Horizontal tooth displacement and premolar occurrence in elephants and other elephantiform proboscideans

Abstract

Modern elephants lack permanent premolars and their cheek teeth succeed one another by an unusual horizontal tooth displacement mechanism. The fossil record demonstrates that this mechanism characterises elephantimorph proboscideans and first evolved in the late Oligocene. Horizontal tooth displacement provides elephantimorphs with an adaptive advantage over more primitive proboscideans with vertical tooth replacement and concurrent function of all adult teeth. Premolars were lost convergently in diverse elephantimorph taxa with small or no lower tusks and foreshortened symphyses, including independently in crown elephant genera. New evidence reveals the presence of premolars in early species of Loxodonta and loss of premolars in the Loxodonta clade by the mid-Pliocene. Rare occurrences of premolars in mammoths support the hypothesis that these teeth were lost by suppression of genetic and molecular processes responsible for their development. Retention of premolars in Elephas planifrons indicates independent loss of premolars in Elephas and mammoths, and that Elephas had multiple migrations out of Africa, once pre- and once post-loss of premolars in the genus. Unfortunately, the effects of dwarfing are thought to obscure the phylogenetic affinities of fossil elephants from Sulawesi and Java in the genus Stegoloxodon that retain permanent premolars.     

The Sizes of Elephant Groups in Zoos: Implications for Elephant Welfare

This study examined the distribution of 495 Asian elephants (Elephas maximus) and 336 African elephants (Loxodonta africana) in 194 zoos, most of which were located in Europe (49.1%) and North America (32.6%). Cows outnumbered bulls 4 to 1 (Loxodonta) and 3 to 1 (Elephas). Groups contained 7 or fewer: mean, 4.28 (σ = 5.73). One fifth of elephants lived alone or with one conspecific. Forty-six elephants (5.5%) had no conspecific. Many zoos ignore minimum group sizes of regional zoo association guidelines. The American Zoo and Aquarium Association recommends that breeding facilities keep herds of 6 to 12 elephants. The British and Irish Association of Zoos and Aquariums recommends keeping together at least 4 cows over 2 years old. Over 69% Asian and 80% African cow groups—including those under 2 years—consisted of fewer than 4 individuals. Recently, Europe and North America have made progress with some zoos no longer keeping elephants and with others investing in improved facilities and forming larger herds. The welfare of individual elephants should outweigh all other considerations; zoos should urgently seek to integrate small groups into larger herds.     

Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies

 The isotope enrichment ɛ* of ¹³C between tooth enamel of large ruminant mammals and their diet is 14.1 ± 0.5‰. This value was obtained by analyzing both the dental enamel of a variety of wild and captive mammals and the vegetation that comprised their foodstuffs. This isotope enrichment factor applies to a wide variety of ruminant mammals. Non-ruminant ungulates have a similar isotope enrichment, although our data cannot determine if it is significantly different. We also found a ¹³C isotope enrichment ɛ* of 3.1 ± 0.7‰ for horn relative to diet, and 11.1 ± 0.8‰ for enamel relative to horn for ruminant mammals. Tooth enamel is a faithful recorder of diet. Its isotopic composition can be used to track changes in the isotopic composition of the atmosphere, determine the fraction of C₃ or C₄ biomass in diets of modern or fossil mammals, distinguish between mammals using different subpathways of C₄ photosynthesis,and identify those mammals whose diet is derived from closed-canopy habitats. Received: 1 July 1998 / Accepted: 9 February 1999     

Tetrachloroethene dechlorination kinetics by Dehalospirillum multivorans immobilized in upflow anaerobic sludge blanket reactors

