Genome sequencing of four Aureobasidium pullulans varieties: biotechnological potential, stress tolerance, and description of new species

Basidioascus undulatus: genome, origins, and sexuality

Basidioascus undulatus is a soil basidiomycete belonging to the order Geminibasidiales. The taxonomic status of the order was unclear as originally it was only tentatively classified in the class Wallemiomycetes. The fungi in Geminibasidiales have an ambiguously defined sexual cycle. In this study, we sequenced the genome of B. undulatus to gain insights into its sexuality and evolutionary origins. The assembled genome draft was approximately 32 Mb in size, had a median nucleotide coverage of 24X, and contained 6123 predicted genes. Previous morphological descriptions of B. undulatus relied on interpretation of putative sexual structures. In this study, nuclear staining and confocal microscopy showed meiosis occurring in basidia and genome analysis confirmed the existence of genes involved in meiosis and mating. Using 35 protein-coding genes extracted from genomic information, phylogenomic and molecular dating analyses confirmed that B. undulatus indeed belongs to a lineage distantly related to Wallemia while retaining a basal position in Agaricomycotina. These results, combined with differences in septal pore morphology, led us to move the order Geminibasidiales out of the Wallemiomycetes and into the new class Geminibasidiomycetes cl. nov. Finally, the concept of Agaricomycotina is emended to include both Wallemiomycetes and Geminibasidiomycetes.

Non-rainfall moisture activates fungal decomposition of surface litter in the Namib Sand Sea

The hyper-arid western Namib Sand Sea (mean annual rainfall 0-17 mm) is a detritus-based ecosystem in which primary production is driven by large, but infrequent rainfall events. A diverse Namib detritivore community is sustained by minimal moisture inputs from rain and fog. The decomposition of plant material in the Namib Sand Sea (NSS) has long been assumed to be the province of these detritivores, with beetles and termites alone accounting for the majority of litter losses. We have found that a mesophilic Ascomycete community, which responds within minutes to moisture availability, is present on litter of the perennial Namib dune grass Stipagrostis sabulicola. Important fungal traits that allow survival and decomposition in this hyper-arid environment with intense desiccation, temperature and UV radiation stress are darkly-pigmented hyphae, a thermal range that includes the relatively low temperature experienced during fog and dew, and an ability to survive daily thermal and desiccation stress at temperatures as high as 50°C for five hours. While rainfall is very limited in this area, fog and high humidity provide regular periods (≥ 1 hour) of sufficient moisture that can wet substrates and hence allow fungal growth on average every 3 days. Furthermore, these fungi reduce the C/N ratio of the litter by a factor of two and thus detritivores, like the termite Psammotermes allocerus, favor fungal-infected litter parts. Our studies show that despite the hyper-aridity of the NSS, fungi are a key component of energy flow and biogeochemical cycling that should be accounted for in models addressing how the NSS ecosystem will respond to projected climate changes which may alter precipitation, dew and fog regimes.

β-(1 → 3)-Glucanolytic yeasts from Brazilian grape microbiota: production and characterization of β-glucanolytic enzymes by Aureobasidium pullulans 1WA1 cultivated on fungal Mycelium

A total of 95 yeast strains were isolated from the microbiota of different grapes collected at vineyards in southern Brazil. The yeasts were screened for β-(1 → 3)-glucanases using a newly developed zymogram method that relies upon the appearance of clearance zones around growing colonies cultured on agar–botryosphaeran medium and also by submerged fermentation on nutrient medium containing botryosphaeran, a (1 → 3),(1 → 6)-β-d-glucan. Among 14 β-(1 → 3)-glucanase-positive yeasts identified, four strains produced the highest β-glucanolytic activities and were evaluated for enzyme production on cellobiose, botryosphaeran, and mycelial biomass from Botryosphaeria rhodina (MAMB-05). Yeast strain 1WA1 produced the highest β-(1 → 3)-glucanase and β-glucosidase activities and was identified by molecular characterization as Aureobasidium pullulans. The physicochemical properties of the crude β-glucanolytic enzyme preparation were characterized, and the preparation was used to hydrolyze several β-d-glucans (laminarin, botryosphaeran, lasiodiplodan, pustulan, and curdlan). The production and physicochemical properties of the β-glucanolytic preparation enable its potential applications in wine enology and production of prebiotics through hydrolysis of β-d-glucans.

Chaophilic or chaotolerant fungi: a new category of extremophiles?

It is well known that few halophilic bacteria and archaea as well as certain fungi can grow at the highest concentrations of NaCl. However, data about possible life at extremely high concentrations of various others kosmotropic (stabilizing; like NaCl, KCl, and MgSO4) and chaotropic (destabilizing) salts (NaBr, MgCl2, and CaCl2) are scarce for prokaryotes and almost absent for the eukaryotic domain including fungi. Fungi from diverse (extreme) environments were tested for their ability to grow at the highest concentrations of kosmotropic and chaotropic salts ever recorded to support life. The majority of fungi showed preference for relatively high concentrations of kosmotropes. However, our study revealed the outstanding tolerance of several fungi to high concentrations of MgCl2 (up to 2.1 M) or CaCl2 (up to 2.0 M) without compensating kosmotropic salts. Few species, for instance Hortaea werneckii, Eurotium amstelodami, Eurotium chevalieri and Wallemia ichthyophaga, are able to thrive in media with the highest salinities of all salts (except for CaCl2 in the case of W. ichthyophaga). The upper concentration of MgCl2 to support fungal life in the absence of kosmotropes (2.1 M) is much higher than previously determined to be the upper limit for microbial growth (1.26 M). No fungal representatives showed exclusive preference for only chaotropic salts (being obligate chaophiles). Nevertheless, our study expands the knowledge of possible active life by a diverse set of fungi in biologically detrimental chaotropic environments.