Lipid-based Metabolism Research Articles

Metabolic and immune status of Pacific white shrimp Penaeus vannamei concerning farming conditions

Biomarkers for monitoring shrimp health have been proposed but scarcely evaluated at the farm level. We analyzed several indicators of energy status in shrimp under farming conditions concerning stocking densities (100 m-2 with biofloc, 15 and 7 m-2). The influence of the year's season (temperature) was also analyzed, and, finally, an unfortunate event of White spot syndrome virus (WSSV) infection occurred on the 7 m-2 farms, adding another condition. At shrimp sampling from ponds, the effect of acute handling stress was also analyzed for indicators typically affected by such procedure with a 3- and 10-fold increase in glucose and lactate levels in hemolymph, respectively, regardless of density. This response was partially blunted at lower temperatures and WSSV incidence. Increased levels of protein in the hepatopancreas, adenylic energy charge (AEC) in both hepatopancreas and muscle and phosphagens in muscle were observed in shrimp from the 100 m-2 farms, suggesting a better nutritional and energetic status in shrimp cultured at high density with biofloc technology. Shrimp with WSSV presented lower hemocyanin levels in hemolymph, most likely associated with its role in the immune response. In WSSV-infected shrimp, the stress response regarding glucose increase was blunted, whereas a stress-induced increase in triglycerides (TG) levels in hemolymph was observed only with WSSV. Increased TG levels in those shrimp hepatopancreas could indicate a switch from carbohydrate to lipid-based metabolism associated with the preferential use of carbohydrates (Warburg effect) for virus replication in the early infection state.

The Antarctic Weddell seal genome reveals evidence of selection on cardiovascular phenotype and lipid handling

The Weddell seal (Leptonychotes weddellii) thrives in its extreme Antarctic environment. We generated the Weddell seal genome assembly and a high-quality annotation to investigate genome-wide evolutionary pressures that underlie its phenotype and to study genes implicated in hypoxia tolerance and a lipid-based metabolism. Genome-wide analyses included gene family expansion/contraction, positive selection, and diverged sequence (acceleration) compared to other placental mammals, identifying selection in coding and non-coding sequence in five pathways that may shape cardiovascular phenotype. Lipid metabolism as well as hypoxia genes contained more accelerated regions in the Weddell seal compared to genomic background. Top-significant genes were SUMO2 and EP300; both regulate hypoxia inducible factor signaling. Liver expression of four genes with the strongest acceleration signals differ between Weddell seals and a terrestrial mammal, sheep. We also report a high-density lipoprotein-like particle in Weddell seal serum not present in other mammals, including the shallow-diving harbor seal.

Fluorescence based rapid optical volume screening system (OVSS) for interrogating multicellular organisms

Continuous monitoring of large specimens for long durations requires fast volume imaging. This is essential for understanding the processes occurring during the developmental stages of multicellular organisms. One of the key obstacles of fluorescence based prolonged monitoring and data collection is photobleaching. To capture the biological processes and simultaneously overcome the effect of bleaching, we developed single- and multi-color lightsheet based OVSS imaging technique that enables rapid screening of multiple tissues in an organism. Our approach based on OVSS imaging employs quantized step rotation of the specimen to record 2D angular data that reduces data acquisition time when compared to the existing light sheet imaging system (SPIM). A co-planar multicolor light sheet PSF is introduced to illuminate the tissues labelled with spectrally-separated fluorescent probes. The detection is carried out using a dual-channel sub-system that can simultaneously record spectrally separate volume stacks of the target organ. Arduino-based control systems were employed to automatize and control the volume data acquisition process. To illustrate the advantages of our approach, we have noninvasively imaged the Drosophila larvae and Zebrafish embryo. Dynamic studies of multiple organs (muscle and yolk-sac) in Zebrafish for a prolonged duration (5 days) were carried out to understand muscle structuring (Dystrophin, microfibers), primitive Macrophages (in yolk-sac) and inter-dependent lipid and protein-based metabolism. The volume-based study, intensity line-plots and inter-dependence ratio analysis allowed us to understand the transition from lipid-based metabolism to protein-based metabolism during early development (Pharyngula period with a critical transition time, tau _c = 50 h post-fertilization) in Zebrafish. The advantage of multicolor lightsheet illumination, fast volume scanning, simultaneous visualization of multiple organs and an order-less photobleaching makes OVSS imaging the system of choice for rapid monitoring and real-time assessment of macroscopic biological organisms with microscopic resolution.

