Investigation of repeated batch propagation strategy.

The repeated batch operation mode is generally considered to have the advantage of a higher productivity in comparison with other modes such as batch and continuous culture. This process is similar to fed batch process except that some culture volume is periodically removed from the vessel and replaced with fresh medium. In this study, batch cultivations of Schizosaccharomyces pombe (S. pombe) in shake flasks and in bioreactor was set up in a Edinburg minimal media (EMM2m) supplemented with glucose at 20 g/1. From these experiments the basic growth kinetics of S.pombe have been investigated. In order to determine the best operating conditions and to gain a better understanding of this organism, the effect of various culture conditions such as age and size of inoculum and the effect of initial glucose concentration on growth kinetics and on culture performance was studied. These results indicate that glucose is a limiting nutrient and can consume by the cells after 18 of the inoculation. The preliminary repeated batch cultivations in shake flasks were carried out under different harvest fractions. Variation in cell number during batches was observed using 80% as harvest fraction but cell concentration and glucose consumption in each cycle can be remain constant (steady state response) during repeated batch cultivation with 90% as harvest fraction. Therefor harvest fraction of 90% and dilution cycle time of 18 hr was selected for repeated batch cultivation in a bioreactor. Under this feeding policy, the experiments were accomplished using 9 and 20 batch cycles. Reproducible culture response was resulted by using this strategy. However In most cycle, cell number did not oscillated but in some cycles a fluctuation was observed which seems to represent chaotic cell dynamics. This study show that repeated batch cultivation can be applied as very reliable process and reproducible results can expected when other growth condition are constant. Thus applying this process is successful most of the time and high yield and productivity can be expected