“Bacillus thermoantarcticus” sp. nov., from Mount Melbourne,Antarctica: a novel thermophilic species

 A novel thermophilic Gram-positive bacillus, “Bacillus thermoantarcticus”, isolated from geothermal soil near the crater of Mount Melbourne, is described. The organism grows at an optimal temperature of 63^°C at pH 6.0, is oxidase-positive, catalase-negative and produces an exopolysaccharide, an exocellular xylanase, an intracellular alcohol dehydrogenase and exo- and endocellular α-glucosidase(s). The sequence of 16S rDNA is very similar to that of “Bacillus thermoglucosidasius”; however, the guanine-plus-cytosine (G+C) content is 8 mol% higher. The type strain is “Bacillus thermoantarcticus” (DSM 9572). Received : 3 February 1995/Accepted : 12 May 1995     

Timemresolved fluorescence of S-100a protein: effect of Ca, Mg and unilamellar vesicles of egg phosphatidylcholine

Phase-modulation fluorescence lifetime measurements were used to study the single Trp residue of the Ca²⁺-binding protein S-100a both in the absence and in the presence of Ca²⁺ and/or Mg²⁺. Trp fluorescence decay for the protein was satisfactorily described by Lorentzian lifetime distributions centered around two components (approximately 4 ns and 0.5 ns). Lifetime values were unchanged by 2 mM Ca²⁺, but the fractional intensity associated with longer lifetime increased up to 75%. In the presence of Mg²⁺, the Ca²⁺ induced increase of the fractional intensity associated with longer lifetime was only 57%. For the protein in buffer, about the 85% of the recovered anisotropy was associated to a rotational correlation time of 6.7 ns. After the addition of Ca²⁺, this value was increased to 16.08 ns. In the presence of Mg²⁺, Ca⁺² increased the rotational correlation time to 33.75 ns. Similar studies were performed with S-100a interacting with egg phosphatidylcholine vesicles (SUV). Our data suggest that the conformation of the protein may be influenced by structural features of the lipidic membrane. Moreover, data obtained in the presence of Mg²⁺ indicate some interaction between lipids and S-100, likely mediated by this ion.     

Thermodynamic basis of site-specific cooperativity

Cooperative phenomena in biological macromolecules arise from the interaction of many distinct subsystems, such as structural domains or binding sites. Cooperative properties of the system as a whole, like protein folding or allosteric transitions, are subject to the restrictions imposed by thermodynamic stability. These restrictions, however, do not apply in the case of individual subsystems open to interactions with the rest of the macromolecule. The site-specific properties of such subsystems can be understood in general thermodynamic terms from those of a multicomponent system under particular conditions. The analogy provides a thermodynamic basis for site-specific Cooperativity. © 1994 John Wiley & Sons, Inc.     

Prevention of Carbon Tetrachloride-Induced Lipid Peroxidation in Liver Microsomes from Dehydroepiandrosterone-Pretreated Rats

Dehydroepiandrosterone (DHEA), a lipid soluble steroid, administered to rats (100 mg/kg b.wt) by a single intraperitoneal injection, increases to twice its normal level in the liver microsomes. Microsomes so enriched become resistant to lipid peroxidation induced by incubation with carbon tetrachloride in the presence of a NADPH-regenerating system: also the lipid peroxidation-dependent inactivation of glucose-6-phosphatase and gamma-glutamyl transpetidase due to the haloalkane are prevented. Noteworthy, the liver microsomal drug-metabolizing enzymes and in particular the catalytic activity of cytochrome P₄₅₀IIE1, responsible for the CCl₄-activation, are not impaired by the supplementation with the steroid. Consistently, in DHEA-pretreated microsomes the protein covalent binding of the trichloromethyl radical (CCl₃°), is similar to that of not supplemented microsomes treated with CCl₄. It thus seems likely that DHEA protects liver microsomes from oxidative damage induced by carbon tetrachloride through its own antioxidant properties rather than inhibiting the metabolism of the toxin.     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Heat tolerance of marine ectotherms in a warming Antarctica

