Differences in strategies to combat osmotic stress in Burkholderia cenocepacia elucidated by NMR-based metabolic profiling

Aims: To investigate mechanisms of osmotic tolerance in Burkholderia cenocepacia, a member of the B. cepacia complex (Bcc) of closely related strains, which is of clinical as well as environmental importance. Methods and Results: We employed NMR‐based metabolic profiling (metabolomics) to elucidate the metabolic consequences of high osmotic stress for five isolates of B. cenocepacia. The strains differed significantly in their levels of osmotic stress tolerance, and we identified three different sets of metabolic responses with the strains least impacted by osmotic stress exhibiting higher levels of the osmo‐protective metabolites glycine‐betaine and/or trehalose. Strains either increased concentrations or had constitutively high levels of these metabolites. Conclusions: Even within the small set of B. cenocepacia isolates, there was a surprising degree of variability in the metabolic responses to osmotic stress. Significance and impact of the study: The metabolic responses, and hence osmotic stress tolerance, vary between different B. cenocepacia isolates. This study provides a first look into the potentially highly diverse physiology of closely related strains of one species of the Bcc and illustrates that physiological or clinically relevant phenotypes are unlikely to be inferable from genetic relatedness within this species group.     

Activation of autophagy is required for muscle homeostasis during physical exercise

Skeletal muscle fibers of collagen VI null (Col6a1?/?) mice show signs of degeneration due to a block in autophagy, leading to the accumulation of damaged mitochondria and excessive apoptosis. Attempts to induce autophagic flux by subjecting these mutant mice to long-term or shorter bursts of physical activity are unsuccessful (see Grumati, et al., pp. 1415–23). In normal mice, the induction of autophagy in the skeletal muscles post-exercise is able to prevent the accumulation of damaged organelles and maintain cellular homeostasis. Thus, these studies provide an important connection between autophagy and exercise physiology.     

Activation of autophagy is required for muscle homeostasis during physical exercise

Skeletal muscle fibers of collagen VI null (Col6a12/2) mice show signs of degeneration due to a block in autophagy, leading to the accumulation of damaged mitochondria and excessive apoptosis. Attempts to induce autophagic flux by subjecting these mutant mice to long-term or shorter bursts of physical activity are unsuccessful (see Grumati, et al., pp. 1415–23). In normal mice, the induction of autophagy in the skeletal muscles post-exercise is able to prevent the accumulation of damaged organelles and maintain cellular homeostasis. Thus, these studies provide an important connection between autophagy and exercise physiology.     

Can sunbleak Leucaspius delineatus or topmouth gudgeon Pseudorasbora parva disperse through saline waters?

In order to determine the potential for the invasive fishes sunbleak Leucaspius delineatus and topmouth gudgeon Pseudorasbora parva to disperse through saline waters their behaviour and physiology were investigated during exposure to salinities of 10·0 and 12·5. Increased salinity caused an increase in whole body cortisol in both species, but sunbleak and topmouth gudgeon showed very different metabolic and behavioural responses to the salinity stress. Sunbleak displayed increased swimming activity in brackish water, which may be important for dispersal through saline waters in the wild, although there were increased metabolic costs associated with this behaviour. Conversely, topmouth gudgeon showed a reduction in both swimming activity and metabolic rate in brackish waters. A pronounced depression in food intake (70–80%) was shown by both species during the salinity exposures. Both sunbleak and topmouth gudgeon, however, showed a full recovery of food intake within 24 h following return to fresh water. Despite the fact that exposure to saline waters is stressful, and affects both physiology and behaviour, rapid recovery of appetite after return to fresh water suggests that short-term use of brackish waters is a feasible dispersal route for sunbleak and topmouth gudgeon in the wild.     

Impact of low pH and aluminium on nitrogen uptake and metabolism in roots of <Emphasis Type=Italic>Lotus japonicus</Emphasis>

The effect of low pH and aluminum on nitrogen uptake and metabolism was studied in roots of Lotus japonicus grown in hydroponic cultures. The low pH slightly suppressed root elongation, and this effect was accompanied by the suppression of nitrate and ammonia uptake, as well as the nitrate reductase activity. In spite of high resistance of young Lotus plants to short-term Al application, the one-day treatment of Al strongly reduced nitrate uptake and also the activity of nitrate reductase (NRA) in the apical parts of roots. The glutamine synthetase activity was also suppressed by Al treatment, but in lower extent. On the other hand, the ammonium uptake and nitrite reductase activity stayed unchanged by Al treatment and the values were practically the same as in control plants. These results support the view that nitrate uptake and nitrate reduction might be the main processes responsible for Al induced growth retardation in Lotus plants grown in mineral acid soils.     

Retracted: Tusk shells in trouble? Physiology and behavior in response to changing temperature in a scaphopod (Mollusca: Scaphopoda: Dentaliida)

Scaphopods (tusk shells) are infaunal marine predators that occur at locally high densities in coastal and deep‐sea mud habitats, and as consumers of foraminifera they are important in carbon cycling. We investigated oxygen metabolism and burying behavior of the scaphopod Rhabdus rectius and its responses to altered temperatures. These are the first measurements of oxygen uptake rates for any member of this taxonomic class. In response to elevated temperatures, oxygen uptake rates increased, but the ability of animals to bury themselves in sediment was compromised. Female scaphopods were significantly larger than males and, when corrected for body mass, oxygen uptake rates were consistently higher for female individuals than for males. This is consistent with previous anecdotal observations of females in other scaphopod species being larger and potentially more active. In conditions of declining oxygen availability, individuals of Rhabdus rectius showed strong oxyregulatory ability by maintaining the same oxygen uptake rate displayed in normoxic conditions. The ability to maintain normal metabolic functioning even in conditions of oxygen limitation would benefit a species living in a benthic environment that may be prone to temporary or transient anoxic events. Yet the decrease in normal escape response in moderately elevated temperatures indicates these animals may be at risk from rising sea temperatures.     

