ORIGINAL PAPER Modeling bacterial quorum sensing in open and closed environments: potential discrepancies between agar plate and culture flask experiments Dóra Bihary & Marietta Tóth & Ádám Kerényi & Vittorio Venturi & Sándor Pongor Received: 28 December 2013 /Accepted: 10 April 2014 /Published online: 19 June 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Quorum sensing (QS) is a process of bacterial communication and cooperation mediated by the release of jointly exploited signals and “public goods” into the environ- ment. There are conflicting reports on the behavior of mutants deficient in the release of these materials. Namely, mutants that appear perfectly viable and capable of outgrowing wild type cells in a closed model system such as a culture flask, may not be viable or invasive on open surfaces such as agar plates. Here we show via agent-based computational simula- tions that this apparent discrepancy is due to the difference between open and closed systems. We suggest that the exper- imental difference is due to the fact that wild type cells can easily saturate a well-mixed culture flask with signals and public goods so QS will be not necessary after a certain time point. As a consequence, QS-deficient mutants can continue to grow even after the wild type population has vanished. This phenomenon is not likely to occur in open environments including open surfaces and agar plate models. In other words, even if QS is required for survival, QS deficient mutants may grow faster initially in short term laboratory experiments or computer simulations, while only WT cells appear stable over longer time scales, especially when adaptation to changing environments is important. Keywords Bacterial communication . Agent-based model . Quorum sensing . Cooperation . Cheating Introduction Quorum sensing (QS) is a cell–cell communication process in which bacteria release and detect molecular signals called autoinducers, which enables them to monitor cell population density and make a variety of coordinated responses [1]. 1 Acyl homoserine lactones (AHLs), the major class of autoinducer signals used by Gram-negative bacteria, consist of a conserved homoserine lactone ring coupled to an acyl side chain, which may vary from 3 to 18 carbons in length. All AHLs are believed to diffuse freely across the cell envelope; however, efflux pumps may actively export some longer chain AHLs [2]. In a typical AHL-QS circuit, the AHL signals are synthesized by a LuxI-type protein. At a critical concentration, the AHL binds to a LuxR-type protein, and the LuxR-AHL complex acts on target genes that affect a variety of cellular processes [3] including the production of exoenzymes and exopolysaccharides. As these QS-regulated factors are re- leased into the environment and are accessible to other cells, they are often referred to as “public goods”, i.e., openly accessible means of intercellular cooperation. For instance, cells of the ubiquitous opportunistic pathogen Pseudomonas aeruginosa have two AHL-QS systems (see, e.g., [4, 5]). In 1 Definition of terms used in this paper: QS Quorum sensing; QS system: a QS system of Psuedomanas aeruginosa consists of two fundamental genes, abbreviated here as R and I; rhl the QS system of P. aeruginosa that controls rhamnolipid production. It consists of the genes rhlR and rhlI; las the QS system of P. aeruginosa that controls elastase production. It consists of the genes lasR and lasl; SN a non-communicating mutant with the I gene (either lasI, rhlI or both) deleted. These mutants do not produce the signal, but react to it. SB a non-cooperating mutant with the R gene (either lasR, rhlR or both) deleted. These mutants produce a very low level of signal, but do not respond to it. This paper belongs to Topical Collection 9th European Conference on Computational Chemistry (EuCo-CC9) D. Bihary : M. Tóth : S. Pongor Pázmány Péter Catholic University, 1083 Budapest, Hungary Á. Kerényi Institute of Biophysics, Szeged Biological Research Center, 6726 Szeged, Hungary V. Venturi : S. Pongor (*) International Centre for Genetic Engineering and Biotechnology, 34149 Trieste, Italy e-mail: pongor@icgeb.org J Mol Model (2014) 20:2248 DOI 10.1007/s00894-014-2248-y