Abstract
Phytoplankton cells are excellent biosensors for environmental monitoring and toxicity assessments in different natural systems. Green algae, in particular, appear to be more responsive to copper (Cu) disturbances. This is interesting considering that Cu pollution in coastal environments has increased over the last century, with enormous repercussions to marine ecosystems. Unfortunately, no high-throughput method exists for the environmental monitoring of Cu toxicity in seawater. To assess potential uses as biosensors of Cu pollution, high-throughput screening was performed on five luminescence reporter lines constructed in the green algae Ostreococcus tauri RCC745. The reporter line expressing the iron storage ferritin protein fused to luciferase (Fer-Luc) was the most sensitive, responding to Cu concentrations in the µM range. Fer-Luc was also the most sensitive reporter line for detecting toxicity in mining-derived polluted seawater predominantly contaminated by soluble Cu. Nevertheless, the Cyclin-Dependent-Kinase A (CDKA) reporter was most suitable for detecting the toxicity of copper-mine tailing effluents containing other metals (e.g., iron). These results highlight that Ostreococcus biosensors can serve as a reliable, inexpensive, and automated, high-throughput laboratory approach for performing seawater analyses of coastal areas subjected to metal disturbances. When challenged with Cu, Ostreococcus tauri not only evidenced a rapid, transcriptional response for the tested genes, but also showed changes in a broad range of genes, especially as related to the stress response. Overall, the obtained results reinforce that a single biosensor is insufficient when dealing with complex mixtures of toxic compounds in natural environments.
Highlights
Biosensors contain biological components that react to target substances, and these reactions generate an readable signal proportional to the concentration of the compound of interest or of associated by-products (D’Souza, 2001; Balootaki and Hassanshahian, 2014; Kaur et al, 2015)
Luminescent lines included a broad spectrum of genes and genetic constructions involved in different biological processes, including the circadian clock (CCA1), cell division (CDKA), metal homeostasis regulation (Fer), and phosphate transport (HapT) (Moulager et al, 2010; Sanchez-Ferandin et al, 2013)
All luciferase reporter lines displayed dose-dependent growth inhibition in response to Cu amendments. These results suggest that Cu has a global toxic effect on the physiology and growth of O. tauri, a finding similar to prior reports for other phytoplankton species (Davis et al, 2006; Stuart et al, 2009; Jordi et al, 2012)
Summary
Biosensors contain biological components (e.g., cells) that react to target substances (e.g., pollutants), and these reactions generate an readable signal (e.g., photon emission) proportional to the concentration of the compound of interest or of associated by-products (D’Souza, 2001; Balootaki and Hassanshahian, 2014; Kaur et al, 2015). Ostreococcus tauri is a model photosynthetic organism used to study biological processes (Corellou et al, 2009; Lozano et al, 2014), including cell division (Moulager et al, 2010), circadian clock architecture (O’Neill et al, 2011), iron metabolism (Botebol et al, 2015; Lelandais et al, 2016), and vitamin assimilation (Paerl et al, 2017) These applications as a model organism arise due to unique characteristics, including a small size, compact sequenced genome, and ease of genetic manipulation. Genomic analyses in Ostreococcus spp. suggest that Cu is an essential cofactor in cellular processes, such as in photosynthesis, where cytochrome b is replaced by the Cu protein plastocyanin (Piganeau et al, 2011), and in iron acquisition, where multicopper oxidase is the only transporting component in the O. tauri genome (Palenik et al, 2007)
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