Detoxification in Saccharomyces cerevisiae under phenolics stress

Conference poster, 2013

Phenolic compounds, commonly found in woods hydrolysates and biorefinery side streams are products of lignin breakdown during wood pretreatment. They are formed alongside other products such as organic acids and furaldehydes. Phenolic compounds are widely varied and are known to be inhibitory to cell performance, thus making the efficient bioconversion of lignocellulose biomass to products such as bioethanol, a difficult task. As part of our aim at developing robust Saccharomyces cerevisiae for lignocellulosic fermentation, we have studied the interaction of S. cerevisiae cells with a selected subset of phenolic compounds. Three phenolic compounds; 3-methoxy-4-hydroxycinnamaldehyde, 3-methoxy-4-hydroxycinnamic acid and 4-hydroxycinnamic acid, were selected as representative phenolic compounds and model substrates. These substances represent phenolic aldehydes and acids thus providing an opportunity to closely compare different phenolic compound groups on the same –cinnamic- structural background, at the same time they offer a chance to probe the influence of side groups such as the methoxy group on the phenolic compound toxicity. Our studies show that when S. cerevisiae is exposed to the selected phenolic compounds, the cells carry out a process of detoxification that involves several conversion steps in transforming the toxic phenolic compounds to other phenolic compounds with much higher toxicity limits that confirm them to be less toxic. The toxicity limit here has been defined as the concentration at which S. cerevisiae performance in the presence of phenolic compounds is decreased to about 20% in comparison to the control in Yeast minimal Mineral medium without phenolic compounds. Furthermore, products and observed patterns of the conversion indicate that S. cerevisiae likely employs a common conversion route for the different phenolic compounds.