Question 1. How would you isolate a thermophilic chemolithotroph that uses sulfur compounds as a source of energy and electrons? What changes 1n the incubation system would be needed to 1solate bacteria using sulfur compounds 1n anaerobic respiration? How would you tell which process 1s taking place through an analysis of the sulfur molecules present in the spent medium?
Question 2. Certain chemicals block ATP synthesis by allowing protons and other 10ns to leak across membranes, disrupting the charge and proton gradients established by electron flow through an ETC. Does this observation support the chemiosmosis hypothesis? Explain your reasoning.
Question 3. Two flasks of E. coli are grown 1n batch culture 1n the same medium (2% glucose and amino acids; no nitrate) and at the same temperature (37°C). Culture #1 1s well aerated. Culture #2 1s anoxic. After 16 hours the following observations are made:
- (Culture #1 has a high cell density; the cells appear to be 1n stationary phase, and the glucose level 1n the medium is reduced to 1.2%.
- (Culture #2 has a low cell density; the cells appear to be 1in logarithmic phase, although their doubling time 15 prolonged. The glucose level is reduced to 0.2%.
This phenomenon is known as the Pasteur effect. Like Pasteur did, figure out why culture #2 has so little glucose remaining relative to culture #1, even though culture #2 displayed slower growth and has less biomass. (Hint: It may be helpful to think about gas mileage obtained with a sports car versus an old clunker.)