Human societycreated historically the most destructive environment throughout history through more than nine billion metric tons of plastics since the middle of the 20th century, with production to reach an additional 30 billion metric tons by 2060. This very rapid fast growth results in increasing amounts of untreated waste that is equal to nearly seven billion metric tons and that will have entered either a landfill or a natural ecosystem (e.g., oceans, rivers, lakes) and represents a major challenge cannot been addressed using available mechanical or chemical recycling methods. Traditional recycling fails to properly recycle materials because of both lower quality and increased degradation of materials during processing,only an estimated 9% of plastic waste to be properly recycled globally, while the majority of plastics is burned or landfilled. Thus, plastic waste continues to represent in a form of “white pollution”. When, plastics degrade into microplastic and nano plastic particles, they pollute our air, water, and food sources, introducing toxic additives, carcinogens, and other chemical agents into people and our daily life. To counter these types of challenges, a field of science called eco-microbiology is growing that has begun to research solutions to plastic waste through exploration of how microorganisms and other biological systems have evolved in different ways to degrade these synthetic materials.
The major discovery of this study happened when scientists in Sakai, Japan, they found a new type of bacteria, Ideonellasakaiensis, that live in the sediment found at a bottle recycling facility. This new species of bacteria is very unique because it only consumes polyethylene terephthalate (PET) which is the same type of plastic that is used to make millions of plastic water and soda bottles each year. I. sakaiensis doesn’t just live on top of the plastic but they are able to use the plastic as anenergy source. I. sakaiensis use two different enzymes that act like scissors and cut through the entire polymer chain. The first enzyme, called PETase, cuts the long and tough chains of the plastic into small pieces and then the second enzyme, called MHETase, cut down the small pieces into their original chemical structure which is terephthalic acid and ethylene glycol. Once the bacteria break the plastic into these two chemicals, they can be absorbed into the bacteria’s cell membrane and provide energy for the bacteria’s cellular functions, thus converting trash into life.
Despite this discovery, researchers discovered that natural occurring enzymes typically are not strong or fast enough for large scale degradation. Natural enzymes typically are degraded by the high temperatures required for large-scale recycling of plastics, or they do not work on all types of plastics, so the solution for this has been through the use of artificial intelligence and generative protein design to increase the speedof development of these enzymes by continually evolving them in a laboratory. Scientists have recently developed a new machine-learning-based enzyme called FAST-PETase that is extremely stable and effective at moderate temperatures when breaking down plastics, something that the majority of previous enzyme variants would have required temperatures above 70 °C in order to be effective and would not have lasted for long enough to be useful. Therefore, scientists make use of AI models to predict which mutations to introduce to the enzyme that would strengthen the enzyme’s structure yielded a variant that can break down plastic waste in under 24 hours; and the creation of ‘super’ enzymes by linking PETase and MHETase together physically into a single entity to breakdown plastic waste would give much faster breakdown than if these two enzymes were to work together, the broken plastic could convert enzyme from one active site to the active site of the next without further delay.
Researchers are now exploring different sources of plastics degradation in the fungal kingdom and in the gut of specific insect species. Fungi can break down complex plastics (e.g., polyurethane insulations and furniture) effectively. For example, Aspergillus niger can use thin, filamentous structures called mycelia to penetrate the plastic substrate and produce enzymes that weakens bonds in the substrate chemically. Researchers have identified that in the case of cockroaches (i.e., Blapticadubia) and mealworms, their gut bacteria can work in normal biological processes to degrade polystyrene. They not only fragment plastic, but it also utilizes the processes of fragmentation within its energy pathways making an adaptation to human made synthetic materials.
“While microbial technologies can rapidly decompose plastic, they cannot yet match current global production rates. To succeed, these biological solutions require worldwide single-use plastic regulations and improved waste collection systems, highlighting the need for a more circular relationship with manufactured goods.”
Figure 1 Microbes use enzymes like PETase and MHETase to break down plastic. This cycle converts plastic into simpler compounds and biomass.
In addition to destroying waste, researchers are now looking at how to “bio-upcycle” plastic into much higher-value products, breaking it down to its base elements, by using engineered microbes to convert various components of plastic into bioplastics or to create other useful compounds from the chemicals found in PET bottles and similar materials (for example, specialized bacteria are used to convert chemicals recovered from PET bottles into polyhydroxyalkanoates (PHA), naturally biodegradable plastics). This shows a circular loop where the original plastic can be converted to bioplastics that can be safely biodegraded in the environment, thus providing easier solutions to the plastic pollution problem. Some researchers are even considering developing plastics derived from plastics as a sustainable source of jet fuel or in pharmaceutical industry. To commercialize this process, scientists are working on creating “microbial consortia” in which different bacterial species will work together as one to carry out various tasks needed throughout the entire process. One single species would do most of the initial release of the polymer, and then other species would do most of the processing of the smaller molecule fragments produced by the first group.
There are generally four stages that describe the biological degradation of plastics. The initial stage is biodeterioration, creates a biofilm on surface of the plastic. This biofilm changes majorly both the physical and chemical properties of the plastic. Next is bio-fragmentation, in which enzymes from microbes fragment or break down long polymer chains of the plastic into smaller molecules. The third stage is assimilation, where the microbe joins these smaller fragmented plastic molecules into its cell. The final stage is mineralization, in which the plastic is completely reduced to non-toxic substances such as water and carbon dioxide. However, as microbes degrade the plastic, the microbes may also release toxic chemical additives that can be present in plastic to give it special properties such as being flexible. Additives such as bisphenol A (BPA) and various phthalates have been shown to disrupt the endocrine systems of both humans and wildlife.
An important area of research can examine ecological risks associated with large-scale use of these so-called “plastic-eating” microbes, particularly with their potential impact on microbe communities (i.e., the “plastisphere”), mobile habitats, and the transfer of genes between species. Difficulties exist regarding engineered genotypes designed for degrading plastics (or antibiotic resistance) being distributed with ecologically significant wild bacterial species. The introduction of large numbers of special microbes into any ecosystem can affect ecosphere functions, mainly ones with cycling carbon and nitrogen, which maintains ecological balance in soils and water. Scientists have stated that the use of biological tools should be managed in a controlled manner and under strictly managed conditions within industry, rather than deposited into the environment. Current scientific opinion is that microbial technologies will be important to the overall solution as the world moves forward and the implementation of the United Nations Global Plastic Process Act. Although we have the ability to create enzyme designs that can completely decompose a bottle in one day, current technology cannot match the number of new plastic products manufactured per day. Newer developments must also supported by worldwide regulations and passing laws on decreasing the production of single use plastic, as well as improving systems to collect waste plastic from their environment; if such system is developed, these biological developments will be encouraged globally and further supported. We are capable of playing an importantpart to adapt to this environment by using biological technology is an important lesson about how tough nature can be; this also gives us the need for an understanding of how we should engage with and use our manufactured goods in a more circular manner.
(The author is Affiliated with Chandigarh University, Gharuan,Mohali. The views, opinions and conclusions expressed in this article are those of the authors and aren’t necessarily in accord with the views of “Kashmir Horizon”)
