A rapid screening method to assess soil algal toxicity: Non-destructive sampling of algal cells using culture medium extraction

- Soil algal toxicity was evaluated by different algal extraction methods.
- Soil algal toxicity by culture medium extraction can analyze multiple endpoints.
- Culture medium extraction is the recommended method for screening soil toxicity.

Populations of soil-living algae serve as important proxies for the level of metal toxicity in contaminated soils, therefore, there is a need for efficient bioassays to effectively monitor these populations. This study evaluated two approaches for the extraction of algal cells from soil for further analysis. One method employed direct solvent extraction of chlorophyll from the algae. A second method utilized indirect isolation of algal cells from culture media incubated for 24 h. The utility of both methods was compared by estimating the relative viability of Chlorococcum infusionum and Chlamydomonas reinhardtii grown in the presence of varying concentrations of Ni. The biomass of C. infusionum and C. reinhardtii decreased as a result of both extraction approaches. The direct extraction of algal chlorophyll with ethanol proved to be the simpler and more direct procedure; however, the process destroyed the cells and, therefore, only allowed for the measurement of a single endpoint. The indirect culture medium extraction was at least as sensitive as the direct extraction method in the measurement of chlorophyll, but allowed for the analysis of multiple endpoints. The culture medium method was used to characterize the biomass, photosynthetic activity, cell size, cell granularity, cell membrane permeability, and esterase activity of C. infusionum and C. reinhardtii to assess cell viability of cultures grown in increasing concentrations of Ni. Factors were measured by flow cytometry. Photosynthetic activity was inhibited, and cell size, membrane permeability, and esterase activity of C. reinhardtii were all affected when exposed to Ni-treated soil. This study demonstrated that the culture medium extraction method is preferable; allows for the analysis of multiple endpoints, such as photosynthetic and flow cytometric analyses of soil algae; has a shorter extraction period (24 h); and can, therefore, be used as an efficient and effectively screening method for soil toxicity.

125