Exploring the Penicillium marneffei genome

Penicillium marneffei is a dimorphic fungus that intracellularly infects the reticuloendothelial system of humans and bamboo rats. Endemic in Southeast Asia, it infects 10% of AIDS patients in this region. The absence of a sexual stage and the highly infectious nature of the mould-phase conidia have impaired studies on thermal dimorphic switching and host-microbe interactions. Genomic analysis, therefore, could provide crucial information. Pulsed-field gel electrophoresis of genomic DNA of P. marneffei revealed three or more chromosomes (5.0, 4.0, and 2.2 Mb). Telomeric fingerprinting revealed 6-12 bands, suggesting that there were chromosomes of similar sizes. The genome size of P. marneffei was hence about 17.8-26.2 Mb. G+C content of the genome is 48:8 mol%. Random exploration of the genome of P. marneffei yielded 2303 random sequence tags (RSTs), corresponding to 9% of the genome, with 11.7, 6.3, and 17.4% of the RSTs having sequence similarity to yeast-specific sequences, non-yeast fungus sequences, and both (common sequences), respectively. Analysis of the RSTs revealed genes for information transfer (ribosomal protein genes, tRNA synthetase subunits, translation initiation, and elongation factors), metabolism, and compartmentalization, including several multi-drug-resistance protein genes and homologues of fluconazole-resistance gene. Furthermore, the presence of genes encoding pheromone homologues and ankyrin repeat-containing proteins of other fungi and algae strongly suggests the presence of a sexual stage that presumably exists in the environment.