Abstract
The tolerant mechanism of yeast to the combination of three inhibitors (furfural, phenol and acetic acid) was investigated using 2-DE combined with MALDI-TOF/TOF-MS. The stress response and detoxification related proteins (e.g., Ahp1p, Hsp26p) were expressed higher in the tolerant yeast than in the parental yeast. The expressions of most nitrogen metabolism related proteins (e.g. Gdh1p, Met1p) were higher in the parental yeast, indicating that the tolerant yeast decreases its nitrogen metabolism rate to reserve energy, and possesses high resistance to the stress of combined inhibitors. Furthermore, upon exposure to the inhibitors, the proteins related to protein folding, degradation and translation (e.g., Ssc1p, Ubp14p, Efb1p) were all significantly affected, and the oxidative stress related proteins (e.g., Ahp1p, Grx1p) were increased. Knockdown of genes related to the oxidative stress and unfolded protein response (Grx1, Gre2, Asc1) significantly decreased the tolerance of yeast to inhibitors, which further suggested that yeast responded to the inhibitors mainly by inducing unfolded protein response. This study reveals that increasing the detoxification and tolerating oxidative stress, and/or decreasing the nitrogen metabolism would be promising strategies in developing more tolerant strains to the multiple inhibitors in lignocellulose hydrolysates.
Highlights
A wide range of inhibitory compounds including furan derivatives, weak acids, and phenolic compounds are generated during the pretreatment and hydrolysis of lignocellulosic materials [1]
PFA caused the degradation of proteins in parental yeast, which resulted in a decrease of total proteins
One category of proteins is related to the stress response involved in the unfolded protein response (UPR), while the other is to adjust cells' metabolism to overcome the deleterious effects of PFA
Summary
A wide range of inhibitory compounds including furan derivatives, weak acids, and phenolic compounds are generated during the pretreatment and hydrolysis of lignocellulosic materials [1]. These inhibitors are toxic and strongly reduce ethanol yield and productivity by affecting the performance of fermenting microorganisms. It has been reported that furfural, acetic acid and phenol all cause the accumulation of reactive oxygen species and induce the oxidative stress in yeast cells [4,12±15]. The mechanisms of inhibition acting upon yeast during fermentation of lignocellulosic hydrolysates have been studied intensively, but mainly focusing on the effect of one inhibitor (e.g. furfural or acetic acid). The molecular mechanism of ethanologenic yeast in response to multiple inhibitors is still unclear, which is an obstacle for the development of recombinant microorganisms that are tolerant to multiple inhibitors via approaches from metabolic engineering and synthetic biology
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