Bacterial disinfection by the photo-Fenton process: Extracellular oxidation or intracellular photo-catalysis?

In this work, we evidence that despite the addition of the Fenton reagents in the bulk, the photo-Fenton mediated inactivation is mainly an intracellular process. We compare the inactivation kinetics of a typical E. coli strain that can exchange solutes with its environment through its outer membrane porins with its porinless mutant counterpart. The transport of Fe2+ and H2O2 into the bacterial cell was hypothesized to be the limiting factor of the photo-Fenton-mediated inactivation. This important pathway that could initiate intracellular oxidative chain reactions would be evidenced by the use of a porinless bacterial strain, derivative of MC4100 (TK821). The comparison among the typical E. coil K12 (ATCC 23716) and TK821 showed that the processes that constitute the photo-Fenton (solar, solar/Fe2+, solar/H2O2) are greatly modified between the two strains. ATCC 23716 was always inactivated faster than the TK821, and a 45% and 150% difference in inactivation rate was measured for the solar/Fe2+ and the solar/H2O2 processes. The photo-Fenton process inactivation rates were doubled, and the contribution of the intracellular and extracellular pathways was estimated. The mechanisms taking place in the bulk were twice as important for TK821, while the inverse was estimated for the intracellular events in ATCC 23716. The results of this work demonstrate that porins are essentially a regulator of the photo-Fenton disinfection, and that is mainly an intracellular advanced oxidation process.