Salt-tolerant, heat-resistant enzymes found in Colombian mangrove soils share structural features with known enzymes and could offer new candidates for plastic recycling.
Twelve enzymes with predicted capacity to degrade polyethylene terephthalate (PET) have been identified in Colombian mangrove soils. The enzymes, described in Nature Communications by researchers at King Abdullah University of Science and Technology (KAUST) and Universidad de los Andes, are salt-tolerant and potentially heat-resistant - properties that could make them suited to industrial recycling conditions where contaminated or marine-exposed plastic waste often carries residual salt.
Three of the 12 could remain active at temperatures where PET becomes easier to break down, and a further two have structural features the researchers describe as distinct from any previously characterised PET-degrading enzyme. No PETases - enzymes that break down PET - from mangrove environments have been identified before these findings.
Rice husks open the door
The enzymes were not found by adding plastic to soil. The team set up experiments with mangrove soil from Baru Island, treating samples with either PET particles or rice husks. All 12 candidates came from the rice husk samples. None appeared in those treated with PET.
Plant polymers contain the same type of chemical bond found in PET. Rice husks selected for microbes whose enzymes target that bond - and can therefore also act on plastic. The mangrove setting, with its naturally high salinity, meanwhile selected for salt-tolerant organisms whose enzymes could function in industrial recycling conditions.
The enzymes were identified by analysing DNA from the soil samples rather than by observing them break down plastic directly. They are computational predictions, not experimentally confirmed. Jimenez wrote that the team is “now looking for financial support to further characterize these predicted enzymes and compare them with benchmark PETases.”
Enzymatic PET recycling has advanced towards commercial scale in recent years, with Carbios, the French biotech, now building the first industrial plants. Most work in the field focuses on engineering known enzymes for improved performance - the mangrove study instead looks at naturally occuring instances for new candidates.
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