Tetrachloroethene (C₂Cl₄) dechlorination kinetics in upflow anaerobic sludge blanket (UASB) reactors was determined after introducing de novo activities into the granular sludge. These activities were introduced by immobilizing Dehalospirillum multivorans in a test reactor containing unsterile granular sludge, and in a reference reactor, R1, containing sterile granular sludge. A second reference reactor, R2, contained only unsterile granular sludge and served as a control. The kinetic experiments were performed by pulsing the reactors with C₂Cl₄ in a recirculating batch mode. Formate and acetate were added as electron donor and carbon source. Both reactors inoculated with D. multivorans dechlorinated C₂Cl₄ to an equimolar amount of C₂H₂Cl₂ with only traces of C₂HCl₃ in the effluent. In the control reactor, C₂HCl₃ accumulated before C₂H₂Cl₂ was produced. A computer simulation program (AQUASIM) was used to estimate the kinetic parameters. The half-saturation constants (K _s) for C₂Cl₄ and C₂HCl₃ were almost equal in the reactors containing D.␣multivorans (17 μM and 18 μM for C₂Cl₄; 26 μM and 28 μM for C₂HCl₃), indicating no influence of sludge bacteria on the affinity of D. multivorans for C₂Cl₄ and C₂HCl₃. The maximum dechlorination rates (k _m X _B) were about twice as high in the reactor containing D.␣multivorans immobilized in sterile sludge (11 mmol C₂Cl₄ l sludge⁻¹ day⁻¹ and 27 mmol C₂HCl₃ l sludge⁻¹ day⁻¹) than in the test reactor (4.4 mmol C₂Cl₄ l sludge⁻¹ day⁻¹ and 15 mmol C₂HCl₃ l sludge⁻¹ day⁻¹). Compared to other C₂Cl₄-degrading systems, the dechlorination rates of the inoculated reactors and their affinities for C₂Cl₄ and C₂HCl₃ were high. Therefore, introduction of de novo activity is promising for the use of anaerobic reactors to bioremediate C₂Cl₄-polluted water. Received: 5 November 1998 / Received revision: 25 January 1999 / Accepted: 31 January 1999     

Complete degradation of tetrachloroethene in coupled anoxic and oxic chemostats

Anaerobic tetrachloroethene(C₂Cl₄)-dechlorinating bacteria were enriched in slurries from chloroethene-contaminated soil. With methanol as electron donor, C₂Cl₄ and trichloroethene (C₂HCl₃) were reductively dechlorinated to cis-1,2-dichloroethene (cis-C₂H₂Cl₂), whereas, with l-lactate or formate, complete dechlorination of C₂Cl₄ via C₂HCl₃, cis-C₂H₂Cl₂ and chloroethene (C₂H₃Cl) to ethene was obtained. In oxic soil slurries with methane as a substrate, complete co-metabolic degradation of cis-C₂H₂Cl₂ was obtained, whereas C₂HCl₃ was partially degraded. With toluene or phenol both of the above were readily co-metabolized. Complete degradation of C₂Cl₄ was obtained in sequentially coupled anoxic and oxic chemostats, which were inoculated with the slurry enrichments. Apparent steady states were obtained at various dilution rates (0.02–0.4 h⁻¹) and influent C₂Cl₄-concentrations (100–1000 μM). In anoxic chemostats with a mixture␣of␣formate and glucose as the carbon and electron source, C₂Cl₄ was transformed at high rates (above␣140 μmol l⁻¹ h⁻¹, corresponding to 145 nmol Cl⁻ min⁻¹ mg protein⁻¹) into cis-C₂H₂Cl₂ and C₂H₃Cl. Reductive dechlorination was not affected by addition of 5 mM sulphate, but strongly inhibited after addition of 5 mM nitrate. Our results (high specific dechlorination rates and loss of dechlorination capacity in the absence of C₂Cl₄) suggest that C₂Cl₄-dechlorination in the anoxic chemostat was catalysed by specialized dechlorinating bacteria. The partially dechlorinated intermediates, cis-C₂H₂Cl₂ and C₂H₃Cl, were further degraded by aerobic phenol-metabolizing bacteria. The maximum capacity for chloroethene (the sum of tri-, di- and monochloro derivatives removed) degradation in the oxic chemostat was 95 μmol l⁻¹ h⁻¹ (20 nmol min⁻¹ mg protein⁻¹), and that of the combined anoxic → oxic reactor system was 43.4 μmol l⁻¹ h⁻¹. This is significantly higher than reported thus far. Received: 17 April 1997 / Received revision: 6 June 1997 / Accepted: 7 June 1997     

