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Bacterial biofilms are multicellular structures enclosed in an extracellular polymeric matrix and are associated with chronic infections in clinical settings. Previous research has shown that the unique anatomy of biofilms affects resource acquisition by individual cells, which in turn affects metabolic activity and survival within the biofilm. Furthermore, biofilm anatomy is associated with antimicrobial susceptibility. However, the arrangement of cells within biofilm structures, the genetic determinants of this arrangement, and the physiological importance of this pattern are not well understood.In this study, Dietrich, Dayton, and colleagues reported Pseudomonas aeruginosa Cells form longitudinally aligned stripes across the biofilm, and this physical arrangement affects the uptake and distribution of substrates across the biofilm, as well as susceptibility to antimicrobial treatments.
Next, the authors performed experiments to reveal the genetic determinants of cell arrangement within microscopic-scale biofilms. To do this, they screened for mutants lacking key regulators of biofilm formation and physiology. Microscopic images of mixed biofilms from each mutant showed that the vast majority of the mutants exhibited a similar striated cell arrangement phenotype to the wild type. However, the analysis also showed that this longitudinal packing phenotype was altered in some biofilms, with the authors identifying three additional phenotypes – bundling, disordering and aggregation. Specifically, cells defective in the production and function of type IV pili formed bundled biofilms, suggesting that retractable pili are required for the formation of stripes seen in wild-type biofilms. Furthermore, cells lacking certain global gene expression regulators or cells defective in O-antigen biosynthesis can lead to phenotypic disorders. Finally, mutant cells that produce lipopolysaccharide that does not attach O antigen develop an aggregation phenotype.
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