Question

a scientist constructs a recombinant bacterial plasmid that contains a gene conferring resistance to the antibiotic tetracycline (tet). the scientist transforms cultures of e. coli bacteria with the recombinant plasmid, then incubates the cultures overnight on plates containing media without tetracycline (tet-) and with tetracycline (tet+). assuming the transformation protocol was successful, which of the following best predicts the bacterial growth pattern expected after the incubation period? = no bacterial growth = some bacterial growth = high bacterial growth choose 1 answer: a tet - tet + b tet - tet + c tet - tet + d tet - tet +

Explanation:

1. First, understand bacterial transformation and antibiotic resistance: The recombinant plasmid has a tetracycline resistance gene. When E. coli is transformed with this plasmid, the bacteria with the plasmid gain tetracycline resistance.
2. Analyze growth on tet - (no tetracycline) media: E. coli (whether transformed or not) can grow well in the absence of tetracycline. Since the transformation protocol was successful, most (or all) of the bacteria in the culture can grow here, so there should be high bacterial growth (the white circle) on tet - plates.
3. Analyze growth on tet + (with tetracycline) media: Only the bacteria that have taken up the recombinant plasmid (and thus have the tetracycline resistance gene) can grow. Since transformation efficiency is not 100% (not all bacteria will take up the plasmid), there will be some bacterial growth (the dotted circle) on tet + plates, not high (because not all bacteria are resistant) and not no growth (because some are resistant).
4. Now match with the options:

• Option A: tet + has no growth, which is wrong because some bacteria are resistant.
• Option B: tet - has high growth (correct) and tet + has some growth (correct), which matches our analysis.
• Option C: tet - has some growth (wrong, should be high as E. coli grows well without tetracycline) and tet + has high growth (wrong, not all bacteria are resistant).
• Option D: tet - has no growth (wrong, E. coli grows well without tetracycline).

Answer:

B. tet - (white circle), tet + (dotted circle)