Genome analysis reveals horizontal gene transfer in penicillium marneffei

Abstract

BACKGROUND: Penicillium marneffei is the most important thermal dimorphic fungus causing respiratory, skin and systemic mycosis in Southeast Asia. The appearance of the HIV pandemic saw the emergence of the infection as an important opportunistic mycosis in immunocompromised patients. Besides HIV positive patients, P. marneffei infections have been reported in other immunocompromised patients. Despite its medical importance and its unusual thermal dimorphic capability, a large part of the ecology and epidemiology of P. marneffei remains unknown. The natural habitat of the fungus and its exact route of transmission have not been described. The advent of complete genome sequencing has led to the recognition of horizontal gene transfer (HGT) as a potentially important mechanism in the genome evolution in prokaryotes. In comparison, HGT is less well known in eukaryotes. As there are more and more eukaryotic whole genome sequencing become available, study of HGT among eukaryotic is possible. OBJECTIVES: In this poster, we report the horizontal transfer of several genes from bacterial lineages that known to populate the soil environment. These events might be clues to the natural habitat of P. marneffei and provide insight on its ecology in the natural environment. METHODS: P. marneffei strain PM1 wan isolated from a HIV-negative patient with culture-documented penicilliosis in Hong Kong. The genome was sequenced and assembled. Potentially horizontally transferred genes are identified by BLAST against NCBI GenBank database. Sequences of selected P. marneffei genes were manually corrected. P. marneffei strain PM1 was cultured and the target genes were sequenced. RESULTS: A total of 10,060 genes were predicted in the P. marneffei genome by FGENESH. 9927 informative genes were subjected to BLAST search, 288 of them were found to have a better alignment with the bacterial sequences that the reference A. fumigatus, A. nudulans and N. crassa sequences. 6 genes were identified to be HGT candidates with good support from the trees constructed by phylogenetic methods. Phylogenies of HGT candidates are suggestive of transfer mainly from soil bacteria, especially proteobacteria. CONCLUSION: We were able to identify reliably 6 genes from P. marneffei that are potential HGT candidates. And the soil-derived bacteria source of these 6 genes provided evidence for P. marneffei to be a soil organism.