Work performed:
(1) Phytoplankton – bacterial interactions:
-We combined measurements of organosulfur concentrations and cycling rates with sequencing of taxonomic and functional genes, to assess if microbial activity rates can be predicted by the occurrence and expression of the relevant genes. This has been conducted with sample collections from previous expeditions to Antarctic and tropics as well as from the SUMMIT Mediterranean cruise (June 2021). [Masdeu-Navarro et al., Front. Mar. Sci. 9: 944141 (2022); Mangot, Simó et al., in preparation]
-During the SUMMIT-Moorea Expedition, additions of dimethylsulfoniopropionate (DMSP), acrylate, and glucose triggered N2 fixation rates by heterotrophic bacteria, and we are currently investigating how they upregulated the expression of N2 fixation genes. [Cerdán et al., in preparation]
-We conducted in situ chemotaxis assays (ISCA) to investigate if diazotrophs (N2 fixers) are enriched among bacteria attracted by DMSP [Mangot et al., work in progress]. ISCAs also served to demonstrate synergistic attraction of bacteria by DMSP and polysaccharides [Clerc et al., Nature Comm. 14: 8080 (2023)]
-We experimentally showed that marine sponges and their endosymbiotic bacteria consume volatile sulfur and bromine-containing compounds. [Simó et al., in review in Environ. Sci. Technol.]
-We described the distribution of sulfur compounds, alkylamines and other volatiles in Antarctic seawaters and sea ice. [Rocchi et al., Biogeosci. 22: 3429–3448 (2025); Crabeck et al., in review in Elementa]
-We showed how the volatile compound isoprene is consumed in the surface ocean. [Simó et al., Comm. Earth Environ. 3: 20 (2022)]
(2) Phytoplankton – phytoplankton interactions:
-We have identified the membrane transporter for the uptake of the algal osmolyte DMSP by eukaryotic phytoplankton. The candidate protein was suggested by radioisotope and transcriptomic assays, and its function was confirmed by functional complementation of a mutant of the bacterium Escherichia coli with the PaDT gene from a eukaryotic picoalga. Further experiments supported that exogenous DMSP incorporation as an energy-saving strategy. Finally, we showed the global and taxonomic spread of PaDT expression in the surface ocean. [Simó et al., submitted (2025)]
(3) Predator – phytoplankton interactions:
-We conducted chemotaxis experiments to investigate if protist grazing on phytoplankton is modulated by chemical signals, and if this oriented grazing facilitates the recovery of the prey population from physiological stress. Video cell tracking of predator swimming, cell counting of prey, and measurement of prey physiological stress level and recovery enabled to confirm that model herbivore protists are attracted by the algal osmolyte DMSP, this induces preferential grazing on sunlight-stressed algal cells, and subsequently accelerates prey population recovery from stress. [Güell-Bujons et al., ISME J. 18: wrae130 (2024); Güell-Bujons et al., in preparation]
-We investigated how organosulfur compounds are involved in phytoplankton bloom biomass control by viruses. [Vincent et al., Nature Comm. 4: 510 (2023); Vaqué et al., Antarctic Sci. 37: 265-277 (2025)]
(4) Modelling:
-We developed a numerical 1D model of organosulphur cycling across microbial food web interactions. [LeGland et al., Limnol Oceanogr. 69: 140-157 (2023)]
- We developed diagnostic and machine learning models for a revised assessment of the climate effects of global oceanic emissions of volatile sulfur in present and future scenarios [Wohl et al., Sci. Adv. 10: eadq2465 (2024); Joge et al., PNAS 122 (23): e2502077122] We also contributed to model isoprene emissions from the Southern Ocean. [Ferracci et al., Nature Comm. 15: 2571 (2024)]
