Photosynthetic Oxygen Research Articles

Lichens Bite the Dust - A Bioweathering Scenario in the Atacama Desert.

SummaryBioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.

Kinetic characterization of microalgal-bacterial systems: Contributions of microalgae and heterotrophic bacteria to the oxygen balance in wastewater treatment

Abstract Metabolic activities of microalgae and heterotrophic bacteria were characterized in terms of dissolved O2 uptake and production rates under dark and light conditions, assessing the contribution of both microbial groups to the O2 balance during wastewater treatment. Up to 13 kinetic and stoichiometric parameters were determined, allowing a quantitative description of the O2 production and uptake dynamics. Under dark conditions, the maximum specific O2 uptake rates for microalgae and bacteria were 14.73 ± 2.02 mgO2 gVSS−1 h−1 and 2.37 ± 1.52 mgO2 gVSS−1 h−1, respectively. Microalgae were therefore the largest O2 consumers under dark conditions, being responsible for up to 86 % of the total heterotrophic respiration. Under light conditions (photosynthetic metabolism for microalgae and heterotrophic metabolism for bacteria), microalgae supported a maximum specific O2 production rate of 13.76 ± 1.48 mgO2 gVSS-1 h-1, while bacteria supported a maximum specific O2 uptake of 2.37 ± 1.52 mgO2 gVSS-1 h-1. The oxygenation performance of the microalgal community was therefore superior to the O2 respiration of heterotrophic bacteria under light conditions. The kinetic characterization performed provides critical information about the photosynthetic oxygenation potential, microbial growth and heterotrophic O2 uptake, which is essential for design, optimization, and modeling of wastewater treatment processes.

Adaptation of Coccomyxa sp. to Extremely Low Light Conditions Causes Deep Chlorophyll and Oxygen Maxima in Acidic Pit Lakes.

Deep chlorophyll maxima (DCM) and metalimnetic oxygen maxima (MOM) are outstanding biogeochemical features of acidic pit lakes (APL). However, knowledge of the eukaryotic phototrophs responsible for their formation is limited. We aimed at linking the dynamics of phototrophic communities inhabiting meromictic APL in Spain with the formation of these characteristic layers. Firstly, the dynamics of DCM and MOM and their relation to physico-chemical parameters (photosynthetically active radiation (PAR), pH, dissolved ferric iron concentration, temperature), pigments and nutrient distribution is described; secondly, the phototrophic community composition is studied through a combination of microscopy, biomolecular and “omics” tools. Phototrophic communities of the studied APL show a low diversity dominated by green microalgae, specifically Coccomyxa sp., which have been successfully adapted to the chemically harsh conditions. DCM and MOM are usually non-coincident. DCM correspond to layers where phototrophs have higher chlorophyll content per cell to cope with extremely low PAR (<1 µmol m−2 s−1), but where photosynthetic oxygen production is limited. MOM correspond to shallower waters with more light, higher phytoplankton biomass and intense photosynthetic activity, which affects both oxygen concentration and water temperature. The main drivers of DCM formation in these APL are likely the need for nutrient uptake and photo-acclimation.

Mantle degassing related to changing redox and thermal conditions during the Precambrian supercontinent cycle

The C-O-H cycling of the early shallow Earth is suggested to be closely related to mantle degassing and speciation processes. These processes are influenced by the mantle’s thermal and redox states, which have changed significantly in different mantle reservoirs during Earth’s protracted history. However, the link between speciation of C-O-H magmatic volatiles and the temporal changes of the mantle’s thermal and redox states in different mantle reservoirs remains elusive. We test this link through chemical equilibrium modeling of C-O-H magmatic volatiles to assess its influences on shallow C-O-H cycling and the oxidization history of the shallow Earth. We find that a rapid oxidization of Archean mantle related to recycling of oceanic crust, core-mantle material exchange, or evolution of primitive mantle redox heterogeneities can strongly reduce the fraction of reducing compositions (e.g., H2 and CH4) in volcanic gases, which then consumed less photosynthetic oxygen, leading to a net increase of atmospheric oxygen and triggering the Great Oxidation Event (GOE) at 2.4–2.3 Ga. After the GOE, mantle degassing at rifts, mid ocean ridges, and plumes became more oxidizing and thus triggered later atmospheric oxidation synchronous with supercontinent breakup. Our results support that the oxidation of the atmosphere in the Precambrian was influenced by mantle oxidation, upwelling and/or degassing, especially during the GOE.

