A microbially driven transformation system was developed for the oxidative
degradation of pentachlorophenol (PCP). The system was based on a free radi
cal-generating Fenton reaction between bacterially produced Fe(II) and H2O2
. The Fe(III)-reducing, facultative anaerobe Shewanella putrefaciens strain
200 was used as a catalyst for both Fe(III) reduction and H2O2 production
by alternating between anaerobic and aerobic conditions in liquid batch cul
tures supplemented with Fe(III). The highest observed PCP degradation rate
was approximately 0.31 mu M h(-1). Tetrachlorohydroquinone (TCHQ) and tetra
chlorocatechol (TCC) were formed as the principal PCP transformation produc
ts, indicating that PCP oxidation proceeded via hydroxyl radical ((OH)-O-.)
attack on the ortho and para positions of the aromatic ring. PCP was degra
ded, and TCHQ and TCC were produced in a chemically driven (biomimetic) sys
tem where H2O2 and Fe(II) were supplied at concentrations comparable to tho
se detected in the microbially driven system. PCP was not degraded (and PCP
transformation products were not produced) in a set of control experiments
that included (i) the presence of Fe(II)-chelating agents or radical scave
nging compounds, (ii) strict aerobic or anaerobic conditions, (iii) the sub
stitution of NO3- for Fe(III) as anaerobic electron acceptor, and (iv) the
omission of S. putrefaciens. The microbially driven Fenton reaction system
operated at neutral pH and required neither addition of exogenous H2O2 nor
UV irradiation to regenerate Fe(II). The newly developed system may provide
the basis for novel Fenton-type bioremediation strategies.