Effect of feed cycling on plasmid stabilization during continuous fermentation: The case of variable plasmid loss probability

Abstract

The effect of feed cycling on the stability of plasmid-bearing cells during continuous fermentation has been analysed for the case where the probability of loss of the plasmid varies with time. The model consists of a system of delayed differential equations. By using a square-wave profile of the dilution rate, a two-fold increase in the concentration of plasmid-bearing cells and the recombinant product can be achieved over what is possible with a constant dilution rate. The dilution rate has a stronger effect than the frequency. These results agree qualitatively with reported experiments. The plasmid loss probability and the differential growth rate show fluctuations for a square-wave variation in the dilution rate, and even with a constant dilution rate they stabilise only after a length of time. These observations show that it is particularly important to account for variable plasmid loss probability in the initial phase of fermentation.On a analysk I'effet du cyclage de I'alimentation sur la stabilitC des cellules porteuses de plasmide en fermentation continue pour le cas oa la probabilitd de perte de plasmide varie dans le temps. Le modtle se compose d'un systtme d'kquations diffkrentielles retardkes. Avec un profil en ondes carrtes de la vitesse de dilution, on peut obtenir une augmentation dans la concentration de cellules porteuses de plasmide et le produit recombinant d'un facteur deux en comparaison & ce qui est possible avec une vitesse de dilution constante. La vitesse de dilution exerce un effet plus grand que la frequence. Ces rksultats montrent un bon accord qualitatif avec les expkriences dtcrites. La probabilitk de perte de plasmide et le taux de croissance diffkrentiel montrent des fluctuations pour une vitesse de dilution qui varie en ondes carrees, et m&me avec une vitesse de dilution constante ces deux facteurs se stabilisent seulement aprts un certain temps. Ces observations montrent qu'il est particulitrement important de tenir compte de la variabilitk de la probabilitk de perte de plasmide dans la phase initiale de fermentation.

Expression of GAL genes in a mutant strain of Saccharomyces cerevisiae lacking GAL80: quantitative model and experimental verification

“…The advent of genetic engineering has heralded the use of recombinant strains for the production of novel foreign proteins. Owing to the metabolic load introduced by the synthesis of foreign protein, the growth rate of the recombinant strain is less than that of the wild‐type [1–3]. One of the methods that can be employed to overcome this is to de‐link the growth and the protein‐production phase.…”

An evaluation of a neural network for the start-up phase of a continuous recombinant fermentation subject to disturbances

“…In the non-dimensional model r = tD a.nd, thus, for a. given time, r depends on the dilution rate. Recognising this, t was fixed at 1 hour, short enough to be within the start-up phase (Patnaik,1993b(Patnaik, ,1994b, and the end-point of r wa.s determined by the dilution rate D.…”