Effects of temperature and hypoxia on respiration, photorespiration, and photosynthesis of seagrass leaves from contrasting temperature regimes

Abstract In near-future climate change scenarios, elevated ocean temperatures with higher and more frequent peaks are anticipated than at present. Moreover, increased eutrophication and higher primary and secondary productivity will affect the oxygen levels of shallow-water coastal ecosystems, creating hypoxic conditions that can be experienced regularly, especially in dense vegetated systems. These climate-related events may impose detrimental effects on the primary productivity of seagrass. To evaluate such effects, this study combined gas exchange measurements with pulse amplitude-modulated fluorometry to assess the impact of short-time exposure to a range of water temperatures at ambient and low-oxygen levels on mitochondrial respiration, chlorophyll fluorescence (based on the Fv/F0 ratio), photosynthetic oxygen evolution, and photorespiration in leaf segments of the temperate seagrass Zostera marina and the tropical seagrass Thalassia hemprichii. We found that mitochondrial respiration in both Z. marina and T. hemprichii increased with higher temperatures up to 40°C and that low O2 caused significantly reduced respiration rates, particularly in T. hemprichii. Elevated water temperature had a clear negative effect on the Fv/F0 of both seagrass species, indicating damage or inactivation of the photosynthetic apparatus, even when light is not present. Moreover, damage to the photosynthetic apparatus was observed as an effect of elevated temperature combined with low O2 during darkness, resulting in subsequent lower photosynthesis in light. Photorespiration was present, but not promoted by increased temperature alone and will thus not further contribute to productivity losses during warmer events (when not carbon limited). This study demonstrates the negative impact of hypoxic stress and elevated temperatures on seagrass productivity, which may influence the overall health of seagrass plants as well as oxygen and carbon fluxes of shallow-water coastal ecosystems in warmer climate scenarios.

Integrating solar photovoltaic capacitor into algal-bacterial photo-bioelectrochemical system towards all-weather synchronous enhanced antibiotic and nitrogen removal from wastewater

Algal-bacterial photo-bioelectrochemical system (ABPBS) operated with daily light/dark cycle provides a novel approach for sustainable treatment of wastewater through the uses of solar energy and bioenergy. However, it can not be effectively driven when the photosynthetic oxygen supply by algae at the cathode stops at night. In this study, a solar photovoltaic capacitor discharging was integrated into the ABPBS to achieve all-weather synchronous enhanced antibiotic and nitrogen removal from wastewater. The results showed that 3.3 F, 10 F and 100 F capacitor discharge increased the degradation rate of florfenicol (FLO) by 44%, 89%, and 582% at the anode, the removal rate of ammonia nitrogen by 20.4%, 39.8%, and 55.6%, the accumulated nitrate was decreased by 70.0%, 86.5%, and 93.3%, and the accumulated nitrite was decreased by 48.6%, 45.7%, and 87.1% at the biocathode, respectively. There was a significant positive correlation between the capacity of the capacitor and its ability to promote FLO degradation and nitrogen removal. The capacitor discharge promoted the photosynthetic oxygen release and biocatalytic oxygen reduction, and stimulated the growth of functional bacteria capable of degrading complex organics through extracellular electron transfer in the anode and diverse nitrogen removal bacteria in the cathode, but there were structural differences of functional bacteria groups induced by the different capacities of capacitor discharges.

Cell Wall Reinforcements Accompany Chilling and Freezing Stress in the Streptophyte Green Alga Klebsormidium crenulatum.