MicroRNA profiling in the Weddell seal suggests novel regulatory mechanisms contributing to diving adaptation

BackgroundThe Weddell Seal (Leptonychotes weddelli) represents a remarkable example of adaptation to diving among marine mammals. This species is capable of diving > 900 m deep and remaining underwater for more than 60 min. A number of key physiological specializations have been identified, including the low levels of aerobic, lipid-based metabolism under hypoxia, significant increase in oxygen storage in blood and muscle; high blood volume and extreme cardiovascular control. These adaptations have been linked to increased abundance of key proteins, suggesting an important, yet still understudied role for gene reprogramming.In this study, we investigate the possibility that post-transcriptional gene regulation by microRNAs (miRNAs) has contributed to the adaptive evolution of diving capacities in the Weddell Seal.ResultsUsing small RNA data across 4 tissues (brain, heart, muscle and plasma), in 3 biological replicates, we generate the first miRNA annotation in this species, consisting of 559 high confidence, manually curated miRNA loci. Evolutionary analyses of miRNA gain and loss highlight a high number of Weddell seal specific miRNAs.Four hundred sixteen miRNAs were differentially expressed (DE) among tissues, whereas 80 miRNAs were differentially expressed (DE) across all tissues between pups and adults and age differences for specific tissues were detected in 188 miRNAs. mRNA targets of these altered miRNAs identify possible protective mechanisms in individual tissues, particularly relevant to hypoxia tolerance, anti-apoptotic pathways, and nitric oxide signal transduction. Novel, lineage-specific miRNAs associated with developmental changes target genes with roles in angiogenesis and vasoregulatory signaling.ConclusionsAltogether, we provide an overview of miRNA composition and evolution in the Weddell seal, and the first insights into their possible role in the specialization to diving.

A glucose-insulin-potassium solution improves glucose intake in hypoxic cardiomyocytes by a differential expression of glucose transporters in a metabolic syndrome model

Among the last consequences of metabolic syndrome are cardiovascular complications such as infarcts. The hypoxic heart switches its lipid-based metabolism to carbohydrates, and a glucose-insulin-potassium (GIK) solution can be the metabolic support to protect the organ. Due to the physiology and cardiac risks associated with the metabolic syndrome, we studied the effect of GIK solution during hypoxia in a metabolic syndrome model by observing the participation of glucose transporters (GLUTs). The metabolic syndrome characteristics were established by giving a 30% sucrose drinking solution to Wistar rats for 24 weeks. The GIK solution's effect on myocyte glucose uptake during hypoxia and oxygenation was observed using a colorimetric method, and Western blot technique visualized the GLUT participation. Oxygenated control myocytes consumed 1.7 +/- 0.2 μg of glucose per gram of fresh tissue per hour using the GLUT1, and during hypoxia, they incorporated 41.1% more glucose by GLUT1 and GLUT4. The GIK solution improved glucose uptake in oxygenation by 70.5% through GLUT1. In hypoxia, the uptake was 21% more than the hypoxic control group and by both GLUTs too. Oxygenated metabolic syndrome myocytes uptake was similar to control cells but achieved by both carriers in oxygenation and hypoxia. Also, the GIK solution had a better response in both oxygenation (113%) and hypoxia (71%). Despite the metabolic energy disorders of this syndrome, the GIK solution protects cardiomyocytes, in conditions of hypoxia, through the modulation of both GLUTs. So, this solution can be considered a useful resource during a heart attack in cases of metabolic syndrome.

