Effect of oxygen enrichment on morphology, growth, and heterologous protein production in chemostat cultures of Aspergillus niger B1-D

The response of steady state chemostat cultures of a recombinant Aspergillu s niger (B1-D), secreting both a heterologous enzyme (Hen Egg White Lysozym e [HEWL]) and a native enzyme (Glucoamylase), to varying levels of O-2 enri chment of the process gas was evaluated. Formation of both the native and t he foreign enzyme increased with increasing O-2 supply. Conversely, biomass levers and total extracellular protein levels were generally not increased under O-2 enriched conditions. Two distinct micromorphologies were apparen t ;in these cultures, one, typically seen under O-2 limiting conditions (i. e. at 0 and 10% enrichment levels) tended to be represented by Long, spars ely branched hyphal elements, with low percentages of "active" length (i. e . how much of the hypha is cytoplasm filled); whilst, a second micromorphol ogy, typical of O-2 enriched cultures at 30 and 50% O-2 enrichment, was rep resented by shorter hyphal elements, with more branching and a higher % "ac tive" length. At these higher O-2 levels, formation of a yellow pigment occ urred, and signs of culture autolysis were noted. At 50% enrichment, a "str anded" aggregate morphology was apparent, possibly as a response to a hyper oxidant state. Production of both the native enzyme and HEWL correlated wel l with a simple morphological measure (tip number) or, with % "active" leng th. It is proposed the morphological changes noted in the cultures were ass ociated with the increased production of both HEWL and glucoamylase. (C) 19 99 John Wiley & Sons, Inc.