Adaptation strategies in freezing resistance were investigated in Klebsormidium crenulatum, an early branching streptophyte green alga related to higher plants. Klebsormidium grows naturally in unfavorable environments like alpine biological soil crusts, exposed to desiccation, high irradiation and cold stress. Here, chilling and freezing induced alterations of the ultrastructure were investigated. Control samples (kept at 20°C) were compared to chilled (4°C) as well as extracellularly frozen algae (−2 and −4°C). A software-controlled laboratory freezer (AFU, automatic freezing unit) was used for algal exposure to various temperatures and freezing was manually induced. Samples were then high pressure frozen and cryo-substituted for electron microscopy. Control cells had a similar appearance in size and ultrastructure as previously reported. While chilling stressed algae only showed minor ultrastructural alterations, such as small inward facing cell wall plugs and minor alterations of organelles, drastic changes of the cell wall and in organelle distribution were found in extracellularly frozen samples (−2°C and −4°C). In frozen samples, the cytoplasm was not retracted from the cell wall, but extensive three-dimensional cell wall layers were formed, most prominently in the corners of the cells, as determined by FIB-SEM and TEM tomography. Similar alterations/adaptations of the cell wall were not reported or visualized in Klebsormidium before, neither in controls, nor during other stress scenarios. This indicates that the cell wall is reinforced by these additional wall layers during freezing stress. Cells allowed to recover from freezing stress (−2°C) for 5 h at 20°C lost these additional cell wall layers, suggesting their dynamic formation. The composition of these cell wall reinforcement areas was investigated by immuno-TEM. In addition, alterations of structure and distribution of mitochondria, dictyosomes and a drastically increased endoplasmic reticulum were observed in frozen cells by TEM and TEM tomography. Measurements of the photosynthetic oxygen production showed an acclimation of Klebsormidium to chilling stress, which correlates with our findings on ultrastructural alterations of morphology and distribution of organelles. The cell wall reinforcement areas, together with the observed changes in organelle structure and distribution, are likely to contribute to maintenance of an undisturbed cell physiology and to adaptation to chilling and freezing stress.

Bacteria and photosynthetic cells in a photobioreactor treating real municipal wastewater: Analysis and quantification using flow cytometry

Wastewater born microalgal-bacterial consortia in closed photobioreactors (PBRs) have demonstrated high efficiency in pollutant removal, relying only on photosynthetic oxygenation. However, their qualitative and quantitative composition is still poorly understood.This paper describes the extension of flow cytometry in order to analyze a microalgal-bacterial consortium developed in a long-term PBR treating real wastewater. A multi-step procedure was proposed to obtain an accurate flow cytometry (FCM) analysis. Ultrasonication at specific applied energy of 90 kJ L−1 was identified as optimal for sample pre-treatment to recover the maximum number of bacteria and photosynthetic cells while avoiding their disruption. Fluorescence and scattering signals were used to distinguish and quantify microalgae and bacteria.In the tested consortium, bacteria (marked green with SYBR-Green I) were 98% of total cells (on average 1.2E+12 cells/L) while microalgae (having red autofluorescence) accounted for only 2% of total cells (2.8E+10 cells/L). Microalgae were characterized by a biovolume 2 orders of magnitude larger than bacteria, resulting in a photosynthetic biomass quantitatively comparable to bacteria.The proposed FCM approach represents a valuable tool with which to enhance knowledge about the composition and quantification of microorganisms in PBRs, which have not yet been fully understood.

Safety of photosynthetic Synechococcus elongatus for in vivo cyanobacteria-mammalian symbiotic therapeutics.

