Novel Insights into Filtration Studies of Streptomyces Coelicolor Fermentation Broth for Inoculation of Membrane Gradostat Reactor

Abstract

Secondary metabolites are mostly produced in batch or fed-batch mode because the limiting environment necessary for this kind of metabolism cannot be maintained on the long run during conventional fermentation. A membrane gradostat reactor (MGR) could offer a possible solution for this issue since its special design enables permanent biofilm renewal and secondary metabolite production at the same time. In this research, the inoculation of MGR with Streptomyces coelicolor and some of the factors influencing this process were investigated. In the first series of experiments, fermentation broths were filtrated in dead-end mode at three different pH values in order to determine the specific cake resistance. In the second part of the work, two types of capillary membrane modules were inoculated with reverse filtration. All experiments were carried out with two types of broth differing in harvest time. The results of dead-end filtration indicate that both pH value and ageing have a complex impact on filtration properties since αmin and µmax did not coincide in case of neither broth, which would be expected based on filtration equation; moreover, trends of alpha imply that the isoelectric point of the broth varies with harvest time. Maximal alpha (5.1*1015 m/kg) was measured by the more mature broth at pH 7 while all the other alpha values fell between 7.0*1012 and 8.8*1013 m/kg. During inoculation of membrane modules, neither considerable gel layer nor clogging of the pores could be observed. Therefore, these modules are not suitable for inoculation with Streptomyces coelicolor among the investigated circumstances.