The vectoring of cactophilic yeasts by Drosophila

Summary At two locations in the Sonoran Desert, yeasts were sampled from species of Drosophila, the flies' cactus hosts, and other neighboring sources of cactophilic yeasts to determine the relation between the yeasts vectored by the fly and the yeasts found in their breeding sites. D. mojavensis, D. nigrospiracula, and D. mettleri vectored yeast assemblages significantly more similar to the yeast species found on the rot from which the flies were collected than to the yeasts found on other rots from the flies host cactus or other rotting cactus at the same site. Rots with Drosophila had fewer yeast species than those without flies, suggesting that flies were associated with younger rots. Rots with flies and the Drosophila also had more yeast species with the capability to produce ethyl acetate than rots without flies. The results support the contention that cactophilic Drosophila feed on a subset of the yeasts available in an area, and may act to maintain differences among the yeast communities found on different species of cactus.     

The ecology of the yeast flora in necroticOpuntia cacti and of associatedDrosophila in Australia

A survey was made of the yeast communities isolated from necrotic tissue of 4 species of prickly-pear cacti (Opuntia stricta, O. tomentosa, O. monacantha, andO. streptacantha) which have colonized in Australia. Yeast communities were sampled from a number of localities and at different times. Cactus specific yeasts accounted for 80% of the total isolates, and the 3 most common species contributed 63% of the total. Comparisons of the species compositions of the yeast communities indicated that the differences among communities were greater betweenOpuntia species than between different localities within a single cactus species, and also that differences between years were greater than average differences between localities within years. Multivariate statistical tests of association between yeast community and physical features of rots indicated that temperature, pH, and age of rot all exerted some influence on the structure of the yeast community. Similar analyses involvingDrosophila species inhabiting these cactus rots suggested the existence of complex associations betweenDrosophila community, yeast community, and physical and chemical attributes of the cactus necroses.     

Yeast communities of the cactusPilosocereus arrabidae and associated insects in the Sandy Coastal Plains of Southeastern Brazil

The yeast communities from necrotic tissues, decaying flowers and fruits, and from larval feeding sites of the mothSigelgaita sp. in the cactusPilosocereus arrabidae were surveyed in three restinga ecosystems in Southeastern Brazil. Insects associated with these substrates were sampled to verify the vectoring of yeasts. The cactusPilosocereus arrabidae was shown to have four different yeast communities associated with it. Necrotic stems had a diverse yeast community with the prevalent speciesPichia barkeri, Candida sonorensis, Pichia cactophila, Geotrichum sp.,Myxozyma mucilagina andSporopachydermia sp. A, representing about 80% of the total isolates.Pichia sp. A and aCandida domercqii-like species represented more than 90% of the yeast isolates from decaying flowers. Fruits had a heterogeneous yeast community with typical fruit yeasts of the genusKloeckera, basidiomicetous anamorphs of the genusCryptococcus, the black yeastAureobasidium pullulans, Pichia sp. A, aCandida domercqii-like species, and some cactophilic yeasts, especiallyClavispora opuntiae. The feeding site ofSigelgaita sp. larvae hadClavispora opuntiae as the prevalent species. Insect vectors are suggested as one the most important factors influencing the composition of these yeast communities.     

Yeast communities of the cactusPilosocereus arrabidae as resources for larval and adult stages ofDrosophila serido

The feeding behavior ofDrosophila serido on the yeast communities of necrotic stem tissue ofPilosocereus arrabidae were studied in a sand dune ecosystem of Rio de Janeiro, Brazil. The prevalence of cactophilic yeasts includingPichia barkeri, Candida sonorensis andGeotrichum sp. in the crops and external surfaces ofD. serido reflected its association with the cactus habitat. The effective number of yeasts vectored on the surface of flies was higher than that in the crops. Also overlap between the yeasts from stems and from crops was partial suggesting selective feeding by the flies in the substrates visited. The females had a higher effective number of yeast species and a lower similarity than males with the yeast community ofP. arrabidae. This was probably related to the search for oviposition sites by females. The presence ofPichia thermotolerans-like andPichia amethionina varpachycereana in the flies, but not inP. arrabidae stems, indicated thatD. serido was not limited to this cactus species. The larvae and adults lived in different patches with the adults feeding in patches with higher yeast species richness. The larvae had a narrower feeding niche and higher overlap withP. arrabidae, and preferredP. barkeri andPichia cactophila as food. Adult flies fed on patches with the most frequent yeasts except forP. cactophila. Pichia caribaea was found in higher frequency in the adult crops than in the stems. Our data suggested that there was food selection and diet partitioning between adult and larval stages ofD. serido.     

