Distinguish among the three modes of recombination in bacteria.

Transformation is a mode of recombination in bacteria, where bacteria can take up extracellular DNA from its surrounding environment. The DNA that was taken up can then be integrated into the bacterium's own genome.

During transformation, a bacterium becomes "competent" to take up exogenous DNA through its cell membrane. The competence is either naturally present in certain bacteria or induced by particular conditions in the laboratory. A competent bacterium then binds to the free DNA fragment in its environment, forming a complex that aids in the uptake of the DNA. The DNA is transported across the cell membrane, and gets integrated into the bacterial chromosome via homologous recombination.

Transduction is another mode of genetic recombination in bacteria, which involves the transfer of bacterial DNA from one bacterium (the donor) to another (the recipient) via bacteriophages, which are viruses that infect bacteria.

During transduction, a bacteriophage infects the donor bacterium and injects its own genetic material into it. While replicating, the phage may mistakenly package some of the bacterial DNA along with its own genetic material. When the bacteriophage goes on to infect the recipient bacterium, it injects both its own and the donor's DNA into the recipient. The donor's DNA can then be integrated into the recipient bacterium's genome via homologous recombination or by non-homologous mechanisms, eventually leading to genetic changes in the recipient.

Conjugation is the third mode of recombination in bacteria, where bacterial DNA is directly transferred from the donor bacterium to recipient bacterium through a tube-like structure called a pilus.

In conjugation, the donor bacterium possesses a special plasmid called the F (fertility) plasmid, which includes the genes necessary for pilus formation. The F+ (donor) cell forms a pilus and attaches to the F- (recipient) cell. The pilus contracts and brings the two bacterial cells closer. The F plasmid is then replicated and transferred from the donor to the recipient cell, which results in both cells being F+. The recipient bacterium can then integrate the newly acquired DNA into its genome and express the genetic information received from the donor. Having looked at each of the modes of recombination, we can distinguish them based on their mechanisms and features: 1. Transformation involves the uptake of free extracellular DNA by a competent bacterium, while transduction requires the involvement of a bacteriophage for DNA transfer. Conjugation, on the other hand, involves direct cell-to-cell contact and DNA transfer through a pilus. 2. Transformation and transduction involve the integration of the foreign DNA into the recipient bacterium's chromosome mainly through homologous recombination. In contrast, conjugation primarily involves the transfer of plasmid DNA. 3. Transformation can be a natural process or can be induced in a laboratory setting, whereas transduction and conjugation occur naturally between bacteria.