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Deleterious Ca2+ accumulation is central to hypoxic cell death in the brain of most mammals. Conversely, hypoxia‐mediated increases in cytosolic Ca2+ are retarded in hypoxia‐tolerant naked mole‐rat brain. We hypothesized that naked mole‐rat brain mitochondria have an enhanced capacity to buffer exogenous Ca2+ and examined Ca2+ handling in naked mole‐rat cortical tissue. We report that naked mole‐rat brain mitochondria buffer >2‐fold more exogenous Ca2+ than mouse brain mitochondria, and that the half‐maximal inhibitory concentration (IC50) at which Ca2+ inhibits aerobic oxidative phosphorylation is >2‐fold higher in naked mole‐rat brain. The primary driving force of Ca2+ uptake is the mitochondrial membrane potential (Δψm), and the IC50 at which Ca2+ decreases Δψm is ∼4‐fold higher in naked mole‐rat than mouse brain. The ability of naked mole‐rat brain mitochondria to safely retain large volumes of Ca2+ may be due to ultrastructural differences that support the uptake and physical storage of Ca2+ in mitochondria. Specifically, and relative to mouse brain, naked mole‐rat brain mitochondria are larger and have higher crista density and increased physical interactions between adjacent mitochondrial membranes, all of which are associated with improved energetic homeostasis and Ca2+ management. We propose that excessive Ca2+ influx into naked mole‐rat brain is buffered by physical storage in large mitochondria, which would reduce deleterious Ca2+ overload and may thus contribute to the hypoxia and ischaemia‐tolerance of naked mole‐rat brain. Key points: Unregulated Ca2+ influx is a hallmark of hypoxic brain death; however, hypoxia‐mediated Ca2+ influx into naked mole‐rat brain is markedly reduced relative to mice.This is important because naked mole‐rat brain is robustly tolerant against in vitro hypoxia, and because Ca2+ is a key driver of hypoxic cell death in brain.We show that in hypoxic naked mole‐rat brain, oxidative capacity and mitochondrial membrane integrity are better preserved following exogenous Ca2+ stress.This is due to mitochondrial buffering of exogenous Ca2+ and is driven by a mitochondrial membrane potential‐dependant mechanism.The unique ultrastructure of naked mole‐rat brain mitochondria, as a large physical storage space, may support increased Ca2+ buffering and thus hypoxia‐tolerance. [ABSTRACT FROM AUTHOR]

Abstract Sessile benthic organisms like oysters inhabit the intertidal zone, subject to alternating hypoxia and reoxygenation (H/R) episodes during tidal movements, impacting respiratory chain activities and metabolome compositions. We investigated the effects of constant severe hypoxia (90 min at ~ 0% O2 ) followed by 10 min reoxygenation, and cyclic hypoxia (5 cycles of 15 min at ~ 0% O2 and 10 min reoxygenation) on isolated mitochondria from the gill and the digestive gland of Crassostrea gigas respiring on pyruvate, palmitate, or succinate. Constant hypoxia suppressed oxidative phosphorylation (OXPHOS), particularly during Complex I-linked substrates oxidation. It had no effect on mitochondrial reactive oxygen species (ROS) efflux but increased fractional electron leak (FEL). In mitochondria oxidizing Complex I substrates, exposure to cyclic hypoxia prompted a significant drop after the first H/R cycle. In contrast, succinate-driven respiration only showed significant decline after the third to fifth H/R cycle. ROS efflux saw little change during cyclic hypoxia regardless of the oxidized substrate, but Complex I-driven FEL tended to increase with each subsequent H/R cycle. These observations suggest that succinate may serve as a beneficial stress fuel under H/R conditions, aiding in the post-hypoxic recovery of oysters by reducing oxidative stress and facilitating rapid ATP re-synthesis. The impacts of constant and cyclic hypoxia of similar duration on mitochondrial respiration and oxidative lesions in the proteins were comparable indicating that the mitochondrial damage is mostly determined by the lack of oxygen and mitochondrial depolarization. The ROS efflux in the mitochondria of oysters was minimally affected by oxygen fluctuations indicating that tight regulation of ROS production may contribute to robust mitochondrial phenotype of oysters and protect against H/R induced stress.

Sessile benthic organisms like oysters inhabit the intertidal zone, subject to alternating hypoxia and reoxygenation (H/R) episodes during tidal movements, impacting respiratory chain activities and metabolome compositions. We investigated the effects of constant severe hypoxia (90 min at ~ 0% O2) followed by 10 min reoxygenation, and cyclic hypoxia (5 cycles of 15 min at ~ 0% O2 and 10 min reoxygenation) on isolated mitochondria from the gill and the digestive gland of Crassostrea gigas respiring on pyruvate, palmitate, or succinate. Constant hypoxia suppressed oxidative phosphorylation (OXPHOS), particularly during Complex I-linked substrates oxidation. It had no effect on mitochondrial reactive oxygen species (ROS) efflux but increased fractional electron leak (FEL). In mitochondria oxidizing Complex I substrates, exposure to cyclic hypoxia prompted a significant drop after the first H/R cycle. In contrast, succinate-driven respiration only showed significant decline after the third to fifth H/R cycle. ROS efflux saw little change during cyclic hypoxia regardless of the oxidized substrate, but Complex I-driven FEL tended to increase with each subsequent H/R cycle. These observations suggest that succinate may serve as a beneficial stress fuel under H/R conditions, aiding in the post-hypoxic recovery of oysters by reducing oxidative stress and facilitating rapid ATP re-synthesis. The impacts of constant and cyclic hypoxia of similar duration on mitochondrial respiration and oxidative lesions in the proteins were comparable indicating that the mitochondrial damage is mostly determined by the lack of oxygen and mitochondrial depolarization. The ROS efflux in the mitochondria of oysters was minimally affected by oxygen fluctuations indicating that tight regulation of ROS production may contribute to robust mitochondrial phenotype of oysters and protect against H/R induced stress. [ABSTRACT FROM AUTHOR]

Global climate change is closely related to CO2 emissions caused by anthropogenic activities. The marine biogeochemical processes that affect the ocean carbon sink capacity have become a research hotspot, since ocean is a net sink of atmospheric CO2. One of the most significant biological processes is marine microbial respiration, which mediates the switch between carbon “source and sink”, and its rate becomes an essential index of the marine carbon budget research. Currently, a plenty of methods are available for measuring marine microbial respiration rate. It is essential to accurately determine microbial respiration rates via one or more methods due to the diversity of hydrological environments and microbial communities. This review focuses on the principles, advantages, disadvantages and scope of respiratory rate measurement application, and offers an insightful perspective of both conventional and advanced measurement technologies. Therefore, it provides theoretical supports for key technologies applied in analysis of ocean microbial carbon cycling processes under the background of carbon neutrality. [ABSTRACT FROM AUTHOR]

Iron (Fe) deficiency-induced chlorosis can be a serious problem in grapevine cultivation. Measuring genotypic tolerance to this disorder is of vital importance in rootstock selection. In this research, different sources of Fe (FeSO4·7H2O and FeEDTA) were used and their effects were evaluated on the response of a tolerant (‘Thompson Seedless’) and a sensitive (‘Flame Seedless’) grape cultivar. Also, their cross-grafted combinations [‘Flame Seedless’/’Thompson Seedless’ (FS/TS) and ‘Thompson Seedless’/‘Flame Seedless’ (TS/FS)] were evaluated for tolerance to Fe deficiency. Bicarbonate (30 mM) was used for inducing iron deficiency in the plants. Despite the negative effects of bicarbonate, the ‘Thompson Seedless’ maintained a significant chlorophyll index, compared to the ‘Flame Seedless’ cultivar. Gas exchange measurements showed that the bicarbonate had more adverse effects on photosynthesis and water-use-efficiency (WUE) in the ‘Flame Seedless’ cultivar. Despite the bicarbonate toxicity, the photosynthetic system of the FS/TS graft combination showed no significant change in FV/FO, whereas adverse effects occurred significantly in ‘Thompson Seedless’, ‘Flame Seedless’, and their TS/FS graft combination. Bicarbonate decreased the performance index in ‘Flame Seedless’. In conclusion, scions of the susceptible cultivar performed well when grafted on tolerant rootstocks. Such grafting combinations can help plants to cope with the negative effects of bicarbonate toxicity on grapevine.

