Plastics and the microbiome: impacts and solutions

Abstract

Global plastic production has increased exponentially since manufacturing commenced in the 1950’s, including polymer types infused with diverse additives and fillers. While the negative impacts of plastics are widely reported, particularly on marine vertebrates, impacts on microbial life remain poorly understood. Plastics impact microbiomes directly, exerting toxic effects, providing supplemental carbon sources and acting as rafts for microbial colonisation and dispersal. Indirect consequences include increased environmental shading, altered compositions of host communities and disruption of host organism or community health, hormone balances and immune responses. The isolation and application of plastic-degrading microbes are of substantial interest yet little evidence supports the microbial biodegradation of most high molecular weight synthetic polymers. Over 400 microbial species have been presumptively identified as capable of plastic degradation, but evidence for the degradation of highly prevalent polymers including polypropylene, nylon, polystyrene and polyvinyl chloride must be treated with caution; most studies fail to differentiate losses caused by the leaching or degradation of polymer monomers, additives or fillers. Even where polymer degradation is demonstrated, such as for polyethylene terephthalate, the ability of microorganisms to degrade more highly crystalline forms of the polymer used in commercial plastics appears limited. Microbiomes frequently work in conjunction with abiotic factors such as heat and light to impact the structural integrity of polymers and accessibility to enzymatic attack. Consequently, there remains much scope for extremophile microbiomes to be explored as a source of plastic-degrading enzymes and microorganisms. We propose a best-practice workflow for isolating and reporting plastic-degrading taxa from diverse environmental microbiomes, which should include multiple lines of evidence supporting changes in polymer structure, mass loss, and detection of presumed degradation products, along with confirmation of microbial strains and enzymes (and their associated genes) responsible for high molecular weight plastic polymer degradation. Such approaches are necessary for enzymatic degraders of high molecular weight plastic polymers to be differentiated from organisms only capable of degrading the more labile carbon within predominantly amorphous plastics, plastic monomers, additives or fillers.

Plastic ingestion by the Wels catfish (Silurus glanis L.): detailed chemical analysis and degradation state evaluation

“…Additionally, the rate of degradation depends strongly on the amorphous fraction of the polymer, which also varies between different LDPE products ( Chamas et al, 2020 ). Furthermore, over 400 microbial species were assumptive identified as capable to degrade plastics ( Lear et al, 2021 ). Partial biodegradation was reported also for polyethylene ( Ren et al, 2019 ).…”

Microplastics: impacts on corals and other reef organisms

“…It is plausible that MPs also pose a threat, either through pathogen transmission, tissue damage or alteration of the coral microbiome [102,103], resulting in reduced fitness and susceptibility to disease. This includes the skeletal microbiome which is thought to play a critical role in the health of the colony [102,104]. The biofilms that form on MPs, referred to as the 'plastisphere', differ significantly from those in the water column and associated with natural particles, and may cause dysbiosis of the coral microbiome resulting in susceptibility to disease, or may harbour potential pathogens which have been seen to preferentially colonise plastics [102,[105][106][107][108][109][110][111][112][113].…”

Potential Use of Microbial Enzymes for the Conversion of Plastic Waste Into Value-Added Products: A Viable Solution

“…Microbes have the ability to break down highly crystalline polymers; however, their utilization in commercial plastics is restricted. Microbiomes commonly interact with abiotic elements, such as heat and light, to alter polymer structures and enzymatic attack ( Lear et al, 2021 ). Plastics are biodegraded by bacteria, fungi, and algae found in landfill leachate, sewage sludge, and compost.…”