Comparative analysis of the digestive efficiency and nitrogen and energy requirements of the phyllostomid fruit-bat (Artibeus jamaicensis) and the pteropodid fruit-bat (Rousettus aegyptiacus)

Nitrogen (N) and energy (E) requirements of the phyllostomid fruit bat, Artibeus jamaicensis, and the pteropodid fruit bat Rousettus aegyptiacus, were measured in adults that were fed on four experimental diets. Mean daily food intake by A. jamaicensis and R. aegyptiacus ranged from 1.1–1.6 times body mass and 0.8–1.0 times body mass, respectively. Dry matter digestibility and metabolizable E coefficient were high (81.1% and 82.4%, respectively) for A. jamaicensis and (77.5% and 78.0%, respectively) for R. aegyptiacus. Across the four diets, bats maintained constant body mass with mean metabolizable E intakes ranging from 1357.3 kJ · kg^−0.75 · day⁻¹ to 1767.3 kJ · kg^−0.75 · day⁻¹ for A. jamaicensis and 1282.6–1545.2 kJ · kg^−0.75 · day⁻¹ for R. aegyptiacus. Maintenance E costs were high, in the order of 3.6–5.4 times the basal metabolic rate (BMR). It is unlikely that the E intakes that we observed represent a true measure of maintenance E requirements. All evidence seems to indicate that fruit bats are E maximizers, ingesting more E than required and regulating storage by adjusting metabolic output. We suggest that true maintenance E requirements are substantially lower than what we observed. If it follows the eutherian norm of two times the BMR, fruit bats must necessarily over-ingest E on low-N fruit diet. Dietary E content did affect N metabolism of A. jamaicensis. On respective low- and high-E diets, metabolic fecal N were 0.492 mg N · g⁻¹ and 0.756 mg N · g⁻¹ dry matter intake and endogenous urinary N losses were 163.31 mg N · kg^−0.75 · day⁻¹ and 71.54 mg N · kg^−0.75 · day⁻¹. A. jamaicensis required 332.3 mg · kg^−0.75 · day⁻¹ and 885.3 mg · kg^−0.75 · day⁻¹ of total N on high- and low-E diets, respectively, and 213.7 mg · kg^−0.75 · day⁻¹ of truly digestible N to achieve N balance. True N digestibilities were low (29% and 49%) for low- and high-E diets, respectively. For R. aegyptiacus, metabolic fecal N and endogenous urinary N losses were 1.27 mg N · g⁻¹ dry matter intake and 96.0 mg N · kg^−0.75 · day⁻¹, respectively, and bats required 529.8 mg · kg^−0.75 · day⁻¹ (total N) or 284.0 mg · kg^−0.75 · day⁻¹ (truly digestible N). True N digestibility was relatively low (50%). Based on direct comparison, we found no evidence that R. aegyptiacus exhibits a greater degree of specialization in digestive function and N retention than A. jamaicensis. When combined with results from previous studies, our results indicate that all fruit bats appear to be specialized in their ability to retain N when faced with low N diet. Accepted: 24 November 1998     

Maintenance nitrogen requirement of an obligate nectarivore, the honey possum, Tarsipes rostratus

A nitrogen balance feeding trial was carried out with the marsupial honey possum, Tarsipes rostratus, using four pollen-honey diets varying in nitrogen content from 9.4 mg · g⁻¹ to 2.3 mg · g⁻¹ dry matter. The dietary maintenance nitrogen requirement (MNR) was determined by regression analysis as 89 ± 21 mg N · kg^−0.75 · day⁻¹ and the truly digestible MNR was 79 mg N · kg^−0.75 · day^−1.. Regressing nitrogen balance on daily nitrogen intake separately for ten males and seven females revealed that the slopes of the fitted lines did not vary significantly, but the difference in the intercepts approached significance. This suggests that the MNR for females may be lower than that of males. The nitrogen digestibility of the diet was 76% and the biological value (BV) was 58%. A comparison of the MNR of the honey possum with that of other marsupials shows that it is indeed much lower than that of herbivorous macropodid marsupials and is close to that of the sap- and gum-feeding sugar glider, Petarurus breviceps. The endogenous urinary nitrogen excretion (EUN) of the honey possum was 42 mg N · kg^−0.75 · day⁻¹ and a regression analysis with other published data showed that the EUN per unit basal heat production is significantly lower than that of eutherian mammals. Measurements of the actual feeding rates of animals in the field, taken together with the low MNR, do not lend support to the hypothesis that the honey possum exhibits a reduced rate of reproduction due to a deficiency in dietary nitrogen. It is possible that the quality of nitrogen provided by pollen, as reflected in its composition of essential amino acids, may be a limiting factor. Accepted: 15 September 2000     

Use of an industrial effluent as a carbon source for denitrification of a high-strength wastewater

Denitrification of a high-strength synthetic wastewater (150 g NO^- ₃ l^-1) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand l^-1). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of 9.54 g NO^- ₃ l^-1 day^-1 (2.19 g N as NO^- ₃ l^-1 day^-1) with good specific reduction rates: 32.6 mg and 35.2 mg N as NO _x  g volatile suspended solids h^-1, calculated on a single day, for the two-step and the one-step process respectively. Dissimilatory nitrate reduction to ammonium did not occur, even in the one-step process. Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996     

Sulfated extracellular polysaccharide production by the halophilic cyanobacterium Aphanocapsa halophytia immobilized on light-diffusing optical fibers