Diving animals must sustain high activity with limited O2 stores to successfully capture prey. Studies suggest that increasing body O2 stores supports breath-hold diving, but less is known about metabolic specializations that underlie underwater locomotion. We measured maximal activities of 10 key enzymes in locomotory muscles (gastrocnemius and pectoralis) to identify biochemical changes associated with diving in pathways of oxidative and substrate-level phosphorylation and compared them across three groups of ducks—the longest diving sea ducks (eight spp.), the mid-tier diving pochards (three spp.) and the non-diving dabblers (five spp.). Relative to dabblers, both diving groups had increased activities of succinate dehydrogenase and cytochrome c oxidase, and sea ducks further showed increases in citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HOAD). Both diving groups had relative decreases in capacity for anaerobic metabolism (lower ratio of lactate dehydrogenase to CS), with sea ducks also showing a greater capacity for oxidative phosphorylation and lipid oxidation (lower ratio of pyruvate kinase to CS, higher ratio of HOAD to hexokinase). These data suggest that the locomotory muscles of diving ducks are specialized for sustaining high rates of aerobic metabolism, emphasizing the importance of body O2 stores for dive performance in these species. [ABSTRACT FROM AUTHOR]

Heme is an important tetrapyrrole compound, and has been widely applied in food and medicine industries. Although microbial production of heme has been developed with metabolic engineering strategies during the past 20 years, the production levels are relatively low due to the multistep enzymatic processes and complicated regulatory mechanisms of microbes. Previous studies mainly adopted the strategies of strengthening precursor supply and product transportation to engineer microbes for improving heme biosynthesis. Few studies focused on the engineering and screening of efficient enzymes involved in heme biosynthesis. Herein, a growth-coupled, high-throughput selection platform based on the detoxification of Zinc-protoporphyrin IX (an analogue of heme) was developed and applied to directed evolution of coproporphyrin ferrochelatase, catalyzing the insertion of metal ions into porphyrin ring to generate heme or other tetrapyrrole compounds. A mutant with 3.03-fold increase in kcat/KM was selected. Finally, growth-coupled directed evolution of another three key enzymes involved in heme biosynthesis was tested by using this selection platform. The growth-coupled selection platform developed here can be a simple and effective strategy for directed evolution of the enzymes involved in the biosynthesis of heme or other tetrapyrrole compounds.

The crucian carp (Carassius carassius) can survive complete oxygen depletion (anoxia) for several months at low temperatures, making it an excellent model for studying molecular adaptations to anoxia. Still, little is known about how its global proteome responds to anoxia and reoxygenation. By applying mass spectrometry-based proteome analyses on brain, heart and liver tissue from crucian carp exposed to normoxia, five days anoxia, and reoxygenation, we found major changes in particularly cardiac and hepatic protein levels in response to anoxia and reoxygenation. These included tissue-specific differences in mitochondrial proteins involved in aerobic respiration and mitochondrial membrane integrity. Enzymes in the electron transport system (ETS) decreased in heart and increased massively in liver during anoxia and reoxygenation but did not change in the brain. Importantly, the data support a special role for the liver in succinate handling upon reoxygenation, as suggested by a drastic increase of components of the ETS and uncoupling protein 2, which could allow for succinate metabolism without excessive formation of reactive oxygen species (ROS). Also during reoxygenation, the levels of proteins involved in the cristae junction organization of the mitochondria changed in the heart, possibly functioning to suppress ROS formation. Furthermore, proteins involved in immune (complement) system activation changed in the anoxic heart compared to normoxic controls. The results emphasize that responses to anoxia are highly tissue-specific and related to organ function. [ABSTRACT FROM AUTHOR]

This study provides a comprehensive analysis of the eco-physiological responses of the blue crab (Callinectes sapidus) to variations in salinity, shedding light on its adaptability and invasive success in aquatic environments. Gender-specific differences in osmoregulation and Electron Transport System (ETS) activity highlight the importance of considering sex-specific aspects when understanding the physiological responses of invasive species. Females exhibited increased ETS activity at lower salinities, potentially indicative of metabolic stress, while males displayed constant ETS activity across a range of salinities. Osmoregulatory capacity which depended on gender and salinity, was efficient within meso-polyhaline waters but decreased at higher salinities, particularly in males. These findings provide valuable understandings into how C. sapidus specimens in an invaded area responds to salinity changes, important for considerate its distribution through saline pathways during tidal cycle fluctuations. This study shows the importance of interdisciplinary research for effective management of invasive species and conservation of affected aquatic ecosystems. [Display omitted] • Efficient osmoregulation observed in meso-polyhaline waters. • Blue crab's gender-specific osmoregulation and ETS activity responses analysed. • Females showed increased ETS activity at lower salinities. [ABSTRACT FROM AUTHOR]

The crucian carp (Carassius carassius) can survive complete oxygen depletion (anoxia) for several months at low temperatures, making it an excellent model for studying molecular adaptations to anoxia. Still, little is known about how its global proteome responds to anoxia and reoxygenation. By applying mass spectrometry-based proteome analyses on brain, heart and liver tissue from crucian carp exposed to normoxia, five days anoxia, and reoxygenation, we found major changes in particularly cardiac and hepatic protein levels in response to anoxia and reoxygenation. These included tissue-specific differences in mitochondrial proteins involved in aerobic respiration and mitochondrial membrane integrity. Enzymes in the electron transport system (ETS) decreased in heart and increased massively in liver during anoxia and reoxygenation but did not change in the brain. Importantly, the data support a special role for the liver in succinate handling upon reoxygenation, as suggested by a drastic increase of components of the ETS and uncoupling protein 2, which could allow for succinate metabolism without excessive formation of reactive oxygen species (ROS). Also during reoxygenation, the levels of proteins involved in the cristae junction organization of the mitochondria changed in the heart, possibly functioning to suppress ROS formation. Furthermore, proteins involved in immune (complement) system activation changed in the anoxic heart compared to normoxic controls. The results emphasize that responses to anoxia are highly tissue-specific and related to organ function.

The transformation of prostatic epithelial cells to prostate cancer (PCa) has been characterized as a transition from citrate secretion to citrate oxidation, from which one would anticipate enhanced mitochondrial complex I (CI) respiratory flux. Molecular mechanisms for this transformation are attributed to declining mitochondrial zinc concentrations. The unique metabolic properties of PCa cells have become a hot research area. Several publications have provided indirect evidence based on investigations using pre-clinical models, established cell lines, and fixed or frozen tissue bank samples. However, confirmatory respiratory analysis on fresh human tissue has been hampered by multiple difficulties. Thus, few mitochondrial respiratory assessments of freshly procured human PCa tissue have been published on this question. Our objective is to document relative mitochondrial CI and complex II (CII) convergent electron flow to the Q-junction and to identify electron transport system (ETS) alterations in fresh PCa tissue. The results document a CII succinate: quinone oxidoreductase (SQR) dominant succinate oxidative flux model in the fresh non-malignant prostate tissue, which is enhanced in malignant tissue. CI NADH: ubiquinone oxidoreductase activity is impaired rather than predominant in high-grade malignant fresh prostate tissue. Given these novel findings, succinate and CII are promising targets for treating and preventing PCa. [ABSTRACT FROM AUTHOR]