Trichloroethylene degradation and mineralization by pseudomonads and Methylosinus trichosporium OB3b

 To examine the trichloroethylene (C₂HCl₃)-degrading capability of five microorganisms, the maximum rate, extent, and degree of C₂HCl₃ mineralization were evaluated for Pseudomonas cepacia G4, Pseudomonas cepacia G4 PR1, Pseudomonas mendocina KR1, Pseudomonas putida F1, and Methylosinus trichosporium OB3b using growth conditions commonly reported in the literature for expression of oxygenases responsible for C₂HCl₃ degradation. By varying the C₂HCl₃ concentration from 5 μM to 75 μM, V _max and K _m values for C₂HCl₃ degradation were calculated as 9 nmol/(min mg protein) and 4 μM for P. cepacia G4, 18 nmol/(min mg protein) and 29 μM for P. cepacia G4 PR1, 20 nmol/(min mg protein) and 10 μM for P. mendocina KR1, and 8 nmol/(min mg protein) and 5 μM for P. putida F1. This is the first report of these Michaelis-Menten parameters for P. mendocina KR1, P. putida F1, and P. cepacia G4 PR1. At 75 μM, the extent of C₂HCl₃ that was degraded after 6 h of incubation with resting cells was 61%–98%; the highest degradation being achieved by toluene-induced P. mendocina KR1. The extent of C₂HCl₃ mineralization in 6 h (as indicated by concentration of chloride ion) was also measured and varied from 36% for toluene-induced P. putida F1 to 102% for M. trichosporium OB3b. Since C₂HCl₃ degradation requires new bio-mass, the specific growth rate (μ_max) of each of the C₂HCl₃-degradation microorganisms was determined and varied from 0.080/h (M. trichosporium OB3b) to 0.864/h (P. cepacia G4 PR1). Received: 1 May 1995/Received revision: 11 July 1995/Accepted: 26 July 1995     

Energy cost and running mechanics during a treadmill run to voluntary exhaustion in humans

The aim of the present study was to examine the physiological and mechanical factors which may be concerned in the increase in energy cost during running in a fatigued state. A group of 15 trained triathletes ran on a treadmill at velocities corresponding to their personal records over 3000m [mean 4.53 (SD 0.28) m · s⁻¹] until they felt exhausted. The energy cost of running (C _R) was quantified from the net O₂ uptake and the elevation of blood lactate concentration. Gas exchange was measured over 1 min firstly during the 3rd–4th min and secondly during the last minute of the run. Blood samples were collected before and after the completion of the run. Mechanical changes of the centre of mass were quantified using a kinematic arm. A significant mean increase [6.9 (SD 3.5)%, P < 0.001] in C _R from a mean of 4.4 (SD 0.4) J · kg⁻¹ · m⁻¹ to a mean of 4.7 (SD 0.4) J · kg⁻¹ · m⁻¹ was observed. The increase in the O₂ demand of the respiratory muscles estimated from the increase in ventilation accounted for a considerable proportion [mean 25.2 (SD 10.4)%] of the increase in C_R. A mean increase [17.0 (SD 26.0)%, P < 0.05] in the mechanical cost (C _M) from a mean of 2.36 (SD 0.23) J · kg⁻¹ · m⁻¹ to a mean of 2.74 (SD 0.55) J · kg⁻¹ · m⁻¹ was also noted. A significant correlation was found between C _R and C _M in the non-fatigued state (r = 0.68, P < 0.01), but not in the fatigued state (r = 0.25, NS). Furthermore, no correlations were found between the changes (from non-fatigued to fatigued state) in C _R and the changes in C _M suggesting that the increase in C _R is not solely dependent on the external work done per unit of distance. Since step frequency decreased slightly in the fatigued state, the internal work would have tended to decrease slightly which would not be compatible with an increase in C _R. A stepwise regressions showed that the changes in C _R were linked (r = 0.77, P < 0.01) to the changes in the variability of step frequency and in the variability of potential cost suggesting that a large proportion of the increase in C _R was due to an increase in the step variability. The underlying mechanisms of the relationship between C _R and step variability remains unclear. Accepted: 15 September 1997     

