EFFECTS OF ULTRAVIOLET-LIGHT IRRADIATION IN BIOTREATMENT OF ORGANOPHOSPHATES

Excess biomass accumulation in reactor biodegradation processes is und esirable: it increases the disposal cost and upsets the operation of b iological reactors if not properly controlled. In this study, we inves tigated the feasibility of using ultraviolet (UV) light irradiation to reduce biomass accumulation and increase the specific biodegradation activity. UV irradiation has been widely used to introduce DNA damage in bacteria. Here we apply this technology to the biodegradation of or ganophosphates by recombinant Escherichia coli strains that contain a recA mutation and a cloned organophosphate hydrolase gene. We show tha t the recA negative strains after UV irradiation reduce the growth rat e but increase the specific organophosphate hydrolase activity. This i ncrease in specific enzyme activity is not owing to continued protein synthesis from the plasmid after the damage of chromosomal DNA by UV i rradiation. Rather, it is likely to be caused by an increase in membra ne permeability to the substrate. Kinetic analysis suggests that the m embrane transport of paraoxon is the rate-limiting step in its biodegr adation.