Presence Of Autoinducer-2 Research Articles

Dissecting signal molecule AI-2 mediated biofilm formation and environmental tolerance in Lactobacillus plantarum

Quorum sensing (QS) exists in bacteria to communicate with each other and regulate group behaviors in a cell density-dependent manner, which uses signal molecule autoinducer-2 (AI-2) to intra- and inter-species communication. Effects of exogenous AI-2 on biofilm formation and environmental tolerance in Lactobacillus plantarum are the focus of this review. The responses to the exogenous AI-2 cross multiple physiological metabolic behaviors involving the bacteria growth, morphological characterization, biofilm development, extracellular polysaccharides (EPS) amount and related genes expression as well as the environmental stresses tolerance. The cell surface was smoother in the AI-2 supplemented treatments than without AI-2. Meanwhile, AI-2 had ability to promote the growth and formation of biofilm by increasing the yield of EPS, the main components of biofilm. The changes in lamC and ftsH gene expression point to altered regulation for hydrolysis process of polysaccharides as well as the potential for enhanced biofilm formation. The presence of AI-2 also significantly improved (p < 0.01) the tolerance of bile salts in L.plantarum, but the same results did not appear in acid tolerance. In conclusion, AI-2 supplementation could improve the biofilm formation and bile salts tolerance in L.plantarum, and this effect was likely modulated by facilitating EPS production and suppression polysaccharides hydrolysis.

D-Galactose as an autoinducer 2 inhibitor to control the biofilm formation of periodontopathogens.

Autoinducer 2 (AI-2) is a quorum sensing molecule to which bacteria respond to regulate various phenotypes, including virulence and biofilm formation. AI-2 plays an important role in the formation of a subgingival biofilm composed mostly of Gram-negative anaerobes, by which periodontitis is initiated. The aim of this study was to evaluate D-galactose as an inhibitor of AI-2 activity and thus of the biofilm formation of periodontopathogens. In a search for an AI-2 receptor of Fusobacterium nucleatum, D-galactose binding protein (Gbp, Gene ID FN1165) showed high sequence similarity with the ribose binding protein (RbsB), a known AI-2 receptor of Aggregatibacter actinomycetemcomitans. D-Galactose was evaluated for its inhibitory effect on the AI-2 activity of Vibrio harveyi BB152 and F. nucleatum, the major coaggregation bridge organism, which connects early colonizing commensals and late pathogenic colonizers in dental biofilms. The inhibitory effect of D-galactose on the biofilm formation of periodontopathogens was assessed by crystal violet staining and confocal laser scanning microscopy in the absence or presence of AI-2 and secreted molecules of F. nucleatum. D-Galactose significantly inhibited the AI-2 activity of V. harveyi and F. nucleatum. In addition, D-galactose markedly inhibited the biofilm formation of F. nucleatum, Porphyromonas gingivalis, and Tannerella forsythia induced by the AI-2 of F. nucleatum without affecting bacterial growth. Our results demonstrate that the Gbp may function as an AI-2 receptor and that galactose may be used for prevention of the biofilm formation of periodontopathogens by targeting AI-2 activity.

Normal bacterial flora may inhibit Candida albicans biofilm formation by Autoinducer-2.