Carbon:nitrogen ratio interacts with initial concentration of total solids on insecticidal crystal protein and spore production in Bacillus thuringiensis HD-73

A response-surface methodology was used to study the effect of carbon:nitrogen ratio (C:N) and initial concentration of total solids (C _TS) on insecticidal crystal protein production and final spore count. Bacillus thuringiensis var. kurstaki HD-73 was grown in a stirred-tank reactor using soybean meal, glucose, yeast extract, corn steep solids and mineral salts. Soybean meal and glucose were added according to a central composite experimental design to test C:N ratios ranging from 3:1 to 11:1 and C _TS levels from 60␣g/l to 150 g/l. Cry production was quantified using sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The response-surface model, adjusted to the data, indicated that media with a C:N of 7:1 yielded the highest relative Cry production at each C _TS. The spore count was higher at low C:N ratio (4:1) and high C _TS (near 150 g/l). Specific Cry production varied from 0.6 to 2.2 g Cry/10¹⁰ spores. A 2.5-fold increase in C _TS resulted in a six-fold increase of protoxin production at a 7:1 C:N ratio. It is concluded that the best production conditions for Cry and for spores are different and optimization of B. thuringiensis processes should not be done on a spore-count basis but on the amount of Cry synthesized. Received: 5 September 1997 / Received revision: 22 December 1997 / Accepted: 2 January 1998     

Residual fructose and osmolality affect the levels of pneumocandins B0 and C0 produced by Glarea lozoyensis

A high total pneumocandin titer (B₀ + C₀) with a low percentage of the structural isomer pneumocandin C₀ was achieved by carrying out fermentations of Glarea lozoyensis at a high residual fructose concentration (125 g/l initial). When the fermentation was carried out at a low residual fructose concentration (40 g/l initial), pneumocandin production increased by 34%. However, a disproportionate increase in the level of pneumocandin C₀ synthesized (250% increase vs 30% increase for pneumocandin B₀) was observed. Midcycle addition of 150 mM NaCl or 116 mM Na₂SO₄ to low residual fructose fermentations returned the titer and isomer levels to those seen for the high residual fructose fermentation. The increase in pneumocandin C₀ synthesis under low residual fructose conditions appears to be linked to the increase in the synthesis of trans-4 hydroxyproline, with the synthesis of trans-3 hydroxyproline remaining unaffected. This suggests that the formation of pneumocandin C₀ is the result of a misincorporation of trans-4 hydroxyproline instead of trans-3 hydroxyproline by the pneumocandin peptide synthetase, and that the amount of trans-4 hydroxyproline formed dictates the frequency of this misincorporation. Received: 16 February 2000 / Revised: 17 May 2000 / Accepted: 8 June 2000     

