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Bacteria are social creatures that are able to interact and coordinate behaviors with each other in a multitude of ways. The study of such group behaviors in microbes was coined "sociomicrobiology" in 2005. Two such group behaviors in bacteria are quorum sensing (QS) and biofilm formation. At a very basic level, QS is the ability to sense bacterial density via cell-to-cell signaling using self-produced signals called autoinducers, and biofilms are aggregates of cells that are attached to one another via a self-produced, extracellular matrix. Since cells in biofilm aggregates are in close proximity, biofilms represent an ecologically relevant environment for QS. While QS is known to affect biofilm formation in both Gram-negative and Gram-positive species, in this review, we will focus exclusively on Gram-negative bacteria, with an emphasis on Pseudomonas aeruginosa. We will begin by describing QS systems in P. aeruginosa and how they affect P. aeruginosa biofilm formation. We then expand our review to other Gram-negative bacteria and conclude with interesting questions with regard to the effect of biofilms on QS. [ABSTRACT FROM AUTHOR]

Asub-groupofLuxRfamilyofproteinsthatplaysimportantrolesinquorumsensing,aprocessofcell-cellcommunication,iswidespreadinproteobacteria.TheseproteinshaveatypicalmodularstructureconsistingofN-terautoinducerbindingandC-terhelix-turn-helix(HTH)DNAbindingdomains.TheautoinducerbindingdomainrecognizessignalingmoleculeswhicharemostoftenN-acylhomoserinelactones(AHLs)butcouldalsobeothernovelandyetunidentifiedmolecules.Inthisstudywecarriedoutaseriesofspecificdomainswappingandpromoteractivationexperimentsasafirststeptoengineersyntheticsignalingmodules,takingadvantageofthemodularityandtheversatile/diversesignalspecificitiesofLuxRproteins.InourexperimentstheN-terdomainsfromdifferentLuxRhomologswereeitherinterchangedorplacedintandemfollowedbyaC-terdomain.Therationaldesignofthehybridproteinswassupportedbyastructure-basedhomologymodelingstudiesofthreemembersoftheLuxRfamily(i.e.,LasR,RhlR,andOryRbeingchosenfortheiruniqueligandbindingspecificities)andofselectedchimeras.OurresultsrevealthattheseLuxRhomologswereabletoactivatepromoterelementsthatwerenottheirusualtargets;wealsoshowthathybridLuxRproteinsretainedtheabilitytorecognizethesignalspecificfortheirN-terautoinducerbindingdomain.However,theactivityofhybridLuxRproteinscontainingtwoAHLbindingdomainsintandemappearstodependontheorganizationandnatureoftheintroduceddomains.ThisstudyrepresentsadvancesintheunderstandingofthemodularityofLuxRproteinsandprovidesadditionalpossibilitiestousehybridproteinsinbothbasicandappliedsyntheticbiologybasedresearch. [ABSTRACT FROM AUTHOR]

Members of the genus Burkholderia are known to be adept at biofilm formation, which presumably assists in the survival of these organisms in the environment and the host. Biofilm formation has been linked to quorum sensing (QS) in several bacterial species. In this study, we characterized Burkholderia thailandensis biofilm development under flow conditions and sought to determine whether QS contributes to this process. B. thailandensis biofilm formation exhibited an unusual pattern: the cells formed small aggregates and then proceeded to produce mature biofilms characterized by "dome" structures filled with biofilm matrix material. We showed that this process was dependent on QS. B. thailandensis has three acyl-homoserine lactone (AHL) QS systems (QS-1, QS-2, and QS-3). An AHL-negative strain produced biofilms consisting of cell aggregates but lacking the matrix-filled dome structures. This phenotype was rescued via exogenous addition of the three AHL signals. Of the three B. thailandensis QS systems, we show that QS-1 is required for proper biofilm development, since a btaR1 mutant, which is defective in QS-1 regulation, forms biofilms without these dome structures. Furthermore, our data show that the wild-type biofilm biomass, as well as the material inside the domes, stains with a fucose-binding lectin. The btaR1 mutant biofilms, however, are negative for fucose staining. This suggests that the QS-1 system regulates the production of a fucose-containing exopolysaccharide in wild-type biofilms. Finally, we present data showing that QS ability during biofilm development produces a biofilm that is resistant to dispersion under stress conditions. [ABSTRACT FROM AUTHOR]

