Algal growth enhancement by bacteria: Is consumption of photosynthetic oxygen involved?

Abstract: Pseudomonas diminuta and P. vesicularis , two obligate aerobes isolated from laboratory algal cultures, stimulated the growth of the green microalgae Scenedesmus bicellularis and Chlorella sp., without releasing any growth promoting substance. An intimate contact between both microorganisms was necessary for significant algal growth enhancement. The possibility of algal growth stimulation by bacterial attenuation of photosynthetic oxygen tension was indirectly examined by simulating the effect of bacteria through a physical removal of oxygen (air suction). Vacuum-treated cultures showed an increase in growth rate and photosynthetic activity as compared to the control, a result which cannot be explained by differences in CO₂/HCO₃⁻ pump activity. In the presence of P. diminuta , the photosynthetic activity of S. bicellularis was more strongly stimulated under a limited concentration of inorganic carbon. It is suggested that, apart from a CO₂ supply, aerobic bacteria can promote algal growth by reducing the photosynthetic oxygen tension within the microenvironment of the algal cells, thereby creating more favorable conditions for optimal photosynthetic algal growth.     

Xenopus spermatozoon: Is there any correlation between motility and oxygen consumption?

The motility status of Xenopus laevis spermatozoa does not affect their respiration rate. Oxygen consumption for 10⁹ spermatozoa is approximately 0.4 μmol/minute. Oxygen consumption is not increased by gramicidin D, an uncoupler, and it is not blocked by KCN or NaN₃. The adenosine triphosphate (ATP) content of spermatozoa that have been activated is definitely less than that in the spermatozoa that remained immotile. Incubation in KCN, NaN₃, and gramicidin decreases the ATP content and impairs motility. The conclusions of the present study are that in Xenopus spermatozoa motility and oxygen consumption are not correlated, and the composition of the respiratory chain of these spermatozoa presents noteworthy peculiarities.     

Is postexercise hypotension related to excess postexercise oxygen consumption through changes in leg blood flow?

After a single bout of aerobic exercise, oxygen consumption remains elevated above preexercise levels [excess postexercise oxygen consumption (EPOC)]. Similarly, skeletal muscle blood flow remains elevated for an extended period of time. This results in a postexercise hypotension. The purpose of this study was to explore the possibility of a causal link between EPOC, postexercise hypotension, and postexercise elevations in skeletal muscle blood flow by comparing the magnitude and duration of these postexercise phenomena. Sixteen healthy, normotensive, moderately active subjects (7 men and 9 woman, age 20-31 yr) were studied before and through 135 min after a 60-min bout of upright cycling at 60% of peak oxygen consumption. Resting and recovery VO2 were measured with a custom-built dilution hood and mass spectrometer-based metabolic system. Mean arterial pressure was measured via an automated blood pressure cuff, and femoral blood flow was measured using ultrasound. During the first hour postexercise, VO2 was increased by 11 +/- 2%, leg blood flow was increased by 51 +/- 18%, leg vascular conductance was increased by 56 +/- 19%, and mean arterial pressure was decreased by 2.2 +/- 1.0 mmHg (all P <0.05 vs. preexercise). At the end of the protocol, VO2 remained elevated by 4 +/- 2% (P <0.05), whereas leg blood flow, leg vascular conductance, and mean arterial pressure returned to preexercise levels (all P >0.7 vs. preexercise). Taken together, these data demonstrate that EPOC and the elevations in skeletal muscle blood flow underlying postexercise hypotension do not share a common time course. This suggests that there is no causal link between these two postexercise phenomena.     

Are antarctic zooplankton metabolically more cold-adapted than arctic zooplankton? An intra-generic comparison of oxygen consumption rates

Because of the greater age of the antarctic ecosystem in relationto the arctic ecosystem, an elevated metabolic rate and moreobligate stenothermy of antarctic zooplankton compared withtheir arctic counterparts are predicted from the concept ofmetabolic cold adaptation. When oxygen consumption rates werestandardized to 1 mg body nitrogen and 0°C and comparedbetween the species belonging to the same genus, the antarcticrates were greater than arctic rates in Clione (pteropods) andCalanus (copepods), while the reverse was true in Parathemisto(amphipods), Thysanoessa (euphausiids) and Sagitta (chaetognaths).No significant differences were seen in Limacina (pteropods)and Metridia (copepods). These inconsistent results do not supportthe hypothesis of metabolic cold adaptation in the zooplanktonof polar seas.     

Metabolic cold adaptation of polar fish based on measurements of aerobic oxygen consumption: fact or artefact? Artefact!