SummaryThe cyanobacterium Synechococcus elongatus (SE) has been shown to rescue ischaemic heart muscle after myocardial infarction by photosynthetic oxygen production. Here, we investigated SE toxicity and hypothesized that systemic SE exposure does not elicit a significant immune response in rats. Wistar rats intravenously received SE (n = 12), sterile saline (n = 12) or E. coli lipopolysaccharide (LPS, n = 4), and a subset (8 SE, 8 saline) received a repeat injection 4 weeks later. At baseline, 4 h, 24 h, 48 h, 8 days and 4 weeks after injection, clinical assessments, blood cultures, blood counts, lymphocyte phenotypes, liver function tests, proinflammatory cytokines and immunoglobulins were assessed. Across all metrics, SE rats responded comparably to saline controls, displaying no clinically significant immune response. As expected, LPS rats exhibited severe immunological responses. Systemic SE administration does not induce sepsis or toxicity in rats, thereby supporting the safety of cyanobacteria–mammalian symbiotic therapeutics using this organism.

Habitat characteristics mediated partitioning of economically important bivalves in a tropical monsoon-influenced estuary.

Bivalves are benthic organisms inhabiting coastal marine habitats, especially estuarine tidal and mudflats. Due to their high stocking density and rich protein content, they form a major part of the artisanal fishery resource around the world. A clear partitioning in the population of bivalves, Paphia malabarica (Chemnitz, 1782), and Meretrix casta (Gmelin, 1791) in southern (Chicalim) and northern (Siridao) bank of a tropical Zuari estuary influenced by the monsoon along the Indian west coast, is evidenced. This study unravels the reasons for their partitioning in this estuary. Paphia malabarica is an exclusive inhabitant of Chicalim which has silty-sandy sediment, whereas M. casta is exclusive to Siridao, a sandy habitat. Observations showed that this segregation is facilitated by the semi-enclosed nature of habitat at Chicalim with the high amount of degraded and aged sediment organic carbon, high chlorophyll a, elemental, and biochemical components, whereas Siridao experiences the high impact of tidal currents, low sediment organic carbon, and high water column chlorophyll a. The habitat in Siridao gets exposed to UV radiation during low tide, reducing the photosynthetic oxygen production, turning the habitat to periodic anoxia indicated by differences in the TOC:TS ratio. However, such conditions may not influence M. casta, which can derive oxygen from the water column. The fatty acids specific to diatoms, dinoflagellates, higher plants, and partially degraded organic matter in the tissues of P. malabarica indicate their ability to source the food from the sediment and water column, whereas in tissues of M. casta, higher dinoflagellate-specific fatty acids followed by diatom and bacteria indicate water column-derived food. Chicalim can be considered an actively coupled benthic-pelagic habitat, and Siridao as an uncoupled habitat. Thus, the diverse flux of food particles, species-specific feeding ecology, and local hydrodynamics operating at these habitats could be the determining factors in the partitioning of the bivalves. Graphical abstract .

A novel insight into the mode of action of glufosinate: how reactive oxygen species are formed.

Glufosinate targets glutamine synthetase (GS), but its fast herbicidal action is triggered by reactive oxygen species (ROS). The relationship between GS inhibition and ROS accumulation was investigated in Amaranthus palmeri. Glufosinate's fast action is light-dependent with no visual symptoms or ROS formation in the dark. Inhibition of GS leads to accumulation of ammonia and metabolites of the photorespiration pathway, such as glycolate and glyoxylate, as well as depletion of other intermediates such as glycine, serine, hydroxypyruvate, and glycerate. Exogenous supply of glycolate to glufosinate-treated plants enhanced herbicidal activity and dramatically increased hydrogen peroxide accumulation (possibly from peroxisomal glycolate oxidase activity). Glufosinate affected the balance between ROS generation and scavenging. The activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased after glufosinate treatment in an attempt to quench the nascent ROS burst. Low doses of atrazine and dinoseb were used to investigate the sources of ROS by manipulating photosynthetic electron transport and oxygen (O2) evolution. ROS formation depended on electron flow and O2 evolution in photosystem II (PSII). Inhibition of GS disrupted photorespiration, carbon assimilation, and linear electron flow in the light reactions. Consequently, the antioxidant machinery and the water-water cycle are overwhelmed in the presence of light and glufosinate. The O2 generated by the splitting of water in PSII becomes the acceptor of electrons, generating ROS. The cascade of events leads to lipid peroxidation and forms the basis for the fast action of glufosinate.

