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1. Diel Transcriptional Oscillations of a Plastid Antiporter Reflect Increased Resilience of Thalassiosira pseudonana in Elevated CO2

   https://doi.org/10.3389/fmars.2021.633225  

   Valenzuela, Jacob J. ; Ashworth, Justin ; Cusick, Allison ; Abbriano, Raffaela M. ; Armbrust, E. Virginia ; Hildebrand, Mark ; Orellana, Mónica V. ; Baliga, Nitin S. ( May 2021 , Frontiers in Marine Science)

   Acidification of the ocean due to high atmospheric CO 2 levels may increase the resilience of diatoms causing dramatic shifts in abiotic and biotic cycles with lasting implications on marine ecosystems. Here, we report a potential bioindicator of a shift in the resilience of a coastal and centric model diatom Thalassiosira pseudonana under elevated CO 2 . Specifically, we have discovered, through EGFP-tagging, a plastid membrane localized putative Na + (K + )/H + antiporter that is significantly upregulated at >800 ppm CO 2 , with a potentially important role in maintaining pH homeostasis. Notably, transcript abundance of this antiporter gene was relatively low and constant over the diel cycle under contemporary CO 2 conditions. In future acidified oceanic conditions, dramatic oscillation with >10-fold change between nighttime (high) and daytime (low) transcript abundances of the antiporter was associated with increased resilience of T. pseudonana . By analyzing metatranscriptomic data from the Tara Oceans project, we demonstrate that phylogenetically diverse diatoms express homologs of this antiporter across the globe. We propose that the differential between night- and daytime transcript levels of the antiporter could serve as a bioindicator of a shift in the resilience of diatoms in response to high COmore »2 conditions in marine environments.« less
2. Metabolic versatility of the nitrite-oxidizing bacterium Nitrospira marina and its proteomic response to oxygen-limited conditions

   https://doi.org/10.1038/s41396-020-00828-3  

   Bayer, Barbara ; Saito, Mak A. ; McIlvin, Matthew R. ; Lücker, Sebastian ; Moran, Dawn M. ; Lankiewicz, Thomas S. ; Dupont, Christopher L. ; Santoro, Alyson E. ( November 2020 , The ISME Journal)

   The genusNitrospirais the most widespread group of nitrite-oxidizing bacteria and thrives in diverse natural and engineered ecosystems. Nitrospira marinaNb-295^Twas isolated from the ocean over 30 years ago; however, its genome has not yet been analyzed. Here, we investigated the metabolic potential ofN. marinabased on its complete genome sequence and performed physiological experiments to test genome-derived hypotheses. Our data confirm thatN. marinabenefits from additions of undefined organic carbon substrates, has adaptations to resist oxidative, osmotic, and UV light-induced stress and low dissolvedpCO₂, and requires exogenous vitamin B₁₂. In addition,N. marinais able to grow chemoorganotrophically on formate, and is thus not an obligate chemolithoautotroph. We further investigated the proteomic response ofN. marinato low (∼5.6 µM) O₂concentrations. The abundance of a potentially more efficient CO₂-fixing pyruvate:ferredoxin oxidoreductase (POR) complex and a high-affinitycbb₃-type terminal oxidase increased under O₂limitation, suggesting a role in sustaining nitrite oxidation-driven autotrophy. This putatively more O₂-sensitive POR complex might be protected from oxidative damage by Cu/Zn-binding superoxide dismutase, which also increased in abundance under low O₂conditions. Furthermore, the upregulation of proteins involved in alternative energy metabolisms, including Group 3b [NiFe] hydrogenase and formate dehydrogenase, indicate a high metabolic versatility to survive conditions unfavorable for aerobic nitrite oxidation. In summary, themore »genome and proteome of the first marineNitrospiraisolate identifies adaptations to life in the oxic ocean and provides insights into the metabolic diversity and niche differentiation of NOB in marine environments.

