Differential heavy metal sensitivity in seven algal species from the NIES culture collection based on delayed fluorescence assays

Abstract

Seafloor massive sulfide (SMS) deposits are the target of available metallic resources. The toxic impacts of leachable metals from hydrothermal ore by mining operations in marine environments are a concern. However, ecotoxicological knowledge about marine algae, and particularly open ocean species, is still limited. Here, we evaluated the toxic effects of three leachable metals (i.e. Zn, Cu, and Pb) on seven marine algae, including cyanobacteria and eukaryotes, by a delayed fluorescence method. Cyanobacterial Synechococcus and Cyanobium species were sensitive to Zn and Cu, while eukaryotic algae showed various responses to heavy metal species. The prasinophycean Bathycoccus prasinos NIES-2670 was sensitive to all metal species; this strain is a potential test strain to detect the leachable metals. A co-culture experiment showed that the impact on community structure varies depending on leachable metal species. This study demonstrates that surveys across multiple taxonomic groups are necessary to assess the impact of SMS-mining operations on marine ecosystems as a whole.

Propidium Iodide Staining and Flow Cytometry-Based Assessment of Heavy Metal Impact on Marine Phytoplankton

“…The use of cultured strains instead of natural seawater allows us to perform robust and controlled tests for the optimization of FCM. A previous study showed that B. prasinos NIES-2670 is sensitive to Zn, Pb, and Cu (Ota et al 2020); thus, it is an ideal representative test strain for analysis. Considering that previ- ous studies have applied the PI method to algae (Xiao et al 2011, Gumbo et al 2014, Nogueira et al 2015, Suman et al 2015, Zhang et al 2015, and the present validation experiment showed that damaged cells show enhanced yellow to orange fluorescence (Figs.…”

“…Cyanobium sp. NIES-981 is a PE-free cyanobacterium that has been used as a marine test strain (Yamagishi et al 2016, Ota et al 2020). In addition, the whole genome of this strain has been sequenced (Yamaguchi et al 2016), and the strain is used as a model alga in ecotoxicology studies.…”

“…We developed a PI-based FCM assay system using algal cultures to assess the effects of heavy metals. This study targeted four strains from marine environments: a green alga Bathycoccus prasinos NIES-2670 was selected as a representative of eukaryotic algae which are sensitive to Cu, Zn, and Pb (Ota et al 2020); Synechococcus sp. NIES-969 and Prochlorococcus sp.…”