Quantitative and qualitative seasonal changes in the microbial community from the phyllosphere of sugar beet (Beta vulgaris)

Bacteria, yeasts and filamentous fungi colonizing immature, mature and senescing primary leaves of field grown Beta vulgaris (sugar beet) were analysed over a complete growing season. Greatest microbial numbers were detected on senescing primary leaves and these numbers increased over most of the season. The number of colonizers detected on mature leaves was found to be stable over most of the study.Filamentous fungi and yeasts were identified to the genus level and the communities found to have greatest diversity during the summer months. There was no consistent pattern of diversity according to leaf type. Two genera of filamentous fungi, Cladosporium and Alternaria and two yeast genera, Cryptococcus and Sporobolomyces were the most numerous fungal populations isolated. Only 8 filamentous fungi and 3 yeast genera were commonly isolated on PDA (potato dextrose agar).Bacterial strains (1236) were isolated on Tryptic Soy Broth (TSB) agar and identified to species, or in some cases sub-species level, by analysis of their fatty acid methyl ester (FAME) profiles. Isolated bacteria were grouped into 78 named and 37 unnamed species clusters. Greatest number of bacterial species were isolated from young plants and leaves, sampled during the autumn months. Bacterial community diversity was lowest in mid-summer and winter months. Pseudomonas was the most commonly isolated genus and Erwinia herbicola the most common species. P. aureofaciens was the only species isolated from soil that was also isolated from the phyllosphere of B. vulgaris throughout the season.     

Occurrence and Diversity of Yeasts in the Mid-Atlantic Ridge Hydrothermal Fields Near the Azores Archipelago

The yeast community associated with deep-sea hydrothermal systems of the Mid-Atlantic Rift was surveyed for the first time. This study relied on a culture-based approach using two different growth media: a conventional culture medium for yeasts supplemented with sea salts (MYPss) and the same medium additionally supplemented with sulfur (MYPssS). For the evaluation of species diversity, a molecular approach involving minisatellite-primed polymerase chain reaction (MSP-PCR) strain typing and sequence analysis of the D1/D2 domains of the 26S rDNA was followed. In the seven water samples that were studied, the number of colony-forming units per liter (cfu/L) ranged from 0 to 5940. The nonpigmented yeasts were much more abundant than the pink-pigmented ones. This disproportion was not observed in studies of other marine systems and may be due to the unique conditions of hydrothermal vents, characterized by a rich animal and microbial diversity and therefore by the availability of organic compounds utilizable by yeasts. Higher counts of nonpigmented yeast were obtained using MYPss, whereas for pink yeasts, higher counts were obtained using MYPssS. Moreover, among pink yeasts, some of the MSP-PCR classes obtained were composed of isolates obtained only on MYPssS, which might be an indication that these isolates are adapted to the ecosystems of the hydrothermal vents. Twelve phylotypes belonged to the Ascomycota and seven phylotypes belonged to the Basidiomycota. The nonpigmented yeasts were identified as Candida atlantica, C. atmosphaerica, C. lodderae, C. parapsilosis, Exophiala dermatitidis, Pichia guilliermondii, and Trichosporon dermatis, whereas the pigmented yeasts were identified as Rhodosporidium diobovatum, R. sphaerocarpum, R. toruloides, and Rhodotorula mucilaginosa. Some of the yeasts that were found belong to phylogenetic groups that include species reported from other marine environments, and eight phylotypes represent undescribed species. The new phylotypes found at Mid-Atlantic Ridge hydrothermal fields represent 33% of the total number of yeast taxa that were found.     

