Bacterial signalling

Research Interests

Bacteria use small chemical molecules called autoinducers to communicate with one another by a process called quorum sensing. This process enables a population of bacteria to regulate behaviours which are only productive when many bacteria act in concert as a group, similarly to what happens with multi-cellular organisms. Behaviours regulated by quorum sensing are often crucial for successful bacterial-host relationships whether symbiotic and pathogenic. In this laboratory biochemical and genetic approaches are used to study the molecular mechanisms underlying quorum sensing, with an emphasis on systems promoting bacterial inter-species communication. This research includes an integrated study involving elucidation of the chemical molecules that are used as signals, the network components involved in detecting the signals and processing information inside individual cells, and finally characterization of the behaviour of the bacterial community in multi-species bacterial consortia. Our ultimate goal is to understand how bacteria use inter-species cell-cell communication to coordinate population-wide behaviours in consortia and in microbial-host interactions.

The Bacterial Signalling laboratory is seeking post doctoral fellows. If interested please send a letter of motivation, cv and two references to Karina B. Xavier at kxavier@igc.gulbenkian.pt.

Group Members

Michal Sagie	Postdoc
	Tel: 21 446 4675
Osvaldo Ascenso	Trainee
	Tel: 21 446 4675
Catarina Pereira	2006 PDIGC PhD Student
	Tel: 21 446 4675
Rita Valente	2008 PGD PhD Student
	Tel: 21 446 4675

Research Project

Inter-species cell-cell signalling in bacteria

This project focuses on the molecular mechanisms that bacteria use for inter-cellular communication. This process, called quorum sensing, involves the production, release, and response to signal molecules termed autoinducers. Quorum sensing enables a bacterial population to regulate activities as a multi-cellular group. Most autoinducers are species-specific, however one autoinducer called autoinducer-2 (AI-2), is produced and detected by a wide variety of bacteria allowing inter-species communication. This project relies on a multi-disciplinary approach to study AI-2 systems promoting bacterial inter-species communication. By studying quorum sensing in Escherichia coli, we have characterized one of the first AI-2 systems. We will pursue the characterization of the E. coli AI-2 system, and will also investigate novel AI-2 signalling systems in other bacteria to understand the network architecture controlling AI-2 signalling at the species level. We have developed the first laboratory system to study inter-species AI-2 signalling in consortia, so once we identify novel AI-2 circuits, we will use this set up to study inter-species cell-cell communication in complex bacterial communities.

Funding

Marie Curie International Reintegration Grant (031108),
European Commission, and Luso-American Foundation (FLAD) (Portugal)
U.S. NATIONAL SCIENCE FOUNDATION (NSF) Research Network Grants (Proj. 600-10/2006).

Collaborators

Princeton University
Bonnie L. Bassler

Research Project

Identification and characterization of quorum sensing systems involved in bacterial inter-species communication

Many quorum sensing systems have been extensively studied and are well characterized, in some cases new therapies are already being developed to interfere with quorum sensing to inhibit virulence. In most cases quorum sensing systems are regulated by species specific autoinducers and are used for bacterial intra-species communication. In contrast, one autoinducer, termed autoinducer-2 (AI-2), is produced and detected by a wide variety of bacteria and is considered a “universal” bacterial signal that fosters inter-species communication. Since the discovery of AI-2, many laboratories have shown that different bacteria use AI-2 to control an assortment of “niche-specific” behaviours. However, the mechanisms of AI-2 detection and the cognate signal transduction pathways have only been established in two Vibrio species and the enteric bacteria Escherichia coli and Salmonella enteric serovar Typhimurium. The research undertaken in this project involves a biochemical, genetic, and chemical characterization of novel AI-2 signalling systems. Our preliminary results show that the plant symbiont Sinorhizobium meliloti has an AI-2 internalization system similar to the E. coli AI-2 system and we will characterize this system in detail to evaluate its function during the symbiosis S. meliloti establishes with its host the alfalfa plant. Furthermore, to assess the diversity of these systems we will identify and characterize AI-2 detection systems from additional bacterial species, and determine the structure of novel AI-2 signal-receptor complexes to identify the active AI-2 molecules. Mutants impaired in these AI-2 signalling pathways will be constructed, characterized, and used to study bacterial-bacterial, and bacterial-host interactions.

