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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2018-497
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-497
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Dec 2018

Research article | 17 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate Alexandrium minutum during a simulated marine heat wave

Elisabeth Deschaseaux1, James O'Brien1, Nachshon Siboni1, Katherina Petrou1,2, and Justin R. Seymour1 Elisabeth Deschaseaux et al.
  • 1University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia
  • 2University of Technology Sydney, School of Life Sciences, Ultimo, NSW, 2007, Australia

Abstract. The biogenic sulfur compounds dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) are produced and transformed by diverse populations of marine microorganisms and have substantial physiological, ecological and biogeochemical importance spanning organism to global scales. Understanding the production and transformation dynamics of these compounds under shifting environmental conditions is important for predicting their roles in a changing ocean. Here, we report the physiological and biochemical response of Alexandrium minutum, a dinoflagellate with the highest reported intracellular DMSP content, exposed to a 6 day increase in temperature mimicking coastal marine heatwave conditions (+4 °C and +12 °C). Under mild temperature increases (+4 °C), A. minutum growth was enhanced, with no measurable physiological stress response. However, under an acute increase in temperature (+12 °C), A. minutum growth declined, photosynthetic efficiency (FV/FM) was impaired, and enhanced oxidative stress was observed. These physiological responses were accompanied by increased DMS and DMSO concentrations followed by decreased DMSP concentrations. At this higher temperature, we observed a cascading stress response in A. minutum, which was initiated 6 h after the start of the experiment by a spike in DMS and DMSO concentrations and a rapid decrease in FV/FM. This was followed by an increase in reactive oxygen species (ROS) and an abrupt decline in DMS and DMSO on day 2 of the experiment. A subsequent decrease in DMSP coupled with a decline in the growth rate of both A. minutum and its associated total bacterial assemblage coincided with a shift in the composition of the A. minutum microbiome. Specifically, an increase in the relative abundance of OTUs matching the genus Oceanicaulis (17.0 %), Phycisphaeraceae SM1A02 (8.8 %) and Balneola (4.9 %) as well as a decreased relative abundance of Maribacter (24.4 %), Marinoscillum (4.7 %) and Seohaeicola (2.7 %), were primarily responsible for differences in microbiome structure observed between temperature treatments. These shifts in microbiome structure are likely to have been driven by either the changing physiological state of A. minutum cells, shifts in biogenic sulfur concentrations, or a combination of both. We suggest that these results point to the significant effect of heatwaves on the physiology, growth and microbiome composition of the red-tide causing dinoflagellate A. minutum, as well as potential implications for biogenic sulfur cycling processes and marine DMS emissions.

Elisabeth Deschaseaux et al.
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Status: final response (author comments only)
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Elisabeth Deschaseaux et al.
Elisabeth Deschaseaux et al.
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Here we report that abrupt increases in temperature simulating marine heatwaves might have the potential to shape the physiological state and biogenic sulfur production in microalgae involved in harmful algal blooms. Changing physiology and biochemistry seem to trigger a shift in the bacteria community associated with these microalgae. Since microalgae and associated bacteria play an important role in climate regulation, this could have serious consequences for our future ocean and climate.
Here we report that abrupt increases in temperature simulating marine heatwaves might have the...
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