Occurrence of Yeasts in Cloacae of Migratory Birds

Several species of yeast have been reported as pathogens in humans based on increases in immunodeficiency syndromes and as a result of immunosuppressant chemotherapy in cancer treatment. Domestic and wild birds are known to act as carriers of human pathogenic fungi. To gain additional information on the yeasts present in the cloacae of some species of migratory birds, 421 wild birds (24.39% out of 1726 birds caught in Romania, Hungary and Bulgaria) were sampled with the permission of the local judicial authority. The state of conservation of the birds (i.e. post-mortem alterations, colour of the mucosae etc.), along with their age and sex were determined. Samples were collected directly from the cloacae and cultured, and colonies were identified in each positive sample. Yeasts were isolated from 15.7% of the animals sampled, with the highest percentage found in coots (Fulica atra −58.8%) and the lowest in quails (Coturnix coturnix −1.7%). A total of 131 isolates belonging to 15 species of yeast were identified. Rhodotorula rubra was the yeast with the highest number of isolates (28.2%), followed by Cryptococcus albidus (18.4%), Candida albicans (9.2%), Trichosporon cutaneum (8.4%), Candida guilliermondii (6.1%), Candida tropicalis (6.1%) and other species. The present study represents the first survey on the occurrence of yeasts in the cloacae of migratory birds. The prevalence and species of yeasts isolated is discussed on the basis of the ecology, diet, and habitat of the birds.     

Yeast Community Persistence in a Spatially Structured Environment

Abstract Community persistence was investigated in the yeast assemblage inhabiting patches of necrotic stem tissue of the columnar cactus Stenocereus gummosus (pitaya agria). Two surveys, conducted in 1981 and 1996, were compared. The variation in species occurrence in a spatial hierarchy within neuroses, among plants within a location, and among locations, was persistent across the 15-yr time span. The core species had a community similarity coefficient of 0.75, and the rank of their variability was significantly correlated for the two surveys. The physiological potential of the yeasts was distributed in the same manner in 1996 and 1981. Likewise, the rank order of physiological potentials both within plant and between plants was significantly correlated. These results indicate a microbial community that persists regionally, even though individual necroses routinely experience extinction and colonization. The role of an insect vector, Drosophila mojavensis, in community persistence is discussed. Received: 7 July 1997; Accepted: 27 October 1997     

Analysis of the community structure of yeasts associated with the decaying stems of cactus. III.Stenocereus thurberi

Yeast communities in necroses of organpipe cactus (Stenocereus thurberi) were surveyed at 3 localities in Arizona. Quantitative analysis of random samples allows comparisons of the types and numbers of yeasts at 3 levels: within plants, between plants within a locality, and between localities. The analysis shows that the major source of variability is between plants. This pattern is identical with the pattern shown by agria cactus (Stenocereus gummosus) and is thought to be due to sampling different successional stages. No significant differences in estimates of the effective number of yeast species (ENS) in agria and organpipe samples were found. Comparisons of agria, organpipe, and prickly pear (Opuntia) cacti support the hypothesis that cactus chemistry is an important determinant of the yeast community structure which, in turn, is an important determinant of the diversity ofDrosophila species which utilize necrotic cacti as feeding and breeding substrates.     

Saprophagous insect larvae,Drosophila melanogaster,profit from increased species richness in beneficial microbes

Female fruit flies, Drosophila melanogaster, lay their eggs on decaying plant material. Foraging fly larvae strongly depend on the availability of dietary microbes, such as yeasts, to reach the adult stage. In contrast, strong interference competition with filamentous fungi can cause high mortality among Drosophila larvae. Given that many insects are known for employing beneficial microbes to combat antagonistic ones, we hypothesized that fly larvae engaged in competition with the noxious mould Aspergillus nidulans benefit from the presence of dietary yeast species, especially when they are associated with increasingly species rich yeast communities (ranging from one to six yeast species per community). On a nutrient‐limited fruit substrate infested with A. nidulans, both larval survival and development time were positively affected by more diverse yeast communities. On a mould‐free fruit substrate, merely larval development but not survival was found to be affected by increasing species richness of dietary yeasts. Not only yeast diversity had an effect on D. melanogaster life‐history traits, but also the identity of the yeast combinations. These findings demonstrate the importance of the structure and diversity of microbial communities in mutualistic animal–microbe interactions.     

