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

Abstract

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 O2 enrichment of the process gas was evaluated. Formation of both the native and the foreign enzyme increased with increasing O2 supply. Conversely, biomass levels and total extracellular protein levels were generally not increased under O2 enriched conditions. Two distinct micromorphologies were apparent in these cultures, one, typically seen under O2 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 O2 enriched cultures at 30 and 50% O2 enrichment, was represented by shorter hyphal elements, with more branching and a higher % "active" length. At these higher O2 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.

Oxidative stress in fungal fermentation processes: the roles of alternative respiration

“…Gassing batch cultures of A. niger with O 2 -enriched air decreases the size of hyphal elements and increases the proportion of active cytoplasm, but hyphal adhesion occurs at the highest level of O 2 enrichment (50% v/v) (Wongwicharn et al 1999). Similar results have been found where O 2 enrichment results in branched and shorter hyphae (Kreiner et al 2003;Bai et al 2004).…”

“…Oxidative stress, caused by over-oxygenation to bioreactors, adversely affects the production of a recombinant protein from A. niger (Wongwicharn et al 1999;Bai et al 2004). Thus, mitigating oxidative damage could ultimately increase protein production by fungi.…”

Agitation effects on morphology and protein productive fractions of filamentous and pelleted growth forms of recombinant Aspergillus niger

“…The morphology of Aspergillus, filamentous growth forms and/or the shape and size of pelleted growth forms as well as the branching frequency, is influenced by many factors including specific strain properties [22] but also environmental factors such as spore numbers in the inoculum or type of inoculum [23][24][25], medium composition [23,[26][27][28], dissolved oxygen concentration [29][30][31], pH [23,32], temperature [23,27], reactor type and scale [27,33], and power input [23,25,26,28,29,[33][34][35][36].…”

Production of glucose oxidase and catalase by Aspergillus niger free and immobilized in alginate-polyvinyl alcohol beads

“…It is known that the intra-and extracellular CAT and GOX production was related neither to the fungal biomass nor to the size of the pellets, and that catalase production may be directly related to the external layer of the pellet and precisely to the morphology of the hyphae in this region. It has been shown that the ramified morphological form of the hyphae has an important influence on the formation of a range of metabolites by filamentous fungi (Wongwicharn et al, 1999) and that secretion of proteins is primarily associated with the apical and subapical regions, therefore called the active regions (Nykanen et al, 1997;Agger et al, 1998). Immobilization in PVA/alginate beads probably changed some characteristics of the culture, are reflected in the protein excretion and enzyme activities.…”