| dc.description.abstract | All major processes in living systems depend on energy sources. In bacteria undergoing cellular respiration, the central source of energy is the proton motive force (PMF). In addition to ATP synthesis, the PMF directly powers numerous other functions including motility, chemotaxis and cell division. Despite its importance, methods to quantify the PMF in live bacteria are limited. For this reason, the dependence of motility on the PMF is particularly interesting as the former could be used as a quantitative readout of the latter. In this work, we have developed protocols to quantitatively probe the PMF in different bacterial species. We systematically tested the relation between motility and the PMF in a multi-flagellated specie – Bacillus subtilis. Specifically, we measured the relationship between the membrane potential, which is a component of the PMF, and the swimming speeds of individual bacteria. We then compared the swimming speeds against flagellar rotation rates. Comparisons with Escherichia coli revealed that hydrodynamic factors complicate the PMF/flagellar rotation/swimming speed relationships in peritrichous (multi-flagellated) species. Next, we quantified the second component of the PMF – the transmembrane pH gradient - by characterizing pH-sensitive fluorescence proteins in E. coli. We developed a scaling analysis that overcame some of the limitations of the green fluorescent protein (GFP); specifically, the dependence of emissions on protein concentrations. Finally, we worked with a monotrichous bacterial species, Caulobacter crescentus, as their motility is relatively straightforward to interpret owing to the presence of a single flagellum. As the strategies of chemotaxis are poorly understood in this species, we focused on the response of C. crescentus to multiple chemoeffectors. We observed that C. crescentus is poor in chemotaxis despite possessing a rather complicated and elaborate chemotaxis network. It is likely that the so-called chemotaxis network in C. crescentus has a primary function that is different from chemotaxis. | |
