1. Development of eco-friendly bioplastics using microbes

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(1) Background & Objectives

   Because some microbes produce bio-vinyl monomers possessing both complicate structures and radical polymerizabilities, they are able to be utilized as novel building blocks of polymers. However, the monomers which have been found so far are few in number and the technology for production of these monomers is not developed yet. Furthermore, the biosynthetic mechanisms of almost all these monomers are still unknown. More recently, it has been reported that itaconic acid, a bio-vinyl monomer produced by a fungus Aspergillus terreus, and its polymerized materials show anti-inflammatory and anti-tumor activities, respectively, suggesting that they would be useful as a seed compound and medical polymers having these bioactivities.

   The aims of study are to develop screening and production methods for bio-vinyl monomers and to create novel medical polymers having bioactivities such as anti-inflammatory and anti-tumor activities, following to reveal these bioactivities of the monomers.

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(2) Researches

    We have developed a screen method called "DISCOVER (Direct Screening based on Coupling Reactions for Vinyl Compound Producers)" for the bio-vinyl monomers based on two-step coupling reactions, thiol-ene and Heck reactions, with terminal double bonds of the monomers. We are now categorizing the bio-vinyl monomers discovered so far and developing the technology for production of these monomers (Ref., Sci. Reports, 9(1) 16007 (2019)).

   Using the screening method DISCOVER, some novel fungi producing bio-vinyl monomers have been isolated and subsequently these structures have been identified using MS and NMR analyses. Bioactivity assays of the monomers revealed that some of which show anti-tumor activity. We are synthesizing polymeric substances consisting of these monomers and then evaluating these bioactivities.

   A bacterium Escherichia coli has been genetically modified to produce itaconic acid. Based on metabolic engineering, expression of cis-aconitate decarboxylase gene (cad) and aconitase gene (acnB) and inactivation of isocitrate lyase gene (icd) have been demonstrated, leading to itaconic acid production. This would open the way to produce bio-vinyl monomers heterologously (Ref., J. Biosci. Bioeng., 119(5) 548 (2015)).

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(3) Applications & Future works

   Compared to vinyl monomers produced from petroleum, bio-vinyl monomers possess higher number of carbon (more than C5), heteroatoms such as oxygen and nitrogen. Therefore, we can create new types of polymers having distinctive mechanical properties and bioactivities. Metabolic engineering would design the biosynthetic pathways of bio-vinyl monomers and it would enable to produce these monomers using heterologous hosts such as E. coli. Bio-vinyl monomers would be useful as not only building blocks and also seed compounds for drug design. Bio-vinyl innovation would make it possible a new paradigm based on bio-vinyl monomers.

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2. Sugar production from CO2 using electro-fermentation

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(1) Background & Objectives

   To create a low carbon society, it is important to achieve net zero carbon emissions by balancing a amount of carbon released, called "carbon neutrality". Plants possessing photosynthetic function play an important role in fixation of carbon we release. Lithoautotrophic microbes showing much higher growth rate compared to the plants might solve the environmental problems such as global warming, food, and resource issues.

   The aims of study are to develop the production systems for building blocks and sugars from carbon dioxide using photosynthetic and lithoautotrophic microbes by combination with LED-based photobioreactor and electro-fermentation, respectively.

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(2) Researches

   The genetically engineered cyanobacteria produced itaconic acid from carbon dioxide directly. This would be a useful system for monomers from carbon dioxide (Ref., J. Biotechnol., (195) 43 (2015)).

   An lithoautotrophic microbe, Xanthobacter autotrophicus, produces polysaccharides from C1 compound such as carbon dioxide and formic acid. For this bacterium, electro-fermentation providing hydrogen generated by electrolysis of water, as a reductant to fix carbon dioxide, or formic acid generated by electrochemical reduction of carbon dioxide as a reductant and a carbon source would be applicable. We are demonstrating genetic modification of the bacterium in order to improve its sugar productivity, followed by combination with electro-fermentation system. 

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(3) Applications & Future works

   Cyanobacteria produce high-value added materials such as building blocks for polymers, fuels, foods from carbon dioxide without any specialized instrument. By combination of high-cell density fermentation with electro-fermentation would enable the lithoautotroph to produce sugars from carbon dioxide industrially. This might result in no farmland and farm work. In other words, we might obtain foods from not plants but microbes in the future. Sugars are important chemicals as not only foods but also industrial materials. The world population explosion is accelerating and the population will reach to 10 billions people by around 2050. To support the population, a game changing technology must be needed. Our study would be a pioneering technology to solve the environmental problems such as global warming, food, and resource issues, leading to establish the sustainable society.