Whether metabolic cold adaptation in polar fish, based on measurements of aerobic standard metabolic rate, is a fact or an artefact has been a dispute since Holeton asked the question in 1974. So far polar fish had been considered to be metabolically cold adapted because they were reported to have a considerably elevated resting oxygen consumption, or standard metabolic rate, compared with oxygen consumption values of tropical or temperate fish extrapolated to similar low polar temperatures. Recent experiments on arctic and Antarctic fish, however, do not show elevated resting aerobic oxygen consumption values, or standard metabolic rate, and hence it is concluded that that metabolic cold adaptation in the traditional sense is an artefact.     

The effect of light on oxygen consumption in two amphipod crustaceans–the hypogean Niphargus stygius and the epigean Gammarus fossarum

The effects of light on the metabolic rates of the hypogean amphipod Niphargus stygius and the epigean amphipod Gammarus fossarum were compared by measuring oxygen consumption and respiratory electron transport system (ETS) activity. They were exposed to light intensities of 720 and 4700?lx at 10°C. Oxygen consumption increased significantly in N. stygius exposed to both low and high intensities of light, but no significant increase was observed in G. fossarum at either intensity. The increase of oxygen consumption in N. stygius was significantly greater at the higher light intensity. This indicates a stress response in which exploitation of half the metabolic potential for energy production in N. stygius during exposure to high light intensity constitutes an adverse effect on its metabolism, since this species usually uses less than 25% of its total metabolic potential for standard metabolic demands.     

Effects of temperature and dissolved oxygen on heart rate,ventilation rate and oxygen consumption of spangled perch,Leiopotherapon unicolor (Günther 1859), (Percoidei,Teraponidae)

Summary Heart, ventilation and oxygen consumption rates ofLeiopotherapon unicolor were studied at temperatures ranging from 5 to 35°C, and during progressive hypoxia from 100% to 5% oxygen saturation. Biopotentials recorded from the water surrounding the fish corresponded to ventilation movements, and are thought to originate from the ventilatory musculature. Cardio-respiratory responses to temperature and dissolved oxygen follow the typical teleost pattern, with bradycardia, increased ventilation rate and reduced oxygen consumption occurring during hypoxia. However, ventilation rate did not increase at 15°C and below. Ventilation rate showed a slower response to increasing temperature (normoxic Q₁₀=1.39) than heart rate and oxygen consumption (normoxic Q₁₀=2.85 and 2.38).L. unicolor is unable to survive prolonged hypoxia by utilising anaerobic metabolism, but has a large gill surface area which presumably facilitates oxygen uptake in hypoxic environments. Periodic ventilation during normoxia in restingL. unicolor may improve ventilation efficiency by increasing the oxygen diffusion gradient across the gills.Abbreviations EBG electrobranchiogram - ECG electrocardiogram     

Influence of dichloroacetate (DCA) on lactate production and oxygen consumption in neuroblastoma cells: is DCA a suitable drug for neuroblastoma therapy?

Many cancer cells metabolize glucose preferentially via pyruvate to lactate instead to CO(2) and H(2)O (oxidative phosphorylation) even in the presence of oxygen (Warburg effect). Dichloroacetate (DCA) is a drug which is able to shift pyruvate metabolism from lactate to acetyl-CoA (tricarboxylic acid cycle) by indirect activation of pyruvate dehydrogenase (PDH). This can subsequently lead to an increased flow of oxygen in the respiratory chain, associated with enhanced generation of reactive oxygen species (ROS) which may cause apoptosis. In order to investigate if DCA may be suitable for neuroblastoma therapy, it was investigated on three human neuroblastoma cell lines whether DCA can reduce lactate production and enhance oxygen consumption. The data show, that DCA (in the low millimolar range) is able to reduce lactate production, but there was only a slight shift to increased oxygen consumption and almost no effect on cell vitality, proliferation and apoptosis of the three cell lines investigated. Therefore, DCA at low millimolar concentrations seems to be only of minor efficacy for neuroblastoma treatment.     

Are all bony fishes oxygen regulators? Evidence for oxygen regulation in a putative oxygen conformer,the swamp eel Synbranchus marmoratus

This study investigated the oxygen consumption of the putative oxygen conformer marbled swamp eel Synbranchus marmoratus during progressive hypoxia. Earlier studies have not reached an agreement on whether S. marmoratus is a conformer or a regulator. Our results support the view that S. marmoratus is an oxygen regulator, like most bony fishes.     

Influence of body mass, age, and maturation on specific oxygen consumption in a freshwater cichlid fish, Cichlasoma nigrofasciatum (Günther, 1869)

The oxygen consumption of a freshwater convict cichlid (Cichlasoma nigrofasciatum) was determined throughout the fish development from age 74 days to 403 days, covering the period before and after maturation. The specific oxygen consumption decreases with increasing age. The decrease in metabolic rate appears rather in distinct phases. A small increase in the average specific metabolic rate (mainly from the bigger fish) around age 200 days suggests an involvement of internal changes in the fish during a transition period from "young" state to "mature" state. The relationship between the specific oxygen consumption and body mass is determined by maturation and age. Before reaching maturation (before age 200 days) the correlation between specific oxygen consumption and body mass is negative for "young" fish of the same age. After age 200 days, no correlation between both parameters could be found. We suggest from this study that both factors "age" and "size" of the organism have to be considered for determining the metabolism, especially in fish. This study indicates that even in fish, which retain a continuous growing capability until they die, the decrease in the specific oxygen consumption is related to the aging process.     

