Bacterial biofilms are multicellular structures that are encased in a matrix of extracellular polymeric substances and that have been linked to chronic infections in clinical settings. Previous studies have suggested that the distinct anatomy of biofilms affects the access for individual cells to resources, which in turn influences metabolic activity and survival within biofilms. In addition, the biofilm anatomy has been linked to antimicrobial susceptibility. However, how cells are arranged within biofilm structures, the genetic determinants of this arrangement and physiological importance of such patterns have not been well understood. In this study, Dietrich, Dayton and colleagues report that Pseudomonas aeruginosa cells form striations that are packed lengthwise across the biofilm and that this physical arrangement affects substrate uptake and distribution across the biofilm, as well as susceptibility to antimicrobial treatment.

Next, the authors carried out experiments to uncover the genetic determinants of the cellular arrangements within a biofilm at the microscale. To this end, they screened mutants that lacked crucial regulators of biofilm formation and physiology. Microscopy images of mixed biofilms of each mutant revealed that the vast majority of the mutants exhibited the striated cellular arrangement phenotype similar to that of the wild type. However, the analysis also showed that some biofilms had alterations to this lengthwise packing phenotype, and the authors found three additional phenotypes bundled, disordered and clustered. Specifically, cells defective in the production and function of the type IV pilus formed bundled biofilms, which suggests that an extendable and retractable pilus is required for the formation of the striations seen for wild-type biofilms. Moreover, cells lacking certain global gene expression regulators or cells with defects in O-antigen biosynthesis gave rise to the disordered phenotype. Finally, mutant cells that produced lipopolysaccharide without the O-antigen attached produced the clustered phenotype.

Read the original post:
Bacterial architects build the biofilm structures - Nature.com