JB Accepts, published online ahead of print on 6 November 2009

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J. Bacteriol. doi:10.1128/JB.01826-08
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Bistable expression of CsgD in biofilm development of Salmonella enterica serovar Typhimurium

Nina Grantcharova, Verena Peters, Claudia Monteiro, Katherina Zakikhany, and Ute Römling^*

Department of Microbiology, Cell and Tumor Biology, Karolinska Institutet, Stockholm, Sweden

^* To whom correspondence should be addressed. Email: ute.romling{at}ki.se.

Bacterial persistence in the environment and in the infected host is often aided by the formation of exopolymer-enclosed communities, known as biofilms. Heterogeneous gene expression takes place in microcompartments formed within the complex biofilm structure. This study describes cell differentiation within an isogenic bacterial cell population on the example of biofilm formation by Salmonella enterica serovar Typhimurium (S. typhimurium). We analyzed the expression of the major biofilm regulator CsgD at the single-cell level with a chromosomal CsgD-GFP translational fusion. In individual cells CsgD-GFP expression is mostly found in the cytoplasm. Quantitative expression analysis and results from three different models of S. typhimurium biofilms demonstrated that CsgD is expressed in a bistable manner during biofilm development. The CsgD expression is, however, monomodal when CsgD is expressed at higher amounts due to a promoter mutation or elevated levels of the secondary signalling molecule c-di-GMP. High levels of CsgD-GFP are associated with cellular aggregation in all three biofilm models. Furthermore, the subpopulation of cells expressing high amounts of CsgD is engaged in cellulose production during rdar morphotype development and in microcolony formation under conditions of continuous flow. Consequently, bistability at the level of CsgD expression leads to a corresponding pattern of task distribution in S. typhimurium biofilms.