Precise Genomic Riboregulator Control of Metabolic Flux in Microbial Systems.

Engineered microbes can be used for producing value-added chemicals from renewable feedstocks, relieving the dependency on nonrenewable resources such as petroleum. These microbes often are composed of synthetic metabolic pathways; however, one major problem in establishing a synthetic pathway is the challenge of precisely controlling competing metabolic routes, some of which could be crucial for fitness and survival. While traditional gene deletion and/or coarse overexpression approaches do not provide precise regulation, -repressors (CRs) are RNA-based regulatory elements that can control the production levels of a particular protein in a tunable manner.

Improved cellulase expression in diploid yeast strains enhanced consolidated bioprocessing of pretreated corn residues.

In an effort to find a suitable genetic background for efficient cellulolytic secretion, genetically diverse strains were transformed to produce core fungal cellulases namely, β-glucosidase (BGLI), endoglucanase (EGII) and cellobiohydrolase (CBHI) in various combinations and expression configurations. The secreted enzyme activity levels, gene copy number, substrate specificities, as well as hydrolysis and fermentation yields of the transformants were analysed. The effectiveness of the partially cellulolytic yeast transformants to convert two different pre-treated corn residues, namely corn cob and corn husk was then explored.

Identification of superior cellulase secretion phenotypes in haploids derived from natural Saccharomyces cerevisiae isolates.

The yeast Saccharomyces cerevisiae is considered an important host for consolidated bioprocessing and the production of high titres of recombinant cellulases is required for efficient hydrolysis of lignocellulosic substrates to fermentable sugars. Since recombinant protein secretion profiles vary highly among different strain backgrounds, careful selection of robust strains with optimal secretion profiles is of crucial importance. Here, we construct and screen sets of haploid derivatives, derived from natural strain isolates YI13, FINI and YI59, for improved general cellulase secretion.

Heterologous expression of cellulase genes in natural Saccharomyces cerevisiae strains.

Enzyme cost is a major impediment to second-generation (2G) cellulosic ethanol production. One strategy to reduce enzyme cost is to engineer enzyme production capacity in a fermentative microorganism to enable consolidated bio-processing (CBP). Ideally, a strain with a high secretory phenotype, high fermentative capacity as well as an innate robustness to bioethanol-specific stressors, including tolerance to products formed during pre-treatment and fermentation of lignocellulosic substrates should be used.