Reproduction in Bacteria

Bacteria reproduce asexually through binary fission, conidia formation and endospore formation, of which binary fission is by far the most common: under favourable conditions the nuclear material divides first, and a simple median constriction then splits the cell into two identical daughter cells. Under unfavourable conditions, some bacteria (e.g. Bacillus megaterium, Bacillus sphaericus, Clostridium tetani) instead survive by forming thick-walled, dormant resting spores called endospores, which germinate back into active bacteria once conditions improve. Bacteria have no true sexual reproduction involving the formation and fusion of gametes, but they do achieve genetic recombination through three distinct mechanisms. Conjugation (demonstrated by Lederberg and Tatum in E. coli, 1946) is direct DNA transfer between two cells joined by a conjugation tube built from a pilus: the donor cell's F+ plasmid replicates, and a single strand of that plasmid DNA passes across the tube into the recipient (F-) cell, which then synthesises the complementary strand to restore a full double helix. Transformation is the uptake of free DNA released by one bacterium into another; Frederick Griffith demonstrated it in mice in 1928 using Diplococcus pneumoniae, which exists as a virulent, smooth-colony S-type strain and an avirulent, rough-colony R-type strain. Live S-type killed the mouse; live R-type did not; heat-killed S-type alone did not; but a mixture of heat-killed S-type plus live R-type killed the mouse - because the hereditary material released from the dead S-type cells transformed the living R-type cells into virulent S-type cells. Transduction (discovered by Zinder and Lederberg in Salmonella …