FoPaC - The Forest Pathogen Chemical Ecology Lab

We focus our research on forest insects and microbial pathogens, as well as non-pathogenic forest-associated microbes, to unravel the complex interactions that shape forest health and ecosystem dynamics. Our interdisciplinary approach integrates entomology, molecular biology, and microbiology with chemical ecology, using both laboratory and field experiments with insects and microbes.

General introduction

Forest ecosystems host a tremendous diversity of organisms, including filamentous fungi, yeasts, bacteria, and insects. Many of these organisms perform essential ecological functions, such as decomposing dead wood, recycling nutrients, or forming beneficial associations with trees, for example through mycorrhizal partnerships. However, some microbes and insects can act as tree pathogens, overcoming host defenses and often causing high tree mortality. Understanding the interactions among these organisms is therefore essential for forest health and sustainable management.

Among the most prominent insect-associated pathogens are bark beetles, such as Ips typographus and Pityogenes chalcographus, which colonize Norway spruce (Picea abies) and can cause extensive damage under favorable conditions. Although the beetles themselves have been well studied, much less is known about their associated microbial communities and how these microbes influence the success and ecological impact of their insect hosts. Our research aims to elucidate these interactions and to uncover the mechanisms by which microbial symbionts contribute to insect pathogenicity - providing a foundation for future applied work on bark beetle management.

In addition to insect-associated pathogens, we investigate fungal forest pathogens, including Hymenoscyphus fraxineus, the causal agent of European ash dieback. We aim to understand how microbial traits contribute to the success of these pathogens and how they interact with host tree chemistry. Special attention is given to the chemical ecology of these interactions, including the role of microbial metabolites in mediating competition and shaping pathogen dynamics.

Beyond pathogenic organisms, we also study non-pathogenic forest-associated microbes, such as wood-degrading fungi. These species often require specific environmental conditions to thrive and to compete with other microbes. Our research explores their volatile profiles and secreted compounds, examining the chemical strategies they employ in microbial competition and shedding light on their ecological roles within forest ecosystems.

Project 1: Role of bark beetle associated fungi on tree mortality

Main researchers: Dr. Lukas Ernst and Dr. Hui Lyu

Bark beetle infestations in forests are often accompanied by the introduction of filamentous fungi, closely associated with their insect vectors. These fungi are thought to play a key role in enabling beetles to successfully colonize host trees, yet it remains unclear whether they themselves also act as major contributors to tree mortality. In this project, we investigate these interactions by examining plant-microbe relationships at both microscopic and biochemical levels. Using saplings in greenhouse experiments as well as naturally and artificially infested trees in field studies, we assess the virulence of individual fungal strains and explore the mechanisms underlying their pathogenicity. Disease progression is monitored through a combination of microscopy and physiological measurements, while multi-omics approaches are employed to identify metabolites and chemical signals that may contribute to tree decline.

Project 2: Tree colonization by bark beetle fungi – A plant perspective

Main researcher: Dr. Julian David Restrepo Leal

Main collaborator: Dr. Veit Grabe (MPI CE, Microscopy Imaging Service Group)

Mass attacks by bark beetles can lead to extensive tree mortality in forests. During such infestations, the beetles introduce diverse microorganisms into the bark, including filamentous fungi. Some of these fungi are capable of causing tissue necrosis and disrupting water transport in the host tree, which may result in wilting symptoms and, ultimately, tree death. While the general pathogenic potential of these fungi is known, the underlying mechanisms of their virulence - particularly those related to hydraulic failure - remain poorly understood. In this project, we combine plant hydraulics, fluorescence microscopy, micro-X-ray computed tomography, and multi-omics analyses of fungal-inoculated saplings to investigate the processes leading to hydraulic failure. We are also exploring how environmental factors, such as drought, may exacerbate tree mortality during fungal infections.

