Isolation of a High Potential Thermotolerant Strain of Zymomonas mobilis for Ethanol Production at High Temperature Using Ethyl Methane Sulfonate Mutagenesis

The wild-type strain Zymomonas mobilis TISTR548 has a critical temperature for its growth and ethanol production at 38 degrees C. To obtain a high potential thermotolerant strain of this ethanologenic bacterium, this wild-type strain was subjected to chemical mutagenesis using ethyl methane sulfonate (EMS). After EMS treatment, the mutagenized cells were screened at temperatures ranging from 38 to 40 degrees C. The results showed that only six mutant strains, designated ZM EMS-52, ZM EMS-121, ZM EMS-143, ZM EMS-229, ZM EMS-263 and ZM EMS-297, could grow and produce a relatively high level of ethanol at 40 degrees C. Among these mutants, ZM EMS-229 displayed higher growth and ethanol production capacity than did the wild-type and other mutants at 37 and 40 degrees C. This mutant strain also showed greater resistance to high concentrations of ethanol, acetic acid and H(2)O(2 )at high temperature than did the wild-type. These findings suggested that the ZM EMS-229 was a good candidate for high-temperature ethanol fermentation.