Plastic-eating bacteria discovered in the ocean

 Image created by Tim Sandle

Beneath the ocean’s surface, bacteria have evolved specialized enzymes that can digest PET plastic, the material used in bottles and clothes. Researchers at KAUST discovered that a unique molecular signature distinguishes enzymes capable of efficiently breaking down plastic. Found in nearly 80% of ocean samples, these PETase variants show nature’s growing adaptation to human pollution.

A large-scale global study by scientists at KAUST (King Abdullah University of Science and Technology) revealed that these marine microbes are widespread and genetically prepared to consume polyethylene terephthalate (PET) -- the tough plastic used in everyday items like drink bottles and fabrics. Their remarkable ability stems from a distinct structural feature on a plastic-degrading enzyme called PETase. This feature, known as the M5 motif, acts as a molecular signature that signals when an enzyme can truly break down PET. 

For decades, scientists believed PET was almost impossible to degrade naturally. That belief began to shift in 2016, when a bacterium discovered in a Japanese recycling plant was found to survive by consuming plastic waste. It had developed a PETase enzyme capable of dismantling plastic polymers into their building blocks.

Yet it remained unclear whether oceanic microbes had developed similar enzymes independently.

Using a combination of artificial intelligence modeling, genetic screening, and laboratory testing, Duarte and his team confirmed that the M5 motif distinguishes true PET-degrading enzymes from inactive look-alikes. In experiments, marine bacteria carrying the complete M5 motif efficiently broke down PET samples. Genetic activity maps showed that M5-PETase genes are highly active throughout the oceans, especially in areas heavily polluted with plastic.

Global Spread of Plastic-Eating Microbes

To understand how widespread these enzymes are, the researchers examined more than 400 ocean samples collected from across the globe. Functional PETases containing the M5 motif appeared in nearly 80 percent of the tested waters, ranging from surface gyres filled with floating debris to nutrient-poor depths nearly two kilometers below.

In the deep sea, this ability may give microbes an important edge. The ability to snack on synthetic carbon may confer a crucial survival advantage, noted Intikhab Alam, a senior bioinformatics researcher and co-leader of the study.

The discovery highlights a growing evolutionary response: microorganisms are adapting to human pollution on a planetary scale.

Although this adaptation reveals nature's resilience, Duarte cautions against optimism. "By the time plastics reach the deep sea, the risks to marine life and human consumers have already been inflicted," he warns. The microbial breakdown process is far too slow to offset the massive flow of plastic waste entering the oceans each year.

Turning Discovery Into Real-World Solutions

On land, however, the findings could accelerate progress toward sustainable recycling.

The identification of the M5 motif offers a roadmap for engineering faster, more effective enzymes. It reveals the structural traits that work under real environmental conditions rather than just in test tubes. If scientists can replicate and enhance these natural mechanisms, humanity's battle against plastic pollution may find powerful new allies in one of the planet's most unexpected places: the deep ocean.

Research paper 

See: Intikhab Alam, Ramona Marasco, Afaque A Momin et al. Widespread distribution of bacteria containing PETases with a functional motif across global oceans. The ISME Journal, 2025; 19 (1) DOI: 10.1093/ismejo/wraf121

 Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)

Green solutions? Application of microorganisms to boost a sustainable future

 

The effects of microbes on their environment can be beneficial or harmful or inapparent with regard to human measure or observation. Microorganisms can also be purposefully harnessed by scientists to help to improve the environment, such as by responding to a pollution event. A key area is with bioremediation. This provides a potential solution for the elimination of recalcitrant contaminants from the environment. Here either aerobic or anaerobic microorganisms are deployed to remove or neutralise environmental pollutants through their natural metabolic pathways. An example of this is with addressing oil spillages.

 

The purpose of this article is to assess some areas of current research that are foremost focused on utilising microorganisms for the wider good, in terms of environmental

remediation. Here six areas of research are assessed in the form an overview of the research topic.

 

Green solutions? Application of microorganisms to boost a sustainable future,  Pharmig News, Issue 90, pp9-12

 

 Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)

Meet Rhodococcus ruber - the plastic digesting bacterium

 Image by Hvonwerd (Creative Commons: https://microbewiki.kenyon.edu/index.php/File:DSM_44190.jpg)

The bacterium Rhodococcus ruber eats and actually digests plastic. This has been shown in recent laboratory experiments conducted at Royal Netherlands Institute for Sea Research (NIOZ).

 

Based on a model study with plastic in artificial seawater in the laboratory, researchers (led by Maaike Goudriaan) have calculated that bacteria can break down about one percent of the fed plastic per year into carbon dioxide and other substances. This finding may explain what happens to some of the plastic in the oceans.

 

The selected bacterium R. ruber can form a biofilm on plastic in nature. It had also been measured that plastic disappears under that biofilm.

 

R. ruber initially forms a branching mycelium that breaks into shorter rods and cocci as it transitions through different growth phases. R. ruber is characteristically a Gram positive, non-motile, non-spore forming bacteria. It has diverse metabolic and nutritional capabilities depending on the strain, such as utilizing gaseous hydrocarbons, aromatic hydrocarbons, complex polymers, and steroids for carbon and energy sources.

 

To demonstrate the effect, the researchers used a special plastic manufactured with a distinct form of carbon (13C) in it. The plastic was introduced to the bacteria after pretreatment with a UV lamp in a bottle of simulated seawater. The treatment with UV light was necessary because sunlight partially breaks down plastic into bite-sized chunks for bacteria.

 

Sunlight breaks down plastics on the ocean's surfaces. Floating microplastic is broken down into ever smaller, invisible nanoplastic particles that spread across the entire water column, that can then be completely broken down by bacteria. About two percent of visibly floating plastic may disappear from the ocean surface in this way each year.

 

R. ruber is an aerobic chemoorganotroph, meaning the bacterium uses organic compounds as its carbon and energy source through oxidative metabolic pathways. The organism is able to utilize gaseous hydrocarbons, aliphatic hydrocarbons, aromatic hydrocarbons, and xenobiotic substances, such as crude oil and plastics.

 

In time it was noted that a special version of carbon appear as carbon dioxide appeared above the water.

 

While it has been long suspected, this is the first time it has been experimentally demonstrated that bacteria can digest plastic into other molecules. R. ruber is able to use inert polymers, such as polyethylene and polystyrene, as its sole carbon source.

 

Calculations suggest that the total breakdown of plastic into carbon dioxide by bacteria per year is about one percent of the available, although this is estimate is not robust and further research is required to assess the microbial impact.

 

However, while it may appear that microbial digestion is a possible solution to the huge problem of all the plastic floating on and in our oceans the best solution is for humanity to reduce the use of plastic.

 

See:

 

Maaike Goudriaan, Victor Hernando Morales, Marcel T.J. van der Meer, et al. A stable isotope assay with 13C-labeled polyethylene to investigate plastic mineralization mediated by Rhodococcus ruber. Marine Pollution Bulletin, 2023; 186: 114369 DOI: 10.1016/j.marpolbul.2022.114369

 

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)