Flow cytometry for bioprocess control

University dissertation from Stockholm : Bioteknologi

Abstract: During bio-technical processing it is important to monitorbiological parameters such as cell growth, viability andproduct formation. Many of the analyses traditionally used areslow to perform and provide only average data for thepopulation. Flow cytometry is a laser-based technique, whichmeasures physical properties of a cell in a flowing stream, ata rate of several thousand cells per second. It offers theprospect of an at-line, multi-parameter analysis of individualmicroorganisms in a population.In this project several methods for at-line measurements ofbioprocesses were developed such as protocol's for measuringcell concentration, viability and product formation. Theprimary focus was on prokaryotic organisms (E. coli) but eukaryotic organisms (P. pastoris) were included.The possibility to use volumetric cell counting to measurecell concentration (cell number) was evaluated. It was shownthat the method was applicable for high cell density processesof bothE. coliandP. pastoris.The combination of Bis- (1,3-dibutylbarbituric acid)trimethine oxonol (depolarised membranes) and propidium iodide(loss of membrane integrity) as fluorescent markers was usefulto measure viability at-line of cells in high cell densityprocesses. The protocol was shown to be reproducible forE. coliandP. pastoris.The viability staining was used to study the kinetics ofweak organic acids (food preservatives). The protocol provideddata about cell functions such as membrane depolarisation andloss of membrane integrity caused by introducing weak organicacids to shake flask cultures ofE. coli.Labeling inclusion bodies with fluorescent antibodiesprovided a method, which could specifically monitor theincreased accumulation of recombinant promegapoetin proteinwith process time. This technique was further developed forintracellular staining by application of a permeabilising stepbefore labeling with antibodies. Staining of inclusion bodiesdirectly inside permeabilised cells gave information about thedistribution of protein expression in the cell population.In conclusion, flow cytometry provides an at-line, singlecell technique for measurement of several biological parametersin bioprocesses.Key words: flow cytometry, Partec PAS, propidium iodide(PI), bis- (1,3-dibutylbarbituric acid) trimethine oxonol(BOX), Alexa fluor 488, bioprocess,E. coli,P. pastoris, inclusion body, food preservatives,viability, membrane potential