Adaptation of the green seaweed Ulva and its microbiome to cold temperature in Antarctica (COLDULVA)

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The project COLDULVA (read cold-Ulva) investigates the cold adaptation of the green macroalga Ulva, also known as sea lettuce, which occurs worldwide in coastal areas. Ulva is characterised by excellent adaptability to changes in its environment. It is therefore often found in waters heavily polluted by humans, but also under extreme natural conditions such as in Antarctica. However, Ulva´s growth and morphogenesis depend on the associated bacteria releasing growth-promoting compounds (morphogens). Under bacteria-free conditions, Ulva develops into a callus of non-differentiated cells. The project aimed to identify stress-regulated genes and metabolites that are stimulated during the short-term cold response and acclimation under specific consideration of Ulva´s microbiome.Interestingly, cold-adapted (i.e. the Antarctic/cold temperate) Ulva species also grow at a higher temperature. However, the warm temperate U. mutabilis does not grow at low temperature, and neither do the associated essential bacteria. These observations pave the way to decipher the cold-responsive genes and metabolites in Ulva from the perspective of both intrinsic (algal metabolism) and extrinsic (microbiome) factors. COLDULVA will compare the warm temperate model system Ulva mutabilis (originally collected in the Ria Formosa, Portugal) with sampled Antarctic/cold temperate Ulva strains in the Potter Cove at King George Island (Antarctica). We hypothesise that Ulva will react properly to stress if its microbiome also adapts to environmental changes to provide the necessary algal growth-promoting compounds. In the first funding period, the following three approaches were performed to address the key question “Are there key genes and metabolites for adaptation to Antarctic environmental conditions?” Bacteria were isolated from Antarctic temperate Ulva species to promote the growth of the warm temperate Ulva mutabilis at low temperature. Changes in the algal metabolism due to differential gene expression and metabolite production were investigated upon a shift to cold temperature in order to define the Ulva’s core stress-responsive genes and metabolites. COLDULVA aims during its second funding period: (1) To integrate the metabolome and transcriptome data of our split-sample study for identifying genes and metabolites patterns under cold stress conditions. (2) To decipher the natural products involved in Ulva-bacteria symbiosis under cold stress using MALDI MS imaging for spatial and temporal resolution. (3) To quantify the morphogen thallusin in order to unravel its potential role in cold-adaptation of the symbiosis between Ulva and its associated bacteria using dose-response relationships. As a result of the second funding period, COLDULVA will provide insights onto the regulatory networks of bacterial macroalgal interactions and the bacteria-mediated cold adaptation of Ulva, the bacterial settlement on the algal surface and morphogen production under cold stress.