverse crop plants. Strain M43 did not increase in population on cucumber, sunflower, and wheat seeds and was significantly reduced in growth on pea seeds relative to strain 501R3. Populations of M43 were also dramatically lower than those of strain 501R3 in cucumber, pea, sunflower, and wheat rhizosphere in 42 d experiments. Molecular characterization of strain M43 demonstrated that there was a single transposon insertion in the genome of this strain and that this insertion was in a region of the E. cloacae genome with a high degree of DNA sequence similarity with aceF. aceF encodes the dihydrolipoamide acetyltransferase subunit of the pyruvate dehydrogenase complex. Cell lysates from strain 501R3 grown on minimal medium plus 50 mM glycerol and 2 mM acetate contained 0.011 + 0.0036 U pyruvate dehydrogenase activity while cell lysates from M43 grown under identical conditions contained no detectable pyruvate dehydrogenase activity. Additionally, the nutritional use profile of M43 under aerobic and anaerobic conditions was as expected for an ace mutant. Experiments reported here strongly suggest a role for aceF and the pyruvate dehydrogenase complex in colonization of seeds and roots of diverse crop plants by E. cloacae.