Regulation of Hypercompetence in Legionella pneumophila

Abstract

Although many bacteria are known to be naturally competent for DNA uptake, this ability varies dramatically between species and even within a single species, some isolates display high levels of competence while others seem to be completely nontransformable. Surprisingly, many nontransformable bacterial strains appear to encode components necessary for DNA uptake. We believe that many such strains are actually competent but that this ability has been overlooked because standard laboratory conditions are inappropriate for competence induction. For example, most strains of the gram-negative bacterium Legionella pneumophila are not competent under normal laboratory conditions of aerobic growth at 37°C. However, it was previously reported that microaerophilic growth at 37°C allows L. pneumophila serogroup 1 strain AA100 to be naturally transformed. Here we report that another L. pneumophila serogroup 1 strain, Lp02, can also be transformed under these conditions. Moreover, Lp02 can be induced to high levels of competence by a second set of conditions, aerobic growth at 30°C. In contrast to Lp02, AA100 is only minimally transformable at 30°C, indicating that Lp02 is hypercompetent under these conditions. To identify potential causes of hypercompetence, we isolated mutants of AA100 that exhibited enhanced DNA uptake. Characterization of these mutants revealed two genes, proQ and comR, that are involved in regulating competence in L. pneumophila. This approach, involving the isolation of hypercompetent mutants, shows great promise as a method for identifying natural transformation in bacterial species previously thought to be nontransformable.

A Legionella pneumophila -translocated substrate that is required for growth within macrophages and protection from host cell death

“…Isolation of random miniTn10(kan R ) insertions in L. pneumophila chromosome were made by using the suicide transposition vector pJK211 (42). All insertions were transferred into unmutagenized backgrounds by natural transformation (41). Deletion mutations in selected genes on the L. pneumophila chromosome and complementation plasmids were constructed by using standard strategies (42).…”

“…Plasmids were introduced into L. pneumophila by either electroporation (39) or natural transformation (40,41). Isolation of random miniTn10(kan R ) insertions in L. pneumophila chromosome were made by using the suicide transposition vector pJK211 (42).…”

Silencing of natural transformation by an RNA chaperone and a multitarget small RNA

“…One such species is the Gram-negative pathogen Legionella pneumophila, which was found to develop competence under microaerophilic growth, exposure to DNA-damaging agents, or suboptimal growth temperature (11)(12)(13). Possible competence regulatory elements in L. pneumophila were revealed by a genetic screen that identified a gene annotated "proQ, activator of osmoprotectant ProP" as a repressor of natural transformation (14). The proQ gene was initially identified in Escherichia coli as an activator of the proline transporter ProP (15), but recent evidence suggests that this effect is indirect (16).…”

“…Although finO is restricted to IncF plasmids, genome-encoded proteins with a ProQ/FinO domain have been identified, but their function remains elusive (19). As the L. pneumophila ProQ represses natural transformability (14) and to avoid any unfounded inference with proline metabolism, we will refer to it by its locus tag name in the Paris strain, Lpp0148.…”

tfoX (sxy)-dependent transformation of Aggregatibacter (Actinobacillus) actinomycetemcomitans

“…Development of competence in bacteria is usually tightly regulated (Dubnau, 1999;Chen and Dubnau, 2004;Sexton and Vogel, 2004), but it is not yet known what signals competence in A. actinomycetemcomitans. The environmental signal for the development of competence in H. influenzae is not known either, but an increase in adenosine 3′,5′-cyclic monophosphate (cAMP) level triggers the expression of the early competence gene tfoX (Wise et al, 1973;Dorocicz et al, 1993;Redfield et al, 2005).…”