Menaquinone (MK) is an important electron transporter in Escherichia coli. This isoprenoid quinone can transfer electrons to many terminal acceptors, such as fumarate and nitrate, which helps this organism survive under diverse and challenging conditions. As the isoprenoid quinones with various length of isoprenyl tail are widely distributed in nature, the heterologous expression of polyprenyl diphosphate synthases (PDSs) has been investigated using its counterpart, ubiquinone (UQ). In this study, we investigated the MK production by the expression of various heterologous PDS genes from prokaryotic and eukaryotic species, including Saccharomyces cerevisiae COQ1 (hexa-PDS), Haemophilus influenzae hi0881 (hepta-PDS), Synechocystis sp. strain PCC6803 slr0611 (nona-PDS) and Glunocobacter suboxydans ddsA (deca-PDS) in E. coli. We detected specific isoforms of MK, including MK7, MK9, and MK10, via the expression of HI0881, Slr0611 and DdsA respectively, but rarely detect MK6 via the expression of Coq1. As UQ6 was detected in E. coli harboring COQ1, the acceptance of the side chain lengths by MenA (prenyl transferase for MK) was narrower than UbiA (prenyl transferase for UQ). We also identified a mutation in menA in the E. coli AN386 strain and a transposon insertion of IS186 in menC in E. coli KO229 (∆ispB) and its parental strain FS1576. Taken together, these results elucidate the different nature of MenA from UbiA., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Deleterious Ca 2+ accumulation is central to hypoxic cell death in the brain of most mammals. Conversely, hypoxia-mediated increases in cytosolic Ca 2+ are retarded in hypoxia-tolerant naked mole-rat brain. We hypothesized that naked mole-rat brain mitochondria have an enhanced capacity to buffer exogenous Ca 2+ and examined Ca 2+ handling in naked mole-rat cortical tissue. We report that naked mole-rat brain mitochondria buffer >2-fold more exogenous Ca 2+ than mouse brain mitochondria, and that the half-maximal inhibitory concentration (IC 50 ) at which Ca 2+ inhibits aerobic oxidative phosphorylation is >2-fold higher in naked mole-rat brain. The primary driving force of Ca 2+ uptake is the mitochondrial membrane potential (Δψ m ), and the IC 50 at which Ca 2+ decreases Δψ m is ∼4-fold higher in naked mole-rat than mouse brain. The ability of naked mole-rat brain mitochondria to safely retain large volumes of Ca 2+ may be due to ultrastructural differences that support the uptake and physical storage of Ca 2+ in mitochondria. Specifically, and relative to mouse brain, naked mole-rat brain mitochondria are larger and have higher crista density and increased physical interactions between adjacent mitochondrial membranes, all of which are associated with improved energetic homeostasis and Ca 2+ management. We propose that excessive Ca 2+ influx into naked mole-rat brain is buffered by physical storage in large mitochondria, which would reduce deleterious Ca 2+ overload and may thus contribute to the hypoxia and ischaemia-tolerance of naked mole-rat brain. KEY POINTS: Unregulated Ca 2+ influx is a hallmark of hypoxic brain death; however, hypoxia-mediated Ca 2+ influx into naked mole-rat brain is markedly reduced relative to mice. This is important because naked mole-rat brain is robustly tolerant against in vitro hypoxia, and because Ca 2+ is a key driver of hypoxic cell death in brain. We show that in hypoxic naked mole-rat brain, oxidative capacity and mitochondrial membrane integrity are better preserved following exogenous Ca 2+ stress. This is due to mitochondrial buffering of exogenous Ca 2+ and is driven by a mitochondrial membrane potential-dependant mechanism. The unique ultrastructure of naked mole-rat brain mitochondria, as a large physical storage space, may support increased Ca 2+ buffering and thus hypoxia-tolerance., (© 2023 The Authors. The Journal of Physiology © 2023 The Physiological Society.)

Coenzyme Q (CoQ) or ubiquinone functions as an electron transporter in the electron transport system in both prokaryotes and eukaryotes. The isoprenyl side chain of CoQ is modified in some organisms, especially in fungi, for optimal electron transport performance under various conditions. In this study, we investigated the side chain saturated dihydro CoQ (CoQ10(H2)) in Aureobasidium pullulans EXF-150, Sydowia polyspora NBRC 30562, and naturally isolated Plowrightia sp. A37, all of which are melanized Dothideomycetes species within the Ascomycota, and also in filamentous fungi Aspergillus oryzae and Aspergillus terreus. Plowrightia sp. A37 produced the rarely synthesized tetrahydro type CoQ10(H4), especially in glucose-rich medium, during extended cultivation in contrast to CoQ10(H2) in time-limited cultivation. Using liquid chromatography-mass spectrometry, we identified demethoxyubiquinone-H2 (DMQ(H2)) as an indicative intermediate that suggests that the side chain-saturation of CoQ occurs after the formation of DMQ and not always in the last step as previously considered., (© The Author(s) 2024. Published by Oxford University Press on behalf of Japan Society for Bioscience, Biotechnology, and Agrochemistry.)

Characterizing the molecular mechanism through which different carbon sources affect the denitrification process would provide a basis for the proper selection of carbon sources, thus avoiding excessive carbon source dosing and secondary pollution while also improving denitrification efficiency. Here, we selected Thauera linaloolentis as a model organism of denitrification, whose genomic information was elucidated by draft genome sequencing and KEGG annotations, to investigate the growth kinetics, denitrification performances and characteristics of metabolic pathways under diverse carbon source conditions. We reconstructed a metabolic network of Thauera linaloolentis based on genomic analysis to help develop a systematic method of researching electron pathways. Our findings indicated that carbon sources with simple metabolic pathways (e.g., ethanol and sodium acetate) promoted the reproduction of Thauera linaloolentis, and its maximum growth density reached OD600 = 0.36 and maximum specific growth rate reached 0.145 h−1. These carbon sources also accelerated the denitrification process without the accumulation of intermediates. Nitrate could be reduced completely under any carbon source condition; but in the “glucose group”, the maximum accumulation of nitrite was 117.00 mg/L (1.51 times more than that in the “ethanol group”, which was 77.41 mg/L), the maximum accumulation of nitric oxide was 363.02 μg/L (7.35 times more than that in the “ethanol group”, which was 49.40 μg/L), and the maximum accumulation of nitrous oxide was 22.58 mg/L (26.56 times more than that in the “ethanol group”, which was 0.85 mg/L). Molecular biological analyses demonstrated that diverse types of carbon sources directly induced different carbon metabolic activities, resulting in variations in electron generation efficiency. Furthermore, the activities of the electron transport system were positively correlated with different carbon metabolic activities. Finally, these differences were reflected in the phenomenon of electronic competition between denitrifying reductases. Thus we concluded that this was the main molecular mechanism through which the carbon source type affected the denitrification process. In brief, carbon sources with simple metabolic pathways induced higher efficiency of electron generation, transfer, and competition, which promoted rapid proliferation and complete denitrification; otherwise Thauera linaloolentis would grow slowly and intermediate products would accumulate seriously. Our study established a method to evaluate and optimize carbon source utilization efficiency based on confirmed molecular mechanisms.

Myocardial ischemia/reperfusion (I/R) injury leads to significant impairment of cardiac function and remains the leading cause of morbidity and mortality worldwide. Activation of peroxisome proliferator-activated receptor b/d (PPARβ/δ) confers cardioprotection via pleiotropic effects including antioxidant and anti-inflammatory actions; however, the underlying mechanisms are not yet fully elucidated. The aim of this study was to investigate the effect of PPARβ/δ activation on myocardial mitochondrial respiratory function and link this effect with cardioprotection after ischemia/reperfusion (I/R). For this purpose, rats were treated with the PPARβ/δ agonist GW0742 and/or antagonist GSK0660 in vivo. Mitochondrial respiration and ROS production rates were determined using high-resolution fluororespirometry. Activation of PPARβ/δ did not alter mitochondrial respiratory function in the healthy heart, however, inhibition of PPARβ/δ reduced fatty acid oxidation (FAO) and complex II-linked mitochondrial respiration and shifted the substrate dependence away from succinaterelated energy production and towards NADH. Activation of PPARβ/δ reduced mitochondrial stress during in vitro anoxia/reoxygenation. Furthermore, it preserved FAO-dependent mitochondrial respiration and lowered ROS production at oxidative phosphorylation (OXPHOS)-dependent state during ex vivo I/R. PPARβ/δ activation was also followed by increased mRNA expression of components of FAO -linked respiration and of transcription factors governing mitochondrial homeostasis (carnitine palmitoyl transferase 1b and 2-CPT-1b and CPT-2, electron transfer flavoprotein dehydrogenase -ETFDH, peroxisome proliferator-activated receptor gamma co-activator 1 alpha-PGC-1a and nuclear respiratory factor 1-NRF-1). In conclusion, activation of PPARβ/δ stimulated both FAO-linked respiration and PGC-1a/NRF -1 signaling and preserved mitochondrial respiratory function during I/R. These effects are associated with reduced infarct size. [ABSTRACT FROM AUTHOR]

