Applying model approaches in non-model systems: A review and case study on coral cell culture.

Model systems approaches search for commonality in patterns underlying biological diversity and complexity led by common evolutionary paths. The success of the approach does not rest on the species chosen but on the scalability of the model and methods used to develop the model and engage research. Fine-tuning approaches to improve coral cell cultures will provide a robust platform for studying symbiosis breakdown, the calcification mechanism and its disruption, protein interactions, micronutrient transport/exchange, and the toxicity of nanoparticles, among other key biological aspects, with the added advantage of minimizing the ethical conundrum of repeated testing on ecologically threatened organisms. The work presented here aimed to lay the foundation towards development of effective methods to sort and culture reef-building coral cells with the ultimate goal of obtaining immortal cell lines for the study of bleaching, disease and toxicity at the cellular and polyp levels. To achieve this objective, the team conducted a thorough review and tested the available methods (i.e. cell dissociation, isolation, sorting, attachment and proliferation). The most effective and reproducible techniques were combined to consolidate culture methods and generate uncontaminated coral cell cultures for ~7 days (10 days maximum). The tests were conducted on scleractinian corals Pocillopora acuta of the same genotype to harmonize results and reduce variation linked to genetic diversity. The development of cell separation and identification methods in conjunction with further investigations into coral cell-type specific metabolic requirements will allow us to tailor growth media for optimized monocultures as a tool for studying essential reef-building coral traits such as symbiosis, wound healing and calcification at multiple scales.

Iron Availability Modulates the Response of Endosymbiotic Dinoflagellates to Heat Stress.

Warming and nutrient limitation are stressors known to weaken the health of microalgae. In situations of stress, access to energy reserves can minimize physiological damage. Because of its widespread requirements in biochemical processes, iron is an important trace metal, especially for photosynthetic organisms. Lowered iron availability in oceans experiencing rising temperatures may contribute to the thermal sensitivity of reef-building corals, which rely on mutualisms with dinoflagellates to survive. To test the influence of iron concentration on thermal sensitivity, the physiological responses of cultured symbiotic dinoflagellates (genus Breviolum; family Symbiodiniaceae) were evaluated when exposed to increasing temperatures (26 to 30°C) and iron concentrations ranging from replete (500 pM Fe') to limiting (50 pM Fe') under a diurnal light cycle with saturating radiance. Declines in photosynthetic efficiency at elevated temperatures indicated sensitivity to heat stress. Furthermore, five times the amount of iron was needed to reach exponential growth during heat stress (50 pM Fe' at 26-28°C vs. 250 pM Fe' at 30°C). In treatments where exponential growth was reached, Breviolum psygmophilum grew faster than B.minutum, possibly due to greater cellular contents of iron and other trace metals. The metal composition of B.psygmophilum shifted only at the highest temperature (30°C), whereas changes in B.minutum were observed at lower temperatures (28°C). The influence of iron availability in modulating each alga's response to thermal stress suggests the importance of trace metals to the health of coral-algal mutualisms. Ultimately, a greater ability to acquire scarce metals may improve the tolerance of corals to physiological stressors and contribute to the differences in performance associated with hosting one symbiont species over another.