Adipose transcriptome analysis provides novel insights into molecular regulation of prolonged fasting in northern elephant seal pups.

The physiological and cellular adaptations to extreme fasting in northern elephant seals ( Mirounga angustirostris, NES) are remarkable and may help to elucidate endocrine mechanisms that regulate lipid metabolism and energy homeostasis in mammals. Recent studies have highlighted the importance of thyroid hormones in the maintenance of a lipid-based metabolism during prolonged fasting in weaned NES pups. To identify additional molecular regulators of fasting, we used a transcriptomics approach to examine changes in global gene expression profiles before and after 6-8 wk of fasting in weaned NES pups. We produced a de novo assembly and identified 98 unique protein-coding genes that were differentially expressed between early and late fasting. Most of the downregulated genes were associated with lipid, carbohydrate, and protein metabolism. A number of downregulated genes were also associated with maintenance of the extracellular matrix, consistent with tissue remodeling during weight loss and the multifunctional nature of blubber tissue, which plays both metabolic and structural roles in marine mammals. Using this data set, we predict potential mechanisms by which NES pups sustain metabolism and regulate adipose stores throughout the fast, and provide a valuable resource for additional studies of extreme metabolic adaptations in mammals.

Locomotor muscle fibre heterogeneity and metabolism in the fastest large-bodied rorqual: the fin whale (Balaenoptera physalus).

From a terrestrial ancestry, the fin whale (Balaenoptera physalus) is one of the largest animals on Earth with a sprinter anti-predator strategy, and a characteristic feeding mode, lunge feeding, which involves bouts of high-intensity muscle activity demanding high metabolic output. We investigated the locomotor muscle morphology and metabolism of this cetacean to determine whether its muscle profile (1) explains this unique swimming performance and feeding behaviour, (2) is or is not homogeneous within the muscle, and (3) predicts allometric variations inherent to an extreme body size. A predominantly fast-glycolytic phenotype characterized the fin whale locomotor muscle, composed of abundant fast-twitch (type IIA) fibres with high glycolytic potential, low oxidative capacity, relatively small size, and reduced number of capillaries. Compared with superficial areas, deep regions of this muscle exhibited a slower and more oxidative profile, suggesting a division of labour between muscle strata. As expected, the fin whale locomotor muscle only expressed the two slowest myosin heavy chain isoforms (I and IIA). However, it displayed anaerobic (glycolytic) and aerobic (lipid-based metabolism) capabilities higher than would be predicted from the allometric perspective of its extreme body size. Relationships between muscle metabolism and body mass were fibre-type specific. The 'sprinter' profile of the fin whale swimming muscle, particularly of its superficial compartment, supports physiological demands during both high-speed swimming and the lunge, when energy expenditure reaches maximal or supramaximal levels. Comparatively, the slower and more oxidative profile of the deep compartment of this muscle seems to be well designed for sustained, low-intensity muscle activity during routine swimming.

Thyroid hormone-stimulated increases in PGC-1α and UCP2 promote life history-specific endocrine changes and maintain a lipid-based metabolism.

Thyroid hormones (THs) regulate metabolism, but are typically suppressed during times of stressful physiological conditions, including fasting. Interestingly, prolonged fasting in northern elephant seal pups is associated with reliance on a lipid-based metabolism and increased levels of circulating THs that are partially attributed to active secretion as opposed to reduced clearance. This apparent paradox is coupled with complementary increases in cellular TH-mediated activity, suggesting that in mammals naturally adapted to prolonged fasting, THs are necessary to support metabolism. However, the functional relevance of this physiological paradox has remained largely unexplored, especially as it relates to the regulation of lipids. To address the hypothesis that TSH-mediated increase in THs contributes to lipid metabolism, we infused early and late-fasted pups with TSH and measured several key genes in adipose and muscle, and plasma hormones associated with regulation of lipid metabolism. TSH infusion increased the mRNA expressions of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) more than 6.5-fold at 60 min in muscle, and expression of uncoupling protein 2 (UCP2) more than 27-fold during the early fast at 60 min, in adipose. Additionally, during the late fast period, the protein content of adipose CD36 increased 1.1-fold, and plasma nonesterified fatty acid (NEFA) concentrations increased 25% at 120 min, with NEFA levels returning to baseline after 24 h. We show that the TSH-induced increases in THs in fasting pups are functional and likely contribute to the maintenance of a lipid-based metabolism.

