Negotiation of obstacles by fungi in micro-fabricated structures: to turn or not to turn?

Polymer microstructures were used to examine the manner in which fungal filaments negotiate obstacles in confined environments. When faced with an obstacle requiring a right-angle turn, two different responses were observed. In 21% of cases, hyphae turned around the corner and continued growth, while in the remaining 79% of cases, filaments continued apical growth into the corner, resulting in bending of the distal portions of the filament. The different reactions could not be linked to physical constraints (e.g., filament flexibility) since the filament deflection required to negotiate the obstacle was the same in all cases. Instead, the response appeared to be related to the original direction of growth at the time of filament formation (branching), with filaments turning only if the resultant growth vector was no more than 90° from their original branching vector. The results suggest that filaments are somehow able to retain a memory of their original branching direction, consistent with an overall survival strategy based on continued growth away from the colony center and into the surrounding environment.