Removal of tetrachloroethylene in an anaerobic column bioreactor

Removal of tetrachloroethylene (perchloroethylene; C₂Cl₄) by microbial consortia from two sites with different C₂Cl₄ exposure histories was examined in a bench-scale anaerobic column bioreactor. It was hypothesized that optimal removal would be observed in the reactor packed with sediments having an extensive exposure history. Microbial consortia were enriched from hyporheic-zone (HZ) sediments from the Portneuf aquifer near Pocatello, Idaho, and from industrial-zone (IZ) sediments from a highly contaminated aquifer in Portland, Oregon. Lactate and acetate were the electron donors during experiments conducted over 9 and 7 months for HZ and IZ sediments, respectively. In the HZ bioreactor, the retention time ranged from 31 h to 81 h, and inlet C₂Cl₄ concentrations ranged from 0.1 ppm to 1.0 ppm. Dechlorination of C₂Cl₄ averaged 60% and reached a maximum of 78%. An increase in C:N from 27:1 to 500:1 corresponded to an 18% increase in removal efficiency. Trichloroethylene production corresponded to decreased effluent C₂Cl₄; further intermediates were not detected. In the IZ bioreactor, the retention time varied from 34 h to 115 h; the inlet C₂Cl₄ concentration was 1.0 ppm. C₂Cl₄ removal averaged 70% with a maximum of 98%. Trichloroethylene and cis-dichloroethylene were detected in the effluent. Increases in C:N from 50:1 to 250:1 enhanced dechlorination activity. Received: 3 February 1997 / Received revision: 15 May 1997 / Accepted: 1 June 1997     

The spring-mass model and the energy cost of treadmill running

During running, the behaviour of the support leg was studied by modelling the runner using an oscillating system composed of a spring (the leg) and of a mass (the body mass). This model was applied to eight middle-distance runners running on a level treadmill at a velocity corresponding to 90% of their maximal aerobic velocity [mean 5.10 (SD 0.33) m · s⁻¹]. Their energy cost of running (C _r ), was determined from the measurement of O₂ consumption. The work, the stiffness and the resonant frequency of both legs were computed from measurements performed with a kinematic arm. The C _r was significantly related to the stiffness (P < 0.05, r = −0.80) and the absolute difference between the resonant frequency and the step frequency (P < 0.05, r = 0.79) computed for the leg producing the highest positive work. Neither of these significant relationships were obtained when analysing data from the other leg probably because of the work asymmetry observed between legs. It was concluded that the spring-mass model is a good approach further to understand mechanisms underlying the interindividual differences in C _r . Accepted: 18 August 1997     

Energetics of swimming at maximal speeds in humans

The energy cost per unit of distance (C _s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (v), C _s was measured dividing steady-state oxygen consumption (V˙O₂) by the speed (v, metres per second). At supra-maximal v, C _s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E _an+V˙O_2max t _p−V˙O_2max(1−e^{−( t p/)}), where E _an was the amount of energy (kilojoules) derived from anaerobic sources, V˙O_2max litres per second was the maximal oxygen uptake, α (=20.9 kJ · l O₂ ⁻¹) was the energy equivalent of O₂, τ (24 s) was the time constant assumed for the attainment of V˙O_2max at muscle level at the onset of exercise, and t _p (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t _p to an asymptotic value of 0.418 kJ · kg⁻¹ of body mass for t _p ≥ 120 s. The lactic acid component of E _an was obtained from the net increase of lactate concentration after exercise (Δ[La]_b) assuming that, when Δ[La]_b = 1 mmol · l⁻¹ the net amount of metabolic energy released by lactate formation was 0.069 kJ · kg⁻¹. Over the entire range of v, front crawl was the least costly stroke. For example at 1 m · s⁻¹, C _s amounted, on average, to 0.70, 0.84, 0.82 and 0.124 kJ · m⁻¹ in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m · s⁻¹, C _s was 1.23, 1.47, 1.55 and 1.87 kJ · m⁻¹ in the four strokes, respectively. The C _s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly C _s attained a minimum at the two lowest v to increase exponentially at higher v. The C _s in breaststroke was a linear function of the v, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of v occurring in the non-propulsive phase. Accepted: 14 April 1998     

