Title : The effect of microplastics on the enzymatic treatment of seaweed
Abstract:
Seaweeds are a promising source of bioactive compounds known to possess antioxidant, antiviral, antimicrobial, and anticoagulation properties, which makes seaweed an attractive source for biotechnological applications. Brown seaweed is particularly interesting – it is rich in fucoidan and alginate, both associated with numerous health benefits. When plastic waste enters the marine environment, microplastics (MPs) are formed due to biotic and abiotic processes. Many studies have detailed the severe effects of MPs on marine organisms. However, none of these studies have focused on the effect of MPs on seaweed degradation, a natural process that releases valuable nutrients into the marine environment. The aim of this study is therefore to determine the effect of three types of plastics on the ability of carbohydrate-active enzymes (CAZymes) to degrade seaweed and the release of biotechnologically valuable bioactive compounds exhibiting antimicrobial and antioxidant activities.
Brown, green, and red seaweed were collected along the Cape Town coastline, and were dried and ground, defatted, depigmented, and in the case of the brown seaweed, alginate components were extracted. The CAZymes, fucoidanase (Wf GH168), cellulase from Trichoderma reesii, and the small laccase from Streptomyces coelicolor, were produced and purified for application in seaweed degradation. The release of reducing sugars was monitored using the DNS assay, and the optimal biocatalytic conditions were applied to determine whether MPs have an inhibitory effect on the efficacy of the CAZymes in seaweed degradation. Three types of plastics were used for this project. Two bioplastics, namely polyhydroxybutyrate (PHB) and polylactic acid (PLA), and a fossil fuel-based plastic, polyethylene terephthalate (PET) fibres. Results showed that all three types of plastics have some inhibitory effect on the enzyme activity, with PET showing the highest inhibitory potential on all three enzymes, in the absence of seaweed. However, treatment of the seaweed in the presence of the plastics still showed the release of potential bioactive compounds: antimicrobial was observed against the pathogenic yeast, Candida albicans, degradation products exhibited antioxidant activity and showed no cytotoxicity in the HepG2 cell line.
Studies on MPs in the marine environment are usually focused on their impacts on marine organisms and environmental health. However, this study provided insights into the potential interfering role of MPs in natural processes that occur in the marine environment and a bioprocess that plays a key role in accessing the biotechnological potential of seaweed, a resource that contributes to the global Ocean Economy.
