Simultaneous ethanol and bacterial ice nuclei production from sugar beet molasses by a Zymomonas mobilis CP4 mutant expressing the inaZ gene of Pseudomonas syringae in continuous culture

Aim: The aim of this work was to construct a Zymomonas mobilis mutant capab le of simultaneous ethanol and ice nuclei production from agricultural by-p roduct such as sugar beet molasses, in steady-state continuous culture. Methods and Results: A sucrose-hypertolerant mutant of Z. mobilis strain CP 4, named suc(40), capable of growing on 40% (w/v) sucrose medium was isolat ed following N-methy-N'-nitro-N-nitrosoguanidine treatment. Plasmid pDS3154 carrying the inaZ gene of Pseudomonas syringae was conjugally transferred and expressed in suc(40). The potential for simultaneous ethanol and bacter ial ice nuclei production was assessed in steady-state continuous cultures over a range of dilution rates from 0.04 to 0.13 h(-1). In addition, the fa tty acid and phospholipid profile of the three strains was also investigate d. Ethanol production up to 43 g l(-1) was achieved at dilution rates below 0.10 h(-1) in sugar beet molasses. Ice nucleation activity gradually incre ased with increasing dilution rate and the greatest activity, -3.4 log (ice nuclei per cell), was observed at the highest dilution rate (0.13 h(-1)). Both mutant strains displayed a different fatty acid and phospholipid profi le compared with the wild-type strain. Conclusions: The ability of the mutant and recombinant plasmid-containing s trains to grow on high sugar concentrations and in high osmotic pressure en vironments (molasses) can be attributed to their phospholipid and fatty aci d contents. Significance and Impact of the Study: Taking into account that sugar beet m olasses is a low cost agricultural by-product, the simultaneous ethanol and bacterial ice nucleation production achieved under the studied conditions is considered very promising for industrial applications.