Thermotolerant Zymomonas mobilis: Comparison of Ethanol Fermentation Capability with that of an Efficient Type Strain

Zymomonas mobilis is an alternative microorganism to Saccharomyces cerevisiae for ethanol production. To find a thermotolerant Z. mobilis strain, the growth and ethanol production of four isolates in Thailand were compared with those of the efficient strain ZM4 (NRRL B-14023) at different temperatures. One of the selected strains, TISTR 405, was found to grow and produce ethanol even at 39°C to an extent similar to that at 30°C, and the growth and ethanol productivity at 39°C were better than those of ZM4 at 30°C, suggesting that TISTR 405 is suitable for ethanol fermentation at high temperatures. Analysis of genes directly related to ethanol formation or degradation, adhA, adhB and pdc, encoding alcohol dehydrogenase (Adh) A, AdhB and pyruvate decarboxylase, respectively, revealed that these genes were highly conserved in both strains. Comparison of their gene expression and activity of the products in both TISTR 405 and ZM4 at different temperatures or growth phases indicated that there was not a great difference at the transcriptional level, but the total activity of AdhA and AdhB in TISTR 405 was higher than that in ZM4. Both strains showed a significant increase in AdhB activity in the stationary phase.