Mangrove microbes to munch on plastic

A way to select a suite of mangrove bacteria that can transform plastic has been developed that potentially offers a new strategy in the global toolkit of plastic waste cleanup. Researchers have assessed the impact of polyethylene terephthalate (PET) particles and seawater intrusion on the microbiome of mangrove soil and then experimented with an enrichment culture to select a suite of PET-transforming microbes.

Plastic ocean pollution is growing globally at an alarming rate, with plastic fragments found even in deep oceans far from from human habitation. Mangroves are important biodiversity hotspots that offer a range of ecosystem services but are increasingly at risk from many stressors including plastic pollution.

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“Mangrove ecosystems are exposed to high levels of plastic and their soils have been reported to contain diverse microbial communities including plastic-active microorganisms,” explains Diego Javier Jiménez Avella, a research scientist in the Microbial EcoGenomics and Biotechnology Laboratory (MEGBLab) at KAUST, who led this research project. “So we thought these soils could be a good source of microbes with potential for breaking down plastics. Yet microbial diversity and metabolic activities in mangrove soils are still largely unknown.”

Degradation of PET byproduct by novel bacterium 

Analyzing the collective genomic information of two bacterial consortia showed that some bacterial species have novel enzymes capable of breaking down and transforming PET. The novel bacterial genus Mangrovimarina plasticivorans is a particularly important member of these consortia as it carries two genes that code synthesis of monohydroxyethyl terephthalates hydrolases — enzymes that are capable of degrading a PET byproduct.

These results are important as they increase our ecological understanding of PET transformation in nature and describe a novel bacterial genus and enzymes potentially capable of degrading PET. This is also the first time researchers have demonstrated that a bacterial consortia derived from mangrove soils can transform a fossil-fuel-based hydrolysable plastic.

“Engineering microbiomes to effectively transform plastics is an exciting research theme in microbiology and biotechnology,” explains Jiménez. “It is also a daunting task: bioremediation of microplastics in natural marine ecosystems is challenging due to low effectiveness, problems with scalability, testing, implementation, evaluation and legislation.”

Designing enzyme cocktails to degrade PET

The team’s approach to designing microbial inoculants and/or enzyme cocktails capable of accelerating PET degradation could be broadly applied using microbial inocula from a range of terrestrial and aquatic ecosystems. This in turn could identify more novel plastic-degrading microbes or enzymes. 

“These laboratory-scale findings are a step to addressing plastic pollution and require further research and development — such as optimization and scalability — before they can be practically applied,” notes Applied Microbiology International (AMI) Ocean Sustainability Advisory Group member Alexandre S. Rosado, principal investigator at KAUST and leader of the MEGBLab. Alexandre is the AMI Global Ambassador for Saudi Arabia.

Led by KAUST scientists, the research team — a collaboration that began in 2021 with eight institutions in Colombia, Brazil, USA, Germany, Australia, U.K. and Saudi Arabia — anticipates that broad use of this approach could help the design of efficient microbial consortia targeting plastic transformation both in the laboratory and in large-scale industrial settings.

The team are continuing to investigate the selection of plastic-transforming microbial communities from Red Sea mangroves and enzymatic activity of putative novel PET-degrading enzymes found in this study.