Here is graph of describing what happened to a culture when it was exposed to a
ID: 216935 • Letter: H
Question
Here is graph of describing what happened to a culture when it was exposed to a temperature higher than it's maximum temperature 1. The following tow questions are about using heat to kill microorganisms. What is the decimal reduction time for this organism? (1 point) a. CFU/ml 300 200 300400 300 600 00 Time in seconds b. You repeat DRT experiment with a Gram-positive rod and this is the result. Your water bath maintained a constant temperature; your dilution and plating technique is perfect. All the colony morphologies match that ove your original culture. What would cause this result? (1 point) 1000 CFU/ml 10 Time in Seconds 2. Lacl and LacZ are proteins encoded by genes, and there can be mutated forms of them. The place where Lacl binds, lacO, is also a DNA element, and is subject to mutation. In the table below, I've listed a number of potential mutations. I want you to tell me after growing each mutant in a minimal medium with equal parts glucose and lactose, both sugars at 0.2% do you think you'd see blue in a ?-galactosidase assa ? (2 points Mutation: or No Color Change? A Lacl mutated so that it no longer recognizes laco A Lacl that no longer binds lactose A LacZ that no longer cleaves lactose A lac0 mutated so Lacl no longer recognizes it. A one base frame shift mutation after the first 9 bases of laclExplanation / Answer
1. (a) DRT is the time required to kill 90% of the initial population of an organism.
Initial no. of bacteria= 108
After 90% reduction, the no of left bacteria is= 108*10/100=107
From the graph the DRT= 200
(b) The remaining no. of bacteria are heat resistant.
2. In Beta-galactosidase assay X-gal(colourless) is used as substrate, which will be converted to a blue product if beta-galactosidase is expressed from the LacZ gene.
i) Since the LacI, the repressor is mutated, so that it can't bind LacO, there will be constitutive expression of LacZ, so blue colonies.
ii) Lactose( specifically allolactose) doesn't bind to repressor, the repressor will bind the LacO constitutively, thus repressing expression of LacZ. So white colonies.
iii) white colonies
iv) Contitutive lacZ expression, so blue colonies.
v) assuming non-functional lacI, Contitutive lacZ expression, so blue colonies.