Seasonal variation in haematological and biochemical variables in free-ranging subadult brown bears (Ursus arctos) in Sweden.

BackgroundFree-ranging brown bears exhibit highly contrasting physiological states throughout the year. They hibernate 6 months of the year, experiencing a decrease in body temperature, heart rate, respiratory rate and metabolism. An increase in food consumption and the resulting weight gain (mostly through fat storage) prior to hibernation are also part of the brown bear’s annual cycle. Due to these physiological changes, haematological and biochemical variables vary dramatically throughout the year. Seasonal changes in 12 haematological and 34 biochemical variables were evaluated in blood samples collected from 40 free-ranging subadult brown bears (22 females, 18 males) immobilised in Sweden in winter (February-March), spring (April-May), and summer (June).ResultsHigher levels of haemoglobin, haematocrit and red blood cell count, and a lower white blood cell count and mean cell volume was found during hibernation than in spring and summer. Lower values of the enzymes; aspartate aminotransferase (AST), alanine transaminase (ALT), alkaline phosphatase (AP), γ-glutamyl transpeptidase (GGT), glutamate dehydrogenase (GD) and amylase, and increased values of β-hydroxybutyrate (β-HBA) and blood lipids; triglycerides, cholesterol and free fatty acids, were present during hibernation compared to spring and summer.ConclusionsThis study documents significant shifts in haematological and biochemical variables in samples collected from brown bears anaesthetised in winter (February-March) compared to in spring and summer (April-June), reflecting the lowered metabolic, renal and hepatic activity during hibernation. Lower values of enzymes and higher values of blood lipids during hibernation, likely reflect a lipid-based metabolism.

Characterization of the SIRT family of NAD+-dependent protein deacetylases in the context of a mammalian model of hibernation, the thirteen-lined ground squirrel

Hibernating mammals employ strong metabolic rate depression to survive the winter, thereby avoiding the high energy costs of maintaining a euthermic lifestyle in the face of low seasonal temperatures and limited food resources. Characteristics of this natural torpor include a significant reduction in body temperature, a shift to a lipid-based metabolism, global suppression of ATP-expensive activities, and the upregulation of selected genes that mediate biochemical reorganization and cytoprotection. Sirtuin (SIRT) proteins, an evolutionarily conserved family of NAD+-dependent protein deacetylases, have been shown to play important roles in the post-translational regulation of many metabolic and cytoprotective processes, suggesting a potential function for these enzymes in the control of hibernation. To assess this possibility, protein levels of the seven mammalian SIRTs (SIRT1, SIRT2, SIRT3, SIRT4, SIRT5, SIRT6 and SIRT7), total SIRT activity, and the acetylation status of two downstream SIRT targets (SOD2K68 and NF-κB p65K310) were measured in skeletal muscle, liver, brown adipose and white adipose tissues of the hibernating thirteen-lined ground squirrel (Ictidomys tridecemlineatus) over the course of the torpor–arousal cycle. The analysis revealed tissue-specific responses of different SIRTs at various points throughout hibernation, including a potentially interesting correlation between increased levels of SIRT3 protein, heightened total SIRT activity, and decreased acetylation of SIRT3 downstream target SOD2K68 in skeletal muscle during late torpor. These results provide evidence to suggest a possible role for the SIRT family of protein deacetylases in the regulation of the metabolic and cellular protective pathways that mediate the process of mammalian hibernation.

Cardiac depression induced by cocaine or cocaethylene is alleviated by lipid emulsion more effectively than by sulfobutylether-β-cyclodextrin.