Bachtiar et al. (2014) present a very interesting study in which they illustrate the ability of AI-2, produced by Aggregatibacter actinomycetemcomitans to inhibit biofilm formation by the fungal opportunistic pathogen Candida albicans. C. albicans is considered to be the most common fungal pathogen of humans, manifesting itself in the oral cavity (oral candidiasis or thrush), female reproductive tract (commonly referred to as a yeast infection), and less commonly in the digestive tract. It is also a notable blood-borne nosocomial pathogen (reviewed in Moyes and Naglik, 2011). While candidiasis is a complication in immunocompromised patients (Moyes and Naglik, 2011; Gow and Hube, 2012), in most other situations candidiasis arises as a consequence of normal flora disruption (Gow and Hube, 2012). In contrast to the considerable work done on mucosal immunity and other aspects of the immune system, less work has been done on mechanisms whereby normal flora control C. albicans. As part of its virulence, C. albicans does form biofilms through a quorum-regulated developmental process analogous to bacterial biofilms (Chandra et al., 2001; Ramage et al., 2002). Hogan and Kolter (2002) showed that Pseudomonas aeruginosa biofilms could colonize and inhibit C. albicans only when C. elegans was growing in the mycelia form and not the yeast form. These authors found that P. aeruginosa production of type 4 pili, involved in biofilm formation, antimicrobial phenazines, and other virulence factors, notably phospholipase C, were important inhibitors of C. albicans (Hogan and Kolter, 2002). Cruz et al. illustrated how proteins produced by Enterococcus faecalis could inhibit C. albicans hyphal growth and virulence (Cruz et al., 2013). There have also been reports of other specific interactions between individual bacteria and Candida albicans (reviewed in Shirtliff et al., 2009). While these studies address specific mechanisms, relevant to a specific bacterial species' interaction with C. albicans, it does not address the general phenomenon of normal flora inhibition of C. albicans growth and virulence. In this context, the study by Bachtiar et al. (2014), represents an intriguing and very welcome development. Autoinducer 2 (AI-2), encoded by luxS has been likened to a universal quorum signal in that it is produced and responded to by a wide number of bacterial species (Ng and Bassler, 2009). In their study, Bachtiar et al. (2014) focused on the interaction of A. actinomycetemcomitans with C. albicans. Using genetically defined strains, they showed that luxS mutants were unable to inhibit biofilm formation in C. albicans, but that this inhibition could be restored by genetic complementation or through the addition of physiologically-relevant concentrations of synthetic AI-2 or spent media from AI-2-producing A. actinomycetemcomitans. Although A. actinomycetemcomitans, found in the sub-gingival crevice, is normally a minor component of the oral cavity (Ramsey and Whiteley, 2009), the universal presence of AI-2 in many bacteria (Ng and Bassler, 2009) suggests that this signal molecule may represent a heretofore unrecognized general mechanism of the normal flora that protect against C. albicans infections. Certainly, work is needed with other AI-2-producing members of the normal flora to confirm this possibility. In light of the work by Hogan and Kolter (2002), it would also be very appropriate to determine whether AI-2 inhibition of C. albicans was a general phenomenon rather than being restricted to a specific physiological state (i.e., mycelia or yeast growth) of this fungal opportunistic pathogen. In summary, while there is considerable interest in exploiting quorum signal disruption as an antimicrobial therapy (Christensen et al., 2012; Vega et al., 2014), the work of Bachtiar et al. (2014) implies that enhanced C. albicans virulence might be an undesired consequence of this quorum-inhibiting strategy, as is the case with antibiotic-induced normal flora reduction (Gow and Hube, 2012).

Structure and Proposed Mechanism for the pH-Sensing Helicobacter pylori Chemoreceptor TlpB

pH sensing is crucial for survival of most organisms, yet the molecular basis of such sensing is poorly understood. Here, we present an atomic resolution structure of the periplasmic portion of the acid-sensing chemoreceptor, TlpB, from the gastric pathogen Helicobacter pylori. The structure reveals a universal signaling fold, a PAS domain, with a molecule of urea bound with high affinity. Through biophysical, biochemical, and invivo mutagenesis studies, we show that urea and the urea-binding site residues play critical roles in the ability of H.pylori to sense acid. Our signaling model predicts that protonation events at Asp114, affected by changes in pH, dictate the stability of TlpB through urea binding.

Zoosporic plant pathogens produce bacterial autoinducer-2 that affectsVibrio harveyiquorum sensing

The frequent coisolation of bacteria with Phytophthora and Pythium species suggests possible interspecies communication. Zoospore-free fluids (ZFF) from bacteria-free and nutrient-depleted zoospore suspensions were examined to investigate the production of autoinducer-2 (AI-2), a bacterial interspecies signal molecule, by zoosporic oomycetes. ZFF from Phytophthora nicotianae, Phytophthora sojae, and Pythium aphanidermatum triggered luminescence of the Vibrio harve7yi AI-2 reporter, indicating the presence of AI-2 in zoospore extracellular products and the potential of cross-kingdom communication between oomycetes and bacteria. The production of AI-2 by zoospores was confirmed by chemical assays. These results provide a new insight into the physiology and ecology of oomycetes.

