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Chapter 21 : Biofilms
Category: Microbial Genetics and Molecular Biology
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This chapter discusses specific triggers of biofilm formation and how survival in these multicellular communities affects the physiology of the constituent cells. The ability of bacteria to adhere to and form biofilms on virtually every surface makes it particularly important that we understand the mechanisms underlying this sedentary lifestyle. The molecular mechanisms necessary for the formation of biofilms varies from species to species. There is a vast array of research on biofilm communities, but this chapter focuses on a few model organisms to illustrate major similarities and differences between species. Biofilms contain large numbers of cells and, quite importantly, these populations are phenotypically heterogeneous. Cells within the biofilm are constantly consuming available resources and can form structures with a depth of hundreds of microns or more. Stochastic gene expression inherent to individual bacterial cells also adds to the complex distribution of phenotypes of individual cells within a biofilm. Cyclic di-guanosine monophosphate (c-di-GMP) is a second messenger that is important in regulating the transition from a planktonic to biofilm lifestyle in many organisms. Secondary metabolites include most antibiotics and/or pigments and are generally produced during stationary phase as nutrients become depleted. Phenazine mutant colonies have been shown to bind the dye congo red, which is known to specifically interact with the Pel exopolysaccharide in Pseudomonas aeruginosa.
Side view of a vertically thin sectioned colony biofilm from B. subtilis strain NCIB 3610 cells harboring transcriptional reporters for cell type-specific promoters. Shown are overlays of transmitted light and fluorescence images. Top panel: motility (P hag -cfp, colored blue) and sporulation (P sspB -yfp, colored yellow). Bottom panel: matrix production (P yqxM -cfp, colored red) and sporulation (PsspB-yfp, colored green). The edge of the colony is on the left and the agar is at the bottom of the image. Colonies were initiated from single cells and grown on an agar surface for 72 hours at 30°C prior to sectioning. Bar is 50 µm.
Features of biofilms for model organisms a