Flow sensing in mycelial fungi

Hyphae of a variety of mycelial fungi were shown to reorient their direction of growth to grow upstream in a continuous flowing current of liquid medium. Among those tested fungi, Aspergillus niger hyphae was most polarized towards the upstream. Hyphae of A. niger which had been attached to poly-L-lysine coated plates on the base of a continuous-culture flow cell were exposed to a current of medium of flow rates in the range of 0-6400 microns s-1 for 1-4 h. Hyphal tips quickly reoriented towards the upstream of the flowing medium and became aligned parallel to the flow axis as they grew larger. At flow rates above 1600 microns s-1, however, the percentage of polarization of hyphae reached a constant level. With other fungi, germ tube emergence was not polarized but hyphae and branches grew towards the upstream. There was no detectable difference in the pH and oxygen concentration of the flowing medium between inlet and outlet of the flow cell. This result suggests that hyphae of mycelial fungi sense transient flow of liquid medium over their surface and reorient their direction to grow upstream.