Project 3: Functional role of bacteria associated with bark beetles

Main researcher: Jingxian Chen

Main collaborators: Prof. Dr. Martin Kaltenpoth (MPI CE, Department Insect Symbiosis), Ana Patricia Baños Quintana (MPI CE, Department Insect Symbiosis)

Extensive research has demonstrated that symbiotic microorganisms can provide a wide range of functions that help their hosts adapt to specific ecological niches. The Eurasian spruce bark beetle (Ips typographus), which feeds on the nutrient-poor and chemically defended tissues of Norway spruce, faces multiple ecological challenges, including competition with pathogenic fungi. Our research focuses on the core bacterial symbionts of I. typographus and their potential contributions to the beetle’s ecological adaptation. We isolate and culture these bacteria and conduct genomic and phylogenetic analyses to better understand their diversity and evolutionary relationships. In addition, we characterize their nutrient utilization and chemical profiles, including the ability to metabolize plant defense compounds. We also investigate the potential roles of these bacteria in defending the beetle against pathogens and other microbial competitors.

Project 4: Investigating natural compounds affecting bark beetle behavior

Main researcher: Dr. Maximilian Lehenberger

Main collaborators: Prof. Dr. Martin Andersson (Lund University), Dr. Dineshkumar Kandasamy (Lund University), Dr. Christian Paetz (NMR Service Group), Dr. Yoko Nakamura (NMR Service Group)

Bark beetles such as Ips typographus rely heavily on olfactory cues to locate suitable host trees and coordinate mass attacks. Compounds that interfere with these chemical communication pathways - or even act as repellents - hold great potential for environmentally friendly pest management strategies. In this project, we focus on volatile compounds from both fungal and Norway spruce sources that may influence I. typographus behavior. We first isolate and chemically characterize these substances, then assess their biological activity using behavioral bioassays. To understand how the beetles perceive these compounds, we complement these tests with classical methods of chemical ecology such as electrophysiological techniques, including electroantennography (EAG) and single sensillum recordings (SSR). Our integrated approach combines metabolomics and analytical approaches with structural elucidation using NMR spectroscopy. By linking chemical identity with behavioral and physiological responses, we aim to identify natural compounds that modulate bark beetle behavior and gain deeper insight into the chemical mechanisms underlying beetle repellency.

Project 5: Insight into the function of yeasts associated with the bark beetle I. typographus

Main researchers: Ana Patricia Baños Quintana (MPI CE, Department Insect Symbiosis), Leandro Santiago Padilla

Main collaborators: Prof. Dr. Martin Kaltenpoth (MPI CE, Department Insect Symbiosis), Prof. Dr. Miroslav Kolařík (The Czech Academy of Sciences)

Insects are known to form symbiotic associations with specific yeasts, which can provide both nutritional and defensive benefits. In bark beetles such as Ips typographus, yeasts occur frequently, yet little is known about their functional roles and potential benefits to their hosts. In this project, we comprehensively characterize the yeast communities associated with I. typographus to investigate their ecological functions. We combine a range of approaches to elucidate their roles, including nutrient profiling, metabolomics, and analyses of chemical pathways involved in the degradation and metabolism of plant defense compounds. Behavioral assays are used to assess yeast attractiveness, while potential defensive functions are explored through competition assays with pathogenic fungi, as well as analyses of secondary metabolites. Through these studies, we aim to uncover how yeasts may contribute to the success of their beetle host, I. typographus.

Project 6: Insights into the function of fir bark beetle-associated fungi

Main researchers: Sifat Munim Tanin (University of Freiburg), Dr. Maximilian Lehenberger

Main collaborator: Prof. Dr. Peter Biedermann (University of Freiburg)

Besides the well-known spruce-infesting bark beetles, other species of economic importance remain less studied, such as fir (Abies alba)-colonizing bark beetles. In this project, we investigate fungi associated with the fir-infesting bark beetle Pityokteines vorontzowi, focusing on their phylogenetic diversity and chemical ecological roles. Our research aims to understand how these fungi might contribute to the success of their beetle hosts. Specifically, we analyze the nutritional profiles of these fungal species to determine how they can enhance the beetles’ substrate and improve the availability of essential nutrients for their development. In addition, we study the interactions between associated fungi and plant defense compounds present in fir tissues. Using a combination of bioassays with individual compounds and complementary chemical analyses, we examine if and how these fungi are able to metabolize defensive secondary metabolites of the host tree. Through these approaches, we aim to uncover the dual roles of these less-studied bark beetle-associated fungi in supporting host nutrition and mitigating tree defenses, shedding light on the chemical ecological mechanisms underlying beetle-fungus-host interactions.