In aerobic conditions, the proton-motive force drives oxidative phosphorylation (OXPHOS) and the conversion of ADP to ATP. In hypoxic environments, OXPHOS is impaired, resulting in energy shortfalls and the accumulation of protons and lactate. This results in cellular acidification, which may impact the activity and/or integrity of mitochondrial enzymes and in turn negatively impact mitochondrial respiration and thus aerobic ATP production. Naked mole-rats (NMRs) are among the most hypoxia-tolerant mammals and putatively experience intermittent hypoxia in their underground burrows. However, if and how NMR cardiac mitochondria are impacted by lactate accumulation in hypoxia is unknown. We predicted that lactate alters mitochondrial respiration in NMR cardiac muscle. To test this, we used high-resolution respirometry to measure mitochondrial respiration in permeabilized cardiac muscle fibres from NMRs exposed to 4 h of in vivo normoxia (21% O2) or hypoxia (7% O2). We found that: (1) cardiac mitochondria cannot directly oxidize lactate, but surprisingly, (2) lactate inhibits mitochondrial respiration, and (3) decreases complex IV maximum respiratory capacity. Finally, (4) in vivo hypoxic exposure decreases the magnitude of lactate-mediated inhibition of mitochondrial respiration. Taken together, our results suggest that lactate may retard electron transport system function in NMR cardiac mitochondria, particularly in normoxia, and that NMR hearts may be primed for anaerobic metabolism. [ABSTRACT FROM AUTHOR]

Pacific hagfish (Eptatretus stoutii) are an ancient agnathan vertebrate known to be anoxia tolerant. To study their metabolic organization and the role of the mitochondria in anoxia tolerance we developed a novel protocol to measure mitochondrial function in permeabilized cardiomyocytes and how this is affected by one hour of anoxia followed by reoxygenation. When measured at 10 °C the mitochondria had a respiration rate of 2.1 ± 0.1pmol/s/mg WW during OXPHOS with saturating concentrations of glutamate, malate, and succinate. This is comparatively low compared to other ectothermic species. The functional characteristics of the mitochondria were quantified with mitochondrial control ratios. These demonstrated that proton leak contributed to just under 50% of the oxygen flux, with the remainder going towards ATP phosphorylation. Finally, when the preparations were exposed to an anoxia-reoxygenation protocol there was no difference in respiration compared to that of a heart sample from the same animal maintained under normoxia for the same time. When Complex I alone or Complex I and II were stimulated following one hour of anoxia there was no decline in oxygen flux observed. However, if Complex II was activated alone there was a significant decline in respiration. This decrease was however also observed in the mitochondria maintained in normoxia for one hour. In conclusion, Pacific hagfish cardiac mitochondria demonstrated a low rate of oxygen consumption, a loosely coupled electron transfer system, and a resistance to one hour of anoxia. [Display omitted] • First time that mitochondrial function has been measured in hagfish. • The respiration rate of mitochondria in permeabilized hagfish heart tissue is comparatively low compared to that of other ectothermic species. • Mitochondrial proton leak contributed to just under 40% of the O 2 flux, with the remainder going towards ATP phosphorylation. • There was no difference in respiration between control preparations and those exposed to one hour of anoxia followed by reoxygenation. [ABSTRACT FROM AUTHOR]

Succinate-driven reverse electron transport (RET) through complex I is hypothesized to be a major source of reactive oxygen species (ROS) that induces permeability transition pore (PTP) opening and damages the heart during ischemia/reperfusion. Because RET can only generate ROS when mitochondria are fully polarized, this mechanism is self-limiting once PTP opens during reperfusion. In the accompanying article (Korge, P., Calmettes, G., John, S. A., and Weiss, J. N. (2017) J. Biol. Chem. 292, 9882-9895), we showed that ROS production after PTP opening can be sustained when complex III is damaged (simulated by antimycin). Here we show that complex II can also contribute to sustained ROS production in isolated rabbit cardiac mitochondria following inner membrane pore formation induced by either alamethicin or calcium-induced PTP opening. Two conditions are required to maximize malonate-sensitive ROS production by complex II in isolated mitochondria: (a) complex II inhibition by atpenin A5 or complex III inhibition by stigmatellin that results in succinate-dependent reduction of the dicarboxylate-binding site of complex II (site IIf); (b) pore opening in the inner membrane resulting in rapid efflux of succinate/fumarate and other dicarboxylates capable of competitively binding to site IIf The decrease in matrix [dicarboxylate] allows O2 access to reduced site IIf, thereby making electron donation to O2 possible, explaining the rapid increase in ROS production provided that site IIf is reduced. Because ischemia is known to inhibit complexes II and III and increase matrix succinate/fumarate levels, we hypothesize that by allowing dicarboxylate efflux from the matrix, PTP opening during reperfusion may activate sustained ROS production by this mechanism after RET-driven ROS production has ceased.

Myocardial ischemia/reperfusion (I/R) injury leads to significant impairment of cardiac function and remains the leading cause of morbidity and mortality worldwide. Activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) confers cardioprotection via pleiotropic effects including antioxidant and anti-inflammatory actions; however, the underlying mechanisms are not yet fully elucidated. The aim of this study was to investigate the effect of PPARβ/δ activation on myocardial mitochondrial respiratory function and link this effect with cardioprotection after ischemia/reperfusion (I/R). For this purpose, rats were treated with the PPARβ/δ agonist GW0742 and/or antagonist GSK0660 in vivo. Mitochondrial respiration and ROS production rates were determined using high-resolution fluororespirometry. Activation of PPARβ/δ did not alter mitochondrial respiratory function in the healthy heart, however, inhibition of PPARβ/δ reduced fatty acid oxidation (FAO) and complex II-linked mitochondrial respiration and shifted the substrate dependence away from succinate-related energy production and towards NADH. Activation of PPARβ/δ reduced mitochondrial stress during in vitro anoxia/reoxygenation. Furthermore, it preserved FAO-dependent mitochondrial respiration and lowered ROS production at oxidative phosphorylation (OXPHOS)-dependent state during ex vivo I/R. PPARβ/δ activation was also followed by increased mRNA expression of components of FAO -linked respiration and of transcription factors governing mitochondrial homeostasis (carnitine palmitoyl transferase 1b and 2-CPT-1b and CPT-2, electron transfer flavoprotein dehydrogenase -ETFDH, peroxisome proliferator-activated receptor gamma co-activator 1 alpha- PGC-1α and nuclear respiratory factor 1-NRF-1). In conclusion, activation of PPARβ/δ stimulated both FAO-linked respiration and PGC-1α/NRF -1 signaling and preserved mitochondrial respiratory function during I/R. These effects are associated with reduced infarct size.

