Mixed species biofilms act as planktonic cell factories despite isothiazolinone exposure under continuous-flow conditions

The primary approach to managing biofouling in industrial water systems involves the large-scale use of biocides. It is well-established that biofilms are ‘cell factories’ that release planktonic cells even when challenged with antimicrobials. The effect of isothiazolinone on the metabolic activity and biomass of mixed Pseudomonas biofilms was monitored in real-time using the CEMS-BioSpec system. The exposure of biofilms to the minimum inhibitory concentration (1.25 mg L⁻¹) of biocide did not impact planktonic cell production (log 7.5 CFU mL⁻¹), while whole-biofilm metabolic activity and biomass accumulation increased. Only the maximum biocide concentration (80 mg L⁻¹) resulted in a change in planktonic cell yields and temporal inhibition of biofilm activity and biomass, a factor that needs due consideration in view of dilution in industrial settings. Interfacing the real-time measurement of metabolic activity and biomass with dosing systems is especially relevant to optimizing the use of biocides in industrial water systems.