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Metaproteomic insights into the elemental stoichiometry of a changing Southern Ocean

ABSTRACT: We conducted two iron-temperature bioassay incubation experiments during the austral summer of 2018-2019 in the Weddell Sea, Southern Ocean. The first bioassay (BA1) was initiated on December 28th, 2018, approximately 560 km away from the ice edge at 65°S 0.038°E. The second bioassay (BA2) was initiated on January 9th, 2019, approximately 70 km from the ice edge at 70.15°S 11.02°W (Figure 1A). For both bioassays, we collected sea water at 20 m depth using a custom-built ultraclean CTD sampling system – “Titan” (De Baar et al. 2008). We chose this depth to minimize light shock when the microbial community was brought on deck, and to prevent trace metal contamination from the ship. After recovery, Titan was moved into a dedicated, temperature-controlled, trace-metal-clean (TMC) laboratory container where the sea water was used for initial (T0) sampling, and to fill triplicate, 20 L, TMC cubitainers for each iron-temperature treatment. The treatment matrix including four iron-temperature conditions: low iron – low temperature, high iron – low temperature, low iron – high temperature, high iron – high temperature. We did not add any iron to the low iron treatments. We supplemented the high iron treatments with a naturally occurring but rare isotope of 57Fe, which allowed us to differentiate between the added iron and iron already present in the water (mainly 56Fe). For this, we made a 40 µM 57FeCl3 stock solution in 0.1 M trace-metal grade HCl, then added 1 mL of this stock to each of the high iron cubitainers. This resulted in an initial dissolved 57Fe concentration of 2 nM in the high iron treatments. We then sealed the cubitainers and placed them inside temperature-controlled deck incubators where the low temperature treatments were incubated under in situ temperature, and the high temperature treatments were incubated under in situ + 2 °C (Table S1).

INSTRUMENT(S):

ORGANISM(S): Marine Plankton Environmental Sample

SUBMITTER: Loay Jabre

LAB HEAD: Erin M. Bertrand

PROVIDER: PXD042627 | Pride | 2026-06-24

REPOSITORIES: Pride

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			Action	DRS
	211216_1037_097_LJ_01_48.raw	Raw
	211216_1037_097_LJ_01_49.raw	Raw
	211216_1037_097_LJ_02_51.raw	Raw
	211216_1037_097_LJ_02_52.raw	Raw
	211216_1037_097_LJ_03_54.raw	Raw

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Project description:Quantitative RNA sequencing (RNA-seq) and the complementary phenotypic assays were implemented to investigate the transcriptional responses of Chromohalobacter salexigens to osmotic and heat stress. These conditions trigger the synthesis of ectoine and hydroxyectoine, two compatible solutes of biotechnological interest. Our findings revealed that both stresses make a significant impact on C. salexigens global physiology. Apart from compatible solute metabolism, the most relevant adaptation mechanisms were related to “oxidative- and protein-folding- stress responses”, “modulation of respiratory chain and related components”, and “ion homeostasis”. A general salt-dependent induction of genes related to the metabolism of ectoines, as well as repression of ectoine degradation genes by temperature, was observed. Different oxidative stress response mechanisms, secondary or primary, were induced at low and high salinity respectively, and repressed by temperature. A higher sensitivity to H2O2 was observed at high salinity, regardless of temperature. Low salinity induced genes involved in “protein-folding-stress response”, suggesting disturbance of protein homeostasis. Transcriptional shift of genes encoding three types of respiratory NADH dehydrogenases, ATP synthase, quinone pool, Na+/H+ antiporters, and sodium-solute symporters, was observed depending on salinity and temperature, suggesting modulation of the components of the respiratory chain and additional systems involved in the generation of H+ and/or Na+ gradients. Remarkably, the Na+ intracellular content remained constant regardless of salinity and temperature. Disturbance of Na+- and H+-gradients with specific ionophores suggested that both gradients influence ectoine production, but with differences depending on the solute, salinity, and temperature conditions. Flagellum genes were strongly induced by salinity, and further induced by temperature. However, salt-induced cell motility was reduced at high temperature, possibly caused by an alteration of Na+ permeability by temperature, as dependence of motility on Na+-gradient was observed. The transcriptional induction of genes related to the synthesis and transport of siderophores correlated with a higher siderophore production and intracellular iron content only at low salinity. In addition, compared to low salinity external iron increased hydroxyectoine accumulation by 20% at high salinity, but reduced the intracellular content of ectoines by 50% at high salinity plus high temperature. These findings support the relevance of iron homeostasis for osmoadaptation, thermoadaptation and accumulation of ectoines, in C. salexigens

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Metaproteomic insights into the elemental stoichiometry of a changing Southern Ocean

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