Global warming is affecting the Antarctic continent in complex ways. Because Antarctic organisms are specialized to living in the cold, they are vulnerable to increasing temperatures, although quantitative analyses of this issue are currently lacking. Here we compiled a total of 184 estimates of heat tolerance belonging to 39 marine species and quantified how survival is affected concomitantly by the intensity and duration of thermal stress. Species exhibit thermal limits displaced toward colder temperatures, with contrasting strategies between arthropods and fish that exhibit low tolerance to acute heat challenges, and brachiopods, echinoderms, and molluscs that tend to be more sensitive to chronic exposure. These differences might be associated with mobility. A dynamic mortality model suggests that Antarctic organisms already encounter temperatures that might be physiologically stressful and indicate that these ecological communities are indeed vulnerable to ongoing rising temperatures.     

Induction of the human growth hormone gene placed under human hsp70 promoter control in mouse cells: A quantitative indicator of metal toxicity

An in vitro test method for general metal toxicity screening was designed, based on the cellular response to stress. The expression of a transfected human growth hormone gene sequence driven by the human heat-shock protein 70 promoter in NIH/3T3 cells was used as marker of noxious contact with metal compounds. Out of a series of31 metals, 17 were competentfor inducing this stress response system. According to the effective concentration and to the intensity of the response, three different clusters of positive compounds emerged and were ranked as strong, intermediate strength and weak inducers. These results correlated well with data from other in vivo and in vitro metal toxicity studies, including LD₅₀ in mice. Apparently the positivelnegative compounds also fitted well with data from genotoxicity and carcinogenesis studies on metal salts.Abbreviations hGH human growth hormone - hsp70 70 kDa heat-shock protein     

Novel Miscanthus hybrids: Modelling productivity on marginal land in Europe using dynamics of canopy development determined by light interception

New biomass crop hybrids for bioeconomic expansion require yield projections to determine their potential for strategic land use planning in the face of global challenges. Our biomass growth simulation incorporates radiation interception and conversion efficiency. Models often use leaf area to predict interception which is demanding to determine accurately, so instead we use low-cost rapid light interception measurements using a simple laboratory-made line ceptometer and relate the dynamics of canopy closure to thermal time, and to measurements of biomass. We apply the model to project the European biomass potentials of new market-ready hybrids for 2020–2030. Field measurements are easier to collect, the calibration is seasonally dynamic and reduces influence of weather variation between field sites. The model obtained is conservative, being calibrated by crops of varying establishment and varying maturity on less productive (marginal) land. This results in conservative projections of miscanthus hybrids for 2020–2030 based on 10% land use conversion of the least (productive) grassland and arable for farm diversification, which show a European potential of 80.7–89.7 Mt year⁻¹ biomass, with potential for 1.2–1.3 EJ year⁻¹ energy and 36.3–40.3 Mt year⁻¹ carbon capture, with seeded Miscanthus sacchariflorus × sinensis displaying highest yield potential. Simulated biomass projections must be viewed in light of the field measurements on less productive land with high soil water deficits. We are attempting to model the results from an ambitious and novel project combining new hybrids across Europe with agronomy which has not been perfected on less productive sites. Nevertheless, at the time of energy sourcing issues, seed-propagated miscanthus hybrids for the upscaled provision of bioenergy offer an alternative source of renewable energy. If European countries provide incentives for growers to invest, seeded hybrids can improve product availability and biomass yields over the current commercial miscanthus variety.     

Changes in proteoglycan synthesis of chondrocytes in articular cartilage are associated with the time-dependent changes in their mechanical environment

Explant loading experiments were conducted to investigate the effect of load duration on proteoglycan synthesis. A compressive load of 0.1 MPa applied for 10 min was found to stimulate proteoglycan synthesis, while the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanical stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells within soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extracellular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue height, h (i.e. h/a 1). A closed-form analytical solution for this inclusion problem is then presented for the confined compression configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneous, and can be significantly influenced by differences in properties between the cell and the extracellular matrix.