A HIGH-AFFINITY ZN2+ UPTAKE SYSTEM CONTROLS GROWTH AND BIOSYNTHESIS OF AN EXTRACELLULAR, BRANCHED BETA-1,3-BETA-1,6-GLUCAN IN SCLEROTIUM-ROLFSII ATCC-15205

The plant pathogenic fungus imperfectusSclerotium rolfsii ATCC 15025 requires Zn2+ for both growth and biosynthesis of an extracellular, branched β-1,3-β-1,6-glucan in a completely defined mineral medium. Upon rising the external zinc concentration an increased yield of glucan inversely proportional to the yield of biomass was found in the cultivations with the bioreactor, but not in those with shake flasks. The complete carbon balance presented includes oxalic acid as an additional metabolite, secreted in rather high amounts due to the reduced oxygen supply in the viscous culture suspension. Only low amounts of zinc were accumulated. The successful development of an assay for the uptake of65Zn2+ by homogeneous suspensions of zinc-depleted cultures ofS. rolfsii is reported. An energy-dependent highly specific Zn2+ uptake system, sufficient for growth and glucan synthesis, but no efflux system was demonstrated inS. rolfsii. © 1991 Academic Press, Inc.