The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise

The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate (β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O₂) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533 (7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations of β-HB [2.38 (0.18) vs 0.23 (0.01) mmol · l⁻¹, P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol · l⁻¹, P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol · l⁻¹, P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU · l⁻¹] were lower. The 1-h post-exercise excess of V˙O₂ [9.1 (0.25) vs 10.6 (0.25) l, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol · l⁻¹, P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs 1.21 (0.13) nmol · l⁻¹ and 14.30 (1.41) vs 8.20 (1.31) nmol · l⁻¹, P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma β-HB concentration decreased quickly after exercise, attaining ≈30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise. Accepted: 31 January 1997     

Oxygen and electron flow in C4 photosynthesis: Mehler reaction, photorespiration and CO2 concentration in the bundle sheath

The photosynthetic linear electron transport rate in excess of that used for CO₂ reduction was evaluated in Sorghum bicolor Moench. [NADP-malic enzyme (ME)-type C₄ plant], Amaranthus cruentus L. (NAD-ME-type C₄ plant) and Helianthus annuus L. (C₃ plant) leaves at different CO₂ and O₂ concentrations. The electron transport rate (J _F) was calculated from fluorescence using the light partitioning factor (relative PSII cross-section) determined under conditions where excess electron transport was assumed to be negligible: low light intensities, 500 μmol CO₂ · mol⁻¹ and 2% O₂. Under high light intensities there was a large excess of J _F/4 at 10–100% O₂ in the C₃ plant due to photorespiration, but very little in sorghum and somewhat more in amaranth, showing that photorespiration is suppressed, more in the NADP-ME- and less in the NAD-ME-type species. It is concluded that when C₄ photosynthesis is limited by supply of atmospheric CO₂ to the C₄ cycle, the C₃ cycle becomes limited by regeneration of ribulose 1,5-bisphosphate (RuBP) which in turn limits RuBP oxygenase activity and photorespiration. The rate of excess electron transport over that consumed for CO₂ fixation in C₄ plants was very sensitive to the presence of O₂ in the gas phase, rapidly increasing between 0.01 and 0.1% O₂, and at 2% O₂ it was about two-thirds of that at 21% O₂. This shows the importance of the Mehler O₂ reduction as an electron sink, compared with photorespiration in C₄ plants. However, the rate of the Mehler reaction is still too low to fully account for the extra ATP which is needed in C₄ photosynthesis. Received: 8 November 1997 / Accepted: 26 December 1997     

A theoretical study on the reaction mechanism of O<Subscript>2</Subscript> with C<Subscript>4</Subscript>H<Subscript>9</Subscript>• radical

Ab initio calculations have been performed using the complete basis set model (CBS-QB3) to study the reaction mechanism of butane radical (C₄H₉•) with oxygen (O₂). On the calculated potential energy surface, the addition of O₂ to C₄H₉• forms three intermediates barrierlessly, which can undergo subsequent isomerization or decomposition reaction leading to various products: HOO• + C₄H₈, C₂H₅• + CH₂CHOOH, OH• + C₃H₇CHO, OH• + cycle-C₄H₈O, CH₃• + CH₃CHCHOOH, CH₂OOH• + C₃H₆. Five pathways are supposed in this study. After taking into account the reaction barrier and enthalpy, the most possible reaction pathway is C₄H₉• + O₂ → IM1 → TS5 → IM3 → TS6 → IM4 → TS7 → OH• + cycle-C₄H₈O.     

