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1.
William J. Sanders 《Historical Biology》2018,30(1-2):137-156
AbstractModern 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. 相似文献
2.
Paul A. Rees 《Journal of applied animal welfare science : JAAWS》2013,16(1):44-60
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. 相似文献
3.
Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies 总被引:16,自引:0,他引:16
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 相似文献
4.
C. Hörber N. Christensen E. Arvin B. Kiær Ahring 《Applied microbiology and biotechnology》1999,51(5):694-699
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 相似文献
5.
J. Gerritse G. Kloetstra A. Borger G. Dalstra A. Alphenaar J. C. Gottschal 《Applied microbiology and biotechnology》1997,48(4):553-562
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 相似文献
6.
Trichloroethylene degradation and mineralization by pseudomonads and Methylosinus trichosporium OB3b 总被引:1,自引:0,他引:1
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 (μmax) 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 相似文献
7.
R. Candau A. Belli G. Y. Millet D. Georges B. Barbier J. D. Rouillon 《European journal of applied physiology and occupational physiology》1998,77(6):479-485
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 CR. 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 相似文献
8.
R. R. Farrera F. Pérez-Guevara M. de la Torre 《Applied microbiology and biotechnology》1998,49(6):758-765
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 相似文献
9.
Connors N Petersen L Hughes R Saini K Olewinski R Salmon P 《Applied microbiology and biotechnology》2000,54(6):814-818
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 相似文献
10.
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 相似文献
11.
Georges Dalleau Alain Belli Muriel Bourdin Jean-René Lacour 《European journal of applied physiology and occupational physiology》1998,77(3):257-263
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 相似文献
12.
Carlo Capelli Dave R. Pendergast B. Termin 《European journal of applied physiology and occupational physiology》1998,78(5):385-393
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˙O2max
t
p−V˙O2max(1−e−(
t
p/)), where E
an was the amount of energy (kilojoules) derived from anaerobic sources, V˙O2max 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˙O2max 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 相似文献
13.
J. Langfort R. Zarzeczny W. Pilis K. Nazar H. Kaciuba-Ucitko 《European journal of applied physiology and occupational physiology》1997,76(2):128-133
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 相似文献
14.
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 相似文献
15.
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. 相似文献
16.
The microbial production of poly(hydroxyalkanoates) from tallow 总被引:7,自引:0,他引:7
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 相似文献
17.
Effects of climate and atmospheric CO2 partial pressure on the global distribution of C4 grasses: present, past, and future 总被引:5,自引:0,他引:5
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 相似文献
18.
William E. Magnusson M. Carmozina de Araújo Renato Cintra Albertina P. Lima Luiz A. Martinelli Tânia M. Sanaiotti Heraldo L. Vasconcelos Reynaldo L. Victoria 《Oecologia》1999,119(1):91-96
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 相似文献
19.
Effects of Zinc Glycine Chelate on Oxidative Stress,Contents of Trace Elements,and Intestinal Morphology in Broilers 总被引:1,自引:0,他引:1
Wenqiang Ma Haihua Niu Jiang Feng Yong Wang Jie Feng 《Biological trace element research》2011,142(3):546-556
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. 相似文献
20.
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 相似文献