Inhibition of Competence Development, Horizontal Gene Transfer and Virulence in Streptococcus pneumoniae by a Modified Competence Stimulating Peptide

Competence stimulating peptide (CSP) is a 17-amino acid peptide pheromone secreted by Streptococcus pneumoniae. Upon binding of CSP to its membrane-associated receptor kinase ComD, a cascade of signaling events is initiated, leading to activation of the competence regulon by the response regulator ComE. Genes encoding proteins that are involved in DNA uptake and transformation, as well as virulence, are upregulated. Previous studies have shown that disruption of key components in the competence regulon inhibits DNA transformation and attenuates virulence. Thus, synthetic analogues that competitively inhibit CSPs may serve as attractive drugs to control pneumococcal infection and to reduce horizontal gene transfer during infection. We performed amino acid substitutions on conserved amino acid residues of CSP1 in an effort to disable DNA transformation and to attenuate the virulence of S. pneumoniae. One of the mutated peptides, CSP1-E1A, inhibited development of competence in DNA transformation by outcompeting CSP1 in time and concentration-dependent manners. CSP1-E1A reduced the expression of pneumococcal virulence factors choline binding protein D (CbpD) and autolysin A (LytA) in vitro, and significantly reduced mouse mortality after lung infection. Furthermore, CSP1-E1A attenuated the acquisition of an antibiotic resistance gene and a capsule gene in vivo. Finally, we demonstrated that the strategy of using a peptide inhibitor is applicable to other CSP subtype, including CSP2. CSP1-E1A and CSP2-E1A were able to cross inhibit the induction of competence and DNA transformation in pneumococcal strains with incompatible ComD subtypes. These results demonstrate the applicability of generating competitive analogues of CSPs as drugs to control horizontal transfer of antibiotic resistance and virulence genes, and to attenuate virulence during infection by S. pneumoniae

Interbacterial predation as a strategy for DNA acquisition in naturally competent bacteria.

Natural competence enables bacteria to take up exogenous DNA. The evolutionary function of natural competence remains controversial, as imported DNA can act as a source of substrates or can be integrated into the genome. Exogenous homologous DNA can also be used for genome repair. In this Opinion article, we propose that predation of non-related neighbouring bacteria coupled with competence regulation might function as an active strategy for DNA acquisition. Competence-dependent kin-discriminated killing has been observed in the unrelated bacteria Vibrio cholerae and Streptococcus pneumoniae. Importantly, both the regulatory networks and the mode of action of neighbour predation differ between these organisms, with V. cholerae using a type VI secretion system and S. pneumoniae secreting bacteriocins. We argue that the forced release of DNA from killed bacteria and the transfer of non-clonal genetic material have important roles in bacterial evolution