The microbial production of poly(hydroxyalkanoates) from tallow

The bacteria Pseudomonas oleovorans, P. resinovorans, P. putida, and P. citronellolis were evaluated for their ability to grow and produce poly(hydroxyalkanoates) (PHA) using tallow free fatty acids and tallow triglyceride as carbon substrates. Tallow free fatty acids supported cell growth and PHA production for all four organisms, yielding PHA contents of 18%, 15%, 19% and 3% of their cell dry weights for P. oleovorans, P.␣resinovorans, P. putida, and P. citronellolis respectively. Only P. resinovorans, however, was able to grow and produce PHA polymer, with cells attaining a PHA content of 15% of their cell dry weight, using unhydrolyzed tallow as the substrate. Extracts from 46-h cultures of P. resinovorans were found to have a higher esterase activity (12.80 units μl⁻¹min⁻¹) compared to the activities found for cultures of P. oleovorans, P. citronellolis, and P. putida ( < 0.03 units μl⁻¹min⁻¹). Polymer repeat-unit compositions were determined by GC analysis of the β-hydroxymethyl esters of hydrolyzed PHA, and ranged in carbon-chain lengths from C₄ to C₁₄, with some mono-unsaturation in the C₁₂ and C₁₄ side-chains. PHA compositions were similar for the polymers obtained from all four organisms, with repeat units of chain lengths C₈ and C₁₀ predominating. Received: 16 February 1996 / Received revision: 23 May 1996 / Accepted: 10 June 1996     

Effects of climate and atmospheric CO2 partial pressure on the global distribution of C4 grasses: present, past, and future

C₄ photosynthetic physiologies exhibit fundamentally different responses to temperature and atmospheric CO₂ partial pressures (pCO₂) compared to the evolutionarily more primitive C₃ type. All else being equal, C₄ plants tend to be favored over C₃ plants in warm humid climates and, conversely, C₃ plants tend to be favored over C₄ plants in cool climates. Empirical observations supported by a photosynthesis model predict the existence of a climatological crossover temperature above which C₄ species have a carbon gain advantage and below which C₃ species are favored. Model calculations and analysis of current plant distribution suggest that this pCO₂-dependent crossover temperature is approximated by a mean temperature of 22°C for the warmest month at the current pCO₂ (35 Pa). In addition to favorable temperatures, C₄ plants require sufficient precipitation during the warm growing season. C₄ plants which are predominantly graminoids of short stature can be competitively excluded by trees (nearly all C₃ plants) – regardless of the photosynthetic superiority of the C₄ pathway – in regions otherwise favorable for C₄. To construct global maps of the distribution of C₄ grasses for current, past and future climate scenarios, we make use of climatological data sets which provide estimates of the mean monthly temperature to classify the globe into areas which should favor C₄ photosynthesis during at least 1 month of the year. This area is further screened by excluding areas where precipitation is <25 mm per month during the warm season and by selecting areas classified as grasslands (i.e., excluding areas dominated by woody vegetation) according to a global vegetation map. Using this approach, grasslands of the world are designated as C₃, C₄, and mixed under current climate and pCO₂. Published floristic studies were used to test the accuracy of these predictions in many regions of the world, and agreement with observations was generally good. We then make use of this protocol to examine changes in the global abundance of C₄ grasses in the past and the future using plausible estimates for the climates and pCO₂. When pCO₂ is lowered to pre-industrial levels, C₄ grasses expanded their range into large areas now classified as C₃ grasslands, especially in North America and Eurasia. During the last glacial maximum (∼18 ka BP) when the climate was cooler and pCO₂ was about 20 Pa, our analysis predicts substantial expansion of C₄ vegetation – particularly in Asia, despite cooler temperatures. Continued use of fossil fuels is expected to result in double the current pCO₂ by sometime in the next century, with some associated climate warming. Our analysis predicts a substantial reduction in the area of C₄ grasses under these conditions. These reductions from the past and into the future are based on greater stimulation of C₃ photosynthetic efficiency by higher pCO₂ than inhibition by higher temperatures. The predictions are testable through large-scale controlled growth studies and analysis of stable isotopes and other data from regions where large changes are predicted to have occurred. Received: 3 July 1997 / Accepted: 3 December 1997     

Contributions of C3 and C4 plants to higher trophic levels in an Amazonian savanna