Cocaine intoxication leads to over 500,000 emergency department visits annually in the United States and ethanol cointoxication occurs in 34% of those cases. Cardiotoxicity is an ominous complication of cocaine and cocaethylene overdose for which no specific antidote exists. Because infusion of lipid emulsion (Intralipid) can treat lipophilic local anesthetic toxicity and cocaine is an amphipathic local anesthetic, the authors tested whether lipid emulsion could attenuate cocaine cardiotoxicity invivo. The effects of lipid emulsion were compared with the metabolically inert sulfobutylether-β-cyclodextrin (SBE-β-CD; Captisol) in an isolated heart model of cocaine and cocaethylene toxicity to determine if capture alone could exert similar benefit as lipid emulsion, which exhibits multimodal effects. The authors then tested if cocaine and cocaethylene, like bupivacaine, inhibit lipid-based metabolism in isolated cardiac mitochondria. For whole animal experiments, Sprague-Dawley rats were anesthetized, instrumented, and pretreated with lipid emulsion followed by a continuous infusion of cocaine to assess time of onset of cocaine toxicity. For exvivo experiments, rat hearts were placed onto a nonrecirculating Langendorff system perfused with Krebs-Henseleit solution. Heart rate, left ventricle maximum developed pressure (LVdevP), left ventricle diastolic pressure, maximum rate of contraction (+dP/dtmax), maximum rate of relaxation (-dP/dtmax), rate-pressure product (RPP=heart rate×LVdevP), and line pressure were monitored continuously during the experiment. A dose response to cocaine (10, 30, 50, and 100μmol/L) and cocaethylene (10, 30, and 50μmol/L) was generated in the absence or presence of either 0.25% lipid emulsion or SBE-β-CD. Substrate-specific rates of oxygen consumption were measured in interfibrillar cardiac mitochondria in the presence of cocaine, cocaethylene, ecgonine, and benzoylecgonine. Treatment with lipid emulsion delayed onset of hypotension (140seconds vs. 279seconds; p=0.008) and asystole (369seconds vs. 607seconds; p=0.02) in whole animals. Cocaine and cocaethylene induced dose-dependent decreases in RPP, +dP/dtmax, and -dP/dtmaxabs (p<0.0001) in Langendorff hearts; line pressure was increased by cocaine and cocaethylene infusion, but not altered bytreatment. Lipid emulsion attenuated cocaine- and cocaethylene-induced cardiac depression. SBE-β-CDalone evoked a mild cardiodepressant effect (p<0.0001) butattenuated further cocaine- and cocaethylene-induced decrements in cardiac contractility at high concentrations of drug (100μmol/L; p<0.001). Finally, both cocaine and cocaethylene, but not ecgonine and benzoylecgonine, inhibited lipid-dependent mitochondrial respiration by blocking carnitine exchange (p<0.05). A commercially available lipid emulsion was able to delay progression of cocaine cardiac toxicity invivo. Further, it improved acute cocaine- and cocaethylene-induced cardiac toxicity in rat isolated heart while SBE-β-CDwas effective only at the highest cocaine concentration. Further, both cocaine and cocaethylene inhibited lipid-dependent mitochondrial respiration. Collectively, this suggests that scavenging-independent effects of lipid emulsion may contribute to reversal of acute cocaine and cocaethylene cardiotoxicity, and the beneficial effects may involve mitochondrial lipid processing.