The Mechanisms and Role of Photosynthetic Hydrogen Production by Green Microalgae

The review clarifies the mechanisms of H2 production by green microalgae and the physiological role of the [FeFe] hydrogenase in adaptation of these organisms to varying environmental conditions, primarily to anaerobiosis. The work is focused at interrelationships and mutual regulation between biological hydrogen production, photosynthetic electron transport, fermentation and oxygen uptake under anaerobiosis.

Simultaneous antibiotic degradation, nitrogen removal and power generation in a microalgae-bacteria powered biofuel cell designed for aquaculture wastewater treatment and energy recovery

A novel microalgae-bacteria powered biofuel cell (MBBFC) is designed for aquaculture wastewater treatment and energy recovery, in which algal-bacterial cooperation coupling with cathodic bioelectrochemiccal process for efficient nitrogen removal while simultaneously driving anodic bioelectrochemical degradation of antibiotic florfenicol (FLO) with instantaneous electrons uptake from co-substrate. 100 mg/L of ammonia nitrogen is removed completely within 90 h in the algal-bacterial biocathode of MBBFC, mainly attributed to the activity of ammonia oxidizers in the presence of photosynthetic oxygen and the resultant nitrate/nitrite are acceleratively removed by the cathodic bioelectrochemical denitrification. The antibacterial activity of FLO is eliminated through anodic bioelectrochemical enhanced co-metabolic reductive dehalogenation. The feeding 0.5 mg/L of FLO to the anode promotes the growth of Pseudomonas species, which results in a 3.2-fold increase in power output. FLO diffused from the anode to the cathode can exert a selection pressure to the cathodic bacterial community and thereby affecting the nitrogen removal performance of the microalgal-bacterial cathode. The MBBFC shows a great potential for aquaculture wastewater treatment with simultaneously bioelectrical energy recovery.

Influence of ethanol on the productivity of &lt;i&gt;Haematococcus pluvialis&lt;/i&gt;, content of photosynthetic pigments, reactive oxygen species and astaxantin

The effect of ethanol (0.1, 0.3, and 1.6 %) on the content of photosynthetic pigments, astaxanthin, and reactive oxygen species (ROS) in Haematococcus pluvialis (H. pluvialis, strain IBCE H-17), as well as on algae productivity, was studied in terms of dry biomass. Ethanol was found to stimulate in the studied concentrations the accumulation of dry biomass for 3, 7, and 12 days of cultivation on average 2 times. At all used ethanol concentrations, the number of cells increased. So, when using 0.3 % ethanol, the number of cells increased by 2.1; 2.5 and 3.3 times compared with the control culture on days 3, 7 and 15 of haematococcus cell growth. At the same time, a tendency toward a decrease in their size was noted. Ethanol also stimulated the accumulation of photosynthetic pigments. So, after 3 days of incubation in a solution containing 0.1 and 0.3 % ethanol, the content of chlorophyll (Chl) a was 142 and 130 % of that in the control, respectively, Chl b – 126 and 115 %, lutein – 151 and 132 %. The maximum effect was noted for β-carotene – 177 and 157 % compared with the control. The stress conditions created by ethanol led to the generation of ROS, in particular, after 7 days of incubation using 0.1; 0.3 and 1.6 % ethanol, the amount of ROS was 114, 141 and 179 % of that in the control, and after 12 days of incubation, 130, 165 and 183 %, respectively. A significant positive effect of ethanol on the content of astaxanthin was noted. So, after 7 days of incubation, the content of astaxanthin in options of 0.1; 0.3 and 1.6 % increased by 3.6; 4.9 and 4.6 times, respectively, and after 12 days – 8.6; 6.6 and 7.7 times compared with the control. The results indicate the enormous potential of using ethanol as an effective inducer of astaxanthin accumulation in haematococcus cells, as well as an active stimulator of algal productivity.