 The cyanobacterium, Aphanocapsa halo-phytia MN-11, was immobilized in calcium alginate gel and coated on light-diffusing optical fibers (LDOF) for sulfated extracellular polysaccharide production. Results indicated that sulfated extracellular polysaccharide production depends on the number of immobilized cells and the light intensity. In addition, the production rate reached 116.0 mg (mg dry cells)^-1 day^-1 when the cells that were immobilized on LDOF were incubated under a light intensity of 1380 cd sr m^-2 at a cell concentration of 1.0×10⁸ cells/cm³ gel. Cells immobilized on LDOF produced about ten times more sulfated extracellular polysaccharide than those immobilized in calcium alginate beads only (11.7 mg(mg dry cells)^-1day^-1). Received: 31 March 1995/Revised last revision 12 June 1995/Accepted 26 July 1995     

Plant secondary metabolites as mammalian feeding deterrents: separating the effects of the taste of salicin from its post-ingestive consequences in the common brushtail possum (Trichosurus vulpecula)

The effect of the phenolic glycoside, salicin, on food intake of the common brushtail possum (Trichosurus vulpecula) was studied in a series of feeding experiments. Increasing the concentration of salicin in a diet of fruits and cereals led to significant reductions of food intake in the short term (6 days). After prolonged (20 days) exposure to salicin, food intake (19 g kg^−0.75 day⁻¹) was still reduced relative to controls (31 g kg^−0.75 day⁻¹) but not reduced to the same extent as in the short-term experiments. Nonetheless, over these 20 days, common brushtail possums regulated their intake of salicin so as not to exceed a threshold limit of 1.9 ± 0.1 g kg^−0.75 day⁻¹. Manipulative experiments sought to determine whether this threshold intake was in response to pre-ingestive factors (taste) or the post-ingestive consequences of ingesting salicin. Dietary salicin (0.17–5.0% DM) had no significant effect on nitrogen balance or urea metabolism and injection of a specific serotonin receptor antagonist, ondansetron, did not lead to increases in salicin intake as has been found for some other plant secondary metabolites. Similarly, administration of 1.3 g salicin by gavage had no significant effect on the subsequent intake of salicin compared to controls that were gavaged with water. We concluded that pre-ingestive factors were responsible for common brushtail possums limiting their intake of salicin-rich diets rather than any measurable post-ingestive consequence of feeding. Accepted: 7 December 1999     

Digestive performance and digesta passage in the omnivorous greater bilby, Macrotis lagotis (Marsupialia: Peramelidae)

Omnivores such as the greater bilby (Macrotis lagotis) consume a variety of dietary items and often are faced with large changes in the nutrient composition of their food. This paper explores the basis for the dietary flexibility of the bilby by comparing digestive performance and digesta retention patterns of captive bilbies fed either an insect diet (mealworm larvae) or a plant diet (mixed seeds). Mean retention times (MRTs) of particle and solute markers in the gastrointestinal tract did not differ significantly between the two diets, but MRT of the particle marker was significantly longer than that of the solute marker on both the mealworm (particle: 23.5 h; solute: 17.9 h) and mixed seed (particle 33.0 h; solute: 30.2 h) diets. Lack of selective retention of solutes and small particles in the bilby gastrointestinal tract probably restricts them to relatively low-fibre diets, such as those based on seeds rather than leaves and stems of plants. It was observed radiographically that the major sites of digesta retention were the caecum, proximal colon and distal colon, and thus the hindgut is probably the principal site of microbial fermentation. The mealworms were more digestible than the mixed seeds, but digestible energy intake (mealworm: 939 kJ · kg^−0.75 · d⁻¹; mixed seed: 629 kJ · kg^−0.75 · d⁻¹) was high enough for maintenance of body mass and positive nitrogen balance on both diets. Thus, although bilbies may be limited in their ability to utilize high-fibre diets by a lack of selective retention of solutes and small particles in their hindgut, their digestive strategy is flexible enough to accommodate at least some diets of both animal and plant origin. Such a strategy should benefit an animal inhabiting environments in which food resources are unpredictable in their relative abundance. Accepted: 26 May 2000     

The effects of activators of G-proteins,mastoparan and compound 48/80, on the G-protein/adenylate cyclase system in cultured melanophores of the black-moor goldfish,Carassius auratus

 To investigate the functions of GTP-binding protein(s) in the melanosome-aggregating response in fish melanophores, the effects of activators of G-proteins, namely, mastoparan and compound 48/80, were examined in cultured melanophores of the balck-moor goldfish, Carassius auratus. Both mastoparan and compound 48/80 induced an approximately 40% increase in the GTP-hydrolyzing activity in the melanophore membranes compared to the basal level. In intact melanophores, these compounds inhibited the effect of 3-isobutyl-1-methylxanthine, which induced the accumulation of intracellular cAMP. Pretreatment of melanophores with pertussis toxin at 1 μg ⋅ ml^-1 for 15 h attenuated the inhibitory effect of mastoparan on the accumulation of cAMP. However, pretreatment with the toxin only slightly attenuated the inhibitory effect of compound 48/80 on the accumulation of cAMP. In addition, compound 48/80 at 1 mg ⋅ ml^-1 induced full aggregation of the melanosomes in melanophores, though mastoparan at 5 μmol ⋅ l^-1 induced only 10–20% aggregation of melanophores. These results suggest that mastoparan and compound 48/80 can each activate the inhibitory G-protein in goldfish melanophores, which results in inhibition of adenylate cyclase activity. This signal-transduction pathway is involved in the aggregation of melanosomes in these cells. Accepted: 3 June 1996     

Energy requirements of the red kangaroo (<Emphasis Type="Italic">Macropus rufus</Emphasis>): impacts of age,growth and body size in a