Chapter 6, Problem 1P

For bacteria that are ${\text{F}}^{\text{+}}$, Hfr, $\text{F'}$, and ${\text{F}}^{\text{-}}$, perform or answer the following.

a. Describe the state of the F factor.

b. Which of these cells are donors? Which is the recipient?

c. Which of these donors can convert exconjugants to a donor state?

d. Which of these donors can transfer a donor gene to exconjugants?

e. Describe the results of conjugation (i.e., changes in the recipient and the exconjugant) that allow detection of the state of the F factor in a donor strain.

f. Describe a “partial diploid” and how it originates.

Summary Introduction

To review:

For bacterial strains ${\text{F}}^{+}$, $\text{Hfr}$, $\text{F'}$, and ${\text{F}}^{\text{-}}$, answer the following:

Description for the state of the F factor.

Identification and explanation of donor and recipient cells.

Identification and explanation of donor cells that can convert exoconjugants to donor state.

Identification of the donor that can transfer the donor gene to exoconjugants.

Description of results of conjugation that allow detection of the state of the F factor in the donor strain.

Description on partial diploids.

Introduction:

Conjugation is the process of transfer of the DNA from one donor bacterium to a recipient bacterium. It is also known as lateral gene transfer. Conjugation is always occurring between the donor cell and the recipient cell, it does not occur between two donor cells. The exoconjugant cell is the recipient cell that has a modification in their genome by receiving the DNA from a donor cell in the process of conjugation. During conjugation, bacteria come in contact with the help of sex pilus. The bacterium that has sex pilus is the donor - male bacterium, and the bacterium that lacks sex pilus is the recipient - female bacterium.

The cell that has the ability to donate their DNA is called ${\text{F}}^{\text{+}}\text{cell}$. The $\text{F}$ stands for the fertility factor. In contrast, the cell which does not contain fertility factor $\text{(F factor)}$ is called the ${\text{F}}^{\text{-}}\text{cell}$. $\text{Hfr}$ stands for high-frequency recombination cells, which have their genome integrated with conjugative plasmid, i.e., $\text{F}\text{factor}$ of the plasmid. This integration of the $\text{F}$ factor occurs through homologous recombination.

Explanation of Solution

The $\text{F}$ sex factor is the factor present in plasmid or episome (a small part of genome present independently of genome). This factor is present in many forms on the basis of factors include in it.

${\text{F}}^{\text{+}}\text{-}$ The bacterium that has plasmid is ${\text{F}}^{+}$. Plasmid is present in cytoplasm independently of the bacterial genome.

Hfr (high frequency recombination) $\text{-}$ The bacterium that has $\text{F}$ factor completely integrated with its genome is $\text{Hfr}$.

${\text{F}}^{\text{-}}\text{-}$ The bacterium that lacks plasmid or episome but can act as a recipient and receive them from another cell is ${\text{F}}^{\text{-}}$.

$\text{F' -}$ Bacterium in which $\text{F}$ factor is attached with small part of genome.

Donor cell is a cell that donates factor/s to another cell by conjugation. Only that bacterial cell which already has the $\text{F}$ sex factor can transfer it, so ${\text{F}}^{+}$, $\text{Hfr}$, and $\text{F'}$ are donor cells. The bacterial cell, which receives the $\text{F}$ sex factor from the donor through conjugation, is the recipient, i.e., ${\text{F}}^{\text{-}}$.

The ${\text{F}}^{+}$ and $\text{F'}$ bacteria are donor cells and can transfer the F sex factor to exoconjugants through conjugation. Once exoconjugants receive the $\text{F}$ sex factor, they become ${\text{F}}^{+}$ (receive F factor from ${\text{F}}^{+}$) or $\text{F'}$ (receive $\text{F}$ factor from $\text{F'}$); now they can also donate the F factor. The $\text{Hfr}$ are not able to transform exoconjugants into donor bacteria.

Hfr and $\text{F'}$ have some portion of bacterial genome attached to the $\text{F}$ sex factor, so if we cross $\text{F'×}{\text{F}}^{\text{-}}$ and ${\text{Hfr ×F}}^{\text{-}}$, the bacterial gene can be transferred to exoconjugants along with the $\text{F}$ sex factor. on the other hand, ${\text{F}}^{+}$ bacteria have plasmid present in cytoplasm independently of the bacterial genome, so ${\text{F}}^{+}$ is unable to transfer bacterial gene to exoconjugants.