Project 7: The spruce-colonizing bark beetle Pityogenes chalcographus and its fungal community

Main researchers: Niklas Gentsch (B.Sc. thesis), Antonia Papadopulos

Main collaborators: Prof. Dr. Peter Biedermann (University of Freiburg), Dr. Vienna Kowallik (University of Freiburg), Prof. Dr. Patricia Carina Fernandez (University of Buenos Aires)

The bark beetle Pityogenes chalcographus colonizes Norway spruce and is well known for its destructive impact on trees. Despite its ecological and economic importance, little is known about the fungal community associated with this species and how these microbes may contribute to the colonization of phloem tissue. In this project, we investigate the fungal communities associated with P. chalcographus, focusing on their phylogenetic diversity and chemical ecological roles. Our main aim is to understand how these microbes contribute to the beetle’s nutrition, behavior, and interactions with host defenses. Starting from the isolation of filamentous fungi and yeasts, as well as amplicon sequencing, we conduct phylogenetic analyses to characterize the associated microbial communities. Functional analyses include nutritional profiling and metabolomics of the main fungal associates to identify their potential function as food sources, to gain insights into key secondary metabolites, and to assess the potential utilization of plant defense compounds as carbon sources. Volatile collections, behavioral assays, and inhibition tests with individual compounds are used to explore the ecological and defensive roles of these microbes. Additionally, rearing beetles under controlled conditions provides insights into the chemical dynamics within natural nests. Through these combined approaches, we aim to reveal how the microbial associates of P. chalcographus contribute to host nutrition, modulate interactions with plant defenses, and influence beetle ecology, shedding light on the chemical ecological mechanisms underlying beetle-fungus-host interactions.

Project 8: Mycetangia: Highly specialized symbiont transmitting structures in bark and ambrosia beetles

Main researchers: Dr. Maximilian Lehenberger, Dr. Veit Grabe (MPI CE, Microscopy Imaging Service Group)

Main collaborators: Prof. Dr. Martin Kaltenpoth (MPI CE, Department Insect Symbiosis), Prof. Dr. Martin Schebeck (University of Göttingen), Dr. Dineshkumar Kandasamy (Lund University), Ana Patricia Baños Quintana (MPI CE, Department Insect Symbiosis)

Insects that farm or associate with fungi often carry their symbionts in specialized structures that ensure the safe transport and maintenance of microbial partners. Among these, mycetangia are particularly intriguing: sac-like glands found in many ambrosia beetles and some bark beetles, thought to selectively transmit specific fungal mutualists from one tree to another. Despite their ecological importance, the morphology, diversity, and functional mechanisms of these structures remain largely unexplored. In this project, we investigate the mycetangia of bark and ambrosia beetles to better understand how these specialized organs contribute to symbiont transmission. We combine detailed morphological analyses with microbial isolations and molecular tools to gain deeper insights into the fungal communities carried within these structures.

Project 9: The nutritional and defensive function of Alloascoidea hylecoeti, the fungal symbiont of the ship-timber beetle Elateroides dermestoides

Main researchers: Yu Pan, Dr. Maximilian Lehenberger

Main collaborators: Prof. Dr. Leane Lehmann (University of Würzburg), Dr. Peter Gros (Thüringer Landesamt für Landwirtschaft und Ländlichen Raum)

The ship-timber beetle (Coleoptera: Lymexylidae) is one of the few non-social, fungus-farming ambrosia beetles. Unlike many other ambrosia beetles, where brood care is common, females of this species lay eggs on the bark of a tree - colonizing both softwoods and hardwoods - and die shortly thereafter. The larva must survive for up to three years in a highly competitive microbial environment to complete its development. Despite its unique life history, little is known about the beetle or its associated microbial symbiont, a yeast-like fungus belonging to the Saccharomycetales. In this project, we investigate the nutritional contributions of this mutualistic fungus, as well as its defensive secondary metabolites. These traits are compared with those of other bark- and ambrosia-beetle-associated fungi, antagonistic fungi, and common wood-degrading fungi.

