Iron Necessity: The Secret of Wolbachia's Success?

The bacterium Wolbachia (order Rickettsiales) is probably the world's most successful vertically-transmitted symbiont, distributed among a staggering 40% of terrestrial arthropod species. Wolbachia has great potential in vector control due to its ability to manipulate its hosts' reproduction and to impede the replication and dissemination of arboviruses and other pathogens within haematophagous arthropods. In addition, the unexpected presence of Wolbachia in filarial nematodes of medical and veterinary importance has provided an opportunity to target the adult worms of Wuchereria bancrofti, Onchocerca volvulus, and Dirofilaria immitis with safe drugs such as doxycycline. A striking feature of Wolbachia is its phenotypic plasticity between (and sometimes within) hosts, which may be underpinned by its ability to integrate itself into several key processes within eukaryotic cells: oxidative stress, autophagy, and apoptosis. Importantly, despite significant differences in the genomes of arthropod and filarial Wolbachia strains, these nexuses appear to lie on a continuum in different hosts. Here, we consider how iron metabolism may represent a fundamental aspect of host homeostasis that is impacted by Wolbachia infection, connecting disparate pathways ranging from the provision of haem and ATP to programmed cell death, aging, and the recycling of intracellular resources. Depending on how Wolbachia and host cells interact across networks that depend on iron, the gradient between parasitism and mutualism may shift dynamically in some systems, or alternatively, stabilise on one or the other end of the spectrum

Atmosphere-ocean oxygen and productivity dynamics during early animal radiations

The proliferation of large, motile animals 540 to 520 Ma has been linked to both rising and declining O2 levels on Earth. To explore this conundrum, we reconstruct the global extent of seafloor oxygenation at approximately submillion-year resolution based on uranium isotope compositions of 187 marine carbonates samples from China, Siberia, and Morocco, and simulate O2 levels in the atmosphere and surface oceans using a mass balance model constrained by carbon, sulfur, and strontium isotopes in the same sedimentary successions. Our results point to a dynamically viable and highly variable state of atmosphere–ocean oxygenation with 2 massive expansions of seafloor anoxia in the aftermath of a prolonged interval of declining atmospheric pO2 levels. Although animals began diversifying beforehand, there were relatively few new appearances during these dramatic fluctuations in seafloor oxygenation. When O2 levels again rose, it occurred in concert with predicted high rates of photosynthetic production, both of which may have fueled more energy to predators and their armored prey in the evolving marine ecosystem

Geochemical evidence for widespread euxinia in the Later Cambrian ocean

Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth. In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans1, 2, possibly influencing evolutionary events during this time1, 2, 3. Physical evidence of widespread anoxia in Cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored. Here we present sulphur isotope records from six globally distributed stratigraphic sections of later Cambrian marine rocks (about 499 million years old). We find a positive sulphur isotope excursion in phase with the Steptoean Positive Carbon Isotope Excursion (SPICE), a large and rapid excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation4, 5. Numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large-scale anoxic and sulphidic (euxinic) conditions. Independently, molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia. These results identify the SPICE interval as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean. Thus, a redox structure similar to those in Proterozoic oceans6, 7, 8 may have persisted or returned in the oceans of the early Phanerozoic eon. Indeed, the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans.Organismic and Evolutionary Biolog

Sulphur and carbon cycling in the subduction zone mélange

Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks

Does pyrite act as an important host for molybdenum in modern and ancient euxinic sediments?

Molybdenum (Mo) is a popular paleoproxy for tracking the spatiotemporal pattern of euxinic (anoxic and sulfidic) conditions in the ancient ocean, yet surprisingly little is known about the processes leading to its fixation under sulfidic conditions. Pyrite has been proposed to be the main host phase for Mo sequestration. To clarify the role played by pyrite, and thus to refine the utility of this paleoproxy, modern and ancient samples from six different study sites were analyzed, all representing euxinic conditions, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Although pyrite often shows substantial enrichments relative to average crust and even matrix samples of similar size, our results show that most of the Mo in euxinic muds and shales is found in the non-pyrite matrix (80–100%) and not in the pyrite grains (0–20%)—simply because the volume of matrix dominates the bulk sediments/rocks. A relationship between the percent of Mo hosted by pyrite and the sulfur isotope composition of that pyrite is observed and can be linked to post-depositional alteration. Specifically, the oldest, typically most altered samples, show the highest δ^(34)S values because of limited sulfate availability at the time of their formation in the early ocean. In these old samples, the relatively small amount of Mo sequestered initially within pyrite is more likely to have been released to the matrix during the strong recrystallization overprints that these rocks have disproportionately suffered. Despite the universal importance of appreciable H_2S availability during Mo uptake, we conclude that pyrite should be viewed as a nontrivial sink for Mo but clearly not the primary host in most euxinic shales and rather suggest that other burial pathways should be emphasized in future studies of the mechanisms of Mo sequestration in such settings

Defining and Measuring the Patient-Centered Medical Home

The patient-centered medical home (PCMH) is four things: 1) the fundamental tenets of primary care: first contact access, comprehensiveness, integration/coordination, and relationships involving sustained partnership; 2) new ways of organizing practice; 3) development of practices’ internal capabilities, and 4) related health care system and reimbursement changes. All of these are focused on improving the health of whole people, families, communities and populations, and on increasing the value of healthcare

Chromium isotope fractionation during subduction-related metamorphism, black shale weathering, and hydrothermal alteration

