Secretion of heterologous and native proteins, growth and morphology in batch cultures of Aspergillus niger B1-D at varying agitation rates

The influence of bioreactor operational conditions on the micromorphology o f batch cultures of Aspergillus niger B1-D, containing a hen egg white lyso zome (HEWL) marker protein, was examined using computerised image analysis. Significant differences in micromorphology were observed with increased st irrer speed, with shorter organisms with shorter hyphal elements occurring as agitation speed increased, even though mean tip numbers were similar. Th is may explain the observed increase in the total extracellular protein, si nce the ratio of synthetic (tip) to non-synthetic zones became increasingly favourable. HEWL concentrations fell above 500 rpm, probably due to the ef fects of DOT (dissolved oxygen tension) on the glucoamylase HEWL fusion. HE WL was susceptible to proteolytic degradation, by native proteases, during the autolytic phase. Such insights may indicate why a gene from one mould e xpressed in a close relative can give production levels equivalent to level s of native enzymes, while secretion of a gene from a 'distant' source, eg a higher eukaryotic gene, occurs at much lower levels. (C) 1999 Society of Chemical Industry.