Isolation of thermotolerant yeasts for a non-cooling fermentation system in tropical areas

Description

Ambient temperatures in tropical areas are high, therefore ethanol fermenters also show a rise in temperature (up to around 40 ºC) during fermentation. Saccharomyces cerevisiae, the typical fermenting yeast, cannot carry out fermentation under high temperatures because it does not have thermotolerance.

We isolated the thermotolerant yeasts, Kluyveromyces marxianus (Y2) and Issatochenkia orientalis (C19). These yeasts, which have shown greater thermotolerance than S. cerevisiae, can produce ethanol under high temperature conditions (more than 40 ºC) and can tolerate the fermentation inhibitors contained in saccharified lignocellulosic biomass.  Consequently, ethanol fermentation without cooling can be achieved using these yeasts. It is expected to save energy through reduced cooling costs.

These thermotolerant yeasts can grow at higher temperatures than S. cerevisiae. Y2 and C19 strains can grow and ferment at 45 ºC and 42 ºC, respectively (Figs.1A and B). Y2 strain has shown tolerance to furfural, a fural compound, and is relatively insulated from the inhibition by the furfural induced from biomass hydrolysis (Fig. 2A); C19 strain has displayed tolerance to weak acids, hence it is relatively insulated from the inhibition by acetic acid induced from hydrolysis of lignocellulose biomass (Fig. 2B). The kinds of inhibitors to fermentation depend on the type of lignocellulose, therefore, we can select these yeasts as adequate for fermentation in biomass hydrolysis.

In terms of productivity, it can be pointed out that ethanol yield of C19 (73%) is lower than that of Y2 (90%). Additionally, Y2 often produces glycerol as a byproduct when it is incubated under stress conditions. 

Figure, table

  1. Fig.1. Ethanol fermentation by thermotolerant yeasts, Y2(A) and C19(B) in 10%YPD (10% glucose, 2% peptone, 1% yeast extract) at different temperature conditions.

  2. Fig.2. The influence of inhibitors on yeast growth.

Affiliation

Japan International Research Center for Agricultural Sciences Biological Resources and Post-harvest Division

Classification

Research B

Research project

Development of biofuel and biomaterial production technologies using biomass resources in Southeast Asia

Program name

Rural Livelihood Improvement

Term of research

FY 2012 (FY 2011-FY 2015)

Responsible researcher

Murata Yoshinori ( Biological Resources and Post-harvest Division )

KAKEN Researcher No.: 40322664
MIERUKA ID: 001773

Arai Takamitsu ( Biological Resources and Post-harvest Division )

MIERUKA ID: 001768

Kosugi Akihiko ( Biological Resources and Post-harvest Division )

KAKEN Researcher No.: 70425544
MIERUKA ID: 001772

Mori Takashi ( Biological Resources and Post-harvest Division )

ほか
Publication, etc.

Y.Mori et al, (2010)Journal of the Japan Institute of Energy 89, 1147-1152

Japanese PDF

2012_21_A4_ja.pdf112.66 KB

English PDF

2012_21_A4_en.pdf343.58 KB