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3. Community context and pCO2 impact the transcriptome of the “helper” bacterium Alteromonas in co-culture with picocyanobacteria

   https://doi.org/10.1038/s43705-022-00197-2  

   Barreto Filho, Marcelo Malisano ; Lu, Zhiying ; Walker, Melissa ; Morris, J. Jeffrey ( November 2022 , ISME Communications)

   Many microbial photoautotrophs depend on heterotrophic bacteria for accomplishing essential functions. Environmental changes, however, could alter or eliminate such interactions. We investigated the effects of changing pCO₂on gene transcription in co-cultures of 3 strains of picocyanobacteria (Synechococcusstrains CC9311 and WH8102 andProchlorococcusstrain MIT9312) paired with the ‘helper’ bacteriumAlteromonas macleodiiEZ55. Co-culture with cyanobacteria resulted in a much higher number of up- and down-regulated genes in EZ55 than pCO₂by itself. Pathway analysis revealed significantly different transcription of genes involved in carbohydrate metabolism, stress response, and chemotaxis, with different patterns of up- or down-regulation in co-culture with different cyanobacterial strains. Gene transcription patterns of organic and inorganic nutrient transporter and catabolism genes in EZ55 suggested resources available in the culture media were altered under elevated (800 ppm) pCO₂conditions. Altogether, changing transcription patterns were consistent with the possibility that the composition of cyanobacterial excretions changed under the two pCO₂regimes, causing extensive ecophysiological changes in both members of the co-cultures. Additionally, significant downregulation of oxidative stress genes in MIT9312/EZ55 cocultures at 800 ppm pCO₂were consistent with a link between the predicted reduced availability of photorespiratory byproducts (i.e., glycolate/2PG) under this condition and observed reductions in internal oxidative stress loads for EZ55, providing a possible explanationmore »for the previously observed lack of “help” provided by EZ55 to MIT9312 under elevated pCO₂. If similar broad alterations in microbial ecophysiology occur in the ocean as atmospheric pCO₂increases, they could lead to substantially altered ecosystem functioning and community composition.

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4. Loss of transcriptional plasticity but sustained adaptive capacity after adaptation to global change conditions in a marine copepod

   https://doi.org/10.1038/s41467-022-28742-6  

   Brennan, Reid S. ; deMayo, James A. ; Dam, Hans G. ; Finiguerra, Michael B. ; Baumann, Hannes ; Pespeni, Melissa H. ( March 2022 , Nature Communications)

   Adaptive evolution and phenotypic plasticity will fuel resilience in the geologically unprecedented warming and acidification of the earth’s oceans, however, we have much to learn about the interactions and costs of these mechanisms of resilience. Here, using 20 generations of experimental evolution followed by three generations of reciprocal transplants, we investigated the relationship between adaptation and plasticity in the marine copepod,Acartia tonsa, in future global change conditions (high temperature and high CO₂). We found parallel adaptation to global change conditions in genes related to stress response, gene expression regulation, actin regulation, developmental processes, and energy production. However, reciprocal transplantation showed that adaptation resulted in a loss of transcriptional plasticity, reduced fecundity, and reduced population growth when global change-adapted animals were returned to ambient conditions or reared in low food conditions. However, after three successive transplant generations, global change-adapted animals were able to match the ambient-adaptive transcriptional profile. Concurrent changes in allele frequencies and erosion of nucleotide diversity suggest that this recovery occurred via adaptation back to ancestral conditions. These results demonstrate that while plasticity facilitated initial survival in global change conditions, it eroded after 20 generations as populations adapted, limiting resilience to new stressors and previously benign environments.
5. Temperature sensitivity of carbon concentrating mechanisms in the diatom Phaeodactylum tricornutum

   https://doi.org/10.1007/s11120-023-01004-2  

   Li, Meng ; Young, Jodi N. ( March 2023 , Photosynthesis Research)

   Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO₂around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO₂concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatomPhaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates byPtat elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO₂saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO₂into the cell, driven byPt’s ‘chloroplast pump’ was the major inorganic carbon source. However, at 18 °C, upregulation of the chloroplast pump enhanced (while retaining the proportion of) both diffusive CO₂and active HCO₃⁻uptake into the cytosol, and significantly increased chloroplast HCO₃⁻concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO₂into the cell remained constant, active HCO₃⁻uptake across the cell membrane increased resulting inPtdepending equally on both CO₂and HCO₃⁻as inorganic carbon sources. Despitemore »changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of thePtCCM in response to increasing temperatures was discussed.

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