Plastic leachates impair picophytoplankton and dramatically reshape the marine microbiome

Abstract

Background Each year, approximately 9.5 million metric tons of plastic waste enter the ocean with the potential to adversely impact all trophic levels. Until now, our understanding of the impact of plastic pollution on marine microorganisms has been largely restricted to the microbial assemblages that colonize plastic particles. However, plastic debris also leaches considerable amounts of chemical additives into the water, and this has the potential to impact key groups of planktonic marine microbes, not just those organisms attached to plastic surfaces. Results To investigate this, we explored the population and genetic level responses of a marine microbial community following exposure to leachate from a common plastic (polyvinyl chloride) or zinc, a specific plastic additive. Both the full mix of substances leached from polyvinyl chloride (PVC) and zinc alone had profound impacts on the taxonomic and functional diversity of our natural planktonic community. Microbial primary producers, both prokaryotic and eukaryotic, which comprise the base of the marine food web, were strongly impaired by exposure to plastic leachates, showing significant declines in photosynthetic efficiency, diversity, and abundance. Key heterotrophic taxa, such as SAR11, which are the most abundant planktonic organisms in the ocean, also exhibited significant declines in relative abundance when exposed to higher levels of PVC leachate. In contrast, many copiotrophic bacteria, including members of the Alteromonadales, dramatically increased in relative abundance under both exposure treatments. Moreover, functional gene and genome analyses, derived from metagenomes, revealed that PVC leachate exposure selects for fast-adapting, motile organisms, along with enrichment in genes usually associated with pathogenicity and an increased capacity to metabolize organic compounds leached from PVC. Conclusions This study shows that substances leached from plastics can restructure marine microbial communities with the potential for significant impacts on trophodynamics and biogeochemical cycling. These findings substantially expand our understanding of the ways by which plastic pollution impact life in our oceans, knowledge which is particularly important given that the burden of plastic pollution in the marine environment is predicted to continue to rise.

Plastic Leachate Exposure Drives Antibiotic Resistance and Virulence in Marine Bacterial Communities

“…Previously, we examined the effects of exposure to two concentrations of PVC plastic leachate and of zinc, the most abundant inorganic PVC additive, on a marine microbial community via a six-day microcosm experiment, showing that this leads to substantial changes in community composition and function (Focardi et al, 2022). In this study, we have analysed the metagenomic data from Focardi et al (2022), to investigate whether exposure to PVC leachate and/or zinc results in significant enrichment of genes associated with pathogenicity and drug resistance.…”

“…Metagenomic data was obtained from our previous study examining the effects of PVC leachate and zinc, an abundant PVC additive, on a seawater microcosm community (Focardi et al, 2022). Methodology for the leachate preparation, and microcosm experiment set-up has been described in our previous study (Focardi et al, 2022).…”

“…Metagenomic data was obtained from our previous study examining the effects of PVC leachate and zinc, an abundant PVC additive, on a seawater microcosm community (Focardi et al, 2022). Methodology for the leachate preparation, and microcosm experiment set-up has been described in our previous study (Focardi et al, 2022). Briefly, microcosm samples were subject to a six-day exposure to either 1% (0.5g/L) PVC leachate (PVC1), 10% (5g/L) PVC leachate (PVC10), 0.13 mg/L zinc chloride (ZnL), 1.3 mg/mL zinc chloride (ZnH) (zinc being the most abundant inorganic component in leachate from this PVC plastic), or left untreated as control samples (SW).…”

“…DNA extracted from each treatment was used to generate metagenomic libraries at the Ramaciotti Center for Genomics (Sydney, Australia) using the Illumina Nextera DNA Flex library preparation kit, and sequenced on the NovaSeq6000 platform (2x150 bp High Output run). Gene sequences, de-replicated at 98% nucleotide identity, and gene counts for each sample were retrieved from Focardi et al (2022). Detailed methodology for the metagenomic data processing, assembly, gene prediction, and gene counts has been described in our previous study.…”

“…These include the environmental release of chemicals via leaching from plastic particles, which can significantly alter marine microbial communities (Capolupo et al, 2020; Focardi et al, 2022; Gunaalan et al, 2020; Romera-Castillo et al, 2018) and dissemination of pathogenic microorganisms, via rafting on plastic debris (Bhagwat et al, 2021; Bryant et al, 2016; Zettler et al, 2013; Zhang et al, 2022).…”