Abstract
Microorganisms in terrestrial and marine ecosystems are essential to environmental sustainability. In the marine environment, invertebrates often depend on metabolic cooperation with their endosymbionts. Coral reefs, one of the most important marine ecosystems, are based on the symbiosis between a broad diversity of dinoflagellates of the genus Symbiodinium and a wide phyletic diversity of hosts (i.e., cnidarian, molluscan, poriferan). This diversity is reflected in the ecology and physiology of the symbionts, yet the underlying biochemical mechanisms are still poorly understood. We examined metabolite profiles of four cultured species of Symbiodinium known to form viable symbioses with reef-building corals, S. microadriaticum (cp-type A194), S. minutum (cp-type B184), S. psygmophilum (cp-type B224) and S. trenchii (cp-type D206). Metabolite profiles were shown to differ among Symbiodinium species and were found to be affected by their physiological response to growth in different temperatures and light regimes. A combined Random Forests and Bayesian analysis revealed that the four Symbiodinium species examined primarily differed in their production of sterols and sugars, including a C29 stanol and the two sterols C28Δ5 and C28Δ5,22, as well as differences in metabolite abundances of a hexose and inositol. Inositol levels were also strongly affected by changes in temperature across all Symbiodinium species. Our results offer a detailed view of the metabolite profile characteristic of marine symbiotic dinoflagellates of the genus Symbiodinium, and identify patterns of metabolites related to several growth conditions.
Highlights
Microorganisms serve a critical role in both terrestrial and marine ecosystems and are essential to environmental sustainability
To investigate patterns in the algal metabolome related to individual Symbiodinium species or environmental conditions such as different temperatures and light intensities, four different species of cultured Symbiodinium were grown to exponential phase and subjected to gas-chromatography mass spectrometry (GC-MS)
The Symbiodinium species used in this study were S. microadriaticum, (classified as a Symbiodinium cp-type A194 based on clade (A) and fragment length (194bp) of the hypervariable region of domain V in the chloroplast 23S rDNA [cp-type]), S. minutum (Symbiodinium cp-type B184), S. psygmophilum (Symbiodinium cp-type B224) and S. trenchii (Symbiodinium cp-type D206)
Summary
Microorganisms serve a critical role in both terrestrial and marine ecosystems and are essential to environmental sustainability. The endosymbiotic algae reside within the gastroderm of the anthozoan host and utilize metabolic waste to produce photosynthetically derived carbon metabolites that are shared with the host [1,2,3] It is the mutualistic exchange of metabolites between the cnidarian host, the algal symbiont and their associated microbial assemblages (the holobiont), that provides the foundation of the modern coral reef ecosystem and makes significant contributions to global carbon and biogeochemical cycles [4,5]. These ecosystems are being lost at an alarming rate owing to mounting levels of environmental pressures (e.g., [6,7]). We grew four different species of cultured Symbiodinium under a variety of temperature and light conditions to directly measure the effects of environmental growth conditions on the metabolome
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