Currently, the production of biofuels relies on carbohydrate feedstocks sourced from plant-based crop species that compete with edible crop species for arable landmass and potable water. Alternative, photosynthetically derived feedstock sources of carbohydrates can uncouple biofuel production from traditional agriculture and potentially decrease the land footprint required. This project will make use of a genetically engineered strain of a photosynthetic bacterium (cyanobacterium) that will use carbon dioxide in the atmosphere and light to make sucrose (table sugar), which can be fermented to biofuels and bio-products. This microorganism is uniquely capable of rerouting the majority of its photosynthetically fixed carbon towards the production and excretion of sucrose. This engineered cyanobacterium has carbohydrate productivity potential that exceeds that of traditional plant species, and could be used for an alternative carbohydrate feedstock if effective approaches can be designed to scale culture growth and minimize the cost of feedstock recovery. The project will focus on the development of microbial consortia as one means to capitalize upon the productive capacity of these sucrose-secreting cyanobacteria. In this approach, the sugar-secreting cyanobacterium with will be co-cultured with yeast strains that efficiently utilize the carbohydrates and biologically convert them into commodity products without the requirement of sucrose purification or processing. Improvements in the capacity for the yeast stain to robustly grow and utilize cyanobacterial sugars will also ultimately improve the conversion of sucrose into biofuels and bioproducts. Towards this end, a model microbial consortium will be developed whereby engineered yeast will utilize photosynthetically produced sucrose for the production of fatty alcohols, a useful surfactant and potential biofuel additive. This project includes research and educational experiences for a graduate student, as well as undergraduate students through the Plant Genomics Program and Khorana Scholars Program at Michigan State University. In addition, this project involves engagement with an undergraduate research program at Schoolcraft College, and science policy discussions on the use of synthetic biology for biotechnology applications through a Sloan Institute sponsored Delphi policy study.
The overall goal of this project is to develop a co-culture system for the overproduction of sucrose from carbon dioxide and light using engineered strains of cyanobacteria and yeast. The approach relies on a two-step photobiological production of sucrose through co-culture, and will provide fundamental understanding on how engineer of inter-species interactions for this purpose. This project will make use of an engineered cyanobacterial strain, Synechococcus elongatus PCC 7942 (S. elongatus) recently developed in the PI?s laboratory that is genetically stable and capable of rerouting up to 85% of its fixed carbon towards excreted sucrose. This strain possesses a high specific activity for photosynthetic production and therefore has considerable potential as an alternative carbohydrate feedstock source if scaled culturing can mitigate three challenges, which will be addressed by the proposed research. These challenges are to 1) minimize reactor complexity and cost to a degree consistent with the commodity product value, 2) reduce the costs of purifying, processing, and delivering cyanobacterial carbohydrates to downstream applications, and 3) to reduce the risk of photobioreactor contamination. Towards this end, the project will focus on the development of a direct co-culture of S. elongates with Saccharomyces cerevisiae (yeast) that will flexibly convert the sucrose into added-value compounds. The project will explore specific strategies to improve yeast growth in co-culture, including, improvement of yeast carbon uptake, increased yeast tolerance of cyanobacterial secondary products of photosynthetic metabolism, and enhancement of the flux and specificity of carbon from cyanobacteria to yeast through engineered physical association. These strategies will be evaluated to improve yeast robustness and efficiency of conversion of carbohydrates derived from S. elongatus when grown in co-culture, and a final proof-of-principle production of cetyl alcohol is proposed through the use of an established fatty-alcohol producing yeast strain. Overall, the project has potential to impact the field of algal biofuels by providing an alternative approach for metabolic pathway engineering or by improving upon an attractive algae-derived feedstock. This project includes research and educational experiences for a graduate student, as well as undergraduates through the Plant Genomics Program and Khorana Scholars Program at Michigan State University. In addition, this project involves engagement with an undergraduate research program at Schoolcraft College, and science policy discussions on the use of synthetic biology for biotechnology applications through a Sloan Institute sponsored Delphi policy study.
