My first dissertation chapter compares how different species of Symbiodiniaceae (formerly Symbiodinium) responded to low concentrations.
Summary of findings (link to TL, DR twitter thread): Briefly, we used five species of Symbiodiniaceae (spanning three genera) to investigate the effects of iron limitation on growth and trace metal uptake. Additionally, the concentrations of other trace metals (ex: zinc, manganese, etc.) were examined in cells while growing under iron limitation, which exhibited unique patterns in relative content for each dinoflagellate species. The absolute iron requirement of Symbiodiniaceae reflects their inability to grow without iron. Relative to other microalgae, including other dinoflagellates, Symbiodiniaceae require higher levels of iron concentrations for cell proliferation in addition to maintaining relatively high cellular iron reserves (quotas). Satisfying enzyme cofactors related to the mixotrophic and symbiotic lifestyles of Symbiodiniaceae may dictate their relatively large iron demands.
Aside from lowering cellular iron reserves, each Symbiodiniaceae species had their own way of coping with exposure to iron limitation. Specifically, each species had unique changes of trace metal (Zn, Mn, Cu, Ni, Mo, Co) content, uptake and net use efficiency in response to low iron concentrations. The vast intraspecific variation could be attributed to compensation with other metals, changes in metalloenzyme activity and requirements, different Nitrogen & Phosphorus needs, siderophore activity, ad non-specific metal uptake. The multivariate distribution of Symbiodiniaceae trace metal profiles revealed broad ecological guilds (temperate, tropical, ‘necrotrophic’). These patterns suggest trace metal needs may serve as an axis of Symbiodiniaceae niche diversification and, in part, modulate their local distribution. Furthermore, the differences in trace metal needs of each Symbiodiniaceae is likely important in meeting the metabolic demands of their cnidarian hosts.