Initial work to generate physically robust biofilms for biocatalytic applications revealed that Escherichia coli K-12 can form a floating biofilm at the air-liquid interface, commonly referred to as a pellicle. Unlike other species where pellicle formation is well-characterised, such as Bacillus subtilis, there are few reports of E. coli K-12 pellicles in the literature. In order to study pellicle formation, a growth model was developed and pellicle formation was monitored over time. Mechanical forces, both motility and shaking, were shown to have effects on pellicle formation and development. The role and regulation of curli, an amyloid protein adhesin critical in E. coli K-12 biofilm formation, was studied by using promoter-green fluorescent protein reporters; flow cytometry and confocal laser scanning microscopy were used to monitor curli expression over time and in different locations. Curli were found to be not only crucial for pellicle formation, but also heterogeneously expressed within the pellicle. The components of the extracellular polymeric substances (EPS) in pellicles were analysed by confocal microscopy using lectins, revealing distinct pellicle morphology on the air-facing and medium-facing sides, and spatially- and temporally-regulated generation of the EPS components poly-N-acetyl glucosamine and colanic acid. We discuss the difference between pellicles formed by E. coli K-12, pathogenic E. coli strains and other species, and the relationship between E. coli K-12 pellicles and solid surface-attached biofilms.
Bibliographical noteAcknowledgments: Genome sequencing was provided by MicrobesNG, which is supported by the UK Biotechnology and Biological Sciences Research Council (BBSRC grant number BB/L024209/1). We thank Paolo Landini for pT7-CsgD and pT7-7 and James Leech for pJLC-T. We are extremely grateful to Alessandro Di Maio at the Birmingham Advanced Light Microscopy facility for confocal microscopy assistance and Charles Penn for discussions regarding hypermotility.
- Colanic acid
- Confocal microscopy
- Poly-N-acetyl glucosamine
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology