Assessment of Possible Environmental Impacts Using Flow-Cytometric Analysis of Metal Toxicity in Marine Phytoplankton

Mineral resources are abundant in submarine hydrothermal areas. The development of submarine resources is expected to be accompanied by metal-ore mining. This has raised concerns that mining is detrimental to marine environments because of the presence of heavy metals and arsenic. Innovations in collecting environmental baseline data and new onboard assessment methods for marine environmental impacts are required as a precautionary approach. This study aimed to evaluate the feasibility of an onboard on-chip benchtop flow cytometry (FCM) system and establish a technique to analyze the ecotoxic effects of metals on marine phytoplankton based on the FCM assay. The benchtop unit was installed on the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) research vessel Kaimei. Experiments were conducted onboard using seawater collected onsite. The effects of heavy metals on marine cyanobacteria were evaluated by staining nucleic acids with SYBR Green I and propidium iodide (PI). PI is a stain that permeates membranes differently depending on cell damage. We found that the metal sensitivities of Prochlorococcus in oligotrophic waters differed depending on the ambient nutrients. A similar trend was observed in culture-based laboratory experiments.