Novel and selective microbial amperometric biosensors that use Gluconobacter oxydans cells to monitor the bacterial bioconversion of glycerol (Gly) to 1,3-propanediol (1,3-PD) are described. Two different mediators, ferricyanide and flexible polyvinylimidazole osmium functionalized polymer (Os-polymer), were employed to prepare two different microbial biosensors, both of which gave high detection performance. The good operational stabilities of both types of biosensor were underlined by the ability to detect 1,3-PD throughout 140 h of continuous operation. Both microbial biosensor systems showed excellent selectivity for 1,3-PD in the presence of a high excess of glycerol [selectivity ratios (1,3-PD/Gly) of 118 or 245 for the ferricyanide and Os-polymer systems, respectively]. Further, the robustness of each microbial biosensor was highlighted by the high reliability of 1,3-PD detection achieved (average RSD of standards<2%, and well below 4% for samples). The biosensor implementing the Os-polymer mediator exhibited high selectivity towards 1,3-PD detection and allowed moderate sample throughput (up to 12 h-1) when integrated into a flow system. This system was used to monitor the concentration of 1,3-PD during a real bioprocess. Results from biosensor assays of 1,3-PD in bioprocess samples taken throughout the fermentation were in a very good agreement with results obtained from reference HPLC assays (R2=0.999).

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Ethanol-tolerant and thermo-tolerant yeast strain Saccharomyces cerevisiae C11-3 cells immobilized in calcium pectate and calcium alginate gels were used for ethanol fermentation in a three-reactor system with a gradient temperature control. The fermentation process has been tested in a fixed-bed and a gas-lift arrangement. The gas-lift system was more efficient due to a better mass transport between the phases. Abrasion was more evident in calcium alginate particles, while calcium pectate beads were not significantly damaged. Two different concentrations of alginate were tested and calcium pectate gel was demonstrated to be more suitable as an immobilization material in comparison with calcium alginate due to its mechanical resistance and favourable diffusion parameters, providing an ethanol production of more than 7.5 g dm−3 h−1 over a period of 630 h.