This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team at the Max Planck Institute for Chemical Ecology discovered a previously unknown strategy by which certain fungi neutralize spruce defense compounds. These fungi are introduced into trees by bark beetles, and their success makes it easier for bark beetles to invade the trees.
The researchers showed that many of these introduced fungi can metabolize the trees' chemical defenses and spread rapidly through the bark. Two of them can further deactivate the initial degradation products by binding the sugar molecule ribose to them. These transformed defense compounds are harmless and stable, and they cannot be converted back into the original, more toxic substances by cleaving off the ribose.
The fungus that was most effective at neutralizing spruce defense compounds by binding ribose thrived particularly well in spruce bark. These findings could lead to new methods of combating bark beetle infestations in European forests, such as selectively altering the microbial communities within the trees. The work is published in The ISME Journal.
Spruce trees have highly effective chemical defenses against herbivores and pathogens. The phloem, the living bark tissue responsible for transporting nutrients produced in the needles to the roots, is among the chemically best-protected plant tissues. The phloem lies directly beneath the protective bark and surrounds the wood.
The phloem tissue contains protective chemical substances, particularly phenolic compounds, which can account for up to 5% of the bark's dry weight. Nevertheless, numerous fungi—ranging from pathogens to symbionts of bark beetles—successfully colonize this well-defended tissue. "We wanted to understand the biochemical tricks these fungi use to overcome such a hostile chemical environment, especially since some of these fungi may contribute to massive bark beetle infestations destroying European forests," says study lead author Ruo Sun.
The research team investigated the metabolism of various fungi using molecular biology techniques and chemical analyses. They analyzed the metabolic products of fungi grown on spruce bark or artificial culture media. In the process, they discovered that certain fungi produce new, previously unknown compounds—but only when exposed to the chemicals found in spruce.
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