Carbondioxide affects the growth rate of “oxygen limited”Escherichia coli at low concentrations of oxygen

Summary It is shown that addition of 1% CO₂ in Argon, containing traces of oxygen (<30 ppm O₂) to a described mineral salts medium leads to deblockage of the normal oxygen limited growth pattern ofEscherichia coli (ATCC 1524).     

Metabolic responses of the body to breathing with hypoxic argon–oxygen and nitrogen–oxygen mixtures

We have studied metabolic responses of six male volunteers who were exposed to hypoxic nitrogen–oxygen and argon–oxygen respiratory mixtures under hermetic chamber conditions for a long time. We measured the values of 44 biochemical parameters of venous blood, which reflected the state of different parts of metabolism, as well as the state of organs and tissues. Under the conditions of argon–oxygen respiratory mixture with the level of oxygen of 12.8% within the first five days and 12.0% from six to ten days of the experiment, the activation of processes of anaerobic glycolysis and lipolysis with the development of metabolic acidosis was observed. Against this background, biochemical signs of unfavorable changes in the myocardium were recorded. When we used the nitrogen–oxygen respiratory mixture with the level of oxygen of 13.0% during the first five days of the experiment and 12.1% from the sixth to the tenth day, these changes were expressed much more significantly: the activation of lipolysis and a decrease in the level of serum iron were observed and the signs of damage of mitochondria, depression of the kidney function, and development of hypodynamia were recorded. Complete stabilization of metabolic processes was reached only after seven to eight days of the recovery period for both mixtures. These findings lead to the conclusion that it is physiologically more preferable to use oxygen–argon respiratory mixtures at small immersion depths.     

Are there ecological implications for the proposed energetic restrictions on photosynthetic oxygen evolution at high oxygen concentrations?

It has recently been shown that, in subthylakoid particles prepared using detergent, there is inhibition of oxygen production reactions in photosynthesis by thermodynamic feedback from oxygen build-up, with 50% inhibition at 230 kPa partial pressure of oxygen. This article presents a comprehensive analysis of laboratory data on the effects of high oxygen partial pressures on photosynthesis, and on photo-lithotrophic and chemo-organotrophic growth, of oxygen-producing organisms. The article also contains an analysis of the extent to which high oxygen concentrations occur at the site of photosystem II (PSII) activity under natural conditions today and in the past. The conclusion is that the oxygen concentrations found in nature are very unlikely to reach that needed to cause 50% inhibition of the photosynthetic oxygen production reaction in subthylakoid particles, but that it is just possible that a small part of the inhibition of photosynthesis and of photo-lithotrophic growth by oxygen can be attributed to inhibition of oxygen production by PSII.     

Superoxide anion: Oncogenic reactive oxygen species?

Recent evidence linking intracellular reactive oxygen species to cell survival and/or proliferation signals has resulted in a paradigm shift from the age-old dogma implicating reactive oxygen species exclusively in cell damage and death. It is now accepted that reactive oxygen species play important roles in normal physiological states and that depending on the species involved the effect could be highly varied. In this regard, the effects of the two major reactive oxygen species, superoxide and hydrogen peroxide have been extensively studied. During normal cell growth a tight balance between the two species is kept under check by the cells' anti-oxidant defense systems. Deficiency or defect in this defense armory is invariably associated with neoplasia, thus rendering the intracellular redox status in a state of imbalance and generating a "pro-oxidant" milieu. A variety of model systems have underscored the relationship between a pro-oxidant state and cancer promotion and progression. In this review, we present evidence to support the hypothesis that the effect of intracellular reactive oxygen species on oncogenesis is dependent on the ratio of intracellular superoxide to hydrogen peroxide in that a predominant increase in superoxide supports cell survival and promotes oncogenesis whereas a tilt in favor of hydrogen peroxide prevents carcinogenesis by facilitating cell death signaling.     

NADPH oxidase: a universal oxygen sensor?

NADPH oxidase is classically regarded as a key enzyme of neutrophils, where it is involved in the pathogenic production of reactive oxygen species. However, NADPH oxidase-like enzymes have recently been identified in non-neutrophil cells, supporting a separate role for NADPH-oxidase derived oxygen species in oxygen sensitive processes. This article reviews the current literature surrounding the potential role of NADPH oxidase in the oxygen sensing processes which underlie hypoxic pulmonary vasoconstriction, systemic vascular smooth muscle proliferation, carotid and airways chemoreceptor activation, erythropoietin gene expression, and oxytropic responses of plant cells.