The CSP 'Evaluating the role of fungal endosymbionts in fungal mating and evolution' (Proposal ID: 505815) aims to investigate how endohyphal bacterial symbionts influence the sexual reproduction of their fungal hosts. Isolate BESC-56 was collected northeast of Corvallis, OR, in a community garden of Populus trichocarpa, and was associated with the soil of P. trichocarpa genotype BESC-56.
This project focuses primarily on the Mortierellaceae, a family of non-Dikaryan soil fungi belonging to the subphylum Mortierellomycotina (phylum Mucoromycota). Previous work has demonstrated that the Burkholderia-related endohyphal bacterium described as Mycoavidus cysteinexigens is metabolically dependent upon its fungal host (Linnemannia elongata) for cysteine, due to an incomplete cysteine biosynthetic pathway. Additional work has revealed that bacterial presence is correlated with a decreased production of sexual spores (zygospores), but the genetic and biochemical mechanisms by which this phenomenon occurs remain elusive.
The Mortierellaceae are frequently isolated from soil collected from the fine roots of vascular plants, and isolates have been collected from all seven continents (including Antarctica). Linnemannia elongata is commonly isolated from soil samples using chitin-based baiting methods, due to having an expanded repertoire of chitinase enzymes. Although these fungi are ubiquitous and up to half of isolates harbor endobacteria, much remains unresolved regarding the role bacterial endosymbionts play in the reproductive success and evolutionary history of these fungi. To date, Linnemannia elongata sexual spores (zygospores) have been observed exclusively in heterothallic outcrossing experiments, although homothallism has been reported for other species within the Mortierellaceae (e.g. Entomortierella sugadairana).
