Identification of putative sequence specific PCR primers for detection of the toxigenic fungal species Stachybotrys chartarum

The nucleotide sequence of a c936 bp segment of the nuclear rRNA gene operon was determined for the toxigenic fungal species Stachybotrys chartarum and for other species of Stachybotrys and the related genus Memnoniella. This information was used to infer the phylogenetic relationships of these organisms and to search for sequence specific polymerase chain reaction (PCR) primers for S. chartarum in the internal transcribed spacer (ITS) regions. Searches for candidate primers were performed both by computer using the commercially available Oligo(R) v5.0 primer analysis software package and by manual inspection of the aligned sequences. Primers identified in both types of searches were evaluated for their specificities using a priming efficiency analysis algorithm available in the Oligo(R) 5.0 software. The automated computer searches were unsuccessful in finding S. chartarum-specific primers but did identify a group-specific reverse primer (designated as StacR4) for a phylogenetically related cluster of species that included S. chartarum. Manual searches led to the identification of a reverse primer (designated as StacR3) that was predicted to be specific for only S. chartarum and one other species of Stachybotrys. Experimental PCR analyses using these primers in conjunction with a universal forward primer indicated that the computer-generated amplification efficiency predictions were correct in most instances. A notable exception was the finding that StacR3 was specific only for S. chartarum. The relative merits of different PCR strategies for the detection of S. chartarum employing either one or both of the primers identified in this study are discussed.