Iron sequestration in brown-rot fungi by oxalate and the production of reactive oxygen species (ROS)

• Oxalate-sequestered iron permitted OH generation in presence of chelators and H2O2.
• The presence of oxalate suppressed, but did not stop Fe reduction and CMF reactions.
• Iron sequestration by oxalate was enhanced in lower pH environments.

The biochemical role of oxalate in the fungal solubilization of iron is well known, but additional information is needed on the role that oxalate plays in the brown-rot decay of lignocellulose. In this study iron sequestration from iron and iron oxide-hydroxides was assessed with regard to the function of a chelator-mediated Fenton (CMF) reaction and the generation of reactive oxygen species (ROS). The reactions conducted at the lowest pH condition (pH 2.0) and oxalate concentration (15 μM) generated the greatest amount of FeII, suggesting that pH, rather than oxalate concentration may have a greater impact on Fenton reactions, and specifically the CMF reaction. Moreover, iron oxide-hydroxides that were pre-incubated with oxalate prior to the CMF reaction, generated more ROS than the iron oxide-hydroxides without oxalate incubation. This indicates that an enhanced CMF reaction was promoted by iron sequestration due to oxalate incubation, and also supports previous research showing a pH-dependent iron transfer from oxalate to chelators produced by fungi. Although Fenton reactions were enhanced at low pH, the iron transfer reaction was enhanced at higher pH. In a decay environment, this would limit damaging Fenton reactions from occurring in the low pH environment directly surrounding the fungal hyphae.

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