Differential Interaction ofAggregatibacter(Actinobacillus)actinomycetemcomitansLsrB and RbsB Proteins with Autoinducer 2

Abstract

Our previous studies showed that the Aggregatibacter actinomycetemcomitans RbsB protein interacts with cognate and heterologous autoinducer 2 (AI-2) signals and suggested that the rbsDABCK operon encodes a transporter that may internalize AI-2 (D. James et al., Infect. Immun. 74:4021-4029, 2006.). However, A. actinomycetemcomitans also possesses genes related to the lsr operon of Salmonella enterica serovar Typhimurium which function to import AI-2. Here, we show that A. actinomycetemcomitans LsrB protein competitively inhibits the interaction of the Vibrio harveyi AI-2 receptor (LuxP) with AI-2 from either A. actinomycetemcomitans or V. harveyi. Interestingly, LsrB was a more potent inhibitor of LuxP interaction with AI-2 from V. harveyi whereas RbsB competed more effectively with LuxP for A. actinomycetemcomitans AI-2. Inactivation of lsrB in wild-type A. actinomycetemcomitans or in an isogenic RbsB-deficient strain reduced the rate by which intact bacteria depleted A. actinomycetemcomitans AI-2 from solution. Consistent with the results from the LuxP competition experiments, the LsrB-deficient strain depleted AI-2 to a lesser extent than the RbsB-deficient organism. Inactivation of both lsrB and rbsB virtually eliminated the ability of the organism to remove AI-2 from the extracellular environment. These results suggest that A. actinomycetemcomitans possesses two proteins that differentially interact with AI-2 and may function to inactivate or facilitate internalization of AI-2.Autoinducer 2 (AI-2) is a quorum-sensing signal that was initially identified in Vibrio harveyi (2) and is produced by the luxS gene (28, 29). AI-2 is produced by LuxS-catalyzed cleavage of S-ribosylhomocysteine to produce homocysteine and 4,5-dihydroxy-2,3-pentanedione (36), which in turn undergoes further rearrangement to produce AI-2. However, two distinct structural forms of AI-2 have been identified. Salmonella enterica serovar Typhimurium produces 2R,4S-2,3,3,4-methyltetrahydroxytetrahydrofuran (R-THMF) whereas Vibrio subsp. produce the borate diester form of S-THMF (6, 22). AI-2-dependent quorum sensing is quite complex and is involved in the regulation of a variety of genes in Vibrio species, including the lux operon of V. harveyi. Detection of AI-2 by V. harveyi is mediated by LuxP, a periplasmic AI-2 receptor (6) that associates with the LuxQ sensor kinase-phosphatase (23) and initiates a phosphotransfer cascade involving LuxU (11) and the response regulator LuxO (10). LuxO in turn influences the expression of multiple small regulatory RNAs (Qrr regulators) that influence the expression of LuxR (15, 16), the master regulator of the lux operon (16). Recently, an additional twocomponent system encoded by varSA in Vibrio cholerae has been shown to converge on the quorum-sensing circuit by regulating the expression of the small RNAs encoded by csrBCD which control the expression of Qrr via CsrA (15).LuxS is highly conserved in a wide range of gram-positive and gram-negative bacteria, and many, if not all, of these organisms produ...

Quorum Sensing of Periodontal Pathogens

“…If exogenous autoinducer-2 or a functional luxS gene carrying plasmid is added in the growth medium, normal growth of the biofilm is restored (28). Two periplasmic receptors for autoinducer-2, LsrB and RbsB, were also identified and it was observed that if one or both receptors are inactivated, biofilm growth was either reduced, or completely disabled (29). The fact that Aggregatibacter actinomycetemcomitans also responds to a broad range of autoinducer-2 concentration, is a subject of scientific discussion and further research since the aforementioned periplasmic receptors show different kinetics of interaction with the autoinducer.…”

“…Ako se u medij za rast doda egzogeni autoinduktor-2 ili plazmidi koji nose funkcionalni luxS gen, omogućeno je normalno formiranje biofilma (28). Identificirana su dva periplazmička receptora za autoinduktor-2 -LsrB i RbsB te je uočeno, ako se inaktivira jedan ili oba, formirani biofilm bit će manji, odnosno njegova će formacija biti potpuno onemogućena (29). Predmet je znanstvene rasprave i daljnjih istraživanja reagira li doista Aggregatibacter actinomycetemcomitans na raspon različitih koncentracija autoinduktora-2, s obzirom na to da prije spomenuti periplazmički receptori pokazuju različitu kinetiku interakcije s autoinduktorom.…”

“…Predmet je znanstvene rasprave i daljnjih istraživanja reagira li doista Aggregatibacter actinomycetemcomitans na raspon različitih koncentracija autoinduktora-2, s obzirom na to da prije spomenuti periplazmički receptori pokazuju različitu kinetiku interakcije s autoinduktorom. Čini se da RbsB receptor ima veći afinitet za molekule autoinduktora, što doista sugerira da je Aggregatibacter actinomycetemcomitans sposoban odgovoriti i na veće i na manje koncentracije autoinduktora i tako napredovati u bakterijskim populacijama veće i manje stanične gustoće (29).…”

“…The fact that Aggregatibacter actinomycetemcomitans also responds to a broad range of autoinducer-2 concentration, is a subject of scientific discussion and further research since the aforementioned periplasmic receptors show different kinetics of interaction with the autoinducer. It seems that RbsB interacts with the autoinducer-2 at higher affinity than LsrB, suggesting that Aggregatibacter actinomycetemcomitans is able to act upon both lower and higher autoinducer-2 concentrations and thus thrive in biofilms with both low and high cell density (29).…”

Modification of quorum sensing in bacterial cultures

“…Agregatinobacter actinomycetemcomitans and Haemophilus influenzae use other type of receptors as well for the sensing of AI-2s, the RbsB proteins, which have high homology (above 70%) with the ribose ABC transporter (38,39).…”