LuxS-dependent quorum sensing in Porphyromonas gingivalis modulates protease and haemagglutinin activities but is not essential for virulence

Abstract

Porphyromonas gingivalis is a Gram-negative black-pigmented obligate anaerobe implicated in the aetiology of human periodontal disease. The virulence of P. gingivalis is associated with the elaboration of the cysteine proteases Arg-gingipain (Rgp) and Lys-gingipain (Kgp), which are produced at high bacterial cell densities. To determine whether quorum sensing plays a role in the regulation of Rgp and Kgp, biosensors capable of detecting either Nacylhomoserine lactone (AHLs) or the luxS-dependent autoinducer (AI-2) quorum-sensing signalling molecules in spent culture supernatants were first employed. While no AHLs could be detected, the Vibrio harveyi BB170 biosensor was activated by spent P. gingivalis W50 culture supernatants. The P. gingivalis luxS gene was cloned and demonstrated to restore AI-2 production in the Escherichia coli luxS mutant DH5α. Mutation of luxS abolished AI-2 production in P. gingivalis. Western blotting using antibodies raised against the recombinant protein revealed that LuxS levels increased throughout growth even though AI-2 activity was only maximally detected at the midexponential phase of growth and disappeared by the onset of stationary phase. Similar results were obtained with E. coli DH5α transformed with luxS, suggesting that AI-2 production is not limited by a lack of LuxS protein. Analysis of Rgp and Kgp protease activities revealed that the P. gingivalis luxS mutant produced around 45 % less Rgp and 30 % less Kgp activity than the parent strain. In addition, the luxS mutant exhibited a fourfold reduction in haemagglutinin titre. However, these reductions in virulence determinant levels were insufficient to attenuate the luxS mutant in a murine lesion model of P. gingivalis infection.

luxS mutants of Serratia defective in autoinducer-2-dependent ‘quorum sensing’ show strain-dependent impacts on virulence and production of carbapenem and prodigiosin

“…The peak in AI-2 activity was observed in late-exponential phase in S. marcescens 274 and during the transition into stationary phase in Serratia 39006; the activity then decreased into stationary phase in both strains. These profiles of AI-2 production throughout growth are in accordance with published results in other bacteria (Burgess et al, 2002;Surette & Bassler, 1998).…”

“…Using this model, we showed that the S. marcescens 274 luxS mutant exhibits a subtle but reproducible virulence defect. Attenuation of virulence has been seen in various luxS mutants, for example in N. meningitidis, V. vulnificus and Streptococcus pneumoniae; although in other bacteria, virulence is not significantly altered in the luxS mutant, at least in the chosen model (Burgess et al, 2002;Kim et al, 2003;Schneider et al, 2002;Stroeher et al, 2003;Winzer et al, 2002b). The reduced production of haemolysin and/or prodigiosin by the luxS mutant of S. marcescens 274 may contribute to its altered virulence.…”

“…Its production is dependent on a two-gene operon, shlBA, in which ShlA is the pore-forming protein, and ShlB activates ShlA and transports it out of the cell (Braun et al, 1993). Altered production of secreted virulence factors has been reported in the luxS mutants of other bacteria, for example reduced production of cysteine protease and haemagglutinin activities in P. gingivalis, decreased toxin production in C. perfringens, and enhanced production of haemolysin activity in Streptococcus pyogenes and V. vulnificus (Burgess et al, 2002;Kim et al, 2003;Lyon et al, 2001;Ohtani et al, 2002). In contrast with the latter two strains, in S. marcescens 274, haemolysin production is decreased rather than increased in the luxS mutant.…”

“…in Helicobacter pylori and Proteus mirabilis), through to altered production of virulence determinants (e.g. in Porphyromonas gingivalis, Streptococcus pyogenes and Clostridium perfringens), and decreased virulence (in Neisseria meningitidis, Streptococcus pneumoniae and Vibrio vulnificus) (Burgess et al, 2002;Joyce et al, 2000;Kim et al, 2003;Lyon et al, 2001;Ohtani et al, 2002;Schneider et al, 2002;Stroeher et al, 2003;Winzer et al, 2002b). However, the elucidation of the biosynthetic pathway of AI-2 has revealed a metabolic role for LuxS, in the S-adenosylmethionineutilization pathway (Schauder et al, 2001;Winzer et al, 2002a).…”

Quorum Sensing and Microbial Interactions in Coral Black Band Disease and Coral-Associated Bacteria

“…Additionally, production of both the AHL and AI-2 signals may be influenced by the growth medium (Burgess et al 2002, DeKeersmaecker and Vanderleyden 2003, Boyer and WisniewskiDyé 2009. Thus, signal production may be affected by the chemical substrates in the environment that are available for growth and by the physical environments available for colonization.…”