The best agents degrade bacteria would be biological life forms such as bacteria which multiply by the millions in days and are themselves completely biodegradable. It is towards this challenge that research has been going on, and the latest effort which shows some success has been published in the March 11, 2016 issue of Science by a Japanese group, led by Dr Kanji Miyamoto of Keio University, Kanagawa. The group concentrated on looking for and identifying bacteria from the PET bottle recycling sites, and found one such microbe that they have named Ideonella sakaiensis (the first name identifies the family and the second honors the geographic location where they found the bacterium). I. sakaiensis sticks to the surface of the PET bottle, secretes one molecule which they named PET-ase (the suffix “– ase” denotes an enzyme molecule), which breaks down PET into a smaller building block abbreviated as MHET. MHET is now taken up and broken down by another enzyme in the microbe’s cell (called MHET hydrolase) and hydrolyzed to produce ethylene glycol and terephthalic acid- the two small molecules (called monomers). The I sakaiensis is highly efficient as a safe biodegradable agent. Two interesting points emerge from the Japanese work. One is: can we now isolate the ethylene glycol and terephthalic acid, the two monomers, and reuse them to make PET? This offers a nice self-contained set up where the PET bottles and plastics discarded after use are biodegraded back to the starting materials in a bio-reactor, and then taken to the polymer synthesizing unit which remakes the PET. The other point is more challenging and surely there are molecular biologists already working on it. That is: why not clone the genes that express the enzyme PET-ase and MHET hydrolase into some other properly chosen microbe (other than I.sakaiensis ), using genetic engineering methods and thus attempt to biodegrade PET.
E. coli, a common gut bacteria, can be engineered to produce biodegradable polymers for use in surgical sutures, among other applications.A Korean research team has engineered gut bacteria to create non-natural polymers in a biorefinery; allowing various plastics to be made in an environmentally-friendly and sustainable manner. The research was published in Nature Biotechnology. In the present study, a team headed by Distinguished Professor Lee Sang Yup of the Korea Advanced Institute of Science and Technology (KAIST) adopted a systems metabolic engineering approach to develop a microorganism that can produce various non-natural polymers which have biomedical applications. According to the researchers, this approach is the first successful example of biological production of poly(lactate-co-glycolate) (PLGA) and several novel copolymers from renewable biomass by one-step direct fermentation of metabolically engineered Escherichia coli (E. coli) bacteria. The researchers drew inspiration from the biosynthesis process for polyhydroxyalkanoates, biologically-derived polyesters produced in nature by the bacterial fermentation of sugar or lipid. From there, they designed a metabolic pathway for the biosynthesis of PLGA through microbial fermentation directly from carbohydrates in E. coli strains. PLGA is a biodegradable, biocompatible and non-toxic polymer. PLGA has been widely used in biomedical and therapeutic applications such as surgical sutures, prosthetic devices, drug delivery, and tissue engineering. In order to produce PLGA by microbial fermentation directly from carbohydrates, the team incorporated external and engineered enzymes as catalysts to co-polymerize PLGA while establishing a few additional metabolic pathways for the biosynthesis to produce a range of different non-natural polymers. This bio-based synthetic process for PLGA and other polymers could substitute for existing complicated chemical production methods. Lee and his team has also managed to produce a variety of PLGA copolymers with different monomer compositions such as the US Food and Drug Administration-approved monomers 3-hydroxyburate, 4-hydroxyburate, and 6-hydroxyhexanoate. Newly applied bioplastics such as 5-hydroxyvalerate and 2-hydroxyisovalerate were also made