Regulation of Nigeran Accumulation by Aspergillus aculeatus

Nigeran (mycodextran), an unbranched glucan consisting of alternating α,1–4 and α,1–3 linkages, is accumulated intracellularly byAspergillus aculeatus , under conditions of nitrogen limitation and lowp H (optimump H 5.0). Both conditions are necessary. Nigeran is synthesized de novo from exogenous glucose and accounts for about 20% of the glucose transported by the mycelium. The polymer is diluted out but not degraded when the mycelium is transferred to fresh medium containing NH4 + . Cycloheximide prevents development of the nigeran biosynthetic system. The addition of substrate levels of NH4 + to nigeran-accumulating mycelium immediately suppresses further nigeran buildup, presumably by diverting glucose to the biosynthesis of amino acids, nucleotides, etc.