The Plastisphere and Bacteria: Have We Found the Solution to Plastic Waste?

As we all know by now, unfortunately our seas are filled with pieces of plastic that the human population has thrown away, with a whopping one third of all discarded plastic eventually residing in our oceans. However, what you may not know is that this unwanted waste has formed an entirely new ecosystem under the waves which is now home to a whole host of living beings; say hello to the plastisphere. 

Much like the atmosphere or the hydrosphere, the plastisphere is now considered to be its own region. Yet on closer inspection, scientists have now also classified it as an ecosystem which, by definition, is ‘a biological community of interacting organisms and their physical environment’. Simply, floating plastic in the ocean is now as much an ecosystem as our coral reefs and mangroves. Degraded, multicolour pieces of plastic bottles, shopping bags, lighters and old toys form the physical environment, whilst tiny bacteria and fungi are often found living on their surface, forming the biological community. These communities are sometimes called microbial reefs due to the sheer number of minute organisms which are living there; astonishingly, there could be 1,000 kinds of microbe on a single piece of plastic which is around five millimetres in size! 

Plastic may not sound like a very appealing habitat compared to natural rocks, kelp forests and corals yet once plastic is submerged in water, it attracts carbon, iron, nitrogen and phosphorus and, in turn, these nutrients attract bacteria. Once algae begins to grow on the surface of the plastic, larger organisms also often appear as our trash starts to smell like food. Whilst the term plastisphere was created to describe the microbes living on plastic, it now encompasses much larger creatures like crabs, small fish and jellyfish, many of which may use our trash as a handy raft to travel vast distances across the ocean. The plastisphere has existed for as long as our waste has been cluttering up the ocean but scientists are only just beginning to understand this surprisingly complex slice of the sea. Despite being manmade, the plastisphere is very similar to our other ecosystems such as coral reefs; they contain organisms which photosynthesise, predators and prey, parasites and grazers. Whether we like it or not, our floating plastic is a hub of marine life interactions, many of which are yet to be fully understood. 

However, not everyone is convinced that this new environment is good for our planet. Clumps of floating trash provide a home for species such as barnacles, crabs and sea urchins and allow them to circumnavigate the globe with total ease. This is already increasing the problem of invasive species as American lobsters arrive in Scotland and Asian lionfish appear in the Mediterranean, threatening the natural balance native species have lived in for centuries. It also means bacteria are spreading around the world too, which could have devastating consequences on fragile landscapes such as Antarctica where the marine life has evolved without the presence of many harmful microbes. Yet researchers still have multiple unanswered questions; does plastic actually house more dangerous pathogens than say natural driftwood or tangles of seaweed? Does the fact that plastic is much more persistent and durable than many natural materials make a difference to this new ecosystem? How will it affect our ancient ecosystems? All these questions and more still need to be answered but some of the most interesting questions regard the bacteria themselves and their ability to ‘eat plastic’.

Whilst studying the plastisphere, some scientists have witnessed bacteria actually eating the plastic they are rafting on, leading many to speculate that bacteria could be used as a tactic in our war against waste. In 2016, Japanese scientists found a species of bacteria at a waste site near a bottle factory which had evolved to contain an enzyme which ate plastic. These bacteria were found to be able to digest PET plastic which is the material that the majority of drinks bottles are made from. PET is very difficult to recycle with our traditional methods and so innovators started thinking outside the box about the uses of this new discovery. Since then, multiple groups of scientists around the globe have discovered similar bacteria in various waste sites from Pakistan to America to Germany, all digesting and essentially recycling plastic. Whilst plastics may be a very new material in the grand scheme of evolution, the oil they are made from is not. Bacteria have had millions of years to adapt to oil and similar substances, allowing them to develop enzymes which break down the chemicals oil is made from. It seems that the plastisphere has now also been a site of quick evolution as bacteria have taken this one step further and started snacking on plastic.

This could be a major game changer in our battle to combat plastic waste and French company Carbios is firmly on board and have already created a demonstration plant. They are using an enzyme found in bacteria to break down PET, used in bottles and food packaging, to help break down plastic and enable it to be recycled and used once more. Carbois already has some high profile food and drinks partners who are all hoping that they will be able to sell PET plastic containers produced entirely from enzymatically recycled plastic to help them reach their environmental goals. Other companies are turning to fungi instead which has also shown its preference for snacking on synthetic plastics. Many scientists believe that if we can speed up the digestion process of bacteria and make efficient use of their enzymes, this method could be used on a large scale to tackle our waste problem. 

Using bacteria to help us recycle plastic is still a long way from being a mainstream method and some believe this is a good thing as there are lots of questions we need to answer before we plunge head first into this innovative idea. Bacteria cannot break the polymer chains in plastic back down to their original components of carbon and hydrogen which means that enzymatically recycled plastic can only be used to create yet more plastic; will this stop us from pursuing more natural and sustainable alternatives? Additionally, whilst bacteria appears to be very good at digesting PET, we haven’t yet found microbes which digest hardier plastics such as HDPE which form items like pipes and cleaning product bottles. In a bid to combat overflowing landfills, a few innovators have even gone so far as to suggest that bacteria could be sprayed directly onto plastic which is polluting the environment, rather than used in controlled plants, but this could cause a rise of new, equally damaging problems. For example, when the plastic is broken down, the harmful chemicals which are added to it during the initial manufacture could spill out into the environment. For the bacteria to be able to work fast enough to tackle our mountain of trash, it is likely that they would have to be genetically modified and the thought of releasing new strains of bacteria into our environment seems like an incredibly risky move to make.

With so many unknowns surrounding the use of bacteria to break down plastic, some companies are trialling alternative ways we can use bacteria to our advantage. UK-based Shellworks have taken microbes found in many marine and soil ecosystems and turned them into plastic itself. These microbes naturally feed on carbon sources which help them build up fat as a store of energy, yet this fat can be extracted and behaves much like plastic does. Shellworks already has beauty companies working with them on products such as tubes and bottles which usually end up clogging landfill sites. Once their microbe-based plastic products have come to the end of their use, consumers can add them to the compost pile where the very same bacteria will see them as food and start to eat it, once more building up the fat which can be used to create the plastic; a true circular system.

Whilst the notion of our planet developing a plastisphere sounds mostly horrifying, scientists have been able to gain new insights into our oceans and their inhabitants from these ecosystems. Whilst we still have a lot to learn, the discoveries we have made about bacteria and their power could change the future of waste management. Yet for the time being, bacteria-recycled plastics are just an interesting development to keep an eye on. We can all continue to reduce our plastic use and look towards more sustainable alternatives to help tackle the plastic problem head on. In fact, seaweed-based alternatives are just beginning to boom and with bacteria having millions of years to evolve efficient ways of consuming and digesting seaweed, we could be seeing a new, more natural method of reducing our tower of trash very soon.

By Neve McCracken-Heywood