In situ monitoring of biofilm formations ofEscherichia coli andPseudomonas putida by use of lux and GFP reporters

A plasmid vector containing two reporter genes,mer-lux andlac-GFP, was transformed to bothEscherichia coli andPseudomonas putida. Their cellular activities and biofilm characteristics were investigated in flow-cell units by measuring bioluminescent lights and fluorescent levels of GFP. Bioluminescence was effective to monitor temporal cell activities, whereas fluorescent level of GFP was useful to indicate the overall cell activities during biofilm development. The light production rates ofE. coli andP. putida cultures were dependent upon concentrations of HgCl₂. Mercury molecules entrapped inP. putida biofilms were hardly washed out in comparison with those inE. coli biofilms, indicating thatP. putida biofilms may have higher affinity to mercury molecules thanE. coli biofilms. It was observed thatP. putida expressed GFP cDNA in biofilms but not in liquid cultures. This may indicate that the genetic mechanisms ofP. putida were favorably altered in biofilm conditions to make a foreign gene expression possible.