Long-term cell viability of Rhodopseudomonas palustris immobilised in PVA-based hydrogels

A common problem associated with continuous bioprocesses are the risks of cell washout at high dilution rates, a problem which microbial immobilisation offers a solution for. Previously developed Polyvinyl alcohol-based hydrogels formed at ambient conditions provide suitable physical characteristics to be employed as an immobilisation material. In this study, the long-term cell viability of Rhodopseudomonas palustris immobilised in these hydrogels was investigated, as well as the effects which the gelation process has on the cell viability. The robustness of R. palustris allows for a lenient time frame for gelation and bead removal to occur. Approximately 48 hours is required before the beads can be easily removed from the molds, with cell viability starting to decrease around the 10-day point. Interestingly, the viable application period of the immobilised cells is not limited by cell degradation as previously suspected, but rather by the slow dissolution process of the PVA-based hydrogels. After an investigation period of just short of one year, the cells continued to exhibit a relative cell viability of 90 ± 11 % viable. However, after this period, the beads had lost approximately 50 – 60 % of their initial volume.