With the advent of technological advancements post the industrial revolution, thousands of chemicals are introduced into the market annually to enhance different facets of human life. Among these, pharmaceutical and personal care products (PPCPs), including antibiotics and disinfectants, such as benzalkonium chlorides (BACs), are prominent. BACs, often used for surface and hand disinfection in high concentrations or as preservatives in health products such as nasal sprays and eye drops, may present environmental risks if they seep into irrigation water through prolonged exposure or improper application. The primary objective of this study is to elucidate the tolerance mechanisms that may arise in Lemna minor plants, known for their remarkable capability to accumulate substances efficiently, in response to exogenously applied BACs at varying concentrations. The study applied six different concentrations of BACs, ranging from 0.25 to 10 mg L−1. The experimental period spanned seven days, during which the treatments were conducted in triplicate to ensure reliability and reproducibility of the results. It was observed that low concentrations of BACs (0.25, 0.5 and 1 mg L−1) did not elicit any statistically significant changes in growth parameters. However, higher concentrations of BACs (2.5, 5, and 10 mg L−1) resulted in a reduction in RGR by 20%, 28%, and 36%, respectively. Chlorophyll fluorescence declined significantly at BAC doses of 5 and 10 mg L−1, with F v /F m ratios decreasing by 9% and 15%, and F v /F o ratios by 40% and 39%, respectively. Proline content decreased in all treatment groups, with a 46% reduction at 10 mg L−1 BAC. TBARS and H 2 O 2 contents increased proportionally with BAC dosage, showing the highest increases of 30% and 40% at 10 mg L−1, respectively. The noticeable increase in SOD enzyme activity at BAC concentrations of 0.5, 1, and 2.5 mg L−1, with increases of 2.7-fold, 2.2-fold, and 1.7-fold respectively, along with minimal accumulation of H 2 O 2 , suggests that L. minor plants have a strong tolerance to BAC. This is supported by the efficient functioning of the CAT and GST enzymes, especially evident at the same concentrations, where increased activities effectively reduce the buildup of H 2 O 2. In the AsA-GSH cycle, although variations were observed between groups, the contribution of the GR enzyme to the preservation of GSH content by recycling GSSG likely maintained redox homeostasis in the plant, especially at low concentrations of BACs. The study revealed that L. minor effectively accumulates BAC alongside its tolerance mechanisms and high antioxidant activity. These results underscore the potential for environmental cleanup efforts through phytoremediation. [Display omitted] • L. minor demonstrated elevated levels of H 2 O 2 and TBARS after BAC exposure. • Growth parameters decreased at 2.5, 5 and 10 mg L−1 BAC. • Antioxidant activity increased under low-dose BAC applications. • L. minor exposed to low-dose BAC applications maintain the redox state. [ABSTRACT FROM AUTHOR]

Type 2 diabetes (T2DM) is a persistent metabolic disorder rising rapidly worldwide. It is characterized by pancreatic insulin resistance and β-cell dysfunction. Hyperglycemia induced reactive oxygen species (ROS) production and oxidative stress are correlated with the pathogenesis and progression of this metabolic disease. To counteract the harmful effects of ROS, endogenous antioxidants of the body or exogenous antioxidants neutralise it and maintain bodily homeostasis. Under hyperglycemic conditions, the imbalance between the cellular antioxidant system and ROS production results in oxidative stress, which subsequently results in the development of diabetes. These ROS are produced in the endoplasmic reticulum, phagocytic cells and peroxisomes, with the mitochondrial electron transport chain (ETC) playing a pivotal role. The exacerbated ROS production can directly cause structural and functional modifications in proteins, lipids and nucleic acids. It also modulates several intracellular signaling pathways that lead to insulin resistance and impairment of β-cell function. In addition, the hyperglycemia-induced ROS production contributes to micro- and macro-vascular diabetic complications. Various in-vivo and in-vitro studies have demonstrated the anti-oxidative effects of natural products and their derived bioactive compounds. However, there is conflicting clinical evidence on the beneficial effects of these antioxidant therapies in diabetes prevention. This review article focused on the multifaceted role of oxidative stress caused by ROS overproduction in diabetes and related complications and possible antioxidative therapeutic strategies targeting ROS in this disease. [Display omitted] • Impaired antioxidant system leads to overproduction of free-radicals. • Excess ROS generation causes alteration of cell signaling pathways and homeostasis. • ROS induces disruption of pancreatic β-cell homeostasis and promotes IR. • Targeting the endogenous antioxidant system seems a promising therapeutic approach. [ABSTRACT FROM AUTHOR]

In plants, flooding-induced oxygen deficiency causes severe stress, leading to growth reduction and yield loss. It is therefore important to understand the molecular mechanisms for adaptation to hypoxia. Aquaporins at the plasma membrane play a crucial role in water uptake. However, their role during hypoxia and membrane redox changes is still not fully understood. The influence of 24 h hypoxia induction on hydroponically grown maize (Zea mays L.) was investigated using an oil-based setup. Analyses of physiological parameters revealed typical flooding symptoms such as increased ethylene and H2O2 levels, an increased alcohol dehydrogenase activity, and an increased redox activity at the plasma membrane along with decreased oxygen of the medium. Transcriptomic analysis and shotgun proteomics of plasma membranes and soluble fractions were performed to determine alterations in maize roots. RNA-sequencing data confirmed the upregulation of genes involved in anaerobic metabolism, biosynthesis of the phytohormone ethylene, and its receptors. Transcripts of several antioxidative systems and other oxidoreductases were regulated. Mass spectrometry analysis of the plasma membrane proteome revealed alterations in redox systems and an increased abundance of aquaporins. Here, we discuss the importance of plasma membrane aquaporins and redox systems in hypoxia stress response, including the regulation of plant growth and redox homeostasis. [ABSTRACT FROM AUTHOR]

Naked mole‐rats (NMRs; Heterocephalus glaber) are among the most hypoxia‐tolerant mammals. There is evidence that the NMR brain tolerates in vitro hypoxia and NMR brain mitochondria exhibit functional plasticity following in vivo hypoxia; however, if and how these organelles tolerate ischaemia and how ischaemic stress impacts mitochondrial energetics and redox regulation is entirely unknown. We hypothesized that mitochondria fundamentally contribute to in vitro ischaemia resistance in the NMR brain. To test this, we treated NMR and CD‐1 mouse cortical brain sheets with an in vitro ischaemic mimic and evaluated mitochondrial respiration capacity and redox regulation following 15 or 30 min of ischaemia or ischaemia/reperfusion (I/R). We found that, relative to mice, the NMR brain largely retains mitochondrial function and redox balance post‐ischaemia and I/R. Specifically: (i) ischaemia reduced complex I and II‐linked respiration ∼50–70% in mice, vs. ∼20–40% in NMR brain, (ii) NMR but not mouse brain maintained relatively steady respiration control ratios and robust mitochondrial membrane integrity, (iii) electron leakage post‐ischaemia was lesser in NMR than mouse brain and NMR brain retained higher coupling efficiency, and (iv) free radical generation during and following ischaemia and I/R was lower from NMR brains than mice. Taken together, our results indicate that NMR brain mitochondria are more tolerant of ischaemia and I/R than mice and retain respiratory capacity while avoiding redox derangements. Overall, these findings support the hypothesis that hypoxia‐tolerant NMR brain is also ischaemia‐tolerant and suggest that NMRs may be a natural model of ischaemia tolerance in which to investigate evolutionarily derived solutions to ischaemic pathology. Key points: Ischaemia is highly deleterious to the mammalian brain and this damage is largely mediated by mitochondrial dysfunction.Naked mole‐rats are among the most hypoxia‐tolerant mammals and their brain tolerates ischaemia ex vivo, but the impact of ischaemia on mitochondrial function is unknown.Naked mole‐rat but not mouse brain mitochondria retain respiratory capacity and membrane integrity following ischaemia or ischaemia/reperfusion.Differences in free radical management and respiratory pathway control between species may mediate this tolerance.These results help us understand how natural models of hypoxia tolerance also tolerate ischaemia in the brain. [ABSTRACT FROM AUTHOR]

As milk production in dairy cattle continues to increase, so do the energetic and nutrient demands on the dairy cow. Difficulties making the necessary metabolic adjustments for lactation can impair lactation performance and increase the risk of metabolic disorders. The physiological adaptations to lactation involve the mammary gland and extramammary tissues that coordinately enhance the availability of precursors for milk synthesis. Changes in whole-body metabolism and nutrient partitioning are accomplished, in part, through the bioenergetic and biosynthetic capacity of the mitochondria, providing energy and diverting important substrates, such as AA and fatty acids, to the mammary gland in support of lactation. With increased oxidative capacity and ATP production, reactive oxygen species production in mitochondria may be altered. Imbalances between oxidant production and antioxidant activity can lead to oxidative damage to cellular structures and contribute to disease. Thus, mitochondria are tasked with meeting the energy needs of the cell and minimizing oxidative stress. Mitochondrial function is regulated in concert with cellular metabolism by the nucleus. With only a small number of genes present within the mitochondrial genome, many genes regulating mitochondrial function are housed in nuclear DNA. This review describes the involvement of mitochondria in coordinating tissue-specific metabolic adaptations across lactation in dairy cattle and the current state of knowledge regarding mitochondrial-nuclear signaling pathways that regulate mitochondrial proliferation and function in response to shifting cellular energy need. [ABSTRACT FROM AUTHOR]

