Tritirachium egenum, a thiamine- and siderophore-auxotrophic fungal species isolated from a Penicillium rugulosum

Abstract

Tritirachium egenum sp. nov., a biotrophic mycosymbiont, was found growing in association with a Penicillium rugulosum. This new species was unable to grow in axenic culture on traditional semi-synthetic culture media unless the growth medium was supplemented with a fraction of the culture filtrate of its host. The hot water extract of Alternaria alternata, containing the 'growth factor' of several contact mycosymbionts (biotrophic contact mycoparasites) also supported the growth of T. egenum. Signs, particularly the functional equivalence of this extract and ferrichrome on the T. egenum growth, suggested that this growth factor, referred to in the literature as mycotrophein, could actually be a hydroxamate-type siderophore. Moreover, it was shown that this siderophore-dependent organism had a deficient metabolism requiring, in addition, an exogenous source of thiamine or a precursor molecule of thiamine. Among mycosymbionts of fungi, the nutrient acquisition strategy of T. egenum is new, because it did not live in close association with the cytoplasm of its host. Indeed, it is neither a haustorial mycosymbiont nor a contact mycosymbiont, the two groups into which the biotrophic mycosymbionts of fungi are classified. Moreover, an interfungal association based on the utilization of siderophores has not yet been reported.

Phylogenetic placement of Tritirachium strains from the URM culture collection originally founded by Augusto Chaves Batista (1916-1967) in Brazil, and the description of T. batistae sp. nov.

“…was isolated from a sponge present in the Adriatic Sea (Wang et al 2016). Another Tritirachium strain was isolated as a symbiont associated with Penicillium rugulosum (Beguin 2010).…”

Improving Fungal Cultivability for Natural Products Discovery

“…Likewise, controlled experiments may be difficult to conduct due to the chemical variation of natural exudates and extracts over time and space. A more far-reaching alternative for the host-dependent culturing would be to isolate and characterize growth factors of different types of symbiotic fungi and test these chemical entities for their ability to induce growth in a broader selection of symbiotic fungi, as nicely demonstrated with the discovery and characterization of mycotrophein that was shown to be a hydroxamate-type siderophore (Barnett and Lilly, 1958;Whaley and Barnett, 1963;Beguin, 2010). Repeating such a workflow in a systematic manner could contribute to characterizing several new growth factors that could be applied to culturing as-yet-uncultured fungi in a reproducible and controlled manner.…”

“…In addition to carbon and nitrogen sources and necessary minerals required for any microbiological medium, MMN contains the known growth factors glucose (as part of sucrose), thiamine ( Supplementary Table 2 ), and iron. Iron has an important function as catalyst of cellular reactions in fungi and for this reason fungi enhance its uptake from the environment using siderophores that are shown to facilitate growth of a previously uncultured fungus ( Johnson, 2008 ; Beguin, 2010 ).…”

Delimiting species in Basidiomycota: a review

“…Later, he accepted T. cinnamomeum and T. isariae (de Hoog 1973). Beguin (2010), still only using morphological, physiological, and ecological data, described T. egenum to accommodate a biotrophic mycosymbiont growing in close association with Penicillium rugulosum. Interestingly, this species could initially not be grown in axenic culture, but using a hot water extract of Alternaria alternata allowed growth in vitro.…”