Obstacle Induced Branching in Neurospora crass and Rhizopus oryzae

The branching dynamics and navigation of filamentous fungi that have an apical vesical crescent (AVC) are poorly understood. Here, Rhizopus oryzae (Mucoromycota), which has an AVC, is compared to Neurospora crassa (Ascomycota), which has a Spitzenkörper (Spk), as they navigated microfluidic maze environments varying in pattern. The different maze patterns (diamonds, squares, and chevrons) presented increasing angles of impact, and degrees of obstruction. This investigation addressed questions regarding advantages or disadvantages that a Spk or AVC may provide in hyphal growth. All branching phenomena were compared to the regular branching of unobstructed growth to determine obstacle induced branching. Neurospora crassa generated more branches per impact amongst all three maze types and was unable to complete the chevron maze types. Rhizopus oryzae generated less branches per impact but was able to complete every maze type. The greatest difference in branch formation was seen in the chevron maze design where N. crassa generated a greater number than R. oryzae. Neurospora crassa exhibited a hyperbranching response in the chevron mazes not seen in R. oryzae. Closer inspection of the hyperbranching events revealed that they were composed of initial branching events followed by secondary and tertiary branching events. The directional memory of N. crassa was also observed, and was a characteristic of R. oryzae. While the branching dynamics and navigation of N. crassa and R. oryzae were different, and N. crassa exhibited branching and navigational phenomenon that R. oryzae did not, R. oryzae seemingly had the advantage with its use of an AVC over N. crassa, as it was able to complete every maze type, which N. crassa was unable to do.