Periodic Reporting for period 1 - SCOOBi (Seeking Constraints on Open Ocean Biocalcification)
Okres sprawozdawczy: 2022-12-01 do 2024-05-31
Why are the oceans supersaturated with respect to calcium carbonate? Foraminifera and coccolithophores generate over 2 billion tonnes of carbonate/yr1 but what limits this production? Our lack of understanding of the response of pelagic calcification to environmental change hinders any predictions of the future ocean carbon cycle and ecosystem.
This ground-breaking interdisciplinary project will transform our ability to predict the pelagic calcification response to future human “business as usual” or geoengineered perturbations. It will determine the historic and modern distribution of pelagic calcification rates, and how they are limited by environmental parameters quantitatively, and which factors accelerate calcification. Insights into the cost/benefit trade-off between calcification and growth will hint at emergence and origin of biomineralisation. By resolving mechanistically how cells partition energy and carbon between photosynthesis and calcification via genes and metabolites, and how the efficiency of these pathways is improved, SCOOBI opens the vista to engineering of these pathways including biomimetics and novel natural products.
The objectives are:
Ob1: Use innovative stable isotopic approaches applied to the natural laboratory of the geological record to identify the environmental parameters that trigger the highest pelagic adapted calcification efficiency (PIC/POC) in the modern and Cenozoic ocean.
Ob2: Document how different strategies of cell resource allocation affect the sensitivity of calcification to the environment in different coccolithophore species (Coccolithales versus Isochrysidales): Resolve whether there is a universal trade-off between growth rate and calcification.
Ob3: Detail the physiological and metabolic basis for the calcification efficiency of different species (PIC/POC) of coccolithophores and their sensitivity to environmental limitation and stress.
Ob4: Apply metabolite and large biomolecule composition, extracted from fossils, to document the environmental parameters that have driven changes in calcification efficiency over geological time and in the modern ocean
Ob5: Document the sensitivity of past community and organism-specific calcite production rates (PIC/POC*population size) to environmental parameters via a combination of cutting-edge genomic tools with sediment based estimates
Ob6: Investigate how the environmental sensitivity of calcite production rates, and their carbon isotopic composition, impacts understanding of the past and prediction of the future carbon cycle
This ground-breaking interdisciplinary project will transform our ability to predict the pelagic calcification response to future human “business as usual” or geoengineered perturbations. It will determine the historic and modern distribution of pelagic calcification rates, and how they are limited by environmental parameters quantitatively, and which factors accelerate calcification. Insights into the cost/benefit trade-off between calcification and growth will hint at emergence and origin of biomineralisation. By resolving mechanistically how cells partition energy and carbon between photosynthesis and calcification via genes and metabolites, and how the efficiency of these pathways is improved, SCOOBI opens the vista to engineering of these pathways including biomimetics and novel natural products.
The objectives are:
Ob1: Use innovative stable isotopic approaches applied to the natural laboratory of the geological record to identify the environmental parameters that trigger the highest pelagic adapted calcification efficiency (PIC/POC) in the modern and Cenozoic ocean.
Ob2: Document how different strategies of cell resource allocation affect the sensitivity of calcification to the environment in different coccolithophore species (Coccolithales versus Isochrysidales): Resolve whether there is a universal trade-off between growth rate and calcification.
Ob3: Detail the physiological and metabolic basis for the calcification efficiency of different species (PIC/POC) of coccolithophores and their sensitivity to environmental limitation and stress.
Ob4: Apply metabolite and large biomolecule composition, extracted from fossils, to document the environmental parameters that have driven changes in calcification efficiency over geological time and in the modern ocean
Ob5: Document the sensitivity of past community and organism-specific calcite production rates (PIC/POC*population size) to environmental parameters via a combination of cutting-edge genomic tools with sediment based estimates
Ob6: Investigate how the environmental sensitivity of calcite production rates, and their carbon isotopic composition, impacts understanding of the past and prediction of the future carbon cycle
We have generated and integrated a dataset consisting of carbon isotope ratios of size-separated coccolith calcite from marine sediments with a cell-scale model to interrogate cellular carbon fluxes and pCO2 through the Eocene (~55–34 Ma), Earth’s hottest interval of the past 100 million years. We show that the large coccolithophores that rose to dominate the oceans through the Eocene have higher calcification-to-carbon fixation ratios than their predecessors while the opposite is true for smaller coccolithophores. These changes, which occurred in the context of increasing ocean alkalization, may have played a role in an apparent positive carbon cycle feedback to decreasing pCO2. Our approach also provides independent support of multiproxy-based evidence for general decline through the Eocene in step with temperature. Together, this challenges the emerging view that a general decline in pCO2 reduces calcification on evolutionary timescales (Claxton et al., 2022).
