The iron limitation mosaic in the California Current System: Factors governing Fe availability in the shelf/near-shelf region

The California Current System is a productive eastern boundary region off the coasts of Washington, Oregon, and California. There is strong seasonality to the region, with high levels of rainfall and river input to the coastal ocean during the winter season, and coastal and Ekman upwelling during the spring and summer. Iron (Fe) input to the coastal ocean during the winter months can be stored in the continental shelf mud belts and then be delivered to the surface ocean by upwelling in the spring and summer. There have been a number of studies providing strong evidence of Fe-limitation of diatom growth occurring in regions of the California Current System off of California, and the occurrence of Fe-limitation has been linked with narrow continental shelf mud belt width and low river input. We provide evidence for potential Fe-limitation of diatoms off the southern coast of Oregon in July 2014, just off the shelf break near Cape Blanco in a region with moderate shelf width and river input. Since eastern boundary regions account for a disproportionally large amount of global primary production, this observation of potential Fe-limitation in an unexpected near-shore region of the California Current System has implications for global models of primary productivity. In order to re-evaluate the factors impacting Fe availability, we utilize satellite imagery to compare with historical datasets, and show that unexpected levels of Fe can often be explained by eddies, plumes of upwelled water moving offshore, or lack of recent upwelling

Impaired viral infection and reduced mortality of diatoms in iron-limited oceanic regions

Diatom primary productivity is tightly coupled with carbon export through the ballasted nature of the silica-based cell wall, linking the oceanic silicon and carbon cycles. However, despite low productivity, iron (Fe)-limited regimes are considered ‘hot spots’ of diatom silica burial with enhanced carbon export efficiency, raising questions about the mechanisms driving the biogeochemistry of these regions. Marine viruses are classically recognized as catalysts of remineralization through host lysis, short-circuiting the trophic transfer of carbon and facilitating the retention of dissolved organic matter and associated elements in the surface ocean. Here we used metatranscriptomic analysis of diatoms and associated viruses, along with a suite of physiological and geochemical metrics, to study the interaction between diatoms and viruses in Fe-limited regimes of the northeast Pacific. We found low cell-associated diatom virus diversity and abundance in a chronically Fe-limited region of the subarctic northeast Pacific. In a coastal upwelling region of the California Current, transient iron limitation also substantially reduced viral replication. These observations were recapitulated in Fe-limited cultures of the bloom-forming, centric diatom, Chaetoceros tenuissimus, which exhibited delayed virus-mediated mortality in addition to reduced viral replication. We suggest Fe-limited diatoms escape viral lysis and subsequent remineralization in the surface ocean, providing an additional mechanism contributing to enhanced carbon export efficiency and silica burial in Fe-limited oceanic regimes

Divergent gene expression among phytoplankton taxa in response to upwelling

Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment

Divergent gene expression among phytoplankton taxa in response to upwelling

Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment

Linking the heart and the brain: Neurodevelopmental disorders in patients with catecholaminergic polymorphic ventricular tachycardia

International audienceBACKGROUND:Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an uncommon inherited arrhythmia disorder characterized by adrenergically evoked ventricular arrhythmias. Mutations in the cardiac calcium release channel/ryanodine receptor gene (RYR2) are identified in the majority of patients with CPVT. RyR2 is also the major RyR isoform expressed in the brain.OBJECTIVE:The purpose of this study was to estimate the prevalence of intellectual disability (ID) and other neurodevelopmental disorders (NDDs) in RYR2-associated CPVT (CPVT1) and to study the characteristics of these patients.METHODS:We reviewed the medical records of all CPVT1 patients from 12 international centers and analyzed the characteristics of all CPVT1 patients with concomitant NDDs. We functionally characterized the mutations to assess their response to caffeine activation. We did not correct for potential confounders.RESULTS:Among 421 CPVT1 patients, we identified 34 patients with ID (8%; 95% confidence interval 6%-11%). Median age at diagnosis was 9.3 years (interquartile range 7.0-14.5). Parents for 24 of 34 patients were available for genetic testing, and 13 of 24 (54%) had a de novo mutation. Severity of ID ranged from mild to severe and was accompanied by other NDDs in 9 patients (26%). Functionally, the ID-associated mutations showed a markedly enhanced response of RyR2 to activation by caffeine. Seventeen patients (50%) also had supraventricular arrhythmias. During median follow-up of 8.4 years (interquartile range 1.8-12.4), 15 patients (45%) experienced an arrhythmic event despite adequate therapy.CONCLUSION:Our study indicates that ID is more prevalent among CPVT1 patients (8%) than in the general population (1%-3%). This subgroup of CPVT1 patients reveals a malignant cardiac phenotype with marked supraventricular and ventricular arrhythmias