Primary role of NADH formed by glucose dehydrogenase in ATP provision at the early stage of spore germination in Bacillus megaterium QM B1551

Flow cytometry analysis of germinating Bacillus spores, using membrane potential dye

Germination of Bacillus anthracis spores is necessary for the transcription of plasmidic genes essential to the infection. Assessing germination potential is crucial to predict the risk associated with pathogenic Bacillus exposure. The aim of this study was to set up a viability assay based on membrane potential in order to predict the earliest germination event of spores. B. cereus and two strains of B. subtilis were used. The spores were isolated with a sodium bromide gradient. Approximately 10(7) spores were incubated at 37 degrees C in tryptic soy broth (TSB). Aliquots were harvested at predetermined times and stained with 3,3'-dihexyloxacarbocyanine iodide [DiOC(6)(3)] or with bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC(4)(3)]. Fluorescence characteristics were obtained using flow cytometry. The earliest detectable activation of membrane potential occurred after 15 min of incubation in TSB using DiOC(6)(3). Using DiBAC(4)(3), the earliest detectable signal was after 4 h of incubation. Control experiments using carbonyl cyanide m-chlorophenylhydrazone (CCCP)-treated spores did not show any change in the fluorescence intensity over time. Since no membrane potential and no germination were detected in CCCP-treated spores, the activation of membrane potential seems to be associated with germination. DiOC(6)(3) can be used as an early membrane potential indicator for spores. DiBAC(4)(3), by contrast, is not a early membrane potential marker.

Aggregation, dissociation and unfolding of glucose dehydrogenase during urea denaturation

The effect of urea on glucose dehydrogenase from Bacillus megaterium has been studied by following changes in enzymatic activity, conformation and state of aggregation. It was found that the denaturation process involves several transitions. At very low urea concentrations (below 0.5 M), where the enzyme is fully active and tetrameric, there is a conformational change as monitored by an increase in intensity of the tryptophan fluorescence and a maximum exposure of organized hydrophobic surfaces as reported by the fluorescence of 4,4'-dianilino-1,1'-binaphthyl-5.5'-disulfonic acid. At slightly higher urea concentrations (0.75-2 M), a major conformational transition occurs, as monitored by circular dichroism and fluorescence measurements, in which the enzyme activity is completely lost and is concomitant with the formation of interacting intermediates that lead to a highly aggregated state. Increasing urea concentrations cause a complete dissociation to lead first a partially and eventually the complete unfolded monomer. These phenomena are fully reversible by dilution of denaturant. It is concluded that after urea denaturation, the folding/assembly pathway of glucose dehydrogenase occurs with the formation of intermediate species in which transient higher aggregates appear to be involved.