Wood decay fungi spread mycelial networks in the forest soil and transport (translocate) substances such as water, carbon, and nutrients while decomposing fallen trees and branches, playing an important role in material circulation in forests. Recent studies have reported intelligent behaviors (memory, learning, and decision-making) in these fungi, but how the mycelia regulate their behaviors is not well understood. A research group led by Associate Professor Yu Fukasawa of the Graduate School of Agricultural Science at Tohoku University fed wood blocks as bait to cultured mycelia of the wood decay fungus Pholiota brunnescens, which is closely related to the nameko mushroom (Pholiota microspora). The research group measured changes in electrical potential at multiple positions of each mycelium over 104 days while the mycelia colonized and degraded the wood bait.
The results confirmed that the electrical potential changes were transmitted from the hyphae at the wood bait location to the entire mycelium. Moreover, electrical potential oscillations occurring over 7 days per cycle were observed only at the wood bait location after 60 days of incubation, during which colonization onto the wood baits was considered to have reached completion. The findings suggest that mycelia control their behavior with electrical signals and were published in Scientific Reports.
Provided by Tohoku University
The research group inoculated mycelia of a wood decay fungus in the center of agar plates on circular Petri dishes equipped with six electrodes, which were radially arranged in three directions from the center, and these dishes were incubated at 20℃ for 104 days in the dark. During this period, the potential difference of each electrode relative to the base electrode at the center of the Petri dish was measured every 10 minutes. They prepared three replicate Petri dishes with a sterilized wood block placed as bait on one of the electrodes near the edge of the Petri dish (baited Petri dishes) and three additional control Petri dishes without bait. When the mycelium growing radially from the center reached the location of an electrode, the electrical potential of that electrode increased once and then decreased.
This result indicates that the electrodes detected electrical potential changes associated with mycelial growth. Moreover, only the electrode at the bait location exhibited a distinct oscillation of electrical potential from about 60 days of incubation, with an oscillation period of about 7 days. Furthermore, a causal analysis based on time series data of electrical potentials was performed to determine whether there is a significant causal relationship among the potential change patterns measured at respective electrodes.
The results showed that significant directional causal relationships from the electrode at the bait location to the other electrodes were detected during the first 60 days of incubation only in the baited Petri dishes; however, the causal relationships disappeared after day 60. No such distinct patterns were observed in the control Petri dishes without bait.
These results suggest that electrical signals are sent from the hyphae detecting the bait to other parts of the wood decay mycelium, allowing the entire mycelial body to share information on the bait locations. This mechanism may help efficiently transport the cytoplasm toward the bait and colonize the mycelium onto the bait. The fact that the disappearance of the causal relationships across the electrodes and the appearance of distinct potential oscillations only at the electrode at the bait location coincided at day 60 may suggest that the entire mycelium had already colonized the wood bait and engaged in active degradation by then. There were no active hyphae in other parts of the Petri dish.
The findings suggest that information about external stimuli can be transmitted to and shared by the inside of fungal mycelia. This is important in understanding how organisms without brains manage memory, learning, and decision-making.
Journal Information
Publication: Scientific Reports
Title: Electrical integrity and week-long oscillation in fungal mycelia
DOI: 10.1038/s41598-024-66223-6
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.