We studied the energy flow from C₃ and C₄ plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C₄ plants encountered in our study area were grasses and all C₃ plants were bushes, shrubs or vines. Differences in δ¹³C ratios among bushes (xˉ = −30.8, SD = 1.2), vines (xˉ = −30.7, SD = 0.46) and trees (xˉ = −29.7, SD = 1.5) were small. However the mean δ¹³C ratio of dicotyledonous plants (xˉ = −30.4, SD = 1.3) was much more negative than that of the most common grasses (xˉ = −13.4, SD = 0.27). The insect primary consumers had δ¹³C ratios which ranged from a mean of −29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of −14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for δ¹³C, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher values of δ¹³C (xˉ = −21.7, SD = 1.6; xˉ = −21.9, SD = 1.8, respectively) than the birds (xˉ = −24.8, SD = 1.8) and the only species of mammal resident in the savanna (xˉ = −25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C₄ grasses. Received: 7 May 1998 / Accepted: 30 November 1998     

Effects of Zinc Glycine Chelate on Oxidative Stress,Contents of Trace Elements,and Intestinal Morphology in Broilers

Three hundred and sixty healthy Ross × Ross 1-day-old broilers were used to study the effects of zinc glycine chelate (Zn-Gly) on oxidative stress, contents of trace elements, and intestinal morphology. All broilers were randomly assigned to six treatment groups, which replicates three times. Diets were as follows: (1) control (containing 29.3 mg zinc (Zn)/kg basic diet (0–21 days) and 27.8 mg Zn/kg (22–42 days)); (2) basic diet plus 30 mg Zn/kg from Zn-Gly; (3) basic diet plus 60 mg Zn/kg from Zn-Gly; (4) basic diet plus 90 mg Zn/kg from Zn-Gly; (5) basic diet plus 120 mg Zn/kg from Zn-Gly; and (6) positive control, basic diet plus 120 mg Zn/kg from zinc sulfate (ZnSO₄). The results showed that the addition of 90 or 120 mg/kg Zn-Gly led to an improvement of activity of Cu/Zn superoxide dismutase and glutathione peroxidase and a reduction of malondialdehyde content in livers at 21 and 42 days. With 90 mg/kg Zn-Gly, the content of sera zinc increased by 17.55% (P < 0.05) in 21-day broilers and 10.77% (P > 0.05) in 42-day broilers compared with that of the control. Adding 120 mg/kg Zn-Gly or ZnSO₄ to broilers' diets greatly enhanced the content of zinc in feces at 21 days (P < 0.05) and at 42 days (P < 0.05). For 42-day chickens, increased villus height and decreased crypt depth of the jejunum could be observed in the second growth stage of broilers fed with 90 mg/kg Zn-Gly. Also, intestinal wall thickness decreased (P < 0.05). In addition, adding 90 mg/kg Zn-Gly to the diet markedly elevated villus length of duodenum and decreased crypt depth of ileum (P < 0.05) in 42-day broilers.     

Methanogenic and perchloroethylene-dechlorinating activity of anaerobic granular sludge

The biodegradation and toxicity of tetrachloroethylene (C₂Cl₄) and trichloroethylene (C₂HCl₃) were studied with different anaerobic enrichment cultures using the following electron donors: acetate, propionate, butyrate, methanol, formate and hydrogen. All of them sustained dechlorination except propionate, for which C₂Cl₄ biodegradation rates were not significant. The best results were obtained with butyrate. Hydrogen appeared to be a relevant electron donor for dechlorination with the present cultures. In the presence of specific inhibitors such as bromoethanesulphonate or molybdate, a slight inhibition of dechlorination was observed. According to dechlorination kinetics, Monod-type behaviour was observed up to 120 μM C₂Cl₄ or 200 μM C₂HCl₃ with K _s values around 7 μM for both compounds. Dechlorination was partially inhibited at higher concentrations. In contrast, methanogens, or at least methane production, were more sensitive to the presence of chlorinated ethylenes and inhibition of methanogenesis was observed to different extents over all the C₂Cl₄/C₂HCl₃ concentration range tested, even at the lowest concentrations. Received: 17 April 1998 / Received revision: 18 June 1998 / Accepted: 19 June 1998