Genome rearrangements induce biofilm formation inEscherichia coliC – an old model organism with a new application in biofilm research

Abstract

AbstractEscherichia coliC forms more robust biofilms than the other laboratory strains. Biofilm formation and cell aggregation under a high shear force depends on temperature and salt concentrations. It is the last of fiveE. colistrains (C, K12, B, W, Crooks) designated as safe for laboratory purposes whose genome has not been sequenced. Here we present the complete genomic sequence of this strain in which we utilized both long-read PacBio-based sequencing and high resolution optical mapping to confirm a large inversion in comparison to the other laboratory strains. Notably, DNA sequence comparison revealed the absence of several genes thought to be involved in biofilm formation, including antigen 43,waaSBOJYZULfor LPS synthesis, andcpsBfor curli synthesis. The first main difference we identified that likely affects biofilm formation is the presence of an IS3-like insertion sequence in front of the carbon storage regulatorcsrAgene. This insertion is located 86 bp upstream of thecsrAstart codon inside the −35 region of P4 promoter and blocks the transcription from the sigma32and sigma70promoters P1-P3 located further upstream. The second is the presence of an IS5/IS1182 in front of thecsgDgene, which may drive its overexpression in biofilm. And finally,E. coliC encodes an additional sigma70subunit overexpressed in biofilm and driven by the same IS3-like insertion sequence. Promoter analyses using GFP gene fusions and total expression profiles using RNA-seq analyses comparing planktonic and biofilm envirovars provided insights into understanding this regulatory pathway inE. coli.IMPORTANCEBiofilms are crucial for bacterial survival, adaptation, and dissemination in natural, industrial, and medical environments. Most laboratory strains ofE. coligrown for decadesin vitrohave evolved and lost their ability to form biofilm, while environmental isolates that can cause infections and diseases are not safe to work with. Here, we show that the historic laboratory strain ofE. coliC produces a robust biofilm and can be used as a model organism for multicellular bacterial research. Furthermore, we ascertained the full genomic sequence as well as gene expression profiles of both the biofilm and planktonic envirovars of this classic strain, which provide for a base level of characterization and make it useful for many biofilm-based applications.