High Corticosterone, Not High Energy Cost, Correlates with Reproductive Success in the Burrow-Nesting Ancient Murrelet

Theory and observations suggest that offspring abandonment in animals may occur when the costs to future reproductive output of current reproductive effort outweigh the fitness benefits of rearing the current brood. While hormonal cues (i.e. corticosterone) or energy reserves are believed to be involved, few studies have directly focused on the proximate cues influencing behaviours directly related to reproductive success. To address this information gap, we determined the incubation metabolic rates and corticosterone (CORT) levels of naturally fasting and freely incubating ancient murrelets (Synthliboramphus antiquus). Respiratory quotient (RQ) increased with date, suggesting that incubating ancient murrelets shifted from strictly lipid-based metabolism towards more protein-based metabolism as incubation progressed. Birds that hatched only one nestling had higher levels of circulating CORT than those which hatched two, suggesting that birds which laid only a single egg found incubation more stressful than those which laid two. However, CORT levels and incubation shift lengths were not correlated, suggesting that birds that undertook prolonged incubation shifts did so only when their energy stores were not jeopardized.

Prolonged food deprivation increases mRNA expression of deiodinase 1 and 2, and thyroid hormone receptor β-1 in a fasting-adapted mammal.

Food deprivation in mammals is typically associated with reduced thyroid hormone (TH) concentrations and deiodinase content and activity to suppress metabolism. However, in prolonged-fasted, metabolically active elephant seal pups, TH levels are maintained, if not elevated. The functional relevance of this apparent paradox is unknown and demonstrates variability in the regulation of TH levels, metabolism and function in food-deprived mammals. To address our hypothesis that cellular TH-mediated activity is upregulated with fasting duration, we quantified the mRNA expression and protein content of adipose and muscle deiodinase type I (DI1) and type II (DI2), and TH receptor beta-1 (THrβ-1) after 1, 3 and 7 weeks of fasting in northern elephant seal pups (N=5-7 per week). Fasting did not decrease the concentrations of plasma thyroid stimulating hormone, total triiodothyronine (tT3), free T3, total thyroxine (tT4) or free T4, suggesting that the hypothalamic-pituitary-thyroid axis is not suppressed, but rather maintained during fasting. Mean mRNA expression of adipose DI1 and DI2 increased threefold and fourfold, respectively, and 20- and 30-fold, respectively, in muscle. With the exception of adipose DI1, protein expression of adipose DI2 and muscle DI1 and DI2 increased twofold to fourfold. Fasting also increased adipose (fivefold) and muscle (fourfold) THrβ-1 mRNA expression, suggesting that the mechanisms mediating cellular TH activity are upregulated with prolonged fasting. The data demonstrate a unique, atypical mechanism of TH activity and regulation in mammals adapted to prolonged food deprivation in which the potential responsiveness of peripheral tissues and cellular TH activity are increased, which may contribute to their lipid-based metabolism.

Profound changes in blood parameters during torpor in a South American marsupial

Seasonal torpor or hibernation is a phenomenon characterized by a physiological transition to dormancy (torpor) during challenging periods in terms of energy availability or metabolic load. Extensive physiological reprogramming and changes in gene-expression, immune function, oxygen transport and intermediate metabolism, occur during eutherian hibernation. Here we studied the seasonality of blood parameters, and during daily torpor, in a South American marsupial (Dromiciops gliroides). Seasonal trends in blood parameters showed an increase in hematological parameters during winter, and increases in total proteins, albumin and globulin during autumn. In contrast, torpor induced a drastic drop during most blood parameters. PCV dropped significantly 60%, as well as RBC (58%), hemoglobin concentration (58%), WBC (79%), including neutrophils (51%), eosinophils (84%) and lymphocytes (82%). Biochemical parameters also showed reductions: triglycerides (81%), proteins (32%), albumin (24%), globulins (38%), albumin (24%), creatinine (48%) and glucose (42%). Our results confirm some patterns observed in hibernating eutherians, such as leukopenia, probably caused by sequestration of white blood cells in organs. However, red blood cells and hemoglobin concentration also were reduced, which is to the best of our knowledge has not been reported for marsupials. The observed reduction in biochemical parameters suggests that marsupials, as in eutherians, change from carbohydrate-based to lipid-based metabolism during hibernation. However, the absence of increases in beta-hydroxybutyrate is puzzling. Finally, we found an increase (although non-significant after statistical correction for multiple comparisons) of creatine kinase which together with an increase in neutrophil/lymphocyte ratio could be indicative of muscle lysis and inflammation. These results indicate profound changes in standard physiological processes during torpor.

