Chapter 1 : Factors That Impact Biofilm Structure and Function

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This chapter focuses on the relationships among biofilm development, the environment, and antimicrobial tolerance for the paradigm organism . While a specific strain of consistently produces the same biofilm structure under one laboratory culturing condition, the same strain produces a very different biofilm structure under different culturing conditions. Investigators have discovered that biofilms grown in vitro reproducibly form specific structures that are affected by a plethora of conditions. For , two general biofilm shapes have been observed using the flow cell system: structured biofilms and flat biofilms. While the environmental sensing mechanisms and the regulatory pathways leading to the formation of specific biofilm structures have not been fully elucidated, it is clear that many factors are important for this process. A focus of recent work has been on identifying the signal transduction and regulatory pathways that control biofilm formation and that integrate different environmental signals during biofilm development. The chapter provides an outline about the regulation of biofilm formation by cyclic-di-GMP (c-di-GMP) and two-component systems (TCSs). Researchers are currently trying to determine the nature of these environmental signals, and as they do, our understanding of which environments promote or impair biofilm formation will grow. Microbial fuel cells and wastewater treatment communities are a few examples of engineered, structured communities that could benefit from such an approach.

Citation: Tseng B, Parsek M. 2013. Factors That Impact Biofilm Structure and Function, p 3-20. In Vasil M, Darwin A (ed), Regulation of Bacterial Virulence. ASM Press, Washington, DC. doi: 10.1128/9781555818524.ch1
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Figure 1

Models of flat versus structured biofilm formation in . Initial steps of biofilm formation are suggested to be the same for flat and structured biofilms. After initial steps, however, maturation of the different structures is suggested to follow different developmental pathways. There are two forms of structured biofilms (structured biofilms I and II). Aggregates of cells clonally expand to produce the structured biofilm I phenotype, while motile cells move to top nonmotile aggregates of cells to form mushroom-shaped structures in the structured biofilm II phenotype. Flat biofilms are formed through the clonal expansion of motile cells. Blue cylinders represent motile cells, and orange cylinders represent nonmotile cells. Adapted from Kirisits and Parsek, 2006, with permission from John Wiley and Sons. doi:10.1128/9781555818524.ch1f1

Citation: Tseng B, Parsek M. 2013. Factors That Impact Biofilm Structure and Function, p 3-20. In Vasil M, Darwin A (ed), Regulation of Bacterial Virulence. ASM Press, Washington, DC. doi: 10.1128/9781555818524.ch1
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Figure 2

Type IV pilus mutants form biofilms that are morphologically distinct from those of the wild-type strain. (A) Fourday- old biofilms of wild-type and Δ strains of grown in glucose-based minimal medium. A 1:1 mixture of CFP- and YFP-expressing cells of the same strain was used to initiate the biofilm. (B) Ninety-eight-hour-old biofilms of GFPexpressing wild-type and Δ strains of grown in citrate-based minimal medium. Crosshairs (A) and white triangles (B) indicate the positions of vertical cross sections shown on the right and bottom of each image. Scale bar, 20 μm. Modified from Klausen et al., 2003a (A), and Heydorn et al., 2000 (B), with permission from John Wiley and Sons and the Society for General Microbiology, respectively. doi:10.1128/9781555818524.ch1f2

Citation: Tseng B, Parsek M. 2013. Factors That Impact Biofilm Structure and Function, p 3-20. In Vasil M, Darwin A (ed), Regulation of Bacterial Virulence. ASM Press, Washington, DC. doi: 10.1128/9781555818524.ch1
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Figure 3

The carbon source affects biofilm morphology. Shown are 48-hour-old biofilms of GFP-expressing wild-type and ΔΔ strains of grown in media with different carbon sources. SV, side view (x, z-plane); TD, top down view (x, y-plane). Reproduced from Shrout et al., 2006, with permission from John Wiley and Sons. doi:10.1128/9781555818524.ch1f3

Citation: Tseng B, Parsek M. 2013. Factors That Impact Biofilm Structure and Function, p 3-20. In Vasil M, Darwin A (ed), Regulation of Bacterial Virulence. ASM Press, Washington, DC. doi: 10.1128/9781555818524.ch1
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Figure 4

Overproduction of exopolysaccharides creates more structured biofilms. (A) Five-day-old biofilms of the GFPexpressing wild type (PAO1) and an isogenic, alginate-overproducing (PDO300) strain of grown in defined rich medium. White triangles indicate the position of vertical cross sections shown on the right and bottom of each image. Bar, 20 μm. (B) Three-day-old biofilms of GFP-expressing wild type (WT) and RSCV MJK8 of grown in defined rich medium. Modified from Hentzer et al., 2001 (A), and Kirisits et al., 2005 (B), with permission from the American Society for Microbiology. doi:10.1128/9781555818524.ch1f4

Citation: Tseng B, Parsek M. 2013. Factors That Impact Biofilm Structure and Function, p 3-20. In Vasil M, Darwin A (ed), Regulation of Bacterial Virulence. ASM Press, Washington, DC. doi: 10.1128/9781555818524.ch1
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