A comparison of clinical and food Saccharomyces cerevisiae isolates on the basis of potential virulence factors

Saccharomyces cerevisiae is the most widely used yeast in industrial/commercial food and beverage production and is even consumed as a nutritional supplement. Various cases of fungemia caused by this yeast species in severely debilitated traumatized or immune-deficient patients have been reported in recent years, suggesting that this species could be an opportunistic pathogen in such patients. To determine whether the industrial S. cerevisiae strains can be included in this virulent group of strains, we carried out a comparative study between clinical and industrial yeasts based on the various phenotypic traits associated with pathogenicity in two other yeast species (Candida albicans and Cryptococcus neoformans). The majority of the clinical isolates were found to secrete higher levels of protease and phospholipase, grow better at 42°C and show strong pseudohyphal growth relative to industrial yeasts. However three industrial yeast strains, one commercial wine strain, baker’s yeast and one commercial strain of S. cerevisiae (var. boulardii), were exceptions and based on their physiological traits these yeasts would appear to be related to clinical strains.     

云南高原湖泊杞麓湖冬季可培养酵母菌多样性分析

【目的】探究云南杞麓湖酵母菌群落结构及其与环境因子的相互关系。【方法】采用原位培养方法对杞麓湖14个水样进行酵母菌分离,应用26S r DNA D1/D2区域序列分析,并结合形态及生理生化指标将对分离获得的酵母菌进行鉴定,运用软件bio-dap和Canoco分析酵母菌类群的丰富度及其与环境因子间的相互关系。【结果】从杞麓湖中分离得到321株酵母菌,鉴定为14个属27个种和1个潜在的新类群。Rhodosporidium kratochvilovae和出芽短梗霉(Aureobasidium pullulans)是优势种,分别为总菌株数的29.6%和16.8%。水体总磷含量是影响产色素红冬孢酵母属(Rhodosporidium)分布的重要环境因子,而p H为隐球酵母属(Cryptococcus)分布的一个重要选择条件。【结论】杞麓湖酵母菌具有较为丰富的群落多样性。     

Yeast Communities of Diverse Drosophila Species: Comparison of Two Symbiont Groups in the Same Hosts

The combination of ecological diversity with genetic and experimental tractability makes Drosophila a powerful model for the study of animal-associated microbial communities. Despite the known importance of yeasts in Drosophila physiology, behavior, and fitness, most recent work has focused on Drosophila-bacterial interactions. In order to get a more complete understanding of the Drosophila microbiome, we characterized the yeast communities associated with different Drosophila species collected around the world. We focused on the phylum Ascomycota because it constitutes the vast majority of the Drosophila-associated yeasts. Our sampling strategy allowed us to compare the distribution and structure of the yeast and bacterial communities in the same host populations. We show that yeast communities are dominated by a small number of abundant taxa, that the same yeast lineages are associated with different host species and populations, and that host diet has a greater effect than host species on yeast community composition. These patterns closely parallel those observed in Drosophila bacterial communities. However, we do not detect a significant correlation between the yeast and bacterial communities of the same host populations. Comparative analysis of different symbiont groups provides a more comprehensive picture of host-microbe interactions. Future work on the role of symbiont communities in animal physiology, ecological adaptation, and evolution would benefit from a similarly holistic approach.     

Application of temperature gradient gel electrophoresis to the study of yeast diversity in the estuary of the Tagus river,Portugal

Temperature gradient gel electrophoresis (TGGE) was employed for the assessment of yeast diversity in the estuary of the Tagus river (Portugal). The molecular detection of yeasts was carried out directly from water samples and, in parallel, a cultivation approach by means of an enrichment step was employed. A nested PCR was employed to obtain a fungal amplicon containing the D2 domain of the 26S rRNA gene. For identification the TGGE bands were extracted, re-amplified, and sequenced. Fourteen fungal taxa were detected and all except one were yeasts. Most yeast sequences corresponded to members of the Ascomycota and only three belonged to the Basidiomycota. Five yeasts (four ascomycetes and one basidiomycete) could not be identified to the species level due to the uniqueness of their sequences. The number of species detected after enrichment was higher than the number of taxa found using the direct detection method. This suggests that some yeast populations are present in densities that are below the detection threshold of the method. With respect to the analysis of the yeast community structure, our results indicate that the dominant populations belong to Debaryomyces hansenii, Rhodotorula mucilaginosa, Cryptococcus longus, and to an uncultured basidiomycetous yeast phylogenetically close to Cr. longus. The combined analysis of direct detection and cultivation approaches indicates a similar community structure at the two sampled sites since nine species were present at both localities.     

