Would you expect the fraction of bacteria that are spontaneous rifampin resistant mutants to be higher or lower in a culture that:

you had propagated many times
or one you had just started from a single colony of sensitive bacteria? Why?

To answer this question, we need to understand the concept of spontaneous rifampin resistant mutants and the process of bacterial propagation.

Spontaneous rifampin resistant mutants are bacterial cells that have acquired a genetic mutation, resulting in resistance to the antibiotic rifampin. These mutations can occur randomly and spontaneously within the bacterial population.

When it comes to bacterial propagation, if a culture has been propagated many times, it means that the bacteria have been grown and transferred from one culture to another multiple times. This process potentially exposes the bacteria to various environmental factors and selection pressures, including the presence of rifampin. On the other hand, if the culture is just started from a single colony of sensitive bacteria, it means that the bacteria in the culture have not undergone any previous propagation or exposure to the antibiotic.

Based on this understanding, we would expect the fraction of bacteria that are spontaneous rifampin resistant mutants to be higher in a culture that has been propagated many times compared to one that is just started from a single colony of sensitive bacteria. Here's why:

1. Accumulation of Mutations: As bacteria are propagated over multiple generations, there is a higher probability for genetic mutations to occur. These mutations can lead to rifampin resistance. With each propagation, the chance of acquiring a rifampin-resistant mutation increases, resulting in a higher fraction of resistant mutants in the culture.

2. Selection Pressure: When bacteria are exposed to rifampin during propagation, the antibiotic acts as a selective agent. Only the bacteria that carry rifampin-resistant mutations will survive and reproduce, while sensitive bacteria will be inhibited or killed by the antibiotic. This selective pressure further promotes the growth and dominance of rifampin-resistant mutants in the culture.

In contrast, starting from a single colony of sensitive bacteria means there has been no prior exposure to rifampin or any other selective pressure. Therefore, the chances of having spontaneous rifampin resistant mutants in the population are lower, resulting in a lower fraction of resistant mutants in the culture.

In conclusion, the fraction of bacteria that are spontaneous rifampin resistant mutants would be expected to be higher in a culture that has been propagated many times compared to one that is just started from a single colony of sensitive bacteria.