Due to the growing interest in enhancing dark fermentation and anaerobic digestion via carbon-based additives to exploit different lucrative synergies, process-based optimizations and mechanistic analyses are crucial. Herein, we studied the impacts of carbon supplements on halophilic microbial cultures as a process intensification way towards bioenergy recovery from saline wastewater. Three additives, i.e., powdered activated carbon, multiwall carbon nanotubes and graphene, were examined. Two sets of parallel batch experiments were conducted using archaea-free (for dark fermentation) and mixed (for anaerobic digestion) halophilic cultures at different supplement doses. Adding 30 mg/L of graphene and 100 mg/L of powdered activated carbon exhibited the maximum improvements in dark fermentation (H 2 -production) and anaerobic digestion (biogas production), i.e., ∼28% and ∼27% over the control, respectively. This underscored the dose-dependent impact of different-sized carbon amendments. Both the electron transport system activity and extracellular polymeric substances were improved with all amendments, indicating a stimulated electron transfer flux. However, distinct bacterial compositions were identified when using mixed and archaea-free cultures along with indicators for direct interspecies electron transfer establishment in the presence of archaea. Beyond this, such findings also supported the expanded role of conductive additives on H 2 -producing bacteria, including Clostridium. According to a techno-economic analysis, powdered activated carbon emerged as the best for optimizing bioenergy recovery (in terms of H 2 or biogas) from saline wastewater, providing a solid basis for relevant applications. [Display omitted] [ABSTRACT FROM AUTHOR]

2,3,5-Triphenyl tetrazolium chloride (TTC) staining is a method to distinguish the mitochondrial activity of cells based on the color: colorless TTC turns red when under reducing conditions. Although the assay reflects the mitochondrial activity of cells, which enzyme(s) in the electron transport system contribute to TTC reduction has been unclear. TTC staining assays using gene disruptants related to the electron transport system in Saccharomyces cerevisiae revealed those disruptants related to electron transport from each electron donor to ubiquinone (red colonies) and disruptants that were related to ubiquinol-cytochrome c oxidoreductase and cytochrome c oxidase (white colonies). In addition, when the enzyme activities of ubiquinol-cytochrome c oxidoreductase and cytochrome c oxidase were measured using TTC as the electron acceptor, only ubiquinol-cytochrome c oxidoreductase showed TTC reduction activity, and the activity was enhanced by potassium cyanide, an inhibitor of cytochrome c oxidase. These results indicated that ubiquinol-cytochrome c oxidoreductase is involved in TTC reduction in S. cerevisiae. The fermentation profiles of BY4741UΔ cor1 and BY4741UΔ cox4 , which exhibited no TTC staining activity, were almost identical to that of the parental strain BY4741U. However, cell growth and ethanol and succinate production of the ura3 -mutated strain BY4741, which also exhibited no TTC staining activity, was altered compared to those of BY4741U, indicating that the fermentation profile varies among strains that show no TTC staining activity. The relationship between uracil metabolism and TTC staining activity was also determined based on metabolome analysis. [ABSTRACT FROM AUTHOR]

In plants, flooding-induced oxygen deficiency causes severe stress, leading to growth reduction and yield loss. It is therefore important to understand the molecular mechanisms for adaptation to hypoxia. Aquaporins at the plasma membrane play a crucial role in water uptake. However, their role during hypoxia and membrane redox changes is still not fully understood. The influence of 24 h hypoxia induction on hydroponically grown maize (Zea mays L.) was investigated using an oil-based setup. Analyses of physiological parameters revealed typical flooding symptoms such as increased ethylene and H2O2 levels, an increased alcohol dehydrogenase activity, and an increased redox activity at the plasma membrane along with decreased oxygen of the medium. Transcriptomic analysis and shotgun proteomics of plasma membranes and soluble fractions were performed to determine alterations in maize roots. RNA-sequencing data confirmed the upregulation of genes involved in anaerobic metabolism, biosynthesis of the phytohormone ethylene, and its receptors. Transcripts of several antioxidative systems and other oxidoreductases were regulated. Mass spectrometry analysis of the plasma membrane proteome revealed alterations in redox systems and an increased abundance of aquaporins. Here, we discuss the importance of plasma membrane aquaporins and redox systems in hypoxia stress response, including the regulation of plant growth and redox homeostasis.

Comparison of energy metabolism between the conventional anaerobic-anoxic-oxic (AAO) process and the anoxic-anaerobic-oxic process (reversed AAO) was carried out. Although in terms of biological nutrient removal, both processes offered excellent removal efficiencies for organic matter and total phosphorus, there was a significant difference in regards to nitrogen removal. It was found that the ammonia nitrogen in the effluent in the AAO and the reversed AAO processes was 3.45 ± 0.64 and 1.53 ± 0.48 mg L–1, respectively, with an influent ammonia nitrogen of 23.22 ± 1.77 and 23.07 ± 1.57 mg L–1, respectively (Mixed liquor suspended solids (MLSS): 3,000 ± 500 mg L–1 and HRT: 12 h). This study investigated whether reversing the anaerobic and anoxic compartments could change the microbial activity and eventually promote efficient microorganism removal ability. Several key enzymatic indicators such as, 2,3,5-triphenyl tetrazolium chloride dehydrogenase activity (TTC-DHA), 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride electron transport system (INT-ETS), and adenosine triphosphate were measured and confirmed the improvement in energy metabolism in the reversed AAO process. Owing to the increased microbial activity, both processes showed identical phosphorus removal efficiency while less carbon source was consumed in reversed AAO process. Therefore, more carbon sources can be used for denitrification because of the highly efficient phosphorus removal mechanism. These findings highlight the improved removal capacity of reversed AAO process, demonstrating its real applicability. [ABSTRACT FROM AUTHOR]

Analysis of codon usage bias (CUB) is very much important in perceiving the knowledge of molecular biology, the discovery of a new gene, designing of transgenes and evolution of gene. In this study, we analyzed compositional features and codon usage of MT-CO (COI, COII and COIII) genes among the classes of Arthropoda to explore the pattern of CUB as no research work was reported yet. Nucleotide composition analysis in CO genes suggested that the genes were AT-rich in all the four classes of Arthropoda. CUB was low in all the classes of Arthropoda for MT-CO genes as revealed from a high effective number of codons (ENC). We also found that the evolutionary forces namely mutation pressure and natural selection were the key influencing factors in CUB among MT-CO genes as revealed by correlation analysis between overall nucleotide composition and nucleotide composition at the 3rd codon position. Correspondence analysis suggested that the pattern of CUB was different among the classes of Arthropoda. Further, it was revealed from the neutrality plot that natural selection had a dominant role while mutation pressure exhibited a minor role in structuring the pattern of codon usage in all the classes of Arthropoda across COI, COII and COIII genes. [ABSTRACT FROM AUTHOR]

[Display omitted] • PDDA (5–40 g/kg TSS) reduced hydrogen production from sludge by up to 37 %. • The dark fermentation process was hindered by decreased enzyme activity. • Hydrogen production was more strongly inhibited than hydrogen consumption. • The acetate pathway was converted to the propionate and butyrate pathways. • The dominant bacteria were crowded out by other enriched microorganisms. Polydimethyldiallylammonium chloride (PDDA) is an excellent flocculant for wastewater purification and sludge dewatering, but whether it poses a threat to hydrogen production from waste activated sludge is not known. In this study, the effect and underlying mechanism of PDDA on the dark fermentation of sludge was investigated. The results showed that PDDA reduced cumulative hydrogen production from 3.8±0.1 to 2.4±0.1 mL/g volatile suspended solids at 40 g/kg total suspended solids. PDDA impeded the dark fermentation process by inhibiting the activity of key enzymes, presenting a stronger inhibitory effect on the hydrogen production process than the hydrogen consumption process. Additionally, PDDA inhibited Firmicutes by enriching other microorganisms, thereby impeding hydrogen production via the acetate pathway. This study deepens the understanding of the potential effects of PDDA on sludge treatment and provides a theoretical basis for alleviating the negative effects of quaternary ammonium-based cationic flocculants. [ABSTRACT FROM AUTHOR]

