Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions

Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes—as experienced during re-oxygenation—leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.

Timely and early respiratory rehabilitation in patients with covid 19 pneumonia in a referral hospital

SARS-CoV-2 is a beta-coronavirus of the same subgenus as SARS and MERS viruses, they share the same gene binding receptor, angiotensin converting enzyme (ACE2). (1) The spectrum of disease severity is varied, with the mild form being the most frequent (81%), and severe disease present in 14% of cases, with critical presentation being present in 5%, with a mortality of 2.3%.(2) The post-pneumonia respiratory sequela caused by beta-Coronaviruses is diffuse alveolar damage with fibrotic lesions; the pathophysiological mechanism is multifactorial, which involves activation of transforming growth factor beta (TGF-β)(3), IL1, IL6, MCP1 and TNF-α secondary to epithelial injury and subsequent inflammation. In addition, exposure to high O2 concentrations and effects of barotrauma, caused by advanced oxygen/ventilatory support, activate the pro-fibrotic TGF-β pathway, resulting in aberrant repair characterized by exaggerated deposition of fibroblasts, myofibroblasts and collagen. Forty-seven percent and 25% of patients who survive moderate to severe COVID-19 pneumonia have decreased carbon monoxide diffusion and predicted total lung capacity, respectively. (4)

Carbon Availability and Nitrogen Mineralization Control Denitrification Rates and Product Stoichiometry during Initial Maize Litter Decomposition

Returning crop residues to agricultural fields can accelerate nutrient turnover and increase N2O and NO emissions. Increased microbial respiration may lead to formation of local hotspots with anoxic or microoxic conditions promoting denitrification. To investigate the effect of litter quality on CO2, NO, N2O, and N2 emissions, we conducted a laboratory incubation study in a controlled atmosphere (He/O2, or pure He) with different maize litter types (Zea mays L., young leaves and roots, straw). We applied the N2O isotopocule mapping approach to distinguish between N2O emitting processes and partitioned the CO2 efflux into litter- and soil organic matter (SOM)-derived CO2 based on the natural 13C isotope abundances. Maize litter increased total and SOM derived CO2 emissions leading to a positive priming effect. Although C turnover was high, NO and N2O fluxes were low under oxic conditions as high O2 diffusivity limited denitrification. In the first week, nitrification contributed to NO emissions, which increased with increasing net N mineralization. Isotopocule mapping indicated that bacterial processes dominated N2O formation in litter-amended soil in the beginning of the incubation experiment with a subsequent shift towards fungal denitrification. With onset of anoxic incubation conditions after 47 days, N fluxes strongly increased, and heterotrophic bacterial denitrification became the main source of N2O. The N2O/(N2O+N2) ratio decreased with increasing litter C:N ratio and Corg:NO3− ratio in soil, confirming that the ratio of available C:N is a major control of denitrification product stoichiometry.

Oxygen Management During Collective Aeromedical Evacuation of 36 COVID-19 Patients With ARDS

Objective The ongoing coronavirus disease-2019 pandemic leads to the saturation of critical care facilities worldwide. Collective aeromedical evacuations (MEDEVACS) might help rebalance the demand and supply of health care. If interhospital transport of patients suffering from ARDS is relatively common, little is known about the specific challenges of collective medevac. Oxygen management in such context is crucial. We describe our experience with a focus on this resource. Methods We retrospectively analyzed the first six collective medevac performed during the coronavirus disease-2019 pandemic by the French Military Health Service from March 17 to April 3, 2020. Oxygen management was compliant with international guidelines as well as aeronautical constraints and monitored throughout the flights. Presumed high O2 consumers were scheduled to board the last and disembark the first. Results Thirty-six mechanically ventilated patients were successfully transported within Europe. The duration of onboard ventilation was 185 minutes (145-198.5 minutes), including the flight, the boarding and disembarking periods. Oxygen intake was 1,650 L per patient per flight (1,350-1,950 L patient per flight) and 564 L per patient per hour (482-675 L per patient−1 per hour) and surpassed our anticipation. As anticipated, presumed high O2 consumers had a reduced ventilation duration onboard. The estimations of oxygen consumptions were frequently overshot, and only two hypoxemia episodes occurred. Conclusion Oxygen consumption was higher than expected, despite anticipation and predefined oxygen management measures, and encourages to a great caution in the processing of such collective medevac missions.

Community biofilm-formation, stratification and productivity in serially-transferred microcosms

The establishment of O2 gradients in liquid columns by bacterial metabolic activity produces a spatially-structured environment. This produces a high-O2 region at the top that represents an un-occupied niche which could be colonised by biofilm-competent strains. We have used this to develop an experimental model system using soil-wash inocula and a serial-transfer approach to investigate changes in community-based biofilm-formation and productivity. This involved ten transfers of mixed-community or biofilm-only samples over a total of 10–60 days incubation. In all final-transfer communities the ability to form biofilms was retained, though in longer incubations the build-up of toxic metabolites limited productivity. Measurements of microcosm productivity, biofilm-strength and attachment levels were used to assess community-aggregated traits which showed changes at both the community and individual-strain levels. Final-transfer communities were stratified with strains demonstrating a plastic phenotype when migrating between the high and low-O2 regions. The majority of community productivity came from the O2-depleted region rather than the top of the liquid column. This model system illustrates the complexity we expect to see in natural biofilm-forming communities. The connection between biofilms and the liquid column seen here has important implications for how these structures form and respond to selective pressure.