Genetic exchange

F-pili or sex strands are partofa primitive genetic exchange system in some bacterial species. Part of the genetic material may be passed from one cell to another through the hollow pilus, thus giving rise to a simple form of sexual reproduction. 

For many years, it was thought that binary fission was the only method of reproduction in bacteria, but it is now known that there are three methods of reproduction in which genetic exchange can occur between pairs of cells, and thus a form of sexual reproduction is exhibited. These processes are transformation, conjugation and transduction. Further details ofthese processes as they affect antibiotic resistance will be found in Chapter 9. 

Viney, M.E., Matthews, B.E. and Walliker, D. (1993) Mating in the parasitic nematode Strongyloides ratti proof of genetic exchange. Proceedings of the Royal Society of London B 254, 213-219. 

D. B. Clewell G. M. Dunny, Conjugation and Genetic Exchange in Enterococci. In The Enterococci. Pathogenesis, Molecular Biology, and Antibiotic Resistance M. S. Gilmore, Ed. ASM Press Washington, DC, 2002 pp 265-300. 

In this double-strand break repair model for recombination, the 3 ends are used to initiate the genetic exchange. Once paired with the complementary strand on the intact homolog, a region of hybrid DNA is created that contains complementary strands from two different parent DNAs (the product of step (2)in Fig. 25-31a). Each of the 3 ends can then act as a primer for DNA replication. The structures thus formed, Holliday intermediates (Fig. 25 31b), are a feature of homologous genetic recombination pathways in all organisms. 

Rubio, M. A., Engesser, K. H. Knackmuss, H-J. (1986). Microbial metabolism of chlorosalicylates Accelerated evolution by natural genetic exchange. Archives of Microbiology, 145, 123-5. 

Transduction. Genetic exchange in bacteria that is mediated via phage. 

Transformation. Genetic exchange in bacteria that is mediated via purified DNA. In somatic cell genetics the term is also used to indicate the conversion of a normal cell to one that grows like a cancer cell. 

JJ Perry, JT Staley. Genetic exchange. In Microbiology Dynamics and Diversity. New York Saunders College Publishing, 1997, pp 346-366. 

GF Sprague Jr. Genetic exchange between kingdoms. Curr Opin Genet Dev 1 530-533, 1991. 

Ogunseitan, O. A. (1995). Bacterial genetic exchange in nature. Science Progress, 78(3), 183-204. 

Heterokaryotic hybrids also can be produced by fusing protoplasts to overcome genetic barriers to anastomosis (33. 34. Plasmid-mediated transformants have been successfully produced (TeBeest D.O., unpublished data) in this fungus and with several other Colletotrichum species (35-37). To date, genetic exchange appears limited in Colletotrichum and hybrid isolates often exhibit reduced fitness characterized by reduced growth and sporulation and decreased virulence. 

Whatever the setting of the last common ancestor, there are many aspects of modern cells that have a possible or likely hyperthermophile origin. To possess such a heritage, it is not necessary that a cell s primary ancestral line once occupied a hyperthermophile habitat. There has been much genetic exchange between organisms both within lines and even massively between domains (Figure 6(b)). 

Pili are morphologically and chemically similar to fimbriae, but they are present in much smaller numbers (< 10) and are usually longer. They are involved in the genetic exchange process of conjugation (section 6.3). 

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