Intermediates in the oxidative pathway from torulene to torularhodin in the red yeasts Cystofilobasidium infirmominiatum and C. capitatum (Heterobasidiomycetes, Fungi)

Two red Cystofilobasidium spp. isolated from spring sap-flows of Betula pendula were analysed for their carotenoid content. In Cystofilobasidiuminfirmominiatum, three unusual pigments were detected and identified by structure elucidation as oxidised torulene derivatives.These included 16'-hydroxytorulene and torularhodinaldehyde, two carotenoids known so far only from chemical synthesis or aspostulated biosynthetic intermediates en route to torularhodin. Unprecedented formation of beta-apo-2'-carotenal was also observed. Theproduction of these pigments in pure culture was dependent on enhanced oxidative stress caused by cultivation in well-aerated (indented)flasks with or without 2% ethanol (16'-hydroxytorulene), or with 100 lM duroquinone (torularhodinaldehyde and beta-apo-2'-carotenal).Among these three pigments, only 16'-hydroxytorulene was detected in C. capitatum. Torularhodin, a common end product of carotenoidoxidation in red yeasts, was not produced by either species under any incubation conditions. Biosynthetic aspects of incompleteoxidation of torulene by these Cystofilobasidium spp. are discussed.