Biotechnology and Bioengineering, Vol.65, No.4, 416-424, 1999
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 Aspergillus niger (B1-D), secreting both a heterologous enzyme (Hen Egg White Lysozyme [HEWL]) and a native enzyme (Glucoamylase), to varying levels of O-2 enrichment of the process gas was evaluated. Formation of both the native and the 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 apparent ;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, sparsely branched hyphal elements, with low percentages of "active" length (i. e. how much of the hypha is cytoplasm filled); whilst, a second micromorphology, typical of O-2 enriched cultures at 30 and 50% O-2 enrichment, was represented by shorter hyphal elements, with more branching and a higher % "active" length. At these higher O-2 levels, formation of a yellow pigment occurred, and signs of culture autolysis were noted. At 50% enrichment, a "stranded" aggregate morphology was apparent, possibly as a response to a hyperoxidant state. Production of both the native enzyme and HEWL correlated well with a simple morphological measure (tip number) or, with % "active" length. It is proposed the morphological changes noted in the cultures were associated with the increased production of both HEWL and glucoamylase.
Keywords:PENICILLIUM-CHRYSOGENUM;IMAGE-ANALYSIS;ALPHA-AMYLASE;FILAMENTOUS MICROORGANISMS;BATCH CULTIVATIONS;NEUROSPORA-CRASSA;STRUCTURED MODEL;WALL GROWTH;ORYZAE;GLUCOAMYLASE