Abstract
Biofilms complete a life cycle where cells aggregate, grow and produce a structured community before dispersing to colonize new environments. Progression through this life cycle requires temporally controlled gene expression to maximize fitness at each stage. Previous studies have largely focused on identifying genes essential for the formation of a mature biofilm; here, we present an insight into the genes involved at different stages of biofilm formation. We used TraDIS-Xpress, a massively parallel transposon mutagenesis approach using transposon-located promoters to assay the impact of disruption or altered expression of all genes in the genome on biofilm formation. We identified 48 genes that affected the fitness of cells growing in a biofilm, including genes with known roles and those not previously implicated in biofilm formation. Regulation of type 1 fimbriae and motility were important at all time points, adhesion and motility were important for the early biofilm, whereas matrix production and purine biosynthesis were only important as the biofilm matured. We found strong temporal contributions to biofilm fitness for some genes, including some where expression changed between being beneficial or detrimental depending on the stage at which they are expressed, including dksA and dsbA. Novel genes implicated in biofilm formation included zapE and truA involved in cell division, maoP in chromosome organization, and yigZ and ykgJ of unknown function. This work provides new insights into the requirements for successful biofilm formation through the biofilm life cycle and demonstrates the importance of understanding expression and fitness through time.
Highlights
Bacteria rarely exist planktonically outside of the laboratory and are usually found as part of structured, aggregated communities called biofilms [1]
The 24 h biofilm required both adhesion and matrix production, and after 48 h genes involved in matrix production, cell division and purine biosynthesis were beneficial to biofilm fitness
In concordance with previous work identifying genes whose importance varies with time in the E. coli biofilm, we reported that control of fimbriae expression and motility remained important at each stage of the biofilm life cycle rather than just being involved in initial attachment [28]
Summary
Bacteria rarely exist planktonically outside of the laboratory and are usually found as part of structured, aggregated communities called biofilms [1]. Cells within a biofilm grow more slowly than those in planktonic culture and this reduced level of metabolic activity has been associated with tolerance to antimicrobials, allowing biofilms to be typically 10–1000-fold less sensitive to antibiotics than corresponding strains in planktonic conditions [7, 8]. Biofilms undergo a life cycle that commonly consists of initial attachment to a surface, growth and maturation of the biofilm over time with characteristic production of extracellular matrix components, followed by dispersal of planktonic cells to facilitate colonization of new surfaces [10]. The switch between planktonic and biofilm lifestyles is driven by environmental stimuli promoting large-scale changes in gene expression and regulation that are necessary to support the bacterial community through the life cycle, which is distinct from planktonic growth conditions. Expressing the right genes at the right time and place is critical for efficient production of a biofilm
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