At the time of conjugation, bacterium comes in contact with the help of sex pilus. The bacterium that has sex pilus is the donor - male bacterium, and the bacterium that lacks sex pilus is the recipient - female bacterium. Conjugation tube is formed between the donor and recipient, and F sex factor is transferred from ${\text{F}}^{+}$ to ${\text{F}}^{\text{-}}$; this process is known as lateral gene transfer. Once ${\text{F}}^{\text{-}}$ receives F sex factor from the donor, it becomes ${\text{F}}^{+}$ (receives F factor from ${\text{F}}^{+}$) or $\text{F'}$ (receives F factor from $\text{F'}$). ${\text{F}}^{\text{-}}$ cannot transform into ${\text{F}}^{+}$ or $\text{F'}$ through the cross between $Hfr\times {\text{F}}^{\text{-}}$. The recipient, which receives $\text{F}$ sex factor and becomes ${\text{F}}^{+}$, in this plasmid, gets fused with the host genome and transforms ${\text{F}}^{+}$ to $\text{Hfr}$. This fused plasmid can again cut from genome and come back out; at that time, it carries some portion of the host genome along with it. Now this plasmid is known as $\text{F'}$.

A bacterium that has two copies of some of its genes (not all) is termed as partially diploid. In a bacterium, one copy of the desired gene is present on the bacterial genome, and another copy may be fused with the plasmid. Now, the bacterial cell possesses one complete set of genes and identical copy of portion of the genome.

Example of formation of partial diploid:

$\text{F'}$ strain possesses a plasmid that has gene ${\text{Lac}}^{\text{+}}$(can grow on lactose medium), and ${\text{F}}^{\text{-}}$ strain genome has ${\text{Lac}}^{\text{-}}$(cannot grow on lactose medium). When cross is done between $\text{F'×}{\text{F}}^{\text{-}}$ strain of bacteria, ${\text{F}}^{\text{-}}$ receives plasmid from $\text{F'}$ and becomes $\text{F'}$ strain. Now newly formed $\text{F'}$ has two copies of Lac gene - ${\text{Lac}}^{\text{+}}$ on plasmid and ${\text{Lac}}^{\text{-}}$ on its genome. Now, this newly formed $\text{F'}$ strain is termed as a partial diploid strain.

Conclusion

Conclusions:

The bacterium that has plasmid is ${\text{F}}^{+}$.The bacterium that has $\text{F}$ factor completely integrated with its genome is Hfr. The bacterium that lacks plasmid or episome but can act as a recipient and receive them from another cell is ${\text{F}}^{\text{-}}$.The bacterium in which the F factor is attached with a small part of genome is $\text{F'}$.

${\text{F}}^{+}$, Hfr, and $\text{F'}$ are donor cells. The bacteria which receive the F sex factor from the donor through conjugation is the recipient, i.e. ${\text{F}}^{\text{-}}$.

The ${\text{F}}^{+}$, $\text{F'}$ bacterium are donor cells and can transform exoconjugants to donor strain while Hfr are not able to transform exoconjugants into donor bacterium.

Hfr and $\text{F'}$ can transfer bacterial gene to exoconjugants and ${\text{F}}^{+}$ cannot.

${\text{F}}^{\text{-}}$ receives F sex factor from the donor and becomes ${\text{F}}^{+}$ (receives F factor from ${\text{F}}^{+}$) or $\text{F'}$ (receives $\text{F}$ factor from $\text{F'}$). ${\text{F}}^{\text{-}}$ cannot transform into ${\text{F}}^{+}$ or $\text{F'}$ through the cross between Hfr ×${\text{F}}^{\text{-}}$. The newly ${\text{F}}^{+}$ formed plasmid gets fused with the host genome and transforms ${\text{F}}^{+}$ to Hfr. Bacterium with the fused $\text{F}$ factor comes out back and has small part of genome attached with it; it is termed as $\text{F'}$.

A bacterium that has two copies of some of its genes (not all) is termed as partially diploid.