Intracellular calcification in coccolithophores has been thought to be energy-intensive, necessitating precise energy regulation for the import of substrates and export of coccoliths. Here we apply varied conditions of Mg availability via Mg/Ca ratios, due to its dual interactions with the cellular C cycling and calcification pathways of coccolithophores, to interrogate the physiological context of calcification. We reveal a complex interplay between cellular carbon metabolism and calcification in the ubiquitous coccolithophore species Gephyrocapsa huxleyi (formerly Emiliania huxleyi). Notably, we identify that two energy thresholds for calcification exist: with sufficient energy to initiate calcification being reached between Mg/Ca ratios of 0 and 0.5 and energy to optimize the performance of calcification being attained between Mg/Ca ratios of 0.5 and 5. In energy-limited conditions, the allocation of carbon and energy towards cell growth and core metabolic activities is prioritised over calcification When sufficient energy is present, variations in substrate availability at the site of calcification override any cellular regulation. Beyond the required energy threshold, there is no feedback between calcification performance and cell physiology. It further suggests that as long as the environmental conditions are sufficient to reach the fairly low energy demand, globally G. huxleyi calcification intensity will depend on substrate availability subsequently impacting the global carbon cycle (Ma et al., in prep).
Intracellular calcification in coccolithophores has been thought to be energy-intensive, necessitating precise energy regulation for the import of substrates and export of coccoliths. Here we apply varied conditions of Mg availability via Mg/Ca ratios, due to its dual interactions with the cellular C cycling and calcification pathways of coccolithophores, to interrogate the physiological context of calcification. We reveal a complex interplay between cellular carbon metabolism and calcification in the ubiquitous coccolithophore species Gephyrocapsa huxleyi (formerly Emiliania huxleyi). Notably, we identify that two energy thresholds for calcification exist: with sufficient energy to initiate calcification being reached between Mg/Ca ratios of 0 and 0.5 and energy to optimize the performance of calcification being attained between Mg/Ca ratios of 0.5 and 5. In energy-limited conditions, the allocation of carbon and energy towards cell growth and core metabolic activities is prioritised over calcification When sufficient energy is present, variations in substrate availability at the site of calcification override any cellular regulation. Beyond the required energy threshold, there is no feedback between calcification performance and cell physiology. It further suggests that as long as the environmental conditions are sufficient to reach the fairly low energy demand, globally G. huxleyi calcification intensity will depend on substrate availability subsequently impacting the global carbon cycle (Ma et al., in prep).
The exact molecular mechanisms which direct and control coccolith production are unknown. Limited information is available on the presence and function of proteins incorporated into the coccolith matrix. In this study, we explore the proteins associated with coccoliths derived from a range of coccolithophore species including: the globally-abundant and well-studied Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related Gephyrocapsa oceanica, as well as the larger and more heavily calcified Coccolithus braarudii. Due to limited functional annotation, identified proteins were submitted to NCBI and InterPro packages to identify conserved protein domains functional features. Notably, a number of protein features were consistently seen across species, including; the cell signalling 14-3-3 domain, chromosome segregation SMC ATPase domain, as well as proteins involved in protein degradation and protease inhibition. Building consensus with existing work, we highlight the pentapeptide repeat to be associated with the coccolith matrix, being identified in all three examined species, and propose that this structural motif may play a role in controlling coccolith growth, where post-translational modification may be key. (Dedman et al., submitted).
Here, we report an integrated morphological, ecological and genomic survey across globally distributed G. huxleyi strains to reconstruct evolutionary relationships between morphotypes in relation to their habitats. While G. huxleyi has been considered a single cosmopolitan species, our analyses demonstrate that it has evolved to comprise at least three distinct species, which led us to formally revise the taxonomy of the G. huxleyi complex. Moreover, the first speciation event occurred before the onset of the last interglacial period (~140 ka), while the second followed during this interglacial. Then, further rapid diversifications occurred during the most recent ice-sheet expansion of the last glacial period and established morphotypes as dominant populations across environmental clines. These results suggest that glacial-cycle dynamics contributed to the isolation of ocean basins and the segregations of oceans fronts as extrinsic drivers of micro-evolutionary radiations in extant marine phytoplankton (Bendif et al., 2023).
Here, we report an integrated morphological, ecological and genomic survey across globally distributed G. huxleyi strains to reconstruct evolutionary relationships between morphotypes in relation to their habitats. While G. huxleyi has been considered a single cosmopolitan species, our analyses demonstrate that it has evolved to comprise at least three distinct species, which led us to formally revise the taxonomy of the G. huxleyi complex. Moreover, the first speciation event occurred before the onset of the last interglacial period (~140 ka), while the second followed during this interglacial. Then, further rapid diversifications occurred during the most recent ice-sheet expansion of the last glacial period and established morphotypes as dominant populations across environmental clines. These results suggest that glacial-cycle dynamics contributed to the isolation of ocean basins and the segregations of oceans fronts as extrinsic drivers of micro-evolutionary radiations in extant marine phytoplankton (Bendif et al., 2023).