Selection of photosynthesis and respiration models to assess the effect of environmental conditions on mixed microalgae consortia grown on wastewater

This study aimed at evaluating the effects of different environmental conditions (irradiance, temperature, pH and dissolved oxygen) on a microalgae-bacteria consortium cultivated in a pilot-scale open pond and fed on the liquid fraction of anaerobic digestate. A standardized photo-respirometry protocol was followed to evaluate the activity of microalgae under different conditions. Two datasets (specific photosynthetic oxygen production rates and respiratory oxygen consumption rates) were obtained for each environmental parameter, throughout the entire range of conditions found in the outdoor cultivation system. Different kinetic models available in literature were fitted to experimental data and the resulting outputs were compared through model selection estimators, in order to select the most appropriate equations. The proposed set of equations constitute a modelling tool for the prediction of algal growth rates in algae-bacteria systems, as a function of environmental conditions.

Photo-respirometry to shed light on microalgae-bacteria consortia—a review

The use of phototrophic organisms in wastewater treatment is gaining increasing interest, due to the possibility of exploiting photosynthetic oxygenation, thus lowering treatment costs and environmental impacts. Mixed consortia of phototrophic organisms and aerobic bacteria rapidly develop in photobioreactors receiving wastewaters; in this case, the complex mutualistic interactions among microorganisms cannot be easily described, making difficult to forecast removal efficiencies and biomass productivities. Respirometric methods are applied for evaluating bacterial activity in activated sludge (conventional respirometry) or photosynthetic activity in phototrophic organisms (photorespirometry). Photo-respirometric methods can be also exploited for monitoring algae-bacteria systems and for calibrating mathematical models, allowing for a better comprehension of the interactions involved and a more accurate prediction of system efficiencies. A general protocol and a series of guidelines for conducting photorespirometric tests on algal-bacterial suspensions are here proposed, based on the review of experimental protocols applied to evaluate the effects of several parameters on these systems.

Extraction of photosynthetic electron from mixed photosynthetic consortium of bacteria and algae towards sustainable bioelectrical energy harvesting

Extraction of photosynthetic electron for bioelectrical energy harvesting is an efficient approach to utilize solar energy harvested by photosynthetic microorganisms. To explore this approach in natural and artificial photosynthetic system in which alga and photosynthetic bacteria are usually coexisted, the intracellular electron extraction from mixed photosynthetic consortium of Chlorella vulgaris and Rhodopseudomonas palustris was investigated under three-electrode mode by holding working electrode at different potentials. The mixed-culture biofilm grown at 0 V exhibited a maximum Coulomb efficiency of 42.12% while the peak current (12.2 mA) was 8.07, 1.5, 2.97 and 4.65 fold higher than that produced at −0.4 (1.5 mA), −0.2 (8.06 mA), 0.2 (4.08 mA) and 0.4 V (2.6 mA), respectively. The electrode potential can regulate the dominant species within the biofilm. Large enrichment of Rhodopseudomonas palustris in the biofilm was responsible for the high photosynthetic electron extraction efficiency at 0 V since the photosynthetic electrons extracted by the electrode were mainly derived from photoheterotrophic metabolism of Rhodopseudomonas palustris. Extraction of equivalent amounts of intracellular electron from Chlorella vulgaris required higher potential than that from Rhodopseudomonas palustris and was highly dependent on the presence of exogenous electron mediator. As an electron sacrificer, photosynthetic oxygen released by Chlorella vulgaris could complete electron with electrode. Intracellular electrons can also be extracted from dark respiration, but the peak current (6.4 mA) was 47.54% lower than that produced under illumination (12.2 mA) due to low exoelectrogenic activity of biofilm.

