Sporulation of the Hyphomycete Stachybotrys chartarum Under Three Light Conditions

Patricia Heinsohn1, Ph.D., C.I.H., Sharon Harney, Ph.D., K. Alexandros Exuzides, Ph.D. Menlo Park, CA

Stachybotrys chartarum is a widespread hyphomycete commonly isolated from a variety of substrates including soil and wood. It can be found growing in building materials, which have become wet before or after construction. The inhalation of S. chartarum conidia can cause pneumomycotoxicoses, and a recent study linked S. chartarum to the deaths of infants diagnosed with pulmonary hemosiderosis in Cleveland. While S. chartarum is frequently isolated, the conditions under which it sporulates are unknown and are important issues in assessing indoor air quality. This study reports on the sporulation of S. chartarum under three different artificial light conditions. Two isolates of S. chartarum were inoculated onto two different media, MEA and CMA, and exposed to either 24 hour dark, a light/dark cycle, or 24 hour light. After growth initiation, growth rate and degree of sporulation were measured. Results indicate that growth rate and degree of sporulation differ with light conditions and media. On CMA the initial growth rate under 24 hour light was higher than under light/dark and 24 hour dark. Light/dark conditions were more conducive to early sporulation whereas 24 hour dark delayed sporulation. Sporulation did not occur under any light condition on MEA for six days. The data indicate that under favorable growth conditions, S. chartarum can sporulate under any light condition. Therefore, S. chartarum growing in buildings in dark areas can sporulate for dissemination into the air.