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Appl Environ Microbiol, January 1998, p. 68-73, Vol. 64, No. 1
Departamento de Genética Molecular y
Microbiología, Pontificia Universidad Católica de Chile,
Casilla 114-D, Santiago, Chile,1 and
Forest Products Laboratory, USDA Forest Service, Madison,
Wisconsin 537052
Received 3 September 1997/Accepted 22 September 1997
The ligninolytic system of the basidiomycete Ceriporiopsis
subvermispora is composed of manganese peroxidase (MnP) and
laccase. In this work, the source of extracellular hydrogen peroxide
required for MnP activity was investigated. Our attention was focused
on the possibility that hydrogen peroxide might be generated by MnP itself through the oxidation of organic acids secreted by the fungus.
Both oxalate and glyoxylate were found in the extracellular fluid of
C. subvermispora cultures grown in chemically defined media, where MnP is also secreted. The in vivo oxidation of oxalate was
measured; 14CO2 evolution was monitored after
addition of exogenous [14C]oxalate to cultures at
constant specific activity. In standard cultures, evolution of
CO2 from oxalate was maximal at day 6, although the MnP
titers were highest at day 12, the oxalate concentration was maximal
(2.5 mM) at day 10, and the glyoxylate concentration was maximal (0.24 mM) at day 5. However, in cultures containing low nitrogen levels, in
which the pH is more stable, a better correlation between MnP titers
and mineralization of oxalate was observed. Both MnP activity and
oxidation of [14C]oxalate were negligible in cultures
lacking Mn(II). In vitro assays confirmed that Mn(II)-dependent
oxidation of [14C]oxalate by MnP occurs and that this
reaction is stimulated by glyoxylate at the concentrations found in
cultures. In addition, both organic acids supported phenol red
oxidation by MnP without added hydrogen peroxide, and glyoxylate was
more reactive than oxalate in this reaction. Based on these results, a
model is proposed for the extracellular production of hydrogen peroxide
by C. subvermispora.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Manganese Peroxidase-Dependent Oxidation of
Glyoxylic and Oxalic Acids Synthesized by Ceriporiopsis
subvermispora Produces Extracellular Hydrogen Peroxide
*
Corresponding author. Mailing address: Departamento de
Genética Molecular y Microbiología, Pontificia
Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
Phone: 56-2-6862663. Fax: 56-2-2225515. E-mail:
rvicuna{at}genes.bio.puc.cl.
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