1. You are attempting to identify genes involved in osmoticstress response in Bacillus atrophaeus, a Gram positiveendospore former. For your work, you set up a chemostat(continuous) culture. You remove two samples of culture, expose oneto a high salt concentration, wait five minutes, and then extractall their mRNA. You then label the control with a green fluorescentdie, the experimental with a red fluorescent dye, and thenhybridize the mixture to a microarray. Following analysis, themicroarray reader generates a list of ratios of fluorescence of thespots on the array calculated as red vs. green. The expressionratios of the first five genes (of many thousands!) are asfollows:
Gene A: 1.002
Gene B: 34.271
Gene C: 0.260
Gene D: 27.930
Gene E: 0.997
a. At what stage of growth are your cells in the chemostat?
b. Imagine you repeated the above experiment every day for aweek. How might your results compare if done using cells from acontinuous culture (as above) vs. from a batch culture?Explain.
c. Based on the microarray data, which gene(s) might be involvedin stress response to salt?
d. Which gene(s) might be involved in constitutive (background,needed all the time) functions?
e. Which gene(s) might be involved in a process not essential tosurvival during times of stress?
f. Confident you have identified a number of genes involved inprotecting B. atrophaeus from salt stress response, youdecide to begin by studying one further. How might you geneticallyengineer B. atrophaeus to demonstrate the involvement ofthis gene in stress response to salt?
