A microbial plastic factory for high-quality green plastic

Plastic is a hallmark of our civilization. It is a family of highly formable (hence the name), versatile and durable materials, most of which are also persistent in nature and therefore a significant source of pollution. Moreover, many plastics are produced from crude oil, a non-renewable resource. Engineers and researchers worldwide are searching for alternatives, but none have been found that exhibit the same advantages as conventional plastics while avoiding their problems. One of the most promising alternatives is polylactic acid, which can be produced from plants, but it is brittle and does not degrade well.

To overcome these difficulties, Kobe University bioengineers around TAGUCHI Seiichi together with the biodegradable polymer manufacturing company Kaneka Corporation decided to mix polylactic acid with another bioplastic, called LAHB, which has a range of desirable properties, but most of all it is biodegradable and mixes well with polylactic acid. However, in order to produce LAHB, they needed to engineer a strain of bacteria that naturally produces a precursor, by systematically manipulating the organism's genome through the addition of new genes and the deletion of interfering ones.

In the scientific journal ACS Sustainable Chemistry & Engineering, they now report that they could thus create a bacterial plastic factory that produces chains of LAHB in high amounts, using just glucose as feedstock. In addition, they also show that by modifying the genome, they could control the length of the LAHB chain and thus the properties of the resulting plastic. They were thus able to produce LAHB chains up to ten times longer than with conventional methods, which they call "ultra-high molecular weight LAHB."

Most importantly, by adding LAHB of this unprecedented length to polylactic acid, they could create a material that exhibits all the properties the researchers had aimed for. The resulting highly transparent plastic is much better moldable and more shock resistant than pure polylactic acid, and also biodegrades in seawater within a week. Taguchi comments on this achievement, saying "By blending polylactic acid with LAHB, the multiple problems of polylactic acid can be overcome in one fell swoop, and the so modified material is expected to become an environmentally sustainable bioplastic that satisfies the conflicting needs of physical robustness and biodegradability."

The Kobe University bioengineers, however, dream bigger. The strain of bacteria they used in this work is in principle able to use CO₂ as a raw material. It should thus be possible to synthesize useful plastics directly from the greenhouse gas. Taguchi explains, "Through the synergy of multiple projects, we aim to realize a biomanufacturing technology that effectively links microbial production and material development."

This research was commissioned by the New Energy and Industrial Technology Development Organization of Japan (grant JPNP20005) and funded by the Ministry of Education, Culture, Sports, Science and Technology Japan (grant 19K22069) and the Japan Science and Technology Agency (grant JPMJTM19YC). It was conducted in collaboration with researchers from Kaneka Corporation and the National Institute of Advanced Industrial Science and Technology.