| Stachybotrys chartarum is a mycotoxin-producing, cosmopolitan fungus that occurs on a variety of natural substrates as well as cellulose-based building materials such as drywall and ceiling tiles. This black mold has aroused public interest because it has been implicated in cases of sick building syndrome and pulmonary hemorrhage. Because it is likely that outdoor populations serve as the source of inoculum for mold colonies in water-damaged structures, it is critical to understand the types of environments that support natural populations of S. chartarum. The primary objective of this research was to identify outdoor habitats in north central Florida where S. chartarum is found and the times of year it is most abundant. Several semi-selective media were identified for this purpose; however, detection of S. chartarum from outdoor air was a rare event, suggesting that air sampling would not be appropriate for investigating the occurrence of S. chartarum in outdoor habitats. Instead, traps with pieces of wetted drywall were placed in four habitats in Gainesville, Florida: a pine grove, a citrus grove, a lakeside and a hardwood forest. Over the course of 24 months, S. chartarum was found growing at all four habitats but only rarely, occurring on only 0.02% of the pieces collected. Because the frequency of S. chartarum was so low, most differences in abundance between sites were not significant. Stachybotrys chartarum was recovered most frequently from the citrus grove, and at all sites, it was found only during the summer months. There was a correlation between S. chartarum occurrence and temperature but not with rainfall. The morphological species S. chartarum contains two chemotypes, S. chartarum chemotype S and S. chartarum chemotype A, which produce different mycotoxins. The Florida field isolates were compared phylogenetically using the trichodiene synthase 5 and chitin synthase 1 gene fragments. Seventy percent of the outdoor isolates were identified as S. chartarum chemotype A and only 30% were identified as chemotype S. This may have a positive implication for public health in north central Florida since chemotype A does not produce highly toxic macrocyclic tricothecenes. As a diagnostic tool, neither locus correctly identified all isolates, and more accurate molecular markers should be identified. |