Oxazaborolidine derivatives inducing autoinducer-2 signal transduction in Vibrio harveyi

The bioluminescence of the marine bacterium Vibrio harveyi is controlled by quorum sensing. This effect is mediated by production, accumulation, and auto-detection of the species-specific autoinducer 1 (AI-1), autoinducer 2 (AI-2), and the V. cholerae autoinducer 1 (CAI-1). The V. harveyi AI-2 was recently identified as furanosyl borate diester. We synthesized several oxazaborolidine derivatives that chemically resemble the structure of AI-2. Five oxazaborolidine derivatives (BNO-1 to BNO-5) were tested, however only BNO-1 (3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaborolidine), and BNO-5 (2-butyl-3,4-dimethyl-5-phenyl-1,3,2-oxazaborolidine) strongly induced V. harveyi bioluminescence in V. harveyi mutant (BB170) lacking sensor 1. A dose-dependent relationship between those oxazaborolidine derivatives and bioluminescence induction was observed with this V. harveyi strain (BB170). BNO-1 and BNO-5 did not affect V. harveyi BB886 lacking sensor 2. Using a mutant strain which produces neither AI-1 nor AI-2 ( V. harveyi MM77) we showed that the presence of spent medium containing AI-2 is essential for BNO-1 and BNO-5 activity. This effect was similar when introducing the spent medium and the BNOs together or at a 3-h interval. A comparable induction of bioluminescence was observed when using synthetic DPD (pre-AI-2) in the presence of BNO-1 or BNO-5. The mode of action of BNO-1 and BNO-5 on bioluminescence of V. harveyi is of a co-agonist category. BNO-1 and BNO-5 enhanced AI-2 signal transduction only in the presence of AI-2 and only via sensor 2 cascade. BNO-1 and BNO-5 are the first oxazaborolidines reported to affect AI-2 activity. Those derivatives represent a new class of borates which may become prototypes of novel agonists of quorum sensing mediated by AI-2 in V. harveyi.

Influence of enteric bacteria conditioned media on recovery of Escherichia coli O157:H7 exposed to starvation and sodium hypochlorite

To examine the effect that starvation and sodium hypochlorite stress have on virulence of Escherichia coli O157:H7 and the influence of conditioned media on recovery of stressed cells. Escherichia coli O157:H7 was starved for 5 days then exposed to 1 microg ml(-1) sodium hypochlorite, suspended in defined media Dulbecco's Modified Eagle's Medium supplemented with conditioned media, sampled over a 12-h period; and assayed for growth, production of Shiga toxin (Stx), and attachment to HCT-8 cells. During recovery, stressed and control cells grown in conditioned media exhibited greater attachment efficiencies to HCT-8 cells then cells in DMEM alone. Production of Stx by treated cells mimicked Stx production by control cells suggesting that components of conditioned media assist in recovery. Results showed that levels of autoinducer-2 fluctuate during recovery and growth suggesting involvement of a quorum sensing mechanism during the recovery of stressed E. coli O157:H7. The recovery of stressed E. coli O157:H7 exposed to starvation conditions and HOCl is positively affected by the presence of autoinducer-2 thereby influencing virulence factor production. Food-borne pathogens in a stressed state prior to ingestion can rapidly recover in the presence of bacterial by-products; exhibiting virulence characteristics and presenting a microbial food safety hazard.

Proteome Analysis of Virulence Factor Regulated by Autoinducer-2–like Activity in Escherichia coli O157:H7

Many pathogenic bacteria, including Escherichia coli O157:H7, can control gene expression in a cell density–dependent manner by producing small signaling molecules (autoinducers) in a process known as quorum sensing. In this study, the effects of the autoinducer-2–like activity on the expression of proteins, including virulence factors, in E. coli O157:H7 were characterized by proteomic analysis. Compared with the control, E. coli O157:H7 strains in the presence of autoinducer-2–like activity exhibited elevated virulence by more rapidly forming cell aggregates on epithelial cells and rapidly killing the nematode Caenorhabditis elegans, the surrogate host. Two-dimensional gel electrophoresis revealed 18 proteins that were upregulated by autoinducer-2–like activity and 4 proteins that were down-regulated. These proteins were further characterized by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and are involved in the metabolic process, adaptation and protection, cell motility, secretion, envelope biogenesis, and protein translation. These results indicate that the newly identified proteins are associated with the control of virulence in E. coli O157:H7 and that these proteins can be potential targets for the development of antibiotics and other antimicrobial agents.