Cholesterol and Lipoprotein Dynamics in a Hibernating Mammal

Hibernating mammals cease feeding during the winter and rely primarily on stored lipids to fuel alternating periods of torpor and arousal. How hibernators manage large fluxes of lipids and sterols over the annual hibernation cycle is poorly understood. The aim of this study was to investigate lipid and cholesterol transport and storage in ground squirrels studied in spring, summer, and several hibernation states. Cholesterol levels in total plasma, HDL and LDL particles were elevated in hibernators compared with spring or summer squirrels. Hibernation increased plasma apolipoprotein A-I expression and HDL particle size. Expression of cholesterol 7 alpha-hydroxylase was 13-fold lower in hibernators than in active season squirrels. Plasma triglycerides were reduced by fasting in spring but not summer squirrels. In hibernators plasma β-hydroxybutyrate was elevated during torpor whereas triglycerides were low relative to normothermic states. We conclude that the switch to a lipid-based metabolism during winter, coupled with reduced capacity to excrete cholesterol creates a closed system in which efficient use of lipoproteins is essential for survival.

A Thiolase of Mycobacterium tuberculosis Is Required for Virulence and Production of Androstenedione and Androstadienedione from Cholesterol

Mycobacterium tuberculosis, the causative agent of tuberculosis, is an intracellular pathogen that shifts to a lipid-based metabolism in the host. Moreover, metabolism of the host lipid cholesterol plays an important role in M. tuberculosis infection. We used transcriptional profiling to identify genes transcriptionally regulated by cholesterol and KstR (Rv3574), a TetR-like repressor. The fadA5 (Rv3546) gene, annotated as a lipid-metabolizing thiolase, the expression of which is upregulated by cholesterol and repressed by KstR, was deleted in M. tuberculosis H37Rv. We demonstrated that fadA5 is required for utilization of cholesterol as a sole carbon source in vitro and for full virulence of M. tuberculosis in the chronic stage of mouse lung infection. Cholesterol is not toxic to the fadA5 mutant strain, and, therefore, toxicity does not account for its attenuation. We show that the wild-type strain, H37Rv, metabolizes cholesterol to androst-4-ene-3,17-dione (AD) and androsta-1,4-diene-3,17-dione (ADD) and exports these metabolites into the medium, whereas the fadA5 mutant strain is defective for this activity. We demonstrate that FadA5 catalyzes the thiolysis of acetoacetyl-coenzyme A (CoA). This catalytic activity is consistent with a beta-ketoacyl-CoA thiolase function in cholesterol beta-oxidation that is required for the production of androsterones. We conclude that the attenuated phenotype of the fadA5 mutant is a consequence of disrupted cholesterol metabolism that is essential only in the persistent stage of M. tuberculosis infection and may be caused by the inability to produce AD/ADD from cholesterol.

Biological activity and identification of neuropeptides in the neurosecretory complexes of the cabbage pest insect,Mamestra brassicae(Noctuidae; Lepidoptera)

The need for more environmentally sound strategies of plant protection has become a driving force in physiological entomology to combat insect pests more efficiently. Since neuropeptides regulate key biological processes, these "special agents" or their synthetic analogues, mimetics, agonists or antagonists may be useful tools. We examined brain-suboesophageal ganglia and corpora cardiaca-corpora allata complexes of the cabbage moth, Mamestra brassicae, in order to obtain clues about possible peptide candidates which may be appropriate for the biological control of this pest. With the aid of bioassays, reversed phase high performance liquid chromatography, and mass spectrometry, five neuropeptides were unequivocally identified and the presence of a further three were inferred solely by comparing mass spectra with known peptides. Only one neuropeptide with adipokinetic capability was identified in M. brassicae. Data from the established homologous bioassay indicated that the cabbage moths rely on a lipid-based metabolism which is aided by an adipokinetic hormone (viz. Manse-AKH) that had previously been isolated in many different lepidopterans. Other groups of neuropeptides identified in this study are: FLRFamides, corazonin, allatostatin and pheromonotropic peptide.