Antagonistic interactions between garden yeasts and microfungal garden pathogens of leaf-cutting ants

We investigate the diversity of yeasts isolated in gardens of the leafcutter ant Atta texana. Repeated sampling of gardens from four nests over a 1-year time period showed that gardens contain a diverse assemblage of yeasts. The yeast community in gardens consisted mostly of yeasts associated with plants or soil, but community composition changed between sampling periods. In order to understand the potential disease-suppressing roles of the garden yeasts, we screened isolates for antagonistic effects against known microfungal garden contaminants. In vitro assays revealed that yeasts inhibited the mycelial growth of two strains of Escovopsis (a specialized attine garden parasite), Syncephalastrum racemosum (a fungus often growing in gardens of leafcutter lab nests), and the insect pathogen Beauveria bassiana. These garden yeasts add to the growing list of disease-suppressing microbes in attine nests that may contribute synergistically, together with actinomycetes and Burkholderia bacteria, to protect the gardens and the ants against diseases. Additionally, we suggest that garden immunity against problem fungi may therefore derive not only from the presence of disease-suppressing Pseudonocardia actinomycetes, but from an enrichment of multiple disease-suppressing microorganisms in the garden matrix.     

Analysis of the community structure of yeasts associated with the decaying stems of cactus. II.Opuntia species

A survey was made of yeast species associated with the decaying pads of 3 prickly pear cacti (Opuntia phaeacantha, O. ficus-indica, andO. lindheimeri) in Arizona and Texas. Yeast communities from 12 localities were compared among localities, amongOpuntia species, and with previous data on yeast communities associated with columnar cacti. The results indicate thatOpuntia necroses contain relatively more yeast species with broader physiological abilities in their communities than columnar necroses. It is argued that differences in chemistry of the opuntias and columnar forms in concert with the insect vectors specific for these cacti account for the differences in yeast community structure. It is further hypothesized that the differences in yeast community structure have been important in the evolution and maintenance of species diversity forDrosophila species which live in the decaying stems or cladodes of various cacti. Most of the yeast community evolution in the cacti is postulated to have proceeded by evolution in situ and not by additions and replacements from outside of the system.     

Yeast colonizing the intestine of rainbow trout (Salmo gairdneri) and turbot (Scophtalmus maximus)

Yeast were isolated from the intestine of farmed rainbow trout (Salmo gairdneri), turbot (Scophtalmus maximus), and free-living flat-fish (Pleuronectes platessa and P. flesus). The average number of viable yeasts recovered from farmed rainbow trout was 3.0 × 10³ and 0.5 × 10² cells per gram homogenized intestine for white and red-pigmented yeasts, respectively. The dominant species were Debaryomyces hansenii, Saccharomyces cerevisiae, Rhodotorula rubra, and R. glutinis. In 5 of 10 free-lving marine fish, > 100 viable yeast cells per gram intestinal mucus were recovered. Red-pigmented yeasts dominated and composed >90% of the isolates. Colonization experiments were performed by inoculating rainbow trout and turbot with fish-specific, isolated yeast strains and by examining the microbial intestinal colonization at intervals. Inoculation of experimental fish with pure cultures of R. glutinis and D. hansenii HF1 yielded colonization at a level several orders of magnitude higher than before the inoculation. Up to 3.8 × 10⁴, 3.1 × 10⁶, and 2.3 × 10⁹ viable yeast cells per gram intestine or feces were recovered in three separate colonization experiments. The high level of colonizing yeasts persisted for several weeks. The concentrations of yeasts in the tank water never exceeded 10³ viable cells per milliliter. No traces of fish sickness as a result of high yeast colonization were recorded during any of the colonization experiments. For periods of the experiments, the concentration of aerobic bacteria in the fish intestine was lower than the intestinal yeast concentration. Scanning electron microscopy studies demonstrated a close association of the yeasts with the intestinal mucosa. The mucosal colonization was further demonstrated by separating intestinal content, mucus, and tissue. All compartments were colonized by >10³ viable yeast cells per gram. No bacteria were detected on the micrographs, indicating that their affinity for the intestinal mucosa was less than that of the yeasts. Correspondence to: Thomas Andtid     

Production of the Artemisinin Precursor Amorpha-4,11-diene by Engineered Saccharomyces cerevisiae