The onset of oxidative weathering traced by uranium isotopes

The invention of photosynthesis was a key interval in Earth’s history, initiating major changes in the evolution of the oceans and atmosphere. Many studies suggest that oxygen levels were already enhanced before the Paleoproterozoic Great Oxidation Event (GOE, 2.45–2.32 Ga). However, the timing of the onset of photosynthetic oxygenation, as well as spatio-temporal fluctuations of atmospheric and oceanic oxygen levels are highly debated. Here, we present a new and substantial uranium (U) isotope dataset comprising marine sediments, e.g. black shales, carbonates and iron-rich sedimentary rocks, from the Hamersley Basin (Western Australia), Kaapvaal and Zimbabwe Cratons (both southern Africa) with depositional ages ranging from 3.4 to 2.2 Ga. Sub-recent U mobilization was monitored by analyzing 234U along with δ238U, and detrital U contribution was monitored with [Al]/[U] or [Th]/[U] ratios. Samples with significant authigenic U enrichment (EFU > 2), relative to post-Archean Australian Shale (PAAS), exhibit authigenic δ238U ranging from −0.96 to −0.02‰ (±0.05‰, 2 s.d. long-term reproducibility), which deviates markedly from typical δ238U of the continental crust (−0.40 to −0.20‰). Remarkably, we find increased δ238U variability in the upper Ghaap Group (2.50–2.47 Ga, carbonates and black shales) and the lower Pretoria Group (2.42–2.32 Ga, Duitschland Formation, shales) of the Kaapvaal Craton. The predominantly light U isotope composition of those samples is likely explained by U isotope fractionation related to the onset of partial U mobilization during slow oxidative weathering of uraninite shortly before and during the GOE. The lack of low δ238U values in the Timeball Hill Formation (overlying the Duitschland Formation) indicate the onset of quantitative U mobilization during (modern-style) oxidative weathering of uraninite and other U-bearing minerals with limited U isotope fractionation. These limited U isotope variations measured in the Paleoproterozoic Timeball Hill Formation further suggest that, in contrast to modern oceans, in the period following the GOE, U was largely quantitatively reduced and removed from the water column of the Transvaal basin which remained mainly anoxic at depth.

Photosynthetic Tumor Oxygenation by Photosensitizer‐Containing Cyanobacteria for Enhanced Photodynamic Therapy

AbstractSustained tumor oxygenation is of critical importance during type‐II photodynamic therapy (PDT), which depends on the intratumoral oxygen level for the generation of reactive oxygen species. Herein, the modification of photosynthetic cyanobacteria with the photosensitizer chlorin e6 (ce6) to form ce6‐integrated photosensitive cells, termed ceCyan, is reported. Upon 660 nm laser irradiation, sustained photosynthetic O2 evolution by the cyanobacteria and the immediate generation of reactive singlet oxygen species (1O2) by the integrated photosensitizer could be almost simultaneously achieved for tumor therapy using type‐II PDT both in vitro and in vivo. This work contributes a conceptual while practical paradigm for biocompatible and effective PDT using hybrid microorganisms, displaying a bright future in clinical PDT by microbiotic nanomedicine.

Photosynthetic Tumor Oxygenation by Photosensitizer-Containing Cyanobacteria for Enhanced Photodynamic Therapy.

Sustained tumor oxygenation is of critical importance during type-II photodynamic therapy (PDT), which depends on the intratumoral oxygen level for the generation of reactive oxygen species. Herein, the modification of photosynthetic cyanobacteria with the photosensitizer chlorin e6 (ce6) to form ce6-integrated photosensitive cells, termed ceCyan, is reported. Upon 660 nm laser irradiation, sustained photosynthetic O2 evolution by the cyanobacteria and the immediate generation of reactive singlet oxygen species (1 O2 ) by the integrated photosensitizer could be almost simultaneously achieved for tumor therapy using type-II PDT both in vitro and in vivo. This work contributes a conceptual while practical paradigm for biocompatible and effective PDT using hybrid microorganisms, displaying a bright future in clinical PDT by microbiotic nanomedicine.