Plastisphere in an Antarctic environment: A Microcosm Approach

Description

Illumina 16S rRNA amplicon sequencing from microplastics and quartz samples from a microcosm experiment in Antarctic conditions. Microplastics are ubiquitously present, even in remote regions like the Southern Ocean. Once in the water, they are rapidly colonised by marine microorganisms, forming what is known as the plastisphere. To address this issue in Antarctic waters, we conducted a microcosm experiment. We incubated microplastic pellets (2 to 5 mm nominal granule size) made of polypropylene, polyethylene, polystyrene, and quartz fragments in separate aquarium compartments in triplicate for 33 days in Livingston Island, South Shetland Islands, Antarctica. We analysed the colonisation process and the plastisphere dynamics in polar environmental conditions using scanning electron microscopy, flow cytometry, bacterial cultivation, qPCR, and 16S rRNA gene metabarcoding. Our results indicate that while colonisation occurs rapidly and consistently, biomass formation is slightly slower than in other oceanic regions, suggesting unique environmental constraints. Furthermore, we observed a transition in microbial communities from early- to late-biofilm stages between days 12 and 19. While time was the main driver of the biofilm community, plastic polymer types did not play a significant role in shaping the bacterial community. Additionally, we described the bacterial plastisphere composition in this Antarctic environment. We advocate for more extensive research reporting absolute bacterial densities during colonisation to allow comparison and a better understanding of this process. We further recommend conducting multiple analyses to accurately quantify and follow up on the plastisphere colonisation. The results of this study have implications for future environmental risk assessments in the Southern Ocean. Three independent microcosm experiments were conducted at the Antarctic Spanish Research Station in Livingston Island (South Shetlands, Antarctica) in January - March 2022. Each microcosm was set on compartmentalized twenty-litre glass aquariums, previously sterilised and rinsed with seawater (Fig. S1). Each contained 100 pellets of polyethylene (PE; 2 – 4 mm nominal granule size; density: 0.950 gr cm-3; floating), polypropylene (PP; 3 mm nominal granule size; density: 0.9 gr cm-3; floating), and polystyrene (PS; 3 – 5 mm nominal granule size; density: 1.050 gr cm-3; sinking), and 100 quartz fragments (quartz; 2 – 4 mm nominal granule size; density: 2.2 gr cm-3; sinking) as a control. DNA was extracted to characterize the bacterial communities of the substrates and the surrounding water, and further determine the bacterial abundance in the biofilm during the colonisation. Sequencing of each sample was performed using the Illumina MiSeq platform at the Genomics Unit of Centre for Genomic Regulation Core Facilities (CGR, Barcelona).

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