Funding

Projectos de I&D - Fundação para a Ciência e Tecnologia
Identification and characterization of quorum sensing systems involved in bacterial inter-species communication (PTDC/BIA-BCM/73676/2006)

Collaborators

Swarthmore College
Stephen T. Miller

Research Project

Quorum Sensing in Escherichia coli

This project relies on a multidisciplinary approach to investigate the molecular mechanisms underlying AI-2 quorum sensing in the enteric bacterium Escherichia coli, with an emphasis on its role in bacterial inter-species communication. We have showed that, in E. coli, AI-2-regulates a system that internalizes and degrades the AI-2 signal. Specifically, at high population densities, E. coli uses this system to remove AI-2 produced by itself and also AI-2 produced by other species present in the same co-culture. AI-2 internalization by E. coli has the consequence of interfering with other species’ ability to use AI-2 to regulate their group behaviours by quorum sensing. We predict that this mechanism of interference with AI-2 signalling has important consequences in natural niches colonized by E. coli such as the human gut where many different species of bacterial species co-exist and depend on quorum sensing for efficient colonization.
The E. coli AI-2 internalization process represents the first example of interference with AI-2-mediated quorum sensing. Understanding the natural strategies organisms use to interfere with other species’ ability to communicate, such as in E. coli, can be used as models in the design of clinical and biotechnological strategies intended to manipulate bacterial behaviours. Such studies can lead to the development of new therapies to control functions regulated by quorum sensing, such as virulence, and also to develop biotechnological applications to control industrial scale production of beneficial bacterial products, like antibiotics or recombinant proteins.

Funding

Programa Damião de Góis – Fundação para a Ciência e Tecnologia
Quorum Sensing in Escherichia coli (PPCDT/DG/BIA/82010/2006)

Publications

(Selected) Updated October (2009).

Pereira, C. S., de Regt, A. K., Brito, P. H, Miller, S. T., Xavier, K.B. (2009). Identification of functional LsrB-like autoinducer-2 receptors J Bacteriol. [Epub ahead of print] doi: :10.1128/JB.00976-09

Dia,z Z., Xavier, K. B., Miller, ST. (2009). The crystal structure of the Escherichia coli autoinducer-2 processing protein LsrF PLoS One 4(8) :e6820

Trindade, S., Sousa, A., Xavier, K. B., Dionisio, F., Ferreira, M.G., Gordo, I. (2009). Positive epistasis drives the acquisition of multidrug resistance. PLoS Genet 5(7) :e1000578

Pereira, CS, McAuley, JR, Taga, ME, Xavier, KB, Miller, ST (2008). Sinorhizobium meliloti, a bacterium lacking the autoinducer-2 synthase, responds to AI-2 supplied by other bacteria. Mol. Micro. 70 :1223-35

Bejerano-Sagie, M. and Xavier, K.B. (2007). The Role of Small RNAs in Quorum-Sensing Curr Opin Microbiol. 10 :189-98

Xavier, K.B., Miller, S.T., Lu, W., Kim, J.H., Rabinowitz,J., Pelczer,I., Semmelhack, M.F.and Bassler, B.L. (2007). Phosphorylation and processing of AI-2 in Enteric Bacteria. (See “Point of View” in ACS Chemical Biology. 2: 89-91 and “Research Highlight” in Nature Reviews Microbiology. 5: 246-247 (April 2007)) ACS Chemical Biology 2 :128-136 Link

Xavier, K. B. and Bassler, B. L. (2005). Interference with AI-2-mediated bacterial cell-cell communication. Nature 437 :750-753

Xavier, K.B. and Bassler, B.L. (2005). Regulation of uptake and processing of the quorum-sensing autoinducer AI-2 in Escherichia coli. J. Bacteriol. 187 :238-48

Miller, S. T., Xavier, K. B., Campagna, S. R., Taga, M. E., Semmelhack, M. F., Bassler, B. L. and Hughson, F. M. (2004). Salmonella typhimurium recognizes a chemically distinct form of the bacterial quorum-sensing signal AI-2 Mol. Cell. 15 :677-87

Xavier, K. B. and Bassler, B. L. (2003). LuxS quorum sensing: more than just a numbers game. Curr Opin Microbiol 6 :191-197