Integrated Metabolomics and Morphogenesis Reveal Volatile Signaling of the Nematode-Trapping Fungus Arthrobotrys oligospora

Abstract

The adjustment of metabolic patterns is fundamental to fungal biology and plays vital roles in adaptation to diverse ecological challenges. Nematode-trapping fungi can switch their lifestyle from saprophytic to pathogenic by developing specific trapping devices induced by nematodes to infect their prey as a response to nutrient depletion in nature. However, the chemical identity of the specific fungal metabolites used during the switch remains poorly understood. We hypothesized that these important signal molecules might be volatile in nature. Gas chromatography-mass spectrometry was used to carry out comparative analysis of fungal metabolomics during the saprophytic and pathogenic lifestyles of the model species Arthrobotrys oligospora. Two media commonly used in research on this species, cornmeal agar (CMA) and potato dextrose agar (PDA), were chosen for use in this study. The fungus produced a small group of volatile furanone and pyrone metabolites that were associated with the switch from the saprophytic to the pathogenic stage. A. oligospora fungi grown on CMA tended to produce more traps and employ attractive furanones to improve the utilization of traps, while fungi grown on PDA developed fewer traps and used nematode-toxic furanone metabolites to compensate for insufficient traps. Another volatile pyrone metabolite, maltol, was identified as a morphological regulator for enhancing trap formation. Deletion of the gene AOL_s00079g496 in A. oligospora led to increased amounts of the furanone attractant (2-fold) in mutants and enhanced the attractive activity (1.5-fold) of the fungus, while it resulted in decreased trap formation. This investigation provides new insights regarding the comprehensive tactics of fungal adaptation to environmental stress, integrating both morphological and metabolomic mechanisms.IMPORTANCE Nematode-trapping fungi are a unique group of soil-living fungi that can switch from the saprophytic to the pathogenic lifestyle once they come into contact with nematodes as a response to nutrient depletion. In this study, we investigated the metabolic response during the switch and the key types of metabolites involved in the interaction between fungi and nematodes. Our findings indicate that A. oligospora develops multiple and flexible metabolic tactics corresponding to different morphological responses to nematodes. A. oligospora can use similar volatile furanone and pyrone metabolites with different ecological functions to help capture nematodes in the fungal switch from the saprophytic to the pathogenic lifestyle. Furthermore, studies with A. oligospora mutants with increased furanone and pyrone metabolites confirmed the results. This investigation reveals the importance of volatile signaling in the comprehensive tactics used by nematode-trapping fungi, integrating both morphological and metabolomic mechanisms.

Nematode-Trapping Fungi Produce Diverse Metabolites during Predator–Prey Interaction

“…NTF hold great potential as biocontrol agents to target parasitic nematodes, and, thus, are a subject of interest to scientists. The interactions between NTF and their nematode prey have been studied for several decades, but the underlying molecular mechanisms only began to be revealed in the more recent years [5,[9][10][11]13]. In this study, we have further expanded our understanding of the metabolites of a hundred strains of Arthrobotrys NTF by metabolomic analyses.…”

“…On the other hand, little is known about the metabolome of NTF. Previous studies have shown that A. oligospora produces volatile organic compounds (VOCs) that mimic sex and food cues to attract the nematode prey in the absence of nematodes [10], and a more recent study also reported VOCs produced by A. oligospora during the predation process [11]. Nonetheless, the metabolites produced by NTF induced by the nematode prey during predation remained largely unexplored.To gain more insights into how NTF response to nematode prey during predation, we analyzed the metabolites of 100 wild isolates of three different NTF species, Arthrobotrys oligospora, Arthrobotrys thaumasia, and Arthrobotrys musiformis, which were all collected in Taiwan [12] (Figure 1a,b; Table S1).…”

“…On the other hand, little is known about the metabolome of NTF. Previous studies have shown that A. oligospora produces volatile organic compounds (VOCs) that mimic sex and food cues to attract the nematode prey in the absence of nematodes [10], and a more recent study also reported VOCs produced by A. oligospora during the predation process [11]. Nonetheless, the metabolites produced by NTF induced by the nematode prey during predation remained largely unexplored.…”

Signal pathways involved in microbe–nematode interactions provide new insights into the biocontrol of plant-parasitic nematodes

“…These two media differ in their capacities to induce traps. A compound, maltol, was isolated and shown to be able to stimulate trap formation in A. oligospora [28]. Together, these studies identified many signal molecules and several signal transducers capable of inducing fungal trap formation.…”

Fungi–Nematode Interactions: Diversity, Ecology, and Biocontrol Prospects in Agriculture

“…Under nitrogen starvation, ascaroside-induced morphogens are required for A. oligospora to sense and initiate trap formation in response to the availability of nematode prey [ 24 , 141 ]. Recent studies have also characterized several other morphology-regulating arthrosporol metabolites from A. oligospora and identified them as important signaling cues for hyphal development, nematode attraction, and trap morphogenesis [ 29 , 62 , 142 ].…”