Publication: Improved Algal Toxicity Test System for Robust Omics-Driven Mode-of-Action Discovery in Chlamydomonas reinhardtii

Unicellular algae are used internationally as test organisms in chemical risk assessment. However, existing OECD and ISO toxicity test guidelines for inhibition of algal growth are not sufficiently compatible with large-scale experiments that seek to utilise state-of-the-art omics technologies to discover molecular mode-of-action (MoA). Here, we set out to develop a robust, miniaturised and scalable Chlamydomonas reinhardtii toxicity testing approach tailored to meet these demands. Specific objectives were to showcase the benefit of synchronised versus non-synchronised algal cultures for molecular studies, to design an exposure system with minimal chemical volatilisation yet yielding sufficient algal biomass, and to characterise variability in algal metabolomics data. Chlorobenzene was selected as a model volatile toxicant, and exposure levels measured using gas-chromatography mass spectrometry. Flow cytometry revealed significant changes in sample composition of synchronised cultures, and coordination of cell division and sporulation over a 24-hour period, compared to non-synchronised cells. Synchronised cultures in glass vials showed growth rates above OECD thresholds at previously unachievably-high inoculation cell densities, minimal pH drift and chemical loss over the test duration, and relatively high reproducibility of direct-infusion mass spectrometry metabolic phenotypes over three experimental repeats. The modified test system extends the applicability and capacity of conventional test formats towards large-scale designs required for omics-driven MoA discovery.

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