Biosynthesis of the xanthophyll plectaniaxanthin as a stress response in the red yeast Dioszegia (Tremellales, Heterobasidiomycetes, Fungi)

Abstract

Carotenoid biosynthesis was examined in a phylloplane yeast identified by ITS, 18S and 28S rDNA analysis as a Dioszegia sp. close to D. takashimae. In well-aerated flask or fermentor cultures, this strain produced essentially a single pigment confirmed as the xanthophyll plectaniaxanthin by NMR analysis, at concentrations of 103–175 μg g −1 biomass dry weight. Detailed studies showed increases in plectaniaxanthin concentrations in the presence of 5 mM hydrogen peroxide (1.8-fold), 50 and 100 μM duroquinone (3.1- and 3.7-fold, respectively), and 2% ethanol (4.9-fold). Whereas oxidative stress is known to enhance the biosynthesis of torularhodin or astaxanthin in other red yeasts where they are associated with an antioxidant function, this is the first report implicating plectaniaxanthin in a similar role. At reduced aeration, biosynthesis of plectaniaxanthin was suppressed and its putative precursor γ-carotene accumulated. The carotenoid cyclase inhibitor nicotine (5–20 mM) inhibited plectaniaxanthin formation, with lycopene accumulating stoichiometrically. Hydroxy groups at C-1′ and C-2′ therefore seem to be introduced late in plectaniaxanthin biosynthesis, following cyclization of the β-ionone ring.