Published: June 15th, 2001
Revised: August 12th, 2009
©James Alexander Scott, 2001
Department of Botany, University of Toronto
Fungi are among the most common microbiota in the interiors of buildings, including homes. Indoor fungal contaminants, such as dry-rot, have been known since antiquity and are important agents of structural decay, particularly in Europe. The principal agents of indoor fungal contamination in North America today, however, are anamorphic (asexual) fungi mostly belonging to the phyla Ascomycota and Zygomycota, commonly known as “moulds”.
Broadloom dust taken from 369 houses in Wallaceburg, Ontario during winter, 1994, was serial dilution plated, yielding approximately 250 fungal taxa, over 90% of which were moulds. The ten most common taxa were: Alternaria alternata, Aureobasidium pullulans, Eurotium herbariorum, Aspergillus versicolor, Penicillium chrysogenum, Cladosporium cladosporioides, P. spinulosum, Cl. sphaerospermum, As. niger and Trichoderma viride. Chi-square association analysis of this mycoflora revealed several ecological groups including phylloplane-, soil-, and xerophilic food spoilage fungi.
Genotypic variation was investigated in two common dust-borne species, Penicillium brevicompactum and P. chrysogenum. Nine multilocus haplotypes comprising 75 isolates of P. brevicompactum from 50 houses were detected by heteroduplex mobility assay (HMA) of polymorphic regions in betatubulin (benA), nuclear ribosomal RNA spanning the internal transcribed spacer regions (ITS1-2) and histone 4 (his4) genes. Sequence analysis of the benA and rDNA loci showed two genetically divergent groups. Authentic strains of P. brevicompactum and P. stoloniferum clustered together in the predominant clade, accounting for 86% of isolates. The second lineage contained 14% of isolates, and included collections from the rotting fruit bodies of macrofungi.
Similarly, 5 multilocus haplotypes based on acetyl coenzyme-A synthase (acuA), benA, ITS1-2 and thioredoxin reductase (trxB) genes comprised 198 isolates of P. chrysogenum obtained from 109 houses. A strictly clonal pattern of inheritance was observed, indicating the absence of recombination. Phylogenetic analyses of allele sequences segregated the population into three divergent lineages, encompassing 90%, 7% and 3% of the house dust isolates, respectively. Type isolates of P. chrysogenum and its synonym P. notatum clustered within the secondary lineage, confirming this synonymy. No isolates of nomenclatural status clustered within the predominant lineage; however, this clade contained Alexander Fleming’s historically noteworthy penicillin-producing strain from 1929. Similarly, there was no available name for the minor lineage.