Mrakia fibulata sp. nov., a psychrotolerant yeast from temperate and cold habitats.

Tree fluxes are sugar-rich, sometimes ephemeral, substrates occurring on sites where tree sap (xylem or phloem) is leaking through damages of tree bark. Tree sap infested with microorganisms has been the source of isolation of many species, including the biotechnologically relevant carotenoid yeast Phaffia rhodozyma. Tree fluxes recently sampled in Germany yielded 19 species, including several psychrophilic yeasts of the genus Mrakia. Four strains from tree fluxes represented a potential novel Mrakia species previously known from two isolates from superficial glacial melting water of Calderone Glacier (Italy). The Italian isolates, originally identified as Mrakia aquatica, and two strains from Germany did not show any sexual structures. But another culture collected in Germany produced clamped hyphae with teliospores. A detailed examination of the five isolates (three from Germany and two from Italy) proved them to be a novel yeast species, which is described in this manuscript as Mrakia fibulata sp. nov. (MB 830398), holotype DSM 103931 and isotype DBVPG 8059. In contrast to other sexually reproducing Mrakia species, M. fibulata produces true hyphae with clamp connections. Also, this is the first psychrotolerant Mrakia species which grows above 20 °C. Spring tree fluxes are widespread and can be recognized and sampled by amateurs in a Citizen Science project. This substrate is a prominent source of yeasts, and may harbor unknown species, as demonstrated in the present work. The description of Mrakia fibulata is dedicated to our volunteer helpers and amateurs, like Anna Yurkova (9-years-old daughter of Andrey Yurkov), who collected the sample which yielded the type strain of this species.