Drosophila melanogaster as a model to characterize fungal volatile organic compounds.

Fungi are implicated in poor indoor air quality and may pose a potential risk factor for building/mold related illnesses. Fungi emit numerous volatile organic compounds (VOCs) as alcohols, esters, ethers, ketones, aldehydes, terpenoids, thiols, and their derivatives. The toxicity profile of these VOCs has never been explored in a model organism, which could enable the performance of high throughput toxicological assays and lead to a better understanding of the mechanism of toxicity. We have established a reductionist Drosophila melanogaster model to evaluate the toxicity of fungal VOCs. In this report, we assessed the toxicity of fungal VOCs emitted from living cultures of species in the genera, Trichoderma, Aspergillus, and Penicillium and observed a detrimental effect on larval survival. We then used chemical standards of selected fungal VOCs to assess their toxicity on larval and adult Drosophila. We compared the survival of adult flies exposed to these fungal VOCs with known industrial toxic chemicals (formaldehyde [37%], xylene, benzene, and toluene). Among the tested fungal VOC standards, the compounds with eight carbons (C8) caused greater truncation of fly lifespan than tested non-C8 fungal VOCs and industrial toxins. Our data validate the use of Drosophila melanogaster as a model with the potential to elucidate the mechanistic attributes of different toxic VOCs emitted by fungi and also to explore the potential link between reported human illnesses/symptoms and exposure to water damaged and mold contaminated buildings.

Occurrence of soil- and tick-borne fungi and related virulence tests for pathogenicity to Ixodes scapularis (Acari: Ixodidae).

Ixodes scapularis Say, the blacklegged tick, vectors Borrelia burgdorferi Johnson et al. 1984, the bacterium that causes Lyme disease, the most important vector-borne disease in the United States. Efforts to reduce I. scapularis populations are shifting toward the development of biological control methods. Currently, only a few entomopathogenic fungal species are considered virulent to ticks. We hypothesized that these species may not represent the most abundant local taxa that would be pathogenic to ticks in situ. To identify potential entomopathogenic fungi at a study site in Westchester County, New York, we sampled soils and ticks, extracted and amplified the internal transcribed spacer region of nuclear ribosomal DNA (nrDNA), and compared sequences with those in GenBank. Over three sampling periods from June 2007 to May 2008, 70 fungal taxa were isolated and identified from soils (48 taxa) and ticks (27 taxa; 5 taxa were found both in soil and on ticks) collected in this study, encompassing species in 25 different genera. In laboratory bioassays, 15 fungal taxa were found to be significantly virulent, although none of these were previously considered common pathogens of I. scapularis. Two species, Hypocrea lixii Patouillard 1891 and Penicillium soppii K. M. Zalessky 1927, were tested in field trials by spraying suspensions on forested plots. Mean tick mortality was 71% after treatment with H. lixii, 58% after treatment with P. soppii, and 32% in the control plots. The complete diversity of entomopathogenic fungal species at this site is yet to be defined, but, in general, such fungi appear to be more common in forest habitats where I. scapularis resides than previously thought. Examination of intact fungal communities can provide information that serves as the foundation for site-specific biocontrol programs.

Isolation of entomopathogenic fungi from soils and Ixodes scapularis (Acari: Ixodidae) ticks: prevalence and methods.

Entomopathogenic fungi are commonly found in forested soils that provide tick habitat, and many species are pathogenic to Ixodes scapularis Say, the blacklegged tick. As a first step to developing effective biocontrol strategies, the objective of this study was to determine the best methods to isolate entomopathogenic fungal species from field-collected samples of soils and ticks from an Eastern deciduous forest where I. scapularis is common. Several methods were assessed: (1) soils, leaf litter, and ticks were plated on two types of media; (2) soils were assayed for entomopathogenic fungi using the Galleria bait method; (3) DNA from internal transcribed spacer (ITS) regions of the nuclear ribosomal repeat was extracted from pure cultures obtained from soils, Galleria, and ticks and was amplified and sequenced; and (4) DNA was extracted directly from ticks, amplified, and sequenced. We conclude that (1) ticks encounter potentially entomopathogenic fungi more often in soil than in leaf litter, (2) many species of potentially entomopathogenic fungi found in the soil can readily be cultured, (3) the Galleria bait method is a sufficiently efficient method for isolation of these fungi from soils, and (4) although DNA extraction from ticks was not possible in this study because of small sample size, DNA extraction from fungi isolated from soils and from ticks was successful and provided clean sequences in 100 and 73% of samples, respectively. A combination of the above methods is clearly necessary for optimal characterization of entomopathogenic fungi associated with ticks in the environment.