The effects of bioprocess parameters on extracellular proteases in a recombinant <Emphasis Type="Italic">Aspergillus niger</Emphasis> B1-D |
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Authors: | Qiang Li Linda M Harvey Brian McNeil |
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Affiliation: | (1) Strathclyde Fermentation Centre, Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 204 George Street, Glasgow, G1 1XW, UK |
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Abstract: | Although host proteases are often considered to have a negative impact upon heterologous protein production by filamentous
fungi, relatively little is known about the pattern of their appearance in recombinant fungal bioprocesses. In the present
study, we investigated extracellular proteases from a filamentous fungus, Aspergillus niger B1-D, genetically modified to secrete hen egg white lysozyme (HEWL). Our findings indicate that extracellular protease activity
is only detected after the carbon source is completely utilised in batch cultures. The proteases are predominantly acid proteases
and have optimal temperature for activity at around 45°C. Their activity could be partially inhibited by protease inhibitors,
indicating the existence of at least four kinds of proteases in these culture fluids, aspartic-, serine-, cysteine-, and metallo-proteases.
Oxygen enrichment does not have any noticeable effects on extracellular protease activity except that the onset of protease
activity appears earlier in oxygen enrichment runs. Oxygen enrichment stimulates HEWL production substantially, and we propose
that it is related to fungal morphology. Thermal stress imposed by raising process temperature (from 25 to 30 and 35°C) in
early exponential phase, led to appearance of protease activity in the medium following the heat shock. Continued cultivation
at high temperatures significantly reduced HEWL production, which was associated with increased activity of the extracellular
proteases in these cultures. |
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Keywords: | Heterologous protein Extracellular proteases Hen egg white lysozyme Aspergillus niger Fermentation |
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