Oxidative stress and nitrosative stress, their interaction and implications for bioprocessing

The present study focuses on a series of physiological studies to study oxidative and nitrosative stress and online monitoring of fungal biomass growth in submerged batch cultures of the filamentous fungus Aspergillus niger B1-D, modified to secrete lysozyme. The results of the undertaken studies described here show that increasing concentrations of polymyxin B, added to a bioreactor, increase oxidative stress during cultivation of Aspergillus niger B1-D in a bioreactor. This was shown by the increased superoxide dismutase (SOD) and catalase (CAT) activities after addition of polymyxin B. This increased oxidative stress also results in a decrease in production of lysozyme, which is at least 75% lower in all polymyxin B processes. Varying oxygen transfer rate (OTR), by changing the stirring rate, in the lag phase of a batch fermentation, utilising the Aspergillus niger B1-D strain, results in increased oxidative stress with increased stirring rates. The resulting lysozyme production was at least 75% lower compared to the optimum agitation setting. This optimum setting was 200-400 rpm, which was controlled by the dissolved oxygen tension. Adding increasing amounts of sodium nitroprusside (SNP) reduces oxidative stress resulting in an increased production of lysozyme. The use of SNP also showed increased CAT activities, which points towards an interaction between oxidative and nitrosative stress due to the release of nitric oxide from SNP. Applying an online biomass sensor (Buglab) during batch cultivation of Aspergillus niger B1-D showed that this sensor can accurately monitor fungal biomass growth from 7 g/l onwards.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2014

Author dc:creator

• Kretzers, Ivo

DOI

10.48730/9v97-9a64

Identifier

T13641

OAI identifier oai:identifier

oai:strathclyde:nv935286k