Selective suppression of bacterial contaminants by process conditions during lignocellulose based yeast fermentations
Journal article, 2011

Background Contamination of bacteria in large-scale yeast fermentations is a serious problem and a threat to the development of successful biofuel production plants. Huge research efforts have been spent in order to solve this problem, but additional ways must still be found to keep bacterial contaminants from thriving in these environments. The aim of this project was to develop process conditions that would inhibit bacterial growth while giving yeast a competitive advantage. Results Lactic acid bacteria are usually considered to be the most common contaminants in industrial yeast fermentations. Our observations support this view but also suggest that acetic acid bacteria, although not so numerous, could be a much more problematic obstacle to overcome. Acetic acid bacteria showed a capacity to drastically reduce the viability of yeast. In addition, they consumed the previously formed ethanol. Lactic acid bacteria did not show this detrimental effect on yeast viability. It was possible to combat both types of bacteria by a combined addition of NaCl and ethanol to the wood hydrolysate medium used. As a result of NaCl + ethanol additions the amount of viable bacteria decreased and yeast viability was enhanced concomitantly with an increase in ethanol concentration. The successful result obtained via addition of NaCl and ethanol was also confirmed in a real industrial ethanol production plant with its natural inherent yeast/bacterial community. Conclusions It is possible to reduce the number of bacteria and offer a selective advantage to yeast by a combined addition of NaCl and ethanol when cultivated in lignocellulosic medium such as wood hydrolysate. However, for optimal results, the concentrations of NaCl + ethanol must be adjusted to suit the challenges offered by each hydrolysate.









Eva Albers

Chalmers, Chemical and Biological Engineering, Industrial biotechnology

Emma Johansson

Chalmers, Chemical and Biological Engineering

Carl Johan Franzén

Chalmers, Chemical and Biological Engineering, Industrial biotechnology

Christer Larsson

Chalmers, Chemical and Biological Engineering, Industrial biotechnology

Biotechnology for Biofuels

17546834 (ISSN) 1754-6834 (eISSN)

Vol. 4 59

Driving Forces

Sustainable development

Subject Categories

Industrial Biotechnology

Biochemistry and Molecular Biology

Biological Sciences

Chemical Sciences

Areas of Advance


Life Science Engineering (2010-2018)


Basic sciences



More information