Fungal variegatic acid and extracellular polysaccharides promote the site-specific generation of reactive oxygen species.

This study aims to clarify the role of variegatic acid (VA) in fungal attack by Serpula lacrymans, and also the generation and scavenging of reactive oxygen species (ROS) by the fungus. VA promotes a mediated Fenton reaction to generated ROS after oxalate solubilizes oxidized forms of iron. The fungal extracellular matrix (ECM) β-glucan scavenged ROS, and we propose this as a mechanism to protect the fungal hyphae while ROS generation is promoted to deconstruct the lignocellulose cell wall. A relatively high pH (4.4) also favored Fe(III) transfer from oxalate to VA as opposed to a lower pH (2.2) conditions, suggesting a pH-dependent Fe(III) transfer to VA employed by S. lacrymans. This permits ROS generation within the higher pH of the cell wall, while limiting ROS production near the fungal hyphae, while β-glucan from the fungal ECM scavenges ROS in the more acidic environments surrounding the fungal hyphae.