Plastic-munching bacteria offer hope for recycling

Our lakes, rivers and oceans are increasingly clogged with plastic, along with billions of microscopic fragments of it, from all the useful and incredibly durable products made possible by the oil industry. This deluge of waste has increased exponentially in 60 years. Some 10 million tons of bottles, nets, bags, pails and food wrappers are deliberately or indiscriminately dumped each year into our waterways, where they entangle and kill marine life and damage the organs of creatures, including, possibly, humans, who ingest them. .

What can we do? For 70 years, we have been trying to recycle plastic, without much success. Some think it will never really work, largely because there are so many different types of plastics and they generally can’t be recycled together. Moreover, recycling is always more expensive than making new plastics; the plastics industry is expected to produce three times more plastic in 2040 than today.

Plastic has become so intertwined with our ecosystem that bacteria have evolved to digest it.

Oddly enough, these bugs might now offer a glimmer of hope. One of the biggest hurdles to profitable recycling is finding chemical enzymes that can quickly break down plastic, recovering the molecules originally used to make it, a crucial initial step in reforming and reusing the material.

By studying these plastic-eating bacteria, scientists have discovered enzymes that can break down plastics much faster than was possible a decade ago. It’s a big step up from traditional recycling, which uses heat to melt plastic, leading to a degraded and less useful material. After demonstrating the new technique, a French company called Carbios expects to soon recycle 50,000 tonnes of plastic each year.

But that’s probably just the start. The greatest hope for big breakthroughs in recycling chemistry comes from our current spectacular ignorance of the microbiology of the seas, and the genomics and computer technology that is now poised to change that.

We know very little about the microbes of the world. When biologists study the genetic content of seawater samples, two-thirds of what they find resembles nothing of known organisms. A recent study by researchers at ETH Zurich’s Institute of Microbiology, for example, used computational genomics to analyze more than 1,000 seawater samples from many locations and depths and ended up producing the complete genomes of some 26,000 organisms, 2,700 of which were previously unknown. (We also don’t know much about microbes in soil. Some 99% of genes identified in random samples of topsoil are not found in databases of known microbial genes.)

The microbiome – the universe of all microbial organisms – is a treasure trove of chemical leads to possible new drugs and other potentially useful biochemicals. The ETH Zurich study alone found more than 40,000 new biosynthetic gene clusters – a term used by biologists to refer to small clusters of related genes that together help produce a particular bioactive molecule. For scientists, they are prime candidates in the search for new and useful pharmaceutical compounds.

Such studies also help scientists identify new enzymes capable of digesting plastics. In a study published last year, biologist Aleksej Zelezniak of Sweden’s Chalmers University of Technology and his colleagues identified plastic-degrading enzymes in the genomes of many bacteria, including those from the ocean and soil. . Among oceanic bacteria, they also noted a strong correlation between the diversity of these enzymes and the amount of local plastic pollution. In the brief 60 years that plastic pollution has been with us, bacteria have already responded by developing biochemistry to digest plastic as a food source.

In turn, this bacterial engineering offers clues as to how we might produce better enzymes for recycling. From this bacterial data, using modern genomic methods and machine learning, the researchers were also able to identify more than 30,000 new candidate molecules that are expected to have potent plastic-digesting properties for at least 10 different types of plastic. .

There are, of course, other barriers to plastic recycling, including a broad lack of public engagement. That’s starting to change, spurred in part by China’s ban on importing plastic waste, which has made it harder for Western countries to hide their plastic pollution by shipping it far away.

But we need much stronger commitments from governments to tax plastic packaging and encourage packaging alternatives that use less plastic, or use none at all. If we take these steps, it’s not too wild to hope that in 10 or 20 years, armed with more knowledge about the marine microbiome, scientists will find their way to a set of enzymes capable of rapidly digesting many types of plastics. industry could produce. If that happens, there might be hope for the oceans after all.