Evolution of natural transformation: testing the DNA repair hypothesis in Bacillus subtilis and Haemophilus influenzae.

Abstract

The hypothesis that the primary function of bacterial transformation is DNA repair was tested in the naturally transformable bacteria Bacillus subtilis and Haemophilus influenzae by determining whether competence for transformation is regulated by DNA damage. Accordingly, DNA damage was induced by mitomycin C and by ultraviolet radiation at doses that efficiently induced a known damage-inducible gene fusion, and the ability of the damaged cultures to transform was monitored. Experiments were carried out both under conditions where cells do not normally become competent and under competence-inducing conditions. No induction or enhancement of competence by damage was seen in either organism. These experiments strongly suggest that the regulation of competence does not involve a response to DNA damage, and thus that explanations other than DNA repair must be sought for the evolutionary functions of natural transformation systems.

Condition-dependent sex: who does it, when and why?

“…Although bacteria do not go through meiosis, they do exchange genetic information via horizontal gene transfer or HGT [43], through different mechanisms: transformation, the incorporation of foreign DNA into the genome; conjugation, the horizontal transfer of plasmids; transduction, the transfer of genes carried by infecting phages; and integrons, which facilitate the exchange of gene-cassettes in bacterial populations [44]. Empirical evidence suggests that natural competence for transformation is upregulated by multiple stressors (reviewed in [45]), including DNA damage ( [46], but see also [47]) and starvation [48,49]. However, it has also been suggested that stressed microbes take up DNA for reasons other than the generation of genetic variation, such as nutrient consumption and DNA repair [43].…”

Metabolism and evolution of Haemophilus influenzae deduced from a whole-genome comparison with Escherichia coli

“…E. coli is arguably the best studied of all organisms [7]. In contrast, the information that is currently available on the biochemistry and physiology of H. influenzae is limited ( [3,[8][9][10][11] and references therein). Thus, a comparison of the E. coli and H. influenzae genomes is expected to be instrumental in deducing the metabolism of a poorly characterized bacterium from that of a well understood one.…”

Steady at the wheel: conservative sex and the benefits of bacterial transformation

“…Early experimental evidence indicated an immediate benefit of DNA uptake on transformant survival relative to the remainder of the population in B. subtilis [30][31][32]. However, these earlier results were countered in the same species by evidence that genotoxic stress did not induce competence [33], as predicted by the original idea. A more recent extension of this 'DNA repair hypothesis' proposes that transformation is a general stress response [34].…”