Biotechnological applications of lichen phycobionts: fast bioassay of environmental toxicity

Microbioassays allow for efficient contamination monitoring and control strategies. Free-living microalgae, representative of the aquatic environment, are the most used organisms due to high sensitivity and reproducibility. However, a lack of testing methods representative of terrestrial habitats has long been highlighted. A good unexploited option is the use of lichen phycobionts. The use of appropriate biomarkers leads to a reduction in costs and number of organisms, contributing to cost-efficient, rapid, and sensitive microbioassays. With the aim to develop a fast microbioassay, axenic Asterochloris erici was grown on treated cellulose paper, desiccated and rehydrated with different concentrations of inorganic and organic pollutants. Chlorophyll autofluorescence and free radical content were measured 5 min post-rehydration as energetics and oxidative status biomarkers respectively. Fluorescence microscopical images of exposed phycobionts were also collected. Potassium dichromate and copper sulphate decreased chlorophyll autofluorescence at high concentrations whereas boric and clofibric acids had little effect, all showing LOECs similar to those found in the literature. Heavy metals induced free radical bursts at extremely low concentrations whereas boric and clofibric acid showed modest and fluctuant increases. Microscopical images support fluorometric results and relate free radical bursts with bigger cells. In every case, free radicals LOEC is lower than chlorophyll autofluorescence’s by at least three orders of magnitude, making this microbioassay highly sensitive and fast, as well as low cost and ecologically relevant.