High variability in a mating type linked region in the dry rot fungus Serpula lacrymans caused by frequency-dependent selection?

<p>Abstract</p> <p>Background</p> <p>The mating type loci that govern the mating process in fungi are thought to be influenced by negative frequency-dependent selection due to rare allele advantage. In this study we used a mating type linked DNA marker as a proxy to indirectly study the allelic richness and geographic distribution of mating types of one mating type locus (MAT A) in worldwide populations of the dry rot fungus <it>Serpula lacrymans</it>. This fungus, which causes serious destruction to wooden constructions in temperate regions worldwide, has recently expanded its geographic range with a concomitant genetic bottleneck.</p> <p>Results</p> <p>High allelic richness and molecular variation was detected in the mating type linked marker as compared to other presumably neutral markers. Comparable amounts of genetic variation appeared in the mating type linked marker in populations from nature and buildings, which contrast the pattern observed with neutral genetic markers where natural populations were far more variable. Some geographic structuring of the allelic variation in the mating type linked marker appeared, but far less than that observed with neutral markers. In founder populations of <it>S. lacrymans</it>, alleles co-occurring in heterokaryotic individuals were more divergent than expected by chance, which agrees with the expectation for populations where few mating alleles exists. The analyzed DNA marker displays trans-species polymorphism wherein some alleles from the closely related species <it>S. himantoides </it>are more similar to those of <it>S. lacrymans </it>than other alleles from <it>S. himantoides</it>.</p> <p>Conclusions</p> <p>Our results support the idea that strong negative frequency-dependent selection maintains high levels of genetic variation in MAT-linked genomic regions, even in recently bottlenecked populations of <it>S. lacrymans</it>.</p

Evolution of the dry rot fungus Serpula lacrymans and its allies

This thesis focuses on the natural history of the dry rot fungus Serpula lacrymans and closely related taxa within Serpulaceae. In the first study the phylogenetic relationships within Serpulaceae have been investigated using multi-locus sequencing. In the resulting phylogeny, two mycorrhiza-forming genera, Austropaxillus and Gymnopaxillus, form a monophyletic group nested within the saprotrophic genus Serpula. This confirms a transition from brown-rot to ectomycorrhizal life style that happened once in a monophyletic Serpulaceae, probably between 60 and 40 million years ago in western North America or, alternatively, in Southern temperate regions after long distance dispersal from North America. The second study deals with cryptic speciation within the species complex Serpula himantioides which is the sister species to S. lacrymans. Evidence is provided for five cryptic species by four independent gene phylogenies. One of the phylogenetic species shows little phylogeographical structure at a global scale, indicating recent long-distance dispersal. Some of the lineages show adaptation to certain substrates. North and South America appear as the centre of divergence within this morphospecies. In study III the origin and further worldwide spread of S. lacrymans have been analysed employing different molecular markers. Evidence is provided for that S. lacrymans is divided into two main lineages that probably represent well-differentiated cryptic species; one nonaggressive residing naturally in North America and Asia (var. shastensis), and another aggressive lineage including specimens from all continents, both from natural environments and buildings (var. lacrymans). Mainland Asia is pinpointed as the origin of the aggressive form var. lacrymans, and a few aggressive genotypes have migrated worldwide from Asia to Europe, North and South America and Oceania followed by local population expansions. The fourth study provides a detailed survey of two major invasive populations of S. lacrymans; one from Japan and one from Europe. Both populations have gone through population bottlenecks prior to local expansion. The European population is extremely genetically depleted leading to the presence of only a few VC types in Europe, while the Japanese population appears to be influenced by higher gene flow from the Asian source population and, correspondingly, more VC types occur in Japan. Clonal dispersal seems very infrequent in both populations. In study V, global distribution and richness of mating types (MAT A) in S. lacrymans was studied using a mating type linked genetic marker as a proxy. A high allelic richness and molecular variation was detected in the mating type linked marker as compared to other presumably neutral markers. Little geographic variation was observed in this marker as a contrast to other markers investigated earlier. We observed trans-specific polymorphisms as some alleles from the closely related species S. himantioides are more similar to those of S. lacrymans than other alleles from S. himantioides. Altogether, this thesis illuminates the evolutionary background and the population genetics of the devastating dry rot fungus

Analyzing indoor mycobiomes through a large‐scale citizen science study in Norway

In the built environment, fungi can cause important deterioration of building materials and adverse health effects on occupants. Increased knowledge about indoor mycobiomes from different regions of the world, and their main environmental determinants, will enable improved indoor air quality management and identification of health risks. This is the first citizen science study about indoor mycobiomes at a large geographical scale in Europe, including 271 houses from Norway and 807 dust samples from three house compartments: outside of the building, living room and bathroom. The fungal community composition determined by DNA metabarcoding was clearly different between indoor and outdoor samples, but there were no significant differences between the two indoor compartments. The 32 selected variables, related to the outdoor environment, building features and occupant characteristics, accounted for 15% of the overall variation in community composition, with the house compartment as the key factor (7.6%). Next, the climate was the main driver of the dust mycobiomes (4.2%), while building and occupant variables had significant but minor influences (1.4% and 1.1%, respectively). The house‐dust mycobiomes were dominated by ascomycetes (⁓70%) with Capnodiales and Eurotiales as the most abundant orders. Compared to the outdoor samples, the indoor mycobiomes showed higher species richness, which is probably due to the mixture of fungi from outdoor and indoor sources. The main indoor indicator fungi belonged to two ecological groups with allergenic potential: xerophilic molds and skin‐associated yeasts. Our results suggest that citizen science is a successful approach for unraveling the built microbiome at large geographical scales

The Indoor Mycobiomes of Daycare Centers Are Affected by Occupancy and Climate

13 páginas. 4 figuras.- 4 tablas.- 53 referencias.-Supplemental material is available online onlyMany children spend considerable time in daycare centers and may be influenced by the indoor microorganisms there, including fungi. In this study, we investigate the indoor mycobiomes of 125 daycare centers distributed along strong environmental gradients throughout Norway. Dust samples were collected from doorframes outside and inside buildings using a community science sampling approach. Fungal communities in the dust samples were analyzed using DNA metabarcoding of the internal transcribed spacer 2 (ITS2) region. We observed a marked difference between the outdoor and indoor mycobiomes. The indoor mycobiomes included considerably more yeasts and molds than the outdoor samples, with Saccharomyces, Mucor, Malassezia, and Penicillium being among the most dominant fungal genera. Changes in the indoor fungal richness and composition correlated with numerous variables related to both outdoor and indoor conditions; there was a clear geographic structure in the indoor mycobiome composition that mirrored the outdoor climate, ranging from humid areas in western Norway to drier and colder areas in eastern Norway. Moreover, the number of children in the daycare centers, as well as various building features, influenced the indoor mycobiome composition. We conclude that the indoor mycobiomes in Norwegian daycare centers are structured by multiple factors and are dominated by yeasts and molds. This study exemplifies how community science sampling enables DNA-based analyses of a high number of samples covering wide geographic areas.This research was financially supported by the University of Oslo and the Norwegian Asthma and Allergy Association (NAAF). P.M.M.-S. was funded by the European Union’s Horizon 2020 research and innovation program (Marie Skłodowska-Curie individual fellowship; grant agreement MycoIndoor no. 741332).Peer reviewe