Project 10: Chemical ecology of the ash dieback pathogen Hymenoscyphus fraxineus

Main researchers: Björn Lichnock, Dr. Maximilian Lehenberger

Main collaborators: Dr. Gitta Langer (Nordwestdeutsche Forstliche Versuchsanstalt), Prof. Dr. Susanne Jochner-Oette (Katholische Universität Eichstätt), Dr. Christian Paetz (MPI CE, NMR Service Group)

The ash dieback is a devastating disease that has severely affected the European ash, Fraxinus excelsior. Several years ago, a specific fungus was identified as the causal pathogen, the ascomycete fungus Hymenoscyphus fraxineus. This pathogenic fungus was presumably introduced to Europe from East Asia in the early 1990s. Since its arrival, it has caused extensive damage to F. excelsior, leading to widespread tree mortality and a dramatic decline of ash populations across the continent. In contrast, its close relative, the native H. albidus, is non-pathogenic and coexists as a saprophyte without causing disease symptoms. In this project, we investigate how H. fraxineus interacts with the complex chemical defense system of F. excelsior. Specifically, we focus on how this pathogen metabolizes, tolerates, or even utilizes host defense compounds during infection. We also investigate various metabolites that H. fraxineus produces and accumulates, and how these substances affect ash tissues and defense responses. Our approach integrates metabolomics, bioassays, and chemical analyses. Through compound isolation and structural elucidation using NMR spectroscopy, we aim to identify key fungal metabolites involved in pathogenicity and to elucidate the chemical mechanisms underlying host–pathogen interactions. Through these studies, we seek to uncover how H. fraxineus overcomes the chemical defenses of ash trees and contributes to the ongoing decline of F. excelsior in European forests.

Project 11: Chemical ecology of rare deadwood fungi – the role of volatiles in niche occupation

Main researchers: Prof. Dr. Patricia Carina Fernandez (University of Buenos Aires), Dr. Maximilian Lehenberger

Main collaborators: Prof. Dr. Claus Bässler (University of Bayreuth), Dr. Harald Kellner (Technical University of Dresden)

Deadwood-inhabiting fungi play a crucial role in forest ecosystems by decomposing wood and recycling nutrients. Among them, several rare species are of particular ecological importance, as they often serve as indicators of natural forest structure and habitat continuity. Despite their relevance, very little is known about these rare fungi, primarily because they occur infrequently and often require specific environmental conditions. These fungi typically colonize old or well-decayed wood that is also inhabited by numerous other fungal species, leading to intense interspecific competition. A key question in our research is how these rare fungi manage to persist and maintain their ecological niches within such competitive environments. So far, only a few species have been investigated with respect to their emitted volatile organic compounds (VOCs), and these studies have revealed intriguing and potentially bioactive substances. In this project, we aim to identify and characterize the volatiles produced by various rare deadwood fungi and to study their effects on other, competing fungal species. To achieve this, we combine volatile collection and analysis with a range of bioassays involving fungal competitors, as well as metabolite identification. Through these approaches, we explore the ecological roles of fungal volatiles—such as their potential functions in competition, communication, or defense—and how they may contribute to niche maintenance and species coexistence in forest ecosystems.

Team:

Dr. Lukas Ernst (Postdoc)
Dr. Hui Lyu (Postdoc)
Dr. Julian David Restrepo Leal (Postdoc)
Jingxian Chen (Guest PhD student)
Prof. Dr. Patricia Carina Fernandez (visiting professor)
Beate Rothe (TA)
Natascha Rauch (TA)
Niklas Gentsch (HiWi)
Antonia Papadopulos (HiWi)
Nina Suvajac (HiWi)
Ciara Hübner (HiWi)
Vincent Mattausch (HiWi)

Alumni:

Johanna Staudacher
Yu Pan
Leandro Santiago Padilla
Sapna Menghwar
Vivek Bhadani
Björn Lichnock
Mirkka Jossette Puente Madrid
Stefanie Ungerer
Usara Afia
Syeda Warda Shah Mehak Sherazi
Talha Faheem
Ilka Klose