Assume that all plasmid-containing cells have eight...

Assume that all plasmid-containing cells have eight plasmids; that an antibiotic is present in the medium, and the plasmid-containing cells are totally resistant; and that a newly born, plasmid-free cell has sufficient enzyme to protect a cell and its progeny for three generations. Estimate the fraction of plasmid-containing cells in the population in a batch reactor starting with only plasmid-containing cells after five generations.

Key Concepts

Plasmid?Mediated Antibiotic Resistance

This concept pertains to the ability of cells to resist antibiotic effects by harboring plasmids that encode resistance factors. In the context of the question, only cells containing plasmids are fully resistant to an antibiotic, making the maintenance and distribution of such plasmids crucial to survival in an antibiotic-containing environment.

Plasmid Segregation and Inheritance

During cell division, plasmids present in the parent cell must be distributed to daughter cells. This process can be uneven, and some cells may end up being plasmid?free, despite the parent cell having multiple copies. Understanding the mechanics of plasmid segregation, including the likelihood of plasmid loss, is key in determining changes in the population composition over successive generations.

Batch Reactor Dynamics

A batch reactor is a closed system where organisms grow exponentially until nutrients or growth-inhibiting substances (like antibiotics) come into play. In such settings, the overall cell population dynamics are driven by generation time and exponential increases, which directly influence how subpopulations (plasmid-bearing versus plasmid-free cells) evolve over time.

Transient Enzyme Inheritance (Maternal Protection)

This concept describes the phenomenon where newly born cells that lose plasmids can still temporarily exhibit a resistant phenotype due to the inheritance of enzymes from their plasmid-containing parent. In the presented problem, these enzymes provide protection for a limited number of generations, which must be accounted for when assessing the fraction of resistant cells in the population.

Transcript

00:01 All right, so in this problem, we have a plasmid vector that we want to insert into a bacteria.

00:09 And so let's talk about this vector that they give us first.

00:13 So this plasmid vector is represented by this circle here.

00:16 And in this plasmid vector, there is a gene that i'm going to put in green here that produces ampicillin, which is a type of antibiotic resistance.

00:28 And it also has a gene for green fluorescent protein.

00:34 I should have done that one in green, but it's in blue over here.

00:40 And the gene that produces green fluorescent protein has a restriction site.

00:48 This restriction site is where the dna is going to be cut, and this is the dna sequence that we want to show up in the bacteria.

00:58 And so this plasmid vector will be cut at the state.

01:01 Restriction zite and this dna will be inserted right here.

01:06 And so then that will produce a plasmid vector that would look like this.

01:15 And so it would have what we want is it for it to have all three of these spots, the gene for ampazillin resistance, the gene for the green fluorescent protein, and our dna sequence that we want to insert.

01:27 And so i go through that because that will determine how we sequence the last two steps.

01:34 So let's look at the the steps here and figure out what's going to come first.

01:40 So first, we need to digest the vector with the restriction enzyme so that we can insert the foreign dna in it.

01:56 This is the dna we want to show up in the bacteria.

02:00 And then second, ligate, which is called that because there's a enzyme called ligase that basically lose things together.

02:09 So we're going to ligate that digested plasmid so that it connects back together and has the foreign dna, which would produce this one up here that we was looking at before.

02:24 After that, we're going to transform the host cells, that is the bacteria cells...

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