ABSTRACT
Escherichia coli NADH dehydrogenase-2 (NDH-2) is a primary dehydrogenase in aerobic respiration that shows cupric-reductase activity. The enzyme is encoded by ndh, which is highly regulated by global transcription factors. It was described that the gene is expressed in the exponential growth phase and repressed in late stationary phase. We report the maintenance of NDH-2 activity and ndh expression in the stationary phase when cells were grown in media containing at least 37 mM phosphate. Gene regulation was independent of RpoS and other transcription factors described to interact with the ndh promoter. At this critical phosphate concentration, cell viability, oxygen consumption rate, and NADH/NAD+ ratio were maintained in the stationary phase. These physiological parameters gradually changed, but NDH-2 activity remained high for up to 94 h. Phosphate seems to trigger an internal signal in the stationary phase mediated by systems not yet described.
Subject(s)
Electron Transport , Escherichia coli/physiology , Gene Expression Regulation, Bacterial , NADH Dehydrogenase/biosynthesis , Phosphates/metabolism , Aerobiosis , Artificial Gene Fusion , Bacterial Proteins/metabolism , Escherichia coli/chemistry , Gene Expression , Genes, Reporter , Microbial Viability , NAD/metabolism , Oxygen/metabolism , Pyridines/analysis , Sigma Factor/metabolism , beta-Galactosidase/biosynthesis , beta-Galactosidase/geneticsABSTRACT
13-epi-sclareol is a labdane-type diterpene isolated from the resinous exudates of the medicinal plant species Pseudognaphalium cheiranthifolium (Lam.) Hilliard et Burtt. and P. heterotrichium (Phil.) A. Anderb. This compound has antibacterial activity only against Gram-positive bacteria, showing a bactericidal and lytic action. The interaction of 13- epi-sclareol with the bacterial respiratory chain was analyzed. The compound inhibited oxygen consumption of intact Gram-positive cells, but not with Gram-negative bacteria. The compound inhibited NADH oxidase and cytochrome c reductase activities, while coenzyme Q reductase and the cytochrome c oxidase activities were not affected. These results suggest that the target site of 13-epi-sclareol is located between coenzyme Q and cytochrome c. Using cytoplasmic membrane fractions, the results of the analysis of the enzyme activities associated with the respiratory chain complexes were the same for both Gram-positive and Gram-negative bacteria, indicating that the compound has no access to the cytoplasmic membrane of intact Gram-negative bacteria. Thus, the Gram-negative envelope may act as a physical barrier that prevents the access of this compound to the site of action.