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Title: Transition to quorum sensing in an Agrobacterium population: A stochastic model
Authors: Goryachev A.B. 
Toh D.-J.
Wee K.B.
Lee T. 
Zhang H.-B.
Zhang L.-H. 
Keywords: bacterial protein
TraM protein, bacterial
biological model
cell proliferation
culture medium
gene expression regulation
quorum sensing
Rhizobium radiobacter
sensitivity and specificity
Agrobacterium tumefaciens
Bacterial Proteins
Cell Proliferation
Culture Media
Gene Expression Regulation, Bacterial
Models, Biological
Quorum Sensing
Sensitivity and Specificity
Stochastic Processes
Issue Date: 2005
Citation: Goryachev A.B., Toh D.-J., Wee K.B., Lee T., Zhang H.-B., Zhang L.-H. (2005). Transition to quorum sensing in an Agrobacterium population: A stochastic model. PLoS Computational Biology 1 (4) : 265-275. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
Abstract: Understanding of the intracellular molecular machinery that is responsible for the complex collective behavior of multicellular populations is an exigent problem of modern biology. Quorum sensing, which allows bacteria to activate genetic programs cooperatively, provides an instructive and tractable example illuminating the causal relationships between the molecular organization of gene networks and the complex phenotypes they control. In this work we - to our knowledge for the first time - present a detailed model of the population-wide transition to quorum sensing using the example of Agrobacterium tumefaciens. We construct a model describing the Ti plasmid quorum-sensing gene network and demonstrate that it behaves as an "on-off" gene expression switch that is robust to molecular noise and that activates the plasmid conjugation program in response to the increase in autoinducer concentration. This intracellular model is then incorporated into an agent-based stochastic population model that also describes bacterial motion, cell division, and chemical communication. Simulating the transition to quorum sensing in a liquid medium and biofilm, we explain the experimentally observed gradual manifestation of the quorum-sensing phenotype by showing that the transition of individual model cells into the "on" state is spread stochastically over a broad range of autoinducer concentrations. At the same time, the population-averaged values of critical autoinducer concentration and the threshold population density are shown to be robust to variability between individual cells, predictable and specific to particular growth conditions. Our modeling approach connects intracellular and population scales of the quorum-sensing phenomenon and provides plausible answers to the long-standing questions regarding the ecological and evolutionary significance of the phenomenon. Thus, we demonstrate that the transition to quorum sensing requires a much higher threshold cell density in liquid medium than in biofilm, and on this basis we hypothesize that in Agrobacterium quorum sensing serves as the detector of biofilm formation. Copyright: ? 2005 Goryachev et al.
Source Title: PLoS Computational Biology
ISSN: 1553734X
DOI: 10.1371/journal.pcbi.0010037
Rights: Attribution 4.0 International
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