Trends in Microbiology
Volume 8, Issue 3, 1 March 2000, Pages 128-133
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Review
Horizontal gene transfer and the origin of species: lessons from bacteria

https://doi.org/10.1016/S0966-842X(00)01703-0 Get rights and content

Abstract

In bacteria, horizontal gene transfer (HGT) is widely recognized as the mechanism responsible for the widespread distribution of antibiotic resistance genes, gene clusters encoding biodegradative pathways and pathogenicity determinants. We propose that HGT is also responsible for speciation and sub-speciation in bacteria, and that HGT mechanisms exist in eukaryotes.

Section snippets

Antibiotic resistance: the immediate response

The dissemination of antibiotic resistance genes among human and animal bacterial pathogens and associated commensal populations is the paradigm for HGT on a global scale8. This ‘experiment’ has taken place during the past 50 years, and a significant amount of information has been accrued on the mechanisms of response (evolution) of different bacterial ecosystems to the addition and distribution of large amounts of toxic agents (antibiotics) within the biosphere. This is the best known example

Biodegradation pathways: delayed opportunistic response

Based on studies with antibiotic resistance and its associated genes (e.g. genes for the metabolism of a number of sugars), it is not surprising that HGT has also led to the dissemination of gene clusters (operons) involved in the catabolism of xenobiotics in polluted environments9, 10, 11. The selective pressures are similar to those of antibiotic resistance, but the process of degrading xenobiotic compounds requires more complex genetic systems, usually operons of ten or more genes, or even

Pathogenicity determinants: delayed internalized response

Judging from these examples, it would appear that plasmids, in combination with transposons, are the primary vehicles for HGT in bacteria, at least for emergency responses to strong selection pressures. What other traits do naturally occurring plasmids and transposons carry? The answers to this question could give clues about bacterial responses to other types of stress, and perhaps help discover other evolutionary forces that shaped bacterial species. Plasmids in pathogenic bacteria are loaded

The shaping of a bacterial species

The fact that a number of pathogenicity determinants are presently found on mobile elements, or, alternatively, are fixed in the chromosome but still show remnants of the vehicles that led them there, suggests that chromosomes, classically viewed as essentially immobile, are in fact the ‘genetic necropolis’ of previously mobile genes. Who knows the full extent of micro-geographical terms that will spring from bacterial genomics: we could soon have islets, peninsulas or even genetic

HGT in eukaryotes: the lessons from bacteria

If many bacterial speciation events can be traced to the acquisition or loss of specific sets of genes as a result of HGT, speciation by HGT is not a specific response to defined challenges, but a global evolutionary response of bacterial populations. The E. coli scenarios already discussed provide evidence for this. Why should this not be the case also in eukaryotes and why should they not use the same or very similar mechanisms, being available as they are in prokaryotes? We propose that

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