Response of coral reef dinoflagellates to nanoplastics under experimental conditions

Abstract

Plastic products contribute heavily to anthropogenic pollution of the oceans. Small plastic particles in the micro- and nanoscale ranges have been found in all marine ecosystems, but little is known about their effects upon marine organisms. In this study we examine changes in cell growth, aggregation, and gene expression of two symbiotic dinoflagellates of the family Symbiodiniaceae, Symbiodinium tridacnidorum (clade A3) and Cladocopium sp. (clade C), under exposure to 42-nm polystyrene beads. In laboratory experiments, cell number and aggregation were reduced after 10 days of nanoplastic exposure at 0.01, 0.1, and 10 mg/L concentrations, but no clear correlation with plastic concentration was observed. Genes involved in dynein motor function were upregulated compared to control conditions, while genes related to photosynthesis, mitosis, and intracellular degradation were downregulated. Overall, nanoplastic exposure led to more genes being downregulated than upregulated and the number of genes with altered expression was larger in Cladocopium sp. than in S. tridacnidorum, suggesting different sensitivity to nanoplastic between species. Our data show that nanoplastic inhibits growth and alters aggregation properties of microalgae, which may negatively affect the uptake of these indispensable symbionts by coral reef organisms.

Cell size matters: nano- and micro-plastics preferentially drive declines of large marine phytoplankton due to co-aggregation

“…Following this, entrapped phytoplankton are removed from the water column via precipitation of aggregated material, as has previously been recorded. 39, 88, 94 This process, also observed during exposure with metal oxide nanomaterials, 68, 69 is believed largely responsible for cases of reduced planktonic cell numbers or OD 600 recorded in toxicity testing. 39, 88, 94 Hetero-aggregation between plastic particles and phytoplankton may also act to disrupt photosynthetic processes through possible shading effects, also believed a possible feature of nanomaterial exposure during laboratory investigation.…”

“…39, 88, 94 This process, also observed during exposure with metal oxide nanomaterials, 68, 69 is believed largely responsible for cases of reduced planktonic cell numbers or OD 600 recorded in toxicity testing. 39, 88, 94 Hetero-aggregation between plastic particles and phytoplankton may also act to disrupt photosynthetic processes through possible shading effects, also believed a possible feature of nanomaterial exposure during laboratory investigation. 95 Large aggregates formed upon the cell surface may act to reduce light availability, compromising photosynthetic performance.…”

“…Physical interaction between phytoplankton cells and plastic particles has been regularly reported. 33, 34, 36-39, 88, 93, 94 Typically, advanced imaging techniques ( i . e ., transmission/scanning electron microscopy, fluorescent microscopy) have typically been used to assess this phenomenon, 33,37 with flow cytometric analysis also identified as a tool for this purpose.…”

“…A range of taxa have been adversely impacted by plastics exposure in this manner including dinoflagellates, 88 cyanobacteria 39 and heterotrophic bacteria, 94 in each case following exposure to PS NPs. Such processes may have important ecological consequences.…”

“…b) Shotgun proteomic analysis of E. huxleyi in response to micro-or nano-plastic exposure In response to plastic exposure, microorganisms may alter the regulation of specific cellular processes in order to adapt to-or mitigate stress. Plastic exposure has previously been associated with DNA damage 38 and altered gene function 88,89 in marine phytoplankton. Owing to the apparent enhanced susceptibility of E. huxleyi towards plastics exposure observed during flow cytometric monitoring (section 3.2) and examination of photosynthetic performance (section 3.3a), this species was selected for further investigation of potential toxic mechanisms via shotgun proteomic analysis.…”