Production of Ethanol by Zymomonas Mobilis Mutant : The Effects of Sodium Acetate at pH 5 and No Control pH

Abstract

Zymomonas mobilis is an ethanol producer that has the highest ethanol yield on sugar complex-containing glucose and the potential microorganism to replace yeast for ethanol production (ethanol yields up to 97%). The lignocellulosic pretreatment is needed to increase the ethanol production. However, pretreatment methods will create some inhibitor compounds such as acetic acid that reduces ethanol production. The aims of this study were to know the effect of sodium acetate as a form of acetic acid in medium fermentation that contain higher glucose consentration at pH 5 and no control pH. As reported in this study, the effect of the increasing NaAc level related to the pH. The growth of AcR/2-12 and ZM481 for 24 h at pH 5 were inhibited by NaAc concentration above 100 mM. However, the mutant strain AcR/2-12 on fermentation medium contained 100 g/l glucose and supplemented with 195 mM NaAc at pH 5 was still able to grow well and produced 60 g/l ethanol with the ethanol yield of 0.62 g/g (Yproduct/substrate) in 148 h. Whereas, without no control pH, AcR/2-12 was able to tolerate NaAc up to 250 mM and ZM481 was significantly inhibited at 195 mM NaAc. Under the same condition with no control pH, the glucose was completely consumed in 24 h by AcR/2-12 and 57 g/l ethanol was produced with the ethanol yield of 0.58 g/g (Yp/s).