Genotypic variation in Penicillium chysogenum from indoor environments

We examined 198 isolates of P. chysogenum recovered from 109 houses in Wallaceburg, Ontario, and 25 culture collection isolates including seven ex-type strains. Multilocus genotypes were determined by heteroduplex mobility assay of regions spanning introns in acetyl co-enzyme A synthase, beta-tubulin, thioredoxin reductase and the internal transcribed spacer regions of the nuclear ribosomal subrepeat. Five unique multilocus haplotypes were revealed without evidence of recombination, indicating strictly clonal population structures. Phylogenetic analysis of allele sequences using maximum parsimony resolved three strongly supported lineages. The dominant clade included more than 90% of house isolates in addition to the notable laboratory contaminant isolated by Alexander Fleming in 1929 in Britain. A second clade contained more than 5% of house isolates clustered with the ex-type strains of P. chysogenum and P. notatum. Follow-up sampling of outdoor air in the locality failed to reveal P. chysogenum, confirming the rarity of this fungus in outdoor air.