Influence of Tropolone on Poria placenta Wood Degradation

Abstract

Fenton reactions are believed to play important roles in wood degradation by brown rot fungi. In this context, the effect of tropolone (2-hydroxycyclohepta-2,4,6-trienone), a metal chelator, on wood degradation by Poria placenta was investigated. Tropolone (50 M) strongly inhibits fungal growth on malt agar, but this inhibition could be relieved by adding iron salts. With an experimental system containing two separate parts, one supplemented with tropolone (100 M) and the other not, it was shown that the fungus is able to reallocate essential minerals from the area where they are available and also to grow in these conditions on malt-agar in the presence of tropolone. Nevertheless, even in the presence of an external source of metals, P. placenta is not able to attack pine blocks impregnated with tropolone (5 mM). This wood degradation inhibition is related to the presence of the tropolone hydroxyl group, as shown by the use of analogs (cyclohepta-2,4,6-trienone and 2-methoxycyclohepta-2,4,6-trienone). Furthermore, tropolone possesses both weak antioxidative and weak radical-scavenging properties and a strong affinity for ferric ion and is able to inhibit ferric iron reduction by catecholates, lowering the redox potential of the iron couple. These data are consistent with the hypothesis that tropolone inhibits wood degradation by P. placenta by chelating iron present in wood, thus avoiding initiation of the Fenton reaction. This study demonstrates that iron chelators such as tropolone could be also involved in novel and more environmentally benign preservative systems.

Metschnikowia Strains Isolated from Botrytized Grapes Antagonize Fungal and Bacterial Growth by Iron Depletion

“…Tropolone is a chelating agent with a strong affinity for ferric ions (12,17). Tropolone was placed into holes (0.1, 0.2, 0.5, 1.0, 1.5, and 2.0 mg/hole) in PDA plates seeded with Botrytis conidia, which resulted in growth inhibition similar to that observed with the Metschnikowia isolates (Fig.…”

“…The sensitivity of strains to iron depletion was tested with tropolone (2-hydroxycyclohepta-2,4,6-trienone; T7387; Sigma-Aldrich Co., St. Louis, Mo. ), a chelating agent with a strong affinity for ferric ions (12,17).…”

“…Since recovery also was observed at the edges of the tropolone-generated inhibition zones, the latter possibility is more likely. Numerous fungi can transport nutrients, including iron, between various parts of the mycelium (5,17).…”

Preferential Inhibition of the Magnesium-Dependent Strand Transfer Reaction of HIV-1 Integrase by α-Hydroxytropolones

“…We report here the structure-activity relationship of tropolones available in the National Cancer Institute compound repository on HIV integrase activities. Tropolone derivatives are present in cupressaceous trees from genus Thuja and are probably responsible for resistance of fungal and insect attack on the heartwood (Baya et al, 2001;Diouf et al, 2002;Lim et al, 2005). Our experiments demonstrate the ability of the monomer 7-hydroxytropolones (␣-hydroxytropolones) to preferentially inhibit the ST reaction by interfering with the enzyme catalytic site.…”

Radical scavenging activity of some natural tropolones by density functional theory

“…Diouf et al studied the influence of tropolone on the wood degradation and they found weak antioxidative and radical scavenging properties. Moreover, they also showed tropolone can be used as novel environmentally benign preservative systems [2]. Kadoma and co-workers studied the kinetic radical scavenging activity (RSA) of tropolone by induction period method and found very weak antioxidant properties [3].…”