The physiological control of feeding in corals: a review

Little is known about the factors that control food capture by the coral polyp and the way that internal physiological events may coordinate, or even modify, this behaviour. A total understanding of the nutritional dynamics of corals demands detailed study of their feeding behaviour, and recent advances in behavioural and electrophysiological techniques are starting to provide some insights into how polyps control this behaviour. This review describes our present understanding of the physiological control of feeding behaviour in corals and suggests new studies on food recognition, food capture, and ingestion.     

Uncoupling Protein 1 and Sarcolipin Are Required to Maintain Optimal Thermogenesis,and Loss of Both Systems Compromises Survival of Mice under Cold Stress

The importance of brown adipose tissue as a site of nonshivering thermogenesis has been well documented. Emerging studies suggest that skeletal muscle is also an important site of thermogenesis especially when brown adipose tissue function is lacking. We recently showed that sarcolipin (SLN), an uncoupler of the sarco(endo)plasmic reticulum Ca²⁺ ATPase (SERCA) pump, could contribute to heat production in skeletal muscle. In this study, we sought to understand how loss of UCP1 or SLN is compensated during cold exposure and whether they are both necessary for thermogenesis. Toward this goal, we generated a UCP1;SLN double knock-out (DKO) mouse model and challenged the single and DKO mice to acute and long-term cold exposures. Results from this study show that there is up-regulation of SLN expression in UCP1-KO mice, and loss of SLN is compensated by increased expression of UCP1 and browning of white adipose tissue. We found that the DKO mice were viable when reared at thermoneutrality. When challenged to acute cold, the DKO were extremely cold-sensitive and became hypothermic. Paradoxically, the DKO mice were able to survive gradual cold challenge, but these mice lost significant weight and depleted their fat stores, despite having higher caloric intake. These studies suggest that UCP1 and SLN are required to maintain optimal thermogenesis and that loss of both systems compromises survival of mice under cold stress.     

Prey capture success of Sandwich Terns Sterna sandvicensis varies non‐linearly with water transparency

Human impacts on water transparency may affect plunge‐diving seabirds. We studied prey capture success of Sandwich Terns Sterna sandvicensis as a function of six environmental variables during the breeding season. We observed diving terns in the south eastern North Sea and found a non‐linear optimum curve for the relationship between Secchi transparency and prey capture probability. High capture probability was found at 1.5–2.0 m, with an optimum of 63% at 1.74 m. At a minimum transparency of 0.4 m and at a maximum transparency of 3.2 m, capture probabilities were about halved. Conversion of transparency to total suspended matter (TSM) concentration showed that the optimum concentration for foraging terns would be 5–10 mg/L under mean summer conditions for chlorophyll‐a. However, the summer‐averaged TSM concentrations in the nearshore Dutch coastal waters range between 10 and 30 mg/L, which implies that foraging Terns in the breeding season do not encounter optimal foraging conditions. The Full Plunge Dive, with which the largest diving depth can be achieved, was applied dominantly in clear water, while the Partial Plunge Dive and Contact Dip were applied more frequently in turbid water, thus showing that Sandwich Terns adjust their diving technique in response to water transparency.     

Electrochemical control of redox potential affects methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus

To investigate the precise effect of the redox potential on the methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus by using an electrochemical redox controlling system without adding oxidizing or reducing agents. A bioelectrochemical system was applied to control the redox conditions in culture and to measure the methane‐producing activity of M. thermautotrophicus at a constant potential from +0·2 to ?0·8 V (vs Ag/AgCl). Methane production and growth of M. thermautotrophicus were 1·6 and 3·5 times increased at ?0·8 V, compared with control experiments without electrolysis, respectively, while methanogenesis was suppressed between +0·2 and ?0·2 V. A clear relationship between an electrochemically regulated redox potential and methanogenesis was revealed.

Significance and Impact of the Study

A novel bioelectrochemical method can activate the methanogenesis of M. thermautotrophicus by controlling the redox potential in culture conditions at ?0·8 V, which is a difficult potential to achieve by conventional methods (e.g. by adding reducing agents). This study provides useful insights for the application of a bioelectrochemical system in industrial processes involving methanogens, such as in anaerobic digesters.     

Metabolic response to alarm pheromone in honey bees

Exposure to alarm pheromone elicits increases in oxidative metabolism in Apis mellifera. The following quantitative results are reported: (1) The alarm response, measured by short-term elevated oxygen consumption in each bee, increases with increasing numbers of bees in the test groups. The rate of increase in response per bee shows a group effect which is greatest in small groups (1–100 bees) and remains constant in larger groups (up to 6,700 bees). (2) The pheromone concentration affects the reaction elicited. The greater the dose, the larger is the reaction up to a concentration of 2.4 μg/ml. Greater doses elicit no greater response. (3) Response to the pheromone by winter bees is maximum at 20°C and decreases at air temperatures above or below this value. (4) This metabolic reaction may provide a tool for quantitating temperament of honey bees.