John Wiley & Sons, Ltd.

Optimization of culturing conditions for toxicity testing with the alga Oophila sp. (Chlorophyceae), an amphibian endosymbiont

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Eggs of the yellow‐spotted salamander (Ambystoma maculatum) have a symbiotic relationship with green algae. It has been suggested that contaminants that are preferentially toxic to algae, such as herbicides, may impair the symbiont and, hence, indirectly affect the development of the salamander embryo. To enable testing under near‐standard conditions for first tier toxicity screening, we isolated the alga from field‐collected eggs and identified conditions providing exponential growth rates in the apparent asexual phase of the alga. This approach provided a uniform, single‐species culture, facilitating assessment of common toxicity endpoints and comparison of sensitivity relative to other species. Sequencing of the 18s ribosomal DNA revealed that the isolated alga was closely related to the recently described Oophila amblystomatis but is more similar to other known Chlamydomonas species, suggesting possible biogeographical variability in the genetic identity of the algal symbiont. After a tiered approach to culturing method refinement, a modified Bristol's media with 1 mM NH4+ as nitrogen source was found to provide suitable conditions for toxicity testing at 18°C and 200 μmol m‐2 s‐1 PAR on a 24‐h light cycle. The validity of the approach was demonstrated with Zn2+ as a reference toxicant. Overall, we show that it is possible to screen for direct effects of contaminants on the algal symbiont without the presence of the host salamander, under certain laboratory conditions. Environ Toxicol Chem © 2014 SETAC

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