The thermal sensitivity of ectotherms is largely dictated by the impact of temperature on cellular bioenergetics, particularly on mitochondrial functions. As the thermal sensitivity of bioenergetic pathways depends on the structural and kinetic properties of its component enzymes, optimization of their collective function to different thermal niches is expected to have occurred through selection. In the present study, we sought to characterize mitochondrial phenotypic adjustments to thermal niches in eight ray-finned fish species occupying a wide range of thermal habitats by comparing the activities of key mitochondrial enzymes in their hearts. We measured the activity of four enzymes that control substrate entrance into the tricarboxylic acid (TCA) cycle: pyruvate kinase (PK), pyruvate dehydrogenase complex (PDHc), carnitine palmitoyltransferase (CPT), and hydroxyacyl-CoA dehydrogenase (HOAD). We also assayed enzymes of the electron transport system (ETS): complexes I, II, I + III, and IV. Enzymes were assayed at five temperatures (5, 10, 15, 20, and 25°C). Our results showed that the activity of CPT, a gatekeeper of the fatty acid pathway, was higher in the cold-water fish than in the warmer-adapted fish relative to the ETS (complexes I and III) when measured close to the species optimal temperatures. The activity of HOAD showed a similar pattern relative to CI + III and thermal environment. By contrast, PDHc and PK did not show the similar patterns with respect to CI + III and temperature. Cold-adapted species had high CIV activities compared to those of upstream complexes (I, II, I + III) whereas the converse was true for warm-adapted species. Our findings reveal a significant variability of heart mitochondrial organization among species that can be linked to temperature adaptation. Cold-adapted fish do not appear to compensate for PDHc activity but likely adjust fatty acids oxidation through higher activities of CPT and HOAD relative to complexes I + III.

The mitochondrial oxidative stress theory of aging posits that membrane susceptibility to peroxidation and the organization of the electron transport system (ETS) linked with reactive oxygen species (ROS) generation are two main drivers of lifespan. While a clear correlation has been established from species comparative studies, the significance of these characteristics as potential modulators of lifespan divergences among populations of individual species is still to be tested. The bivalve Arctica islandica, the longest-lived non-colonial animal with a record lifespan of 507 years, possesses a lower mitochondrial peroxidation index (PI) and reduced H2O2 efflux linked to complexes I and III activities than related species. Taking advantage of the wide variation in maximum reported longevities (MRL) among 6 European populations (36–507 years), we examined whether these two mitochondrial properties could explain differences in longevity. We report no relationship between membrane PI and MRL in populations of A. islandica, as well as a lack of intraspecific relationship between ETS complex activities and MRL. Individuals from brackish sites characterized by wide temperature and salinity windows had, however, markedly lower ETS enzyme activities relative to citrate synthase activity. Our results highlight environment-dependent remodeling of mitochondrial phenotypes.

The thermal sensitivity of ectotherms is largely dictated by the impact of temperature on cellular bioenergetics, particularly on mitochondrial functions. As the thermal sensitivity of bioenergetic pathways depends on the structural and kinetic properties of its component enzymes, optimization of their collective function to different thermal niches is expected to have occurred through selection. In the present study, we sought to characterize mitochondrial phenotypic adjustments to thermal niches in eight ray-finned fish species occupying a wide range of thermal habitats by comparing the activities of key mitochondrial enzymes in their hearts. We measured the activity of four enzymes that control substrate entrance into the tricarboxylic acid (TCA) cycle: pyruvate kinase (PK), pyruvate dehydrogenase complex (PDHc), carnitine palmitoyltransferase (CPT), and hydroxyacyl-CoA dehydrogenase (HOAD). We also assayed enzymes of the electron transport system (ETS): complexes I, II, I + III, and IV. Enzymes were assayed at five temperatures (5, 10, 15, 20, and 25°C). Our results showed that the activity of CPT, a gatekeeper of the fatty acid pathway, was higher in the cold-water fish than in the warmer-adapted fish relative to the ETS (complexes I and III) when measured close to the species optimal temperatures. The activity of HOAD showed a similar pattern relative to CI + III and thermal environment. By contrast, PDHc and PK did not show the similar patterns with respect to CI + III and temperature. Cold-adapted species had high CIV activities compared to those of upstream complexes (I, II, I + III) whereas the converse was true for warm-adapted species. Our findings reveal a significant variability of heart mitochondrial organization among species that can be linked to temperature adaptation. Cold-adapted fish do not appear to compensate for PDHc activity but likely adjust fatty acids oxidation through higher activities of CPT and HOAD relative to complexes I + III. [ABSTRACT FROM AUTHOR]

The mitochondrial oxidative stress theory of aging posits that membrane susceptibility to peroxidation and the organization of the electron transport system (ETS) linked with reactive oxygen species (ROS) generation are two main drivers of lifespan. While a clear correlation has been established from species comparative studies, the significance of these characteristics as potential modulators of lifespan divergences among populations of individual species is still to be tested. The bivalve Arctica islandica , the longest-lived non-colonial animal with a record lifespan of 507 years, possesses a lower mitochondrial peroxidation index (PI) and reduced H2O2 efflux linked to complexes I and III activities than related species. Taking advantage of the wide variation in maximum reported longevities (MRL) among 6 European populations (36–507 years), we examined whether these two mitochondrial properties could explain differences in longevity. We report no relationship between membrane PI and MRL in populations of A. islandica , as well as a lack of intraspecific relationship between ETS complex activities and MRL. Individuals from brackish sites characterized by wide temperature and salinity windows had, however, markedly lower ETS enzyme activities relative to citrate synthase activity. Our results highlight environment-dependent remodeling of mitochondrial phenotypes. [ABSTRACT FROM AUTHOR]

Abstract Jellyfish blooms might be driven by the alterations in seawater temperature (SWT) associated with climate change. The physiological responses of jellyfish to changing SWT, however, are poorly understood. Therefore, we asked the question: how do sudden changes (±6 °C) in SWT affect the physiological performance of the jellyfish Cassiopea sp.? We measured the changes in mitochondrial cellular respiration (i.e., in term of the electron transport system (ETS) activity), superoxide dismutase (SOD) activity, and lipid peroxidation (LPO) to assess the jellyfish's physiological performance. In acute treatments (2 h), ETS increased only in response to cooling (to 20 °C) while SOD remained unchanged. In response to chronic treatment (2 weeks), ETS, SOD and LPO increased, while body mass decreased in response to cold (20 °C). In contrast, the heat-treated (32 °C) jellyfish did not increase their metabolic demands nor show signs of oxidative stress (OS). Moreover, they gained body mass. Because chlorophyll-a remained unchanged in all chronic-treated jellyfish, the cold-induced OS is more likely due to cellular respiration, not photosynthesis. Overall, Cassiopea sp. seems more sensitive to decreases in SWT then to increases. Therefore, Cassiopea sp. might benefit from the future projected rises in SWT, which could result in increased population abundance and an expansion in geographic distribution. Overall, these finding add new physiological evidences on jellyfish tolerance and might be used as a framework for further studies aiming at better understanding of jellyfish physiology. Highlights • The jellyfish Cassiopea is more sensitive to cold (20 °C) than warm SWT (32 °C). • Oxidative stress and high energy consumption seem to limit Cassiopea 's successful invasion into colder water bodies. • In Cassiopea , SOD activity is positively correlated with Chla content. • In response to the projected rises in SWT, Cassiopea might increase its population and geographical distribution. [ABSTRACT FROM AUTHOR]