The olive knot disease (Olea europea L.) is caused by the bacterium Pseudomonas savastanoi pv. savastanoi. P. savastanoi pv. savastanoi in the olive knot undergoes interspecies interactions with the harmless endophyte Erwinia toletana; P. savastanoi pv. savastanoi and E. toletana colocalize and form a stable community, resulting in a more aggressive disease. P. savastanoi pv. savastanoi and E. toletana produce the same type of the N-acylhomoserine lactone (AHL) quorum sensing (QS) signal, and they share AHLs in planta. In this work, we have further studied the AHL QS systems of P. savastanoi pv. savastanoi and E. toletana in order to determine possible molecular mechanism(s) involved in this bacterial interspecies interaction/cooperation. The AHL QS regulons of P. savastanoi pv. savastanoi and E. toletana were determined, allowing the identification of several QS-regulated genes. Surprisingly, the P. savastanoi pv. savastanoi QS regulon consisted of only a few loci whereas in E. toletana many putative metabolic genes were regulated by QS, among which are several involved in carbohydrate metabolism. One of these loci was the aldolaseencoding gene garL, which was found to be essential for both colocalization of P. savastanoi pv. savastanoi and E. toletana cells inside olive knots as well as knot development. This study further highlighted that pathogens can cooperate with commensal members of the plant microbiome. IMPORTANCE: This is a report on studies of the quorum sensing (QS) systems of the olive knot pathogen Pseudomonas savastanoi pv. savastanoi and olive knot cooperator Erwinia toletana. These two bacterial species form a stable community in the olive knot, share QS signals, and cooperate, resulting in a more aggressive disease. In this work we further studied the QS systems by determining their regulons as well as by studying QS-regulated genes which might play a role in this cooperation. This represents a unique in vivo interspecies bacterial virulence model and highlights the importance of bacterial interspecies interaction in disease. [ABSTRACT FROM AUTHOR]

A sub-group of LuxR family of proteins that plays important roles in quorum sensing, a process of cell-cell communication, is widespread in proteobacteria. These proteins have a typical modular structure consisting of N-ter autoinducer binding and C-ter helix-turn-helix (HTH) DNA binding domains. The autoinducer binding domain recognizes signaling molecules which are most often N-acyl homoserine lactones (AHLs) but could also be other novel and yet unidentified molecules. In this study we carried out a series of specific domain swapping and promoter activation experiments as a first step to engineer synthetic signaling modules, taking advantage of the modularity and the versatile/diverse signal specificities of LuxR proteins. In our experiments the N-ter domains from different LuxR homologs were either interchanged or placed in tandem followed by a C-ter domain. The rational design of the hybrid proteins was supported by a structure-based homology modeling studies of three members of the LuxR family (i.e., LasR, RhlR, and OryR being chosen for their unique ligand binding specificities) and of selected chimeras. Our results reveal that these LuxR homologs were able to activate promoter elements that were not their usual targets; we also show that hybrid LuxR proteins retained the ability to recognize the signal specific for their N- ter autoinducer binding domain. However, the activity of hybrid LuxR proteins containing two AHL binding domains in tandem appears to depend on the organization and nature of the introduced domains. This study represents advances in the understanding of the modularity of LuxR proteins and provides additional possibilities to use hybrid proteins in both basic and applied synthetic biology based research.

Pseudomonas fuscovaginae was first reported as a pathogen of rice causing sheath rot in plants grown at high altitudes. P. fuscovaginae is now considered a broad-host-range plant pathogen causing disease in several economically important plants. We report what is, to our knowledge, the first draft genome sequence of a P. fuscovaginae strain.

Microbial diseases occur as a result of multifarious host-pathogen interactions. However, invading pathogens encounter a large number of different harmless and beneficial bacterial species, which colonize and reside in the host. Surprisingly, there has been little study of the possible interactions between incoming pathogens and the resident bacterial community. Recent studies have revealed that resident bacteria assist different types of incoming pathogens via a wide variety of mechanisms including cell-cell signaling, metabolic interactions, evasion of the immune response and a resident-to-pathogen switch. This calls for serious consideration of pathogen-microbe interactions in the host with respect to disease severity and progression., (Copyright © 2012 Elsevier Ltd. All rights reserved.)