Assessing thermal adaptation of a global sample of Aspergillus fumigatus: Implications for climate change effects.

Aspergillus fumigatus is a common environmental mold and a major cause of opportunistic infections in humans. It's distributed among many ecological niches across the globe. A major virulence factor of A. fumigatus is its ability to grow at high temperature. However, at present, little is known about variations among strains in their growth at different temperatures and how their geographic origins may impact such variations. In this study, we analyzed 89 strains from 12 countries (Cameroon, Canada, China, Costa Rica, France, India, Iceland, Ireland, New Zealand, Peru, Saudi Arabia, and USA) representing diverse geographic locations and temperature environments. Each strain was grown at four temperatures and genotyped at nine microsatellite loci. Our analyses revealed a range of growth profiles, with significant variations among strains within individual geographic populations in their growths across the temperatures. No statistically significant association was observed between strain genotypes and their thermal growth profiles. Similarly geographic separation contributed little to differences in thermal adaptations among strains and populations. The combined analyses among genotypes and growth rates at different temperatures in the global sample suggest that most natural populations of A. fumigatus are capable of rapid adaptation to temperature changes. We discuss the implications of our results to the evolution and epidemiology of A. fumigatus under increasing climate change.

Extensive Genetic Diversity and Widespread Azole Resistance in Greenhouse Populations of Aspergillus fumigatus in Yunnan, China.

Aspergillus fumigatus is the main cause of invasive aspergillosis (IA) with a high annual global incidence and mortality rate. Recent studies have indicated an increasing prevalence of azole-resistant A. fumigatus (ARAF) strains, with agricultural use of azole fungicides as a potential contributor. China has an extensive agricultural production system and uses a wide array of fungicides for crop production, including in modern growth facilities such as greenhouses. Soils in greenhouses are among the most intensively cultivated. However, little is known about the occurrence and distribution of ARAF in greenhouse soils. Here, we investigated genetic variation and triazole drug susceptibility in A. fumigatus from greenhouses around metropolitan Kunming in Yunnan, southwest China. Abundant allelic and genotypic variations were found among 233 A. fumigatus strains isolated from nine greenhouses in this region. Significantly, ∼80% of the strains were resistant to at least one medical triazole drug, with >30% showing cross-resistance to both itraconazole and voriconazole. Several previously reported mutations associated with triazole resistance in the triazole target gene cyp51A were also found in our strains, with a strong positive correlation between the frequency of mutations at the cyp51A promoter and that of voriconazole resistance. Phylogenetic analyses of cyp51A gene sequences showed evidence for multiple independent origins of azole-resistant genotypes of A. fumigatus in these greenhouses. Evidence for multiple origins of azole resistance and the widespread distributions of genetically very diverse triazole-resistant strains of A. fumigatus in greenhouses calls for significant attention from public health agencies.IMPORTANCE The origin and prevalence of azole-resistant Aspergillus fumigatus have been attracting increasing attention from biologists, clinicians, and public health agencies. Current evidence suggests agricultural fungicide use as a major cause. In southwest China, greenhouses are used to produce large amounts of fruits, flowers, and vegetables for consumers throughout China as well as those in other countries, primarily in southeast Asia. Here, we found a very high frequency (∼80%) of triazole-resistant A. fumigatus in our sample, the highest reported so far, with a significant proportion of these strains resistant to both tested agricultural fungicides and medical triazole drugs. In addition, we found novel allelic and genotypic diversities and evidence for multiple independent origins of azole-resistant genotypes of A. fumigatus in greenhouse populations in this region. Our study calls for a systematic evaluation of the effects of azole fungicide usage in greenhouses on human health.

Variations in sexual fitness among natural strains of the opportunistic human fungal pathogen Aspergillus fumigatus.

Aspergillus fumigatus is a ubiquitous ascomycete fungus, naturally inhabiting the soil and compost piles. Its conidia readily disperse into the atmosphere and cause opportunistic infections known as aspergillosis. With the emerging resistance to many antifungal drugs, our understanding of A. fumigatus epidemiology has become increasingly important for developing effective control and treatment strategies. As a pathogen capable of both sexual and asexual reproduction, mutations causing drug resistance and increased virulence could be spread rapidly in A. fumigatus populations. However, relatively little is known about the distributions of sexual reproductive fitness among natural strains of A. fumigatus. Here we investigated the formation of sexual reproductive structure (i.e. cleistothecia) and sexual spore viability among 60 natural strains of A. fumigatus. These strains were from six geographically distant countries (India, China, Canada, Cameroon, Saudi Arabia, and New Zealand), with 10 strains (including five MAT1-1 strains and five MAT1-2 strains) from each country. These strains were crossed in all combinations with strains of the opposite mating type. In addition, all 60 strains were crossed with either AFB62-1 (MAT1-1) or AFIR928 (MAT1-2), two reference supermater strains. Of the 900 crosses among the 60 natural strains, 136 crosses (15.1%) produced cleistothecia. Our analyses revealed that strains from China had the highest average ability to form cleistothecia, followed by those from New Zealand, Saudi Arabia, India, Canada, and Cameroon. Among the crosses that produced cleistothecia, about 40% produced viable ascospores, with the rate of ascospore germination varied significantly among crosses. Interestingly, neither the ability to form cleistothecia nor ascospore germination rate showed any distinct relationships with either geographic or genetic distance between parental strains. Our results suggest that genetic exchange among geographically and genetically divergent strains of A. fumigatus are possible. However, the rates of genetic exchange likely vary among strains and populations in nature.

Contemporary Gene Flow is a Major Force Shaping the Aspergillus fumigatus Population in Auckland, New Zealand.

Aspergillus fumigatus is a globally distributed opportunistic fungal pathogen capable of causing highly lethal invasive aspergillosis in immunocompromised individuals. Recent studies have indicated that the global population consists of multiple, divergent genetic clusters that are geographically broadly distributed. However, most of the analyzed samples have come from continental Eurasia and the Americas where the effects of ancient versus recent factors are difficult to distinguish. Here, we investigated environmental A. fumigatus isolates from Auckland, New Zealand, a geographically isolated population, and compared them with those from other parts of the world to determine the relative roles of historical differentiation and recent gene flow in shaping A. fumigatus populations. Our data suggest that the Auckland A. fumigatus population contains both unique indigenous genetic elements as well as genetic elements that are similar to those from other regions such as Europe, Africa, and North America. Though the hypothesis of random recombination was rejected, we found abundant evidence for phylogenetic incompatibility and recombination within the Auckland A. fumigatus population. Additionally, susceptibility testing identified two triazole-resistant strains, one of which contained the globally distributed mutation TR34/L98H in the cyp51A gene. Our results suggest that contemporary gene flow, likely due to anthropogenic factors, is a major force shaping the New Zealand A. fumigatus population.