Biomechanics of conidial dispersal in the toxic mold Stachybotrys chartarum.

Conidial dispersal in Stachybotrys chartarum in response to low-velocity airflow was studied using a microflow apparatus. The maximum rate of spore release occurred during the first 5 min of airflow, followed by a dramatic reduction in dispersal that left more than 99% of the conidia attached to their conidiophores. Micromanipulation of undisturbed colonies showed that micronewton (microN) forces were needed to dislodge spore clusters from their supporting conidiophores. Calculations show that airspeeds that normally prevail in the indoor environment disturb colonies with forces that are 1000-fold lower, in the nanonewton (nN) range. Low-velocity airflow does not, therefore, cause sufficient disturbance to disperse a large proportion of the conidia of S. chartarum.

The captured launch of a ballistospore.

Ballistospore discharge is a feature of 30000 species of mushrooms, basidiomycete yeasts and pathogenic rusts and smuts. The biomechanics of discharge may involve an abrupt change in the center of mass associated with the coalescence of Buller's drop and the spore. However this process occurs so rapidly that the launch of the ballistospore has never been visualized. Here we report ultra high-speed video recordings of the earliest events of spore dispersal using the yeast Itersonilia perplexans and the distantly related jelly fungus Auricularia auricula. Images taken at camera speeds of up to 100,000 frames/ s demonstrate that ballistospore discharge does involve the coalescence of Buller's drop and the spore. Recordings of I. perplexans demonstrate that although coalescence may result from the directed collapse of Buller's drop onto the spore, it also may involve the movement of the spore toward the drop. The release of surface tension at coalescence provides the energy and directional momentum to propel the drop and spore away from the fungus. Analyses show that ballistospores launch into the air at initial accelerations in excess of 10,000 g. There is no known analog of this micromechanical process in animals, plants or bacteria, but the recent development of a surface tension motor may mimic the fungal biology described here.