Q.Describe the different methods of sexual reproduction in bacteria.

[!TLDR]

The question asks for a full account of the different methods of sexual (gene-recombining) reproduction in bacteria.

[!ANSWER]

Bacteria exchange genetic material by three methods: conjugation (direct transfer via a sex pilus, Lederberg & Tatum, 1946, E. coli), transformation (uptake of free environmental DNA, Griffith, 1928, S. pneumoniae) and transduction (bacteriophage-mediated transfer, Zinder & Lederberg, 1952, Salmonella typhimurium).

Although bacteria reproduce chiefly by asexual cell division, they can also exchange genetic material between two cells in a way that produces new genetic combinations, and three distinct methods for doing this are recognised.

Conjugation is a process of direct physical contact between two bacterial cells. A donor cell extends a tube-like sex pilus that draws it against a recipient cell, and DNA - often a plasmid - passes across this connecting bridge from the donor into the recipient, giving the recipient a new genetic combination. Conjugation was discovered by Joshua Lederberg and Edward Tatum in 1946, working with the bacterium Escherichia coli.

Transformation does not require any direct contact between two living cells. Instead, a recipient bacterial cell takes up free ('naked') fragments of DNA that happen to be present in its surroundings - commonly released when another bacterial cell has broken down - and incorporates this DNA into its own genome. Transformation was discovered by Frederick Griffith in 1928, through his classic experiments on Streptococcus pneumoniae.

Transduction uses a third party to carry the DNA: a bacteriophage (a virus that infects bacteria) accidentally packages DNA from the bacterial cell it has been replicating in, and when this phage subsequently infects a different bacterial cell, it delivers that DNA into the new host, transferring genetic material indirectly between the two bacteria. Transduction was discovered by Norton Zinder and Joshua Lederberg in 1952, working with Salmonella typhimurium.

[!ANSWER]

The three methods of sexual (gene-recombining) reproduction in bacteria are: conjugation (direct pilus-mediated transfer; Lederberg & Tatum, 1946; E. coli), transformation (uptake of free environmental DNA; Griffith, 1928; S. pneumoniae), and transduction (phage-mediated transfer; Zinder & Lederberg, 1952; Salmonella typhimurium) - in each, DNA moves from a donor cell into a recipient cell, producing a new genetic combination.

• Describing only one or two of the three methods when the question asks for 'the different methods' in full.
• Mixing up which scientist(s) and which organism go with which method - each of the three has a distinct discoverer and a distinct organism in which it was first shown.