Fungal foraging behaviour and hyphal space exploration in micro-structured Soil Chips

Abstract

How do fungi navigate through the complex microscopic maze-like structures found in the soil? Fungal behaviour, especially at the hyphal scale, is largely unknown and challenging to study in natural habitats such as the opaque soil matrix. We monitored hyphal growth behaviour and strategies of seven Basidiomycete litter decomposing species in a micro-fabricated “Soil Chip” system that simulates principal aspects of the soil pore space and its micro-spatial heterogeneity. The hyphae were faced with micrometre constrictions, sharp turns and protruding obstacles, and the species examined were found to have profoundly different responses in terms of foraging range and persistence, spatial exploration and ability to pass obstacles. Hyphal behaviour was not predictable solely based on ecological assumptions, and our results obtained a level of trait information at the hyphal scale that cannot be fully explained using classical concepts of space exploration and exploitation such as the phalanx/guerrilla strategies. Instead, we propose a multivariate trait analysis, acknowledging the complex trade-offs and microscale strategies that fungal mycelia exhibit. Our results provide novel insights about hyphal behaviour, as well as an additional understanding of fungal habitat colonisation, their foraging strategies and niche partitioning in the soil environment.

Fungal behaviour: a new frontier in behavioural ecology

“…There are indications of different types of fungal memory at the hyphal/mycelial level in terms of direction of growth, physiology, metabolism, and cell cycle events. Directional memory is evident at the mycelial level when fungi are foraging for nutrients [10,31] and in hyphae navigating through micrometre-wide channels [32,33] (Box 2), where the Spitzenkörper is thought to act as a gyroscope, allowing the hyphal tips to navigate past barriers and retain their growth direction [33]. There are several examples of yeast cell behaviour being influenced by past events (i.e., having memory).…”

“…These new techniques allow us to mimic the microscale structures of fungal environments (soil, plants, cells, etc.) [66] and to monitor fungal growth, behaviour, and decision making at the scale of individual hyphae, in real time with microscopic precision [32,33]. For example, directional memory was shown in the hyphal tips of the basidiomycete Psilocybe cf.…”

“…For example, directional memory was shown in the hyphal tips of the basidiomycete Psilocybe cf. subviscida when they were growing through such labyrinths, but could sometimes be lost or confused when the hyphae were forced to navigate 'roundabouts' [32] (Figure IIA).…”

Platforms for High-Throughput Screening and Force Measurements on Fungi and Oomycetes

“…Platforms with three-dimensional microfluidic maze-like structures (see Figure 2a), mimicking aspects of the natural environment, have been deployed to evaluate the growth behavior and to analyze the space-searching growth mechanisms of fungal hyphae [28][29][30][31]. Observations of Pycnoporus cinnabarinus hyphae before and after they grew into microstructured areas showed that extension rates were not changed by confinement or obstacles, while hyphal branching rates were almost twice as high within the microstructures [28].…”

“…Observations of Pycnoporus cinnabarinus hyphae before and after they grew into microstructured areas showed that extension rates were not changed by confinement or obstacles, while hyphal branching rates were almost twice as high within the microstructures [28]. Differences in fungal growth and space exploration strategies between fungal species were found using various levels of containment and microstructures on polydimethylsiloxane (PDMS)-based chips [30,31]. Similarly, based on confinement structures on microfluidic chips, Baranger et al grew hyphae of two species, Talaromyces helices and Neurospora crassa into parallel microchannels that had nutrient and water supply carefully controlled, and monitored their growth behavior [32].…”