Reporter genes and fluorescent probes for studying the colonisation of biofilms in a drinking water supply line by enteric bacteria

Biofilms containing diverse microflora were developed on bitumen-painted steel and glass tiles suspended in a chemostat model of a water distribution system. Escherichia coli, taken from a naturally occurring biofilm, was transformed with a plasmid containing the anaerobically induced nirB promoter fused to the lacZ reporter gene. The resulting transformant, PRB1, was introduced into the chemostat. After 7 and 13 days, an E. coli strain with an anaerobically induced Lac+ phenotype was present in the biofilm. Development of an episcopic differential interference contrast technique combined with UV fluorescence microscopy enabled the simultaneous visualization of E. coli in the biofilm using a fluorescent probe to detect expression of the gusA reporter gene and a lacZ fluorescent probe to monitor anaerobic expression of β-galactosidase from pnirB.