Induction of Competence Regulons as a General Response to Stress in Gram-Positive Bacteria

Abstract

Bacterial transformation, a programmed mechanism for genetic exchange originally discovered in Streptococcus pneumoniae, is widespread in bacteria. It is based on the uptake and integration of exogenous DNA into the recipient genome. This review examines whether induction of competence for genetic transformation is a general response to stress in gram-positive bacteria. It compares data obtained with bacteria chosen for their different lifestyles, the soil-dweller Bacillus subtilis and the major human pathogen S. pneumoniae. The review focuses on the relationship between competence and other global responses in B. subtilis, as well as on recent evidence for competence induction in response to DNA damage or antibiotics and for the ability of S. pneumoniae to use competence as a substitute for SOS. This comparison reveals that the two species use different fitness-enhancing strategies in response to stress conditions. Whereas B. subtilis combines competence and SOS induction, S. pneumoniae relies only on competence to generate genetic diversity through transformation.

Structure–function analysis of pneumococcal DprA protein reveals that dimerization is crucial for loading RecA recombinase onto DNA during transformation

“…Pneumococcal transformation requires transient differentiation to competence, during which expression of a specific set of genes (11) allows assembly of the transformasome (6). This dynamic machine involves both membrane and cytosolic proteins (including DprA and RecA), and promotes internalization, protection, and processing of transforming DNA into recombinants.…”

“…This dynamic machine involves both membrane and cytosolic proteins (including DprA and RecA), and promotes internalization, protection, and processing of transforming DNA into recombinants. Competence (or X-state) (11) is induced in exponentially growing cultures by a peptide pheromone, competence-stimulating peptide (CSP) (12), which ultimately activates the synthesis of an alternative sigma factor specific for competence (σ X ) (13). Induction of competence by some antibiotics and DNA-damaging agents (14) supports the view that CSP functions as an alarmone and that competence/ X-state constitutes an SOS substitute for S. pneumoniae (11).…”

Acidic stress induces autolysis by a CSP-independent ComE pathway in Streptococcus pneumoniae

“…Claverys et al (2006) agreed with the idea that the particular state induced by ComE through ComX (named the X-state) is more extensive than competence. They also suggested that the X-state should be considered as a global response to alkaline stress rather than a quorum-sensing mechanism, despite its induction still being dependent on CSP.…”

“…It is assumed that a critical concentration of extracellular CSP is sensed by its receptor, the ComD histidine kinase, leading to autophosphorylation. The transfer of the phosphate group activates ComE, its cognate response regulator, inducing the expression of comCDE and several other operons (for a review, see Claverys et al, 2006). It has been described that another signal transduction system, designated CiaRH, participates in the early control of competence induction.…”

“…Interestingly, Peterson et al (2004) reported that approximately 67 of 124 genes were not related to competence, suggesting that expression of CSP-responsive genes may have other functions apart from genetic transformation. For this reason, Claverys et al (2006) proposed that the X-state (ComX-induced physiological state) is a more appropriate term than competence in S. pneumoniae.…”