Murray cod waterhole woes

According to palaeontological records, two billion years ago atmospheric oxygen levels were a tenth of the levels they are today. Prehistoric water-breathing crustaceans presumably adapted to these low levels, but when oxygen levels rocketed, some creatures took advantage of the metabolic advantages offered and allowed their blood oxygen levels to rise. However,crustaceans seem to have stuck to their old-fashioned low-oxygen habits; they have remarkably low blood oxygenation levels even to this day. Oddly enough,despite the large evolutionary gap between crustaceans and warm-blooded animals, modern mammalian brains share the low oxygenation levels of crab and crayfish circulation. Jean-Charles Massabuau and Laure Corbari at Bordeaux University wondered if this striking similarity was evidence that the crustaceans' prehistoric oxygen regulation strategy was preserved over evolutionary time (p. 4415).Massabuau reasoned that if he could show how primitive water-breathers were able to regulate their tissue oxygenation levels in prehistoric times, this would reveal an early adaptation strategy that could have maintained low tissue oxygenation levels in animals throughout the course of evolution. Massabuau needed a primitive animal, so when Pierre Carbonel told him about tiny creatures called ostracods that hadn't changed much in the past 500 million years, Massabuau realised he had found an `open window into the past'to study ancient oxygen regulation strategies.The team decided to focus on the ostracods' breathing apparatus. Ostracods are minute crustaceans, complete with little appendages that beat rhythmically to waft water into the animal's breathing cavity, where gas exchange occurs by diffusion. Wondering whether the diminutive creatures were able to adjust their breathing rate at different oxygen levels, the team designed miniature aquaria, allowing them to change the oxygenation levels in the mini-habitats. The team videotaped the crustaceans to see whether the animals would beat their breathing appendages faster as oxygen levels dropped. The team were surprised when they saw that the ostracods didn't change the beating frequency of their breathing apparatus at different oxygen levels. Clearly, the ostracods couldn't regulate their ventilation in response to changes in water oxygenation. So how had the animals coped for millions of years?The team suspected that ostracods might regulate their oxygen by choosing to live at particular oxygen levels. To test this, they needed to study the distribution of the little sediment-dwellers in their natural habitat. They didn't have to travel far to collect sediment core samples: the Bay of Arcachon in France, where ostracods live, is right outside their lab. The researchers then determined the ostracods' preferred oxygen levels by measuring the oxygen profile of each sediment sample, freezing and slicing up the samples and counting the number of animals in each slice. The team found that the crustaceans were escaping both oxygen-rich and oxygen-depleted regions and migrating to sediments where the oxygen levels were slightly higher than those required by their tissues. The ostracods were regulating their body oxygenation simply by crawling to their comfort zone.So 500 million years ago, these tiny crustaceans were already managing their tissue oxygenation levels using a behavioural rather than a physiological strategy, which could have been conserved over evolutionary time. But what is the evolutionary advantage to maintaining such low body tissue oxygenation? `One explanation is that metabolism produces oxygen free radicals, which damage cells', says Massabuau, `so maintaining low oxygen levels may protect an animal's tissues from free radical attack'. It seems ostracods may have a very good reason for being stuck in the past.

Two salt‐oxygen‐plant growth experiments, one a solution culture, the other involving soil, were conducted in a greenhouse using tomato plants (Lycopersicon esculentum Rutgers) as the test plant. Plant growth as measured by eight growth indices was shown to be adversely affected by decreasing the oxygen content of the aerating gas from 21% or by increasing the salt level of the growth media from 20 meq/liter. Simultaneous changes in both the oxygen and salt levels generally produced significantly greater changes than could be accounted for by considering the effects brought about by the salt and oxygen levels considered independently.Tomato plants affected by high salt or low oxygen levels had similar characteristics of stunting and small, somewhat cup‐shaped, wrinkled, dark green leaves. Severity of the symptoms increased as either the salt level increased or the oxygen level decreased. Severe symptoms appeared at combinations of oxygen and salt levels which individually did not cause the symptoms to appear.Reducing the oxygen level from 21% had a significantly adverse effect on growth at all salt levels, while increasing the salt level from 20 meq/liter caused varying amounts of growth reduction depending on the oxygen level. At any given level of one treatment, increasing the stress of the other treatment generally resulted in a considerable reduction in growth, although where growth was already markedly decreased, applying a more severe treatment produced smaller additional detrimental effects.In both the solution and soil experiments the salt effect was greatest under conditions of adequate oxygen. Under low or inadequate oxygen levels the salt effect appeared but to a much smaller extent.

