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Summary. Increasing the temperature in chemostat culture of Zymomonas mobilis ATCC 29 191 with low and high glucose concentrations was found to result in a decreasing frequency of septation leading to the formation of long filaments and in increasing outer membrane blebbing. Whether this effect is strain specific or universal in Zymomonas is, unknown. Improvements in the fermentation kinetics could be achieved at elevated temperatures, with an optimum at 33°C.

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SummaryThe performance of Zymomonas mobilis strains ATCC 31 821 and ATCC 31 823 was assessed in batch and continuous culture. In batch culture using a medium containing 250 g/1 glucose, identical maximum specific growth rates of 0.16/h were found, though final biomass concentration and growth yield were significantly lower for ATCC 31 823 than for ATCC 31 821. Final ethanol concentrations in this medium were about 110 g/1 vor both organisms. In continuous culture at increasing dilution rates using a medium containing 100 g/1 glucose, no significant differences were seen between the two strains with respect to the fermentation parameters studied. For ATCC 31 821, maximum rates of glucose uptake (Q~) and ethanol produktion (Qp) of 8.7 g glu/g/h and 4.4 g eth/g/h, respectively, were found. Both strains showed a similar performance at a fixed dilution rate of 0.l/h, where maximum ethanol concentrations of about 68 g/l were reached at a feed glucose concentration of about 139 g/l. At this dilution rate the maximum values of Qs and Qp were about 5.8 g glu/g/h and 2.8 g eth/g/h, respectively. Test tube experiments showed that growth, measured as optical density, Offprint requests to: N. Stevnsborg