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chemical Geology 423 (2016): 19-33, doi:10.1016/j.chemgeo.2016.01.003.Chromium (Cr) isotopes are an emerging proxy for redox processes at Earth’s surface. However, many geological reservoirs and isotope fractionation processes are still not well understood. The purpose of this contribution is to move forward our understanding of (1) Earth’s high temperature Cr isotope inventory and (2) Cr isotope fractionations during subduction-related metamorphism, black shale weathering and hydrothermal alteration. The examined basalts and their metamorphosed equivalents yielded δ53Cr values falling within a narrow range of -0.12±0.13‰ (2SD, n=30), consistent with the previously reported range for the bulk silicate Earth (BSE). Compilations of currently available data for fresh silicate rocks (43 samples), metamorphosed silicate rocks (50 samples), and mantle chromites (39 samples) give δ53Cr values of -0.13±0.13‰, -0.11±0.13‰, and -0.07±0.13‰, respectively. Although the number of high-temperature samples analyzed has tripled, the originally proposed BSE range appears robust. This suggests very limited Cr isotope fractionation under high temperature conditions. Additionally, in a highly altered metacarbonate transect that is representative of fluid-rich regional metamorphism, we did not find resolvable variations in δ53Cr, despite significant loss of Cr. This work suggests that primary Cr isotope signatures may be preserved even in instances of intense metamorphic alteration at relatively high fluid-rock ratios. Oxidative weathering of black shale at low pH creates isotopically heavy mobile Cr(VI). However, a significant proportion of the Cr(VI) is apparently immobilized near the weathering surface, leading to local enrichment of isotopically heavy Cr (δ53Cr values up to ~0.5‰). The observed large Cr isotope variation in the black shale weathering profile provides indirect evidence for active manganese oxide formation, which is primarily controlled by microbial activity. Lastly, we found widely variable δ53Cr (-0.2‰ to 0.6‰) values in highly serpentinized peridotites from ocean drilling program drill cores and outcropping ophiolite sequences. The isotopically heavy serpentinites are most easily explained through a multi-stage alteration processes: Cr loss from the host rock under oxidizing conditions, followed by Cr enrichment under sulfate reducing conditions. In contrast, Cr isotope variability is limited in mildly altered mafic oceanic crust.Funding for this research was provided by Agouron Institute to XLW, National Science Foundation (NSF) EAR-0105927 and EAR-1250269 to JJA, and NSF EAR-1324566 to ES. NJP and CTR acknowledge funding from the Alternative Earths NAI.2017-01-1

Proterozoic ocean redox and biogeochemical stasis

The partial pressure of oxygen in Earth’s atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5–0.543 Ga). However, the trajectory and mechanisms of Earth’s oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8–0.8 Ga). Given the coupling between redox-sensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30–40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1–10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo–N colimited marine biosphere during many periods of Earth’s history

Coupled evolution of nitrogen cycling and redoxcline dynamics on the Yangtze Block across the Ediacaran-Cambrian transition

The authors acknowledge funding support from the NSF FESD and Earth-Life Transitions programs (T.L.), the NASA Astrobiology Institute under Cooperative Agreement No. NNA15BB03A issued through the Science Mission Directorate (T.L.), the key project of the Natural Science Foundation of China (C.-F.C.) (No. 41730424), and the program of China Scholarships Council (Y.C.) (No. 201504910582). Nitrogen and carbon isotope analyses were funded by startup funds from Virginia Tech to B.C.G.The Ediacaran-Cambrian transition is characterized by the evolution of complex eukaryotes and rapid diversification of metazoans. However, linkages between environmental triggers and evolutionary patterns remain unclear. Here, we present high-resolution records of carbon and nitrogen isotopic data (δ13C, δ15N) for a drill core extending from the early Ediacaran Doushantuo Formation to the early Cambrian Jiumenchong Formation, located on the slope of the Yangtze Block. Our data show that sedimentary bulk nitrogen isotope values (δ15Nbulk) decrease progressively from the early Ediacaran to the early Cambrian, broadly concurrent with nitrogen isotope data from other sections throughout the Yangtze Block. During the early Ediacaran, however, δ15Nbulk values from our study are higher (maximum 11.2‰) compared to those from more restricted coeval sections, suggesting a higher degree of denitrification in our slope section. The early Ediacaran δ15Nbulk data from the Yangtze Block may thus provide indirect evidence for an upwelling system that led to a shallower redoxcline in slope environments of the Upper Yangtze region. Widespread light δ15Nbulk values from the early Cambrian (minimum −7.5‰) paired with excess silicate-bound nitrogen throughout much of the Yangtze Block are most parsimoniously interpreted as non-quantitative assimilation of ammonium (NH4+) with relatively high concentrations of NH4+ accumulating in the deep basin. Overall, the spatial and temporal trends in nitrogen cycling across the Yangtze Block suggest that fixed nitrogen was more bioavailable in the Ediacaran-Cambrian Yangtze Basin compared to previously studied Mesoproterozoic sections, although nitrogen speciation in the photic zone may have varied with time. Environmental factors such as oxygen levels and nitrogen bioavailability may have shaped the evolutionary trajectory of life on the Yangtze Block and potentially elsewhere across the Ediacaran-Cambrian transition.PostprintPeer reviewe

Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 463 (2017): 159-170, doi:10.1016/j.epsl.2017.01.032.The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.TL, ZL, and DH thank NSF EAR-1349252. ZL further thanks OCE-1232620. DH, ZL, and TL acknowledge further funding from a NASA Early Career Collaboration Award. TL, AB, NP, DH, and AK thank the NASA Astrobiology Institute. TL and NP received support from the Earth-Life Transitions Program of the NSF. AB acknowledges support from NSF grant EAR-05-45484 and an NSERC Discovery and Accelerator Grants. CW acknowledges support from NSFC grant 40972021