Changes in biomass and elemental composition during early ontogeny of the Antarctic isopod crustacean Ceratoserolis trilobitoides

Changes in biomass and elemental composition (dry mass, DM; carbon, C; hydrogen, H; nitrogen, N) were studied throughout the early ontogeny in the serolid isopod Ceratoserolis trilobitoides from a population off the South Shetland Islands (62°24.35′S, 61°23.77′W). Specimens of C. trilobitoides were sampled using an Agassiz trawl during the expedition ANT XXIII-8 of RV Polarstern in January 2007. Classification of embryos into six developmental stages followed previous studies. No clear size-dependant fecundity relationship was found in ovigerous C. trilobitoides. Egg volume increased by about 160 and 400% from stage I to IV and stage IV to VI, respectively. DM, C, N, and H continuously decreased throughout the early ontogeny from stage I to VI, but DM showed significant increase on reaching the late-V stage and premanca stages. The C:N ratio remained relatively stable throughout stages I to V, followed by a significant drop from about 6.17 to 5.5 in subsequent stages, indicating depletion of lipid resources of maternal origin. The results coincide with previous studies and indicate a shift from a lipid-based metabolism throughout early embryo stages to a protein-based metabolism in the late-V and premanca stage, which requires external energy supply. Given the steep increase in DM in the final phase of embryo development (late-V stage to premanca) and the need for external food supply to exert growth, the possibility of external food supply or cannibalism in early offspring of C. trilobitoides is discussed.

A global estimation of mesozooplankton ammonium excretion in the open ocean

Mesozooplankton ammonium excretion rates in the ocean, based on published data, were studied across all latitudes in order to assess the amount of ammonium excretion by this community. Specific ammonium excretion rates were highest in equatorial waters and decreased rapidly poleward. Global community excretion in the upper 200 m of the oceans, integrated over all latitudes, accounted in general for 1.78+0.60 Gt N.year 21 . Excretion rates showed a decrease from tropical (0.65+0.14 Gt N.year 21 ) to polar waters (0.05+0.02 Gt N.year 21 ). The substrate metabolized by organisms as indicated by the O/N ratio showed a protein-based metabolism of mesozooplankton with the exception of the temperate and subpolar regions, which showed a more lipid-based metabolism. The largest contribution of ammonium to autotrophs was observed in the tropical and subtropical areas, decreasing to polar areas. On a global basis, nutrient regeneration by mesozooplankton in the oceanic realm was estimated to be in the range of 12‐23% of the requirements for phytoplankton and bacterial production.

Aerobic capacities in the skeletal muscles of Weddell seals: key to longer dive durations?

In contrast to terrestrial animals that function under hypoxic conditions but display the typical exercise response of increasing ventilation and cardiac output, marine mammals exercise under a different form of hypoxic stress. They function for the duration of a dive under progressive asphyxia, which is the combination of increasing hypoxia, hypercapnia and acidosis. Our previous studies on short-duration, shallow divers found marked adaptations in their skeletal muscles, which culminated in enhanced aerobic capacities that are similar to those of athletic terrestrial mammals. The purpose of the present study was to assess the aerobic capacity of skeletal muscles from long-duration divers. Swimming and non-swimming muscles were collected from adult Weddell seals, Leptonychotes weddelli, and processed for morphometric analysis, enzymology, myoglobin concentrations and fiber-type distribution. The results showed that the skeletal muscles of Weddell seals do not have enhanced aerobic capacities compared with those of terrestrial mammals but are adapted to maintain low levels of an aerobic lipid-based metabolism, especially under the hypoxic conditions associated with diving. The lower aerobic capacity of Weddell seal muscle as compared with that of shorter-duration divers appears to reflect their energy-conserving modes of locomotion, which enable longer and deeper dives.