The gene encoding for amorpha-4,11-diene synthase from Artemisia annua was transformed into yeast Saccharomyces cerevisiae in two fundamentally different ways. First, the gene was subcloned into the galactose-inducible, high-copy number yeast expression vector pYeDP60 and used to transform the Saccharomyces cerevisiae strain CEN·PK113-5D. Secondly, amorpha-4,11-diene synthase gene, regulated by the same promoter, was introduced into the yeast genome by homologous recombination. In protein extracts from galactose-induced yeast cells, a higher activity was observed for yeast expressing the enzyme from the plasmid. The genome-transformed yeast grows at the same rate as wild-type yeast while plasmid-carrying yeast grows somewhat slower than the wild-type yeast. The plasmid and genome-transformed yeasts produced 600 and 100 μg/l of the artemisinin precursor amorpha-4,11-diene, respectively, during 16-days’ batch cultivation. Revisions requested 14 November 2005; Revisions received 17 January 2006     

Yeast communities in a natural tequila fermentation

Fresh and cooked agave,Drosophila spp., processing equipment, agave molasses, agave extract, and fermenting must at a traditional tequila distillery (Herradura, Amatitan, Jalisco, México) were studied to gain insight on the origin of yeasts involved in a natural tequila fermentations. Five yeast communities were identified. (1) Fresh agave contained a diverse mycobiota dominated byClavispora lusitaniae and an endemic species,Metschnikowia agaveae. (2)Drosophila spp. from around or inside the distillery yielded typical fruit yeasts, in particularHanseniaspora spp.,Pichia kluyveri, andCandida krusei. (3)Schizosaccharomyces pombe prevailed in molasses. (4) Cooked agave and extract had a considerable diversity of species, but includedSaccharomyces cerevisiae. (5) Fermenting juice underwent a gradual reduction in yeast heterogeneity.Torulaspora delbrueckii, Kluyveromyces marxianus, andHanseniaspora spp. progressively ceded the way toS. cerevisiae, Zygosaccharomyces bailii, Candida milleri, andBrettanomyces spp. With the exception ofPichia membranaefaciens, which was shared by all communities, little overlap existed. That separation was even more manifest when species were divided into distinguishable biotypes based on morphology or physiology. It is concluded that crushing equipment and must holding tanks are the main source of significant inoculum for the fermentation process.Drosophila species appear to serve as internal vectors. Proximity to fruit trees probably contributes to maintaining a substantialDrosophila community, but the yeasts found in the distillery exhibit very little similarity to those found in adjacent vegetation. Interactions involving killer toxins had no apparent direct effects on the yeast community structure.     

Basidiomycetous Yeasts from Boletales Fruiting Bodies and Their Interactions with the Mycoparasite <Emphasis Type="Italic">Sepedonium chrysospermum</Emphasis> and the Host Fungus <Emphasis Type="Italic">Paxillus</Emphasis>

Interactions between mushrooms, yeasts, and parasitic fungi are probably common in nature, but are rarely described. Bolete fruiting bodies are associated with a broad spectrum of microorganisms including yeasts, and they are commonly infected with filamentous mycoparasites of the genus Sepedonium (teleomorph Hypomyces). We report the isolation of 17 yeast strains from Paxillus and Xerocomus, 16 of which were obtained from the surface tissue, the primary site of Sepedonium infection. Phylogenetic analyses with the D1/D2 region of the 28S ribosomal gene and the internal transcribed spacers placed the yeasts as Rhodotorula, Rhodosporidium, and Mastigobasidium from the Pucciniomycotina, Cryptococcus, Cystofilobasidium, Holtermanniella, and Trichosporon from the Agaricomycotina, and Kluyveromyces from the Saccharomycotina including the first isolation of Rhodotorula graminis from Europe. To investigate the influence of the yeast strains on the mycoparasite and the host fungus, in vitro assays were conducted with Sepedonium chrysospermum and Paxillus involutus. Both S. chrysospermum growth inhibitory and stimulating yeast strains were detected among the isolates. The number of S. chrysospermum inhibitory yeast strains increased and the number of S. chrysospermum stimulatory yeast strains decreased in the presence of P. involutus in co-cultures. Low nutrient levels in the culture medium also led to an increased number of S. chrysospermum inhibitory yeast strains and ten yeasts inhibited the mycoparasite in spatial separation by a crosswall. Six yeast strains inhibited P. involutus in dual culture, and the inhibitory P. involutus yeast interactions increased to nine in the presence of S. chrysospermum. Our results suggest that the bolete-associated yeasts influence the growth of the mycoparasitic fungus, which may affect the health of the fruiting bodies.