Abstract
Natural transformation is the process by which bacteria can actively take up and integrate exogenous DNA thereby providing a source of genetic diversity. Under specific growth conditions the coordinated expression of several genes – a situation referred to as “competence” – allows bacteria to assemble a highly processive and dedicated system that can import high molecular weight DNA. Within the cell these large imported DNA molecules are protected from degradation and brought to the chromosome for recombination. Here, we report elevated expression of mreB during competence in the Gram-negative pathogen Legionella pneumophila. Interestingly a similar observation had previously been reported in the distantly-related Gram-positive organism Bacillus subtilis. MreB is often viewed as the bacterial actin homolog contributing to bacterial morphogenesis by coordinating peptidoglycan-synthesising complexes. In addition MreB is increasingly found to be involved in a growing number of processes including chromosome segregation and motor-driven motility. Using genetic and pharmacological approaches, we examined the possible role of MreB during natural transformation in L. pneumophila. Our data show that natural transformation does not require MreB dynamics and exclude a direct role of MreB filaments in the transport of foreign DNA and its recombination in the chromosome.
Highlights
Vibrio cholerae[4,12]
ComEA is a small periplasmic protein involved in the DNA uptake system and required for natural transformation of L. pneumophila[39]
A similar situation exists with MreB, its primary function is to coordinate cell wall synthesis it can serve other active processes such as gliding motility[50,51], type IV pilus-dependent twitching motility[33] and infection of bacterial virus[52,53]
Summary
Vibrio cholerae[4,12]. the importance of its increased expression during competence development has been demonstrated in the transformable species Streptococcus pneumoniae and Bacillus subtilis[13,14,15]. Taken together the data strongly suggested a direct role of MreB filaments at various stage of the transport of foreign DNA during the process of natural genetic transformation. This hypothesis has recently been tested in the Gram-positive organism B. subtilis[34]. In contrast to ComGA which is required for natural transformation[35], MreB was found to play no role in natural transformation in B. subtilis as an mreB deletion mutant showed no defect in transformation efficiency In this species, a potential involvement of the actin-like cytoskeleton in natural transformation may be obscured by the presence of two MreB paralogs (Mbl and MreBH) that can partly maintain cell growth and morphogenesis in absence of MreB36. Our data suggest that the co-regulation of MreB and the DNA uptake system is coincidental and that natural transformation occurs without assistance of the MreB cytoskeleton
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