Project description:Natural isolates of Burkholderia pseudomallei (Bp), the causative agent of melioidosis, are known to exhibit diverse phenotypic traits, suggesting significant intraspecies genetic heterogeneity. Using whole-genome Bp microarrays, we experimentally mapped patterns of large-scale genomic variation in 93 South East Asian clinical, environmental, and animal Bp isolates. 14% of the reference Bp K96243 genome was variably present across the strain panel, more than double previous estimates, and both hypothetical proteins and paralogous gene pairs (PGPs) were significantly over-represented in the set of strain-variable genes. Examining patterns of PGP retention and loss, we successfully sub-categorized the PGPs into non-redundant, functionally biased, and completely redundant classes. We then identified 20 novel regions (“islands”) variably present between strains previously missed by computational analysis. Three of these novel islands contained lipopolysaccharide (LPS) biosynthesis genes, and strains lacking one such LPS island demonstrated reduced virulence in mouse infection assays. Clinical isolates associated with human melioidosis were strongly associated with the presence of specific genomic islands, but a common set of virulence-related genes was present in all strains. Our results suggest that most Bp strains possess a core virulence machinery capable of causing disease, but accessory functions provided by mobile elements may predispose distinct host species and ecological niches to specific individual strains. This hierarchical model of Bp virulence reconciles previous conflicting studies comparing Bp environmental and clinical isolates, and suggests novel molecular strategies for disease surveillance and outbreak detection efforts in melioidosis. Keywords: aCGH of 93 Bp strains
Project description:The adaptation of fungal pathogens to the host environment via large-scale genomic changes is a poorly characterized phenomenon. We recently discovered clinical strains of Cryptococcus neoformans, the leading cause of fungal meningoencephalitis in HIV/AIDS patients, which are disomic for chromosome 13. In the current study, we examined the relationship between disomy, expression of the virulence factor melanin and virulence in a mouse model of cryptococcosis. We found that melanin production was correlated with monosomy at chromosome 13, and that disomic variants were less melanized and attenuated for virulence in mice. Changes in the copy number of other chromosomes were also detected in strains showing variation in melanin formation after growth in culture and after passage through mice. A survey of environmental and clinical isolates maintained in culture revealed few occurrences of disomic chromosomes. However, an examination of isolates that were freshly collected from the cerebral spinal fluid of AIDS patients and minimally cultured provided evidence for mixed infections and copy number variation. Overall, these results suggest that the genome of C. neoformans exhibits a greater degree of plasticity than previously appreciated. Importantly, genome variation is associated with virulence factor expression and disease severity, and its occurrence in isolates from AIDS patients suggests that it may have clinical relevance. Genome comparison of clinal and environmental strains vs standard strain H99
Project description:Natural isolates of Burkholderia pseudomallei (Bp), the causative agent of melioidosis, are known to exhibit diverse phenotypic traits, suggesting significant intraspecies genetic heterogeneity. Using whole-genome Bp microarrays, we experimentally mapped patterns of large-scale genomic variation in 93 South East Asian clinical, environmental, and animal Bp isolates. 14% of the reference Bp K96243 genome was variably present across the strain panel, more than double previous estimates, and both hypothetical proteins and paralogous gene pairs (PGPs) were significantly over-represented in the set of strain-variable genes. Examining patterns of PGP retention and loss, we successfully sub-categorized the PGPs into non-redundant, functionally biased, and completely redundant classes. We then identified 20 novel regions (âislandsâ) variably present between strains previously missed by computational analysis. Three of these novel islands contained lipopolysaccharide (LPS) biosynthesis genes, and strains lacking one such LPS island demonstrated reduced virulence in mouse infection assays. Clinical isolates associated with human melioidosis were strongly associated with the presence of specific genomic islands, but a common set of virulence-related genes was present in all strains. Our results suggest that most Bp strains possess a core virulence machinery capable of causing disease, but accessory functions provided by mobile elements may predispose distinct host species and ecological niches to specific individual strains. This hierarchical model of Bp virulence reconciles previous conflicting studies comparing Bp environmental and clinical isolates, and suggests novel molecular strategies for disease surveillance and outbreak detection efforts in melioidosis. Keywords: aCGH of 93 Bp strains genomic DNA of 93 Bp strains were assessed on Bp_array_v2
Project description:The adaptation of fungal pathogens to the host environment via large-scale genomic changes is a poorly characterized phenomenon. We recently discovered clinical strains of Cryptococcus neoformans, the leading cause of fungal meningoencephalitis in HIV/AIDS patients, which are disomic for chromosome 13. In the current study, we examined the relationship between disomy, expression of the virulence factor melanin and virulence in a mouse model of cryptococcosis. We found that melanin production was correlated with monosomy at chromosome 13, and that disomic variants were less melanized and attenuated for virulence in mice. Changes in the copy number of other chromosomes were also detected in strains showing variation in melanin formation after growth in culture and after passage through mice. A survey of environmental and clinical isolates maintained in culture revealed few occurrences of disomic chromosomes. However, an examination of isolates that were freshly collected from the cerebral spinal fluid of AIDS patients and minimally cultured provided evidence for mixed infections and copy number variation. Overall, these results suggest that the genome of C. neoformans exhibits a greater degree of plasticity than previously appreciated. Importantly, genome variation is associated with virulence factor expression and disease severity, and its occurrence in isolates from AIDS patients suggests that it may have clinical relevance.