Engineering Robust Yeast Microbial Systems for Beneficial Biotransformation in Energy and Water Sustainability

Nowadays, over 80% of energy supply relies on the nonrenewable and environmental unfriendly fossil fuels. Meanwhile, occurrence of pharmaceuticals and chemicals originated from our daily life and industrial activities but associated with potential environmental risks in the aquatic environment evokes increasing public concern about reclaimed water. This research stays at the interface of environmental engineering and metabolic engineering, with the goal of manipulating and engineering yeast to enhance renewable energy biofuel production from lignocellulosic residues and to treat contaminants of emerging concerns for water reuse/reclamation.

The development of robust microbial systems to utilize renewable feedstock effectively is important for high-titer biofuels production. Lignocellulosic biomass has been identified as a promising source to produce renewable biofuels but the pretreatment of lignocellulosic biomass generates lignocellulosic hydrolysate that contains fermentation inhibitors. The fermentation inhibitors will adversely affect the growth of industrial microorganisms such as Saccharomyces cerevisiae and prevent economic production of lignocellulosic biofuels. Therefore, it is critical to engineer microbial cell systems with enhanced resistance to fermentation inhibitors. This study employed a genomic library based inverse metabolic engineering approach to successfully identify a novel gene target WHI2 which elicited improved acetic acid resistance in S. cerevisiae. Based on this study, we developed an engineered yeast strain YC1 with superior resistance to acetic acid, furfural and their mixture. The transcriptional changes in YC1 versus the wild-type strain S-C1 under three different inhibitor conditions, including acetic acid alone, furfural alone and mixture of acetic acid and furfural were determined through RNA sequencing.

The establishment of green and cost-effective biotechnology to treat emerging contaminants is also important for advancing water reuse/reclamation. We developed a new type of biocatalyst by immobilizing fungal laccase on the surface of yeast cells using synthetic biology techniques. Followed by SDL study, we fabricated biocatalytic membranes (BCMs) by immobilizing SDL on microporous membranes via inkjet printing and chemical crosslinking. Both SDL and BCMs could effectively treat emerging contaminants.

The research offers a practice to develop robust strains for enhanced lignocellulosic biofuel production and a novel category of enzyme biocatalysts for treating emerging contaminants for water reuse. Our data demonstrated the effectiveness of engineered cell systems in advancing renewable energy production and water treatment. These and similar cell systems could have a critical role in addressing other challenges towards environmental sustainability.