Embryonic stem cells (ESCs) have the ability to generate any kind of cell in the body. They, therefore, have great potential for use in cell therapies for neurodegenerative disorders such as Huntington’s disease. Establishing a culture environment to mimic components of physiological conditions may help to maintain and differentiate ESCs more successfully. One of the important conditions is the level of oxygen. Traditionally, 20% oxygen (O 2 ) has been used to culture cells, but this is much higher than physiological levels (2% O 2 ). In this study, we used the mouse ESC line 46C (Sox1- GFP knock-in) to investigate the effect of physiological oxygen on proliferation of mESCs, and their differentiation to neural progenitors (where Sox1 is expressed) and mature GABAergic neurons. mESCs were cultured in either high (20%, H) or low (2%, L) oxygen levels for four days before induction of differentiation, and subsequently differentiated under either high or low oxygen, in a 2x2 factorial design (H-H, H-L, L-H, L-L). mESCs placed in low oxygen levels during the differentiation phase showed less proliferation (a decreased proportion of Ki67 + cells), complete loss of the self-renewing population (Oct4 + cells), and a decrease in Sox-1 + neural precursors. Consistent with this, neurons generated under low levels of oxygen showed a more mature morphology with an increased number of primary neurites and increased levels of GABA neurotransmitter. There was no significant difference in the percentage of neurons generated from either condition. We conclude that mESC culture in low oxygen conditions promotes maturation during neuronal differentiation and helps eliminate the residual Oct4 + population. The adoption of low oxygen environments during neuronal differentiation may, therefore, decrease teratoma formation and increase the potential for ESC use in cell therapies for neurodegenerative disease.

Phosphorus speciation, transformation, and preservation in the coastal area of Rushan Bay

Mathematical modeling of oxygen levels in a controlled atmosphere store for preservation of apple fruits

The effects of several atmosphere compositions on respiration rates, chemical components and keeping quality of Welsh onion (Allium fistulosum L.) were investigated during storage at 15t. Carbon dioxide production from Welsh onion under continuous stream of air (the flow rate was 7 litter/hr) was 111mgCO2/kg/hr, it being reduced under continuous streams of low oxygen and high carbon dioxide levels. Ascorbic acid, sugar and chlorophyll retention under low oxygen level were better than those in air. Sensory score of Welsh onion withering leaf tip was reduced under low oxygen and high carbon dioxide levels. From these results, atmosphere compositions such as 7.6% O2 + 12.6% CO2 and 4.1% O2 + 17.1% CO2 respectively, gave better keeping quality of Welsh onion while avoiding physiological injury.

Geochemistry of the surface sediments of the Sulu and South China Seas

Effects of targeting lower versus higher arterial oxygen saturations on death or disability in preterm infants.

The physiological response of two species of mussels (Mytilus edulis and M. galloprovincialis) and two species of oysters (Crassostrea gigas and Ostrea edulis) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L−1) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L−1) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.

During follicle maturation, oxygen levels continuously decrease in the follicular fluid and reach lowest levels in the preovulatory follicle. The current study was designed to comprehensively understand effects of low oxygen levels on bovine granulosa cells (GC) using our established estrogen active GC culture model. As evident from flow cytometry analysis the viability of GC was not found to be affected at severely low oxygen condition (1% O2) compared to normal (atmospheric) oxygen condition (21% O2). Estimations of hormone concentrations using competitive radioimmunoassay revealed that the production of estradiol and progesterone was significantly reduced at low oxygen condition. To understand the genome-wide changes of gene expression, mRNA microarray analysis was performed using Affymetrix’s Bovine Gene 1.0 ST Arrays. This resulted in the identification of 1104 differentially regulated genes of which 505 were up- and 599 down-regulated under low oxygen conditions. Pathway analysis using Ingenuity pathway analyzer (IPA) identified 36 significantly affected (p < 0.05) canonical pathways. Importantly, pathways like “Estrogen-mediated S-phase Entry” and “Cyclins and Cell Cycle Regulation” were found to be greatly down-regulated at low oxygen levels. This was experimentally validated using flow cytometry based cell cycle analysis. Up-regulation of critical genes associated with angiogenesis, inflammation, and glucose metabolism, and down-regulation of FSH signaling, steroidogenesis and cell proliferation indicated that low oxygen levels induced early luteinization associated changes in granulosa cells. Identification of unmethylated CpG sites in the CYP19A1 promoter region suggests that granulosa cells were not completely transformed into luteal cells under the present low oxygen in vitro condition. In addition, the comparison with earlier published in vivo microarray data indicated that 1107 genes showed a similar expression pattern in granulosa cells at low oxygen levels (in vitro) as found in preovulatory follicles after the LH surge (in vivo). Overall, our findings demonstrate for the first time that low oxygen levels in preovulatory follicles may play an important role in supporting early events of luteinization in granulosa cells.

Bathyal cold seeps are isolated extreme deep-sea environments characterized by low species diversity while biomass can be high. The Håkon Mosby mud volcano (Barents Sea, 1,280 m) is a rather stable chemosynthetic driven habitat characterized by prominent surface bacterial mats with high sulfide concentrations and low oxygen levels. Here, the nematode Halomonhystera hermesi thrives in high abundances (11,000 individuals 10 cm−2). Halomonhystera hermesi is a member of the intertidal Halomonhystera disjuncta species complex that includes five cryptic species (GD1-5). GD1-5’s common habitat is characterized by strong environmental fluctuations. Here, we compared the transcriptomes of H. hermesi and GD1, H. hermesi’s closest relative. Genes encoding proteins involved in oxidative phosphorylation are more strongly expressed in H. hermesi than in GD1, and many genes were only observed in H. hermesi while being completely absent in GD1. Both observations could in part be attributed to high sulfide concentrations and low oxygen levels. Additionally, fatty acid elongation was also prominent in H. hermesi confirming the importance of highly unsaturated fatty acids in this species. Significant higher amounts of transcription factors and genes involved in signaling receptor activity were observed in GD1 (many of which were completely absent in H. hermesi), allowing fast signaling and transcriptional reprogramming which can mediate survival in dynamic intertidal environments. GC content was approximately 8% higher in H. hermesi coding unigenes resulting in differential codon usage between both species and a higher proportion of amino acids with GC-rich codons in H. hermesi. In general our results showed that most pathways were active in both environments and that only three genes are under natural selection. This indicates that also plasticity should be taken in consideration in the evolutionary history of Halomonhystera species. Such plasticity, as well as possible preadaptation to low oxygen and high sulfide levels might have played an important role in the establishment of a cold-seep Halomonhystera population.

Multiple eukaryotic clades make their first appearance in the fossil record between ~810 and 715Ma. Molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation. Animals require oxygen to fuel their metabolism, and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the Cambrian radiation of large, ecologically diverse animals. Here, paleoredox conditions were investigated in the Fifteenmile Group, Ogilvie Mountains, Yukon, Canada, which hosts an 811Ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals. Iron-based redox proxies, redox-sensitive trace elements, organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects. These data suggest that for this basin, oxygenated shelf waters overlay generally anoxic deeper waters. The anoxic water column was dominantly ferruginous, but brief periods of euxinia likely occurred. These oscillations coincide with changes in total organic carbon, suggesting euxinia was primarily driven by increased organic carbon loading. Overall, these data are consistent with proposed quantitative constraints on Proterozoic atmospheric oxygen being greater than 1% of modern levels, but less than present levels. Comparing these oxygen levels against the likely oxygen requirements of the earliest animals, both theoretical considerations and the ecology of modern oxygen-deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges, eumetazoans or bilaterians. Thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized Neoproterozoic oceans, although these inferred levels would constrain animals to very small sizes and low metabolic rates.

Climate change is causing heatwaves to become longer, more frequent and just plain hotter. For many of us, dealing with oppressive heat comes with several unpleasant challenges, from profuse sweating to feeling tired and sluggish. Humans, however, are not the only ones suffering through unprecedented heatwaves in a warming climate. In a ground-breaking study by Anna Andreassen and her team at the Norwegian University of Science and Technology, the researchers investigated what happens to the brains of larval zebrafish (Danio rerio) during extreme heatwaves, particularly as temperatures approach the upper limit of their heat tolerance. For these small fish, the consequences of unbearable heat are far worse than becoming a little sweaty.Fish can only tolerate temperatures so high. At some point, they lose the ability to swim properly and assume the ‘belly up’ position (termed loss of equilibrium), an indicator of imminent death. For decades, biologists have wondered what happens in the body of fish at their upper temperature limit that prompts this behaviour. Andreassen and her team set out to solve this mystery by testing whether going belly up is caused by the brain not communicating properly with the rest of the body. This miscommunication is thought to occur because high temperatures stop nerve cells in the brain from functioning as they should. But first, the researchers needed a way to visualize the fish's brain activity at extremely high temperatures. Thanks to advances in genetic technology, they were able to study genetically modified zebrafish whose brains emit a fluorescent light when their neurons are active.The researchers gradually increased the water temperature in the tank and observed the nerve cell activity of the genetically modified zebrafish using a microscope that could detect fluorescent light. At their upper temperature limit (approximately 40.9°C), the fish's brains showed very little fluorescence, indicating that the nerve cells were largely inactive. At this temperature, the larval fish were also no longer responsive to stimuli, such as bright lights flickering in front of their eyes. Interestingly, when the water temperature was raised by only 0.5°C above the upper temperature limit, something unexpected happened – the whole brain lit up as if the fish were having a seizure! This seizure-like activity was a sign that the brain had become completely depolarized, meaning that its nerve cells were firing on all cylinders, but not in a controlled manner. As this seizure-like event occurred at temperatures only slightly higher than the upper temperature limit, the team concluded that this is not what causes fish to lose equilibrium. Rather, they suggest that impaired neuron activity at the upper temperature limit is the mechanism underpinning this dangerous phenomenon.The researchers decided to take their study one step further to determine why neurons stop working at the upper temperature limit. They had a hunch that high temperatures limit how much oxygen gets to the brain, which then impairs how its nerve cells function. Andreassen and her team repeated the heat ramping experiment, but this time at high, medium and low oxygen levels. They discovered that larvae exposed to high oxygen levels in the water did better at high temperatures than those in low oxygen; the fish had higher brain activity and recovered faster after being exposed to their upper temperature limit. Overall, these findings suggest that the amount of oxygen in the water plays an important role in controlling how the brain communicates with the body at extremely high temperatures. So, the next time you're sweating profusely in the midst of a summer heatwave, take a deep breath and be thankful that your brain function has remained intact.

Oxygen levels in typical cell culture conditions do not accurately reflect the oxygen levels cells are exposed to within the body. Furthermore, oxygen levels can vary within the tumor microenvironment. These variances can affect how cells respond to a variety of drugs and small molecules often used during cancer treatment. Previous studies have shown altered drug sensitivities in MCF7 cells depending on the oxygen levels the cells are grown in. To further understand how oxygen levels affect drug sensitivity, the response of tumorigenic MCF7 cells were compared to non-malignant MCF10A cells, cultured under low and high oxygen. The goal of this study was to examine the differences in the sensitivity of MCF7 and MCF10A cells to drugs from the Tocriscreen Total compound library when cultured under low and high oxygen levels and for different drug exposure time periods. Cells were grown using standard cell culture conditions (19% oxygen) or low oxygen (5%). Using high-content imaging and high-throughput analysis methods, viability was assessed using two different mechanistic readouts; cellular metabolic activity and membrane permeability. Post-screening analysis was performed to confirm positive hits by performing dose-responses and determining IC50 concentrations using the same reagents as in the screen, and reagents to assess oxidative stress and cellular proliferation. Results showed that viability differed depending on mechanistic readout and platform method used to determine hits as well as duration of exposure to compound. In addition, the response of MCF10A cells was not always identical to that of the MCF7 cells. Post-screening analysis of “hits” indicated different potencies of compounds tested depending on oxygen level and cell type. These data suggest that some drugs may affect MCF7 and MCF10A cells differently depending on environmental oxygen levels and mechanistic readout used to determine cellular health. Citation Format: Michelle Yan, Michael O’Grady, Anderson April, Scott Clarke, Quentin Low, Carolyn DeMarco, Veronica Calderon, Kathy Kihn, Leticia Montoya, Carmen Finnessy, Marcy Wickett. High content screening in MCF7 and MCF10A cells show differential responses depending on oxygen levels and mechanistic readout for viability. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2169.

This paper presents some recent studies on the influence of atmospheres, modified as to their oxygen level and temperature, on the storage life of Wickson plums. Nine temperatures (32°-95° F) were used at each of ten oxygen levels (1-100 per cent). The results show that fruits reached respiration and ripening peaks fastest at 77° in the temperature series, although initial CO2 production increased with temperature to the 95° level. In the oxygen series, the rate of acceleration was roughly proportional to the oxygen tension. Respiration and ripening were increasingly delayed in the lower oxygen levels and at reduced temperatures. At increasing temperatures, fruits in the lowest oxygen levels began to produce as much or more CO2 as fruits in next highest oxygen levels; at 77° the 10 per cent oxygen lot was surpassed by the three lower oxygen lots in reverse order. This is attributed to anaerobic respiration not balanced by the aerobic phases. Ripening failures and loss of vitality of all oxygen lots at 86° and 95° are thought to have resulted from disturbances of the enzyme systems under high temperature.