REPORTER GENES AND FLUORESCENT-PROBES FOR STUDYING THE COLONIZATION OF BIOFILMS IN A DRINKING-WATER SUPPLY LINE BY ENTERIC BACTERIA

Biofilms containing diverse microflora were developed on bitumen-paint ed steel and glass tiles suspended in a chemostat model of a water dis tribution system. Escherichia coli, taken from a naturally occurring b iofilm, was transformed with a plasmid containing the anaerobically in duced nirB promoter fused to the lacZ reporter gene. The resulting tra nsformant, PRB1, was introduced into the chemostat. After 7 and 13 day s, an E. coli strain with an anaerobically induced Lac(+) phenotype wa s present in the biofilm. Development of an episcopic differential int erference 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 an d a lacZ fluorescent probe to monitor anaerobic expression of beta-gal actosidase from pnirB.