Bioconversion of non-edible marine biomass into bioplastics by a novel marine bacterium without going through a complex and costly pretreatment process
Synthetic protein quality control system for functional enzymes and efficient production of secondary metabolites
Expected to replace the current petroleum-based process with microbial cell factories and achieve carbon neutrality and economic feasibility
Professor Sang Woo Seo in the Department of Chemical and Biological Engineering has isolated and engineered an ultrafast-growing marine bacterium that can utilize various carbon sources, including non-edible biomasses, to produce eco-friendly bioplastics.
So far, plastics have been produced from oil and coal with complex chemical reactions, and this process has caused global warming and pollution by microplastics. Various institutes and companies worldwide have studied the production of bioplastics to replace conventional plastics. Although their production of bioplastics is increasing annually, it accounts for only 2% of the total plastic production because of its low economic feasibility since commercialized bioplastics are produced by using expensive edible crops as feedstock, which raises the entire process cost.
Prof. Seo devoted his attention to marine biomass for efficient production of bioplastics with low process cost. Marine biomass such as brown macroalgae is abundant in oceans and non-edible in most countries except for some Asian countries. However, industrial strains such as Escherichia coli and yeast cannot utilize marine algae without complex and costly pretreatment. A novel marine bacterium, Vibrio sp. dhg, isolated by the research team, can directly and efficiently utilize carbon sources from brown macroalgae. It also can grow even with high salt concentrations. For these reasons, it can directly utilize marine algal biomass without pretreatment.
The research team identified genomic information of Vibrio sp. dhg and developed genetic parts and tools to edit its genome. As a result, the engineered strain successfully produced 3-hydroxypropionic acid and 2,3-butanediol, monomers for various plastics, and lycopene. When brown algae without pretreatment were used as feedstock, the marine bacterium could produce 19.2 g/L of ethanol, indicating the strain as a potential platform for bioplastic production.
Vibrio sp. dhg has been further engineered to utilize lignocellulosic sugars. Recently, the research team introduced a xylose-utilizing pathway to the bacterium and conducted adaptive laboratory evolution to grow it fast in a xylose medium. Also, the genome of the evolved strain was edited to utilize various sugars simultaneously. These systemic and synthetic approaches made the strain produce lactate, a monomer of bioplastics, from a lignocellulosic sugar mixture with high productivity (1.15 g/L/h) and yield (0.80 g/gsugar). Although the strain could not assimilate raw lignocellulose yet, this result showed that the Vibrio strain would be used to produce bioplastics from various non-edible biomasses.
In addition to constructing eco-friendly bioplastic production, Prof. Seo and his research team developed a synthetic protein quality control system to enhance full-length translation in bacteria, which is expected to improve the productivity and yield of bioplastics. The system named ProQC harnesses a synthetic gene expression cassette that allows ribosomes only to use intact mRNA as a template. In this system, the cis-trigger element at the 3' end of mRNA can hybridize with the Toehold switch at the 5' end and expose ribosome binding sites for translation. Also, the mRNA becomes circular, ensuring efficient re-initiation of ribosomes.
When the ProQC system to various protein expressions was applied, the bacterial cells synthesized more full-length proteins (up to 250%). In addition, when the enzymes in the biochemical synthesis pathways were expressed under the control of the ProQC system, the target metabolite production levels were increased more than twice.
This technology is expected to increase the efficiency of the production of biopharmaceuticals, industrial enzymes, and particularly bio-based plastics. Along with the novel bacterium utilizing marine biomass, the ProQC system will enable the production of eco-friendly bioplastics with high quality but low process cost, bringing carbon neutrality.