Abstract In addition to the typical electron transport system (ETS) in animal mitochondria responsible for oxidative phosphorylation, in some species there exists an alternative oxidase (AOX) pathway capable of catalyzing the oxidation of ubiquinol and the reduction of oxygen to water. The discovery of AOX in animals is recent and further investigations into its expression, regulation, and physiological role have been hampered by the lack of a tractable experimental model organism. Our recent DNA database searches using bioinformatics revealed an AOX sequence in several marine copepods including Tigriopus californicus. This species lives in tidepools along the west coast of North America and is subject to a wide variety of daily environmental stresses. Here we verify the presence of the AOX gene in T. californicus and the expression of AOX mRNA and AOX protein in various life stages of the animal. We demonstrate that levels of the AOX protein increase in T. californicus in response to cold and heat stress compared to normal rearing temperature. We predict that a functional AOX pathway is present in T. californicus , propose that this species will be a useful model organism for the study of AOX in animals, and discuss future directions for animal AOX research. Highlights • The alternative oxidase gene (AOX) is present and expressed in several copepod species. • We present experimental evidence that AOX is present and expressed in the copepod Tigriopus californicus. • AOX protein levels in T. californicus increase in response to temperature stress. • T. californicus represents an excellent model in which to study AOX physiological function and regulation in animals. [ABSTRACT FROM AUTHOR]

The study of glycolysis, the TCA cycle, and oxidative phosphorylation in animals has yielded a wealth of information about bioenergetics. Less is known about how animals use fuels other than glucose and less characterized enzymes that are also used to provide electrons to the electron transport system. It has become clear that bioenergetic flexibility is employed by a wide variety of animals in order to successfully grow, maintain cells, and reproduce, and has contributed to the exploitation of new environments and ecological niches through evolution. In most cases, the discovery of these “alternative” fuels and non-classical pathways is relatively recent, but is starting to call into question long believed paradigms about the diversity of animal bioenergetics. We present several specific examples of these “alternatives” and the animals that use them and present some implications for animal mitochondrial physiology research. [ABSTRACT FROM AUTHOR]

Reversible protein acetylation is an important regulatory mechanism for modulating protein function. The cellular protein acetylome is in large part dictated by the cellular redox balance, and in particular [NAD + ]. While the relationship between hypoxia, redox balance, energy charge and resulting mitochondrial dysfunction has been examined in the context of hypoxia-linked pathologies, little is known about the direct effects of decreases in environmental oxygen on reversible lysine acetylation, and the resulting modifications to mitochondrial metabolism. To address this knowledge gap, we exposed zebrafish ( Danio rerio ) to 16 h of hypoxia (2.21 kPa) and quantified acetylation levels of 1220 proteins using whole-cell proteomics in samples of brain taken from normoxic and hypoxic zebrafish. In addition, we examined the effects of hypoxia on cytoplasmic and mitochondrial redox status, whole-cell energetics, the activity of the mitochondrial NAD + -dependent deacetylase SIRT3, and electron transport chain complex activities to determine if there is an association between hypoxia-induced metabolic disturbances, protein acetylation, and mitochondrial function. Our results (1) reveal several key changes in the acetylation status of proteins in the brain, primarily within the mitochondria; (2) show significant fluctuations in cytoplasmic and mitochondrial redox status within the brain during hypoxia exposure; and (3) provide evidence that lysine acetylation may be related to large changes in electron transport and ATP-synthase complex activities and adenylate status in zebrafish exposed to hypoxic stress. Together, these data provide new insights into the role of protein modifications in mitochondrial metabolism during hypoxia. [ABSTRACT FROM AUTHOR]

Mammalian torpor is a phenotype characterized by a controlled decline of metabolic rate, generally followed by a reduction in body temperature. During arousal from torpor, both metabolic rate and body temperature rapidly returns to resting levels. Metabolic rate reduction experienced by torpid animals is triggered by active suppression of mitochondrial respiration, which is rapidly reversed during rewarming process. In this study, we analyzed the changes in the maximal activity of key enzymes related to electron transport system (complexes I, III and IV) in six tissues of torpid, arousing and euthermic Chilean mouse-opossums ( Thylamys elegans ). We observed higher maximal activities of complexes I and IV during torpor in brain, heart and liver, the most metabolically active organs in mammals. On the contrary, higher enzymatic activities of complexes III were observed during torpor in kidneys and lungs. Moreover, skeletal muscle was the only tissue without significant differences among stages in all complexes evaluated, suggesting no modulation of oxidative capacities of electron transport system components in this thermogenic tissue. In overall, our data suggest that complexes I and IV activity plays a major role in initiation and maintenance of metabolic suppression during torpor in Chilean mouse–opossum, whereas improvement of oxidative capacities in complex III might be critical to sustain metabolic machinery in organs that remains metabolically active during torpor. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical properties of a Shewanella oneidensis MR-1 biofilm were investigated using a mini-microbial electrochemical system. The performance of the biofilm was shown, using discharge test and cyclic voltammetry investigations, to improve over time. Differential pulse voltammograms were also acquired to determine the type of extracellular electron transfer that took place and to characterize the structure of the microbial biofilm formed on the electrode of the electrochemical system. These results indicated that extracellular electron transfer via a flavin-like mediator chemical predominated as the biofilm grew. The results, combined with a comparison of the measured current density with the calculated value of a seamless single-layered biofilm, also suggested that S. oneidensis MR-1 formed a multi-layered biofilm on the electrode. [ABSTRACT FROM AUTHOR]

We demonstrate the impact of Lobelia dortmanna on the abundance and morphological structure and function of the bacterial biocoenosis occurring in the rhizosphere sediments. The metabolic activity of microorganisms, the intensity of respiration, the efficiency of respiratory chain and membrane integrity was evaluated. The significant influence of L. dortmanna on microbiological processes in the sediments was confirmed. Clearly the high amount, biomass and metabolic and physiological activity of bacteria in the rhizosphere sediments confirmed the stimulating effect of isoetids on sediment bacteria. The rhizosphere is inhabited by microorganisms which are very active in physiological and metabolic terms. This phenomenon is called the rhizosphere effect. The amount of carbon dioxide released in particular sediment zones was predominantly determined by the number of metabolically active cells and not by the respiration rate per single cell. The high respiration rate of bacteria in the rhizosphere was predominantly determined by high DOC concentration, as evidenced by the correlations between the parameters. The development of positive redox potential in the rhizosphere sediments by L. dortmanna was of considerable importance for the intensity of respiratory processes, which confirms the relationship between redox potential and CO 2 concentration in the sediments. The specific system of functional relationships occurring between the roots of L. dortmanna and microorganisms present in bottom sediments is one of the important mechanisms enabling the well-functioning of this macrophyte in the littoral zone of soft-water oligotrophic lakes. [ABSTRACT FROM AUTHOR]

• Ammonia removal was significantly inhibited by RP4 plasmid. • The RP4 plasmid changed ammonia oxidation metabolites to NxO. • The RP4 plasmid inhibited electron transport in N. europaea. • The RP4 plasmid altered energy metabolism in N. europaea. Antibiotic resistance genes (ARGs) have recently become an important public health problem and therefore several studies have characterized ARG composition and distribution. However, few studies have assessed their impact on important functional microorganisms in the environment. Therefore, our study sought to investigate the mechanisms through which multidrug-resistant plasmid RP4 affected the ammonia oxidation capacity of ammonia-oxidizing bacteria, which play a key role in the nitrogen cycle. The ammonia oxidation capacity of N. europaea ATCC25978 (RP4) was significantly inhibited, and NO and N 2 O were produced instead of nitrite. Our findings demonstrated that the decrease in electrons from NH 2 OH decreased the ammonia monooxygenase (AMO) activity, leading to a decrease in ammonia consumption. In the ammonia oxidation process, N. europaea ATCC25978 (RP4) exhibited ATP and NADH accumulation. The corresponding mechanism was the overactivation of Complex Ⅰ, ATPase, and the TCA cycle by the RP4 plasmid. The genes encoding TCA cycle enzymes related to energy generation, including gltA, icd, sucD , and NE0773 , were upregulated in N. europaea ATCC25978 (RP4). These results demonstrate the ecological risks of ARGs, including the inhibition of the ammonia oxidation process and an increased production of greenhouse gases such as NO and N 2 O. [ABSTRACT FROM AUTHOR]