Abstract
BackgroundSecond-generation ethanol production is a clean bioenergy source with potential to mitigate fossil fuel emissions. The engineering of Saccharomyces cerevisiae for xylose utilization is an essential step towards the production of this biofuel. Though xylose isomerase (XI) is the key enzyme for xylose conversion, almost half of the XI genes are not functional when expressed in S. cerevisiae. To date, protein misfolding is the most plausible hypothesis to explain this phenomenon.ResultsThis study demonstrated that XI from the bacterium Propionibacterium acidipropionici becomes functional in S. cerevisiae when co-expressed with GroEL-GroES chaperonin complex from Escherichia coli. The developed strain BTY34, harboring the chaperonin complex, is able to efficiently convert xylose to ethanol with a yield of 0.44 g ethanol/g xylose. Furthermore, the BTY34 strain presents a xylose consumption rate similar to those observed for strains carrying the widely used XI from the fungus Orpinomyces sp. In addition, the tetrameric XI structure from P. acidipropionici showed an elevated number of hydrophobic amino acid residues on the surface of protein when compared to XI commonly expressed in S. cerevisiae.ConclusionsBased on our results, we elaborate an extensive discussion concerning the uncertainties that surround heterologous expression of xylose isomerases in S. cerevisiae. Probably, a correct folding promoted by GroEL-GroES could solve some issues regarding a limited or absent XI activity in S. cerevisiae. The strains developed in this work have promising industrial characteristics, and the designed strategy could be an interesting approach to overcome the non-functionality of bacterial protein expression in yeasts.
Highlights
Second-generation ethanol production is a clean bioenergy source with potential to mitigate fossil fuel emissions
The develop strain BTY34 (Gro, pRSXI2.0) demonstrated an elevated potential for industrial fermentations processes due to its high ethanol yield when compared to a strain containing one of the best xylose isomerase (XI) described in literature
Results in this work strongly support the hypothesis that bacterial XI does not always fold correctly inside the yeast
Summary
Second-generation ethanol production is a clean bioenergy source with potential to mitigate fossil fuel emissions. The engineering of Saccharomyces cerevisiae for xylose utilization is an essential step towards the production of this biofuel. One of the most efficient ways to avoid further fossil based emissions and capture CO2 is through biomass production, with subsequent conversion into biofuels [1]. The yeast Saccharomyces cerevisiae is the microorganism responsible for fermentation in most first-generation (1G) ethanol industries due to its robustness against diverse stresses, high productivity, and elevated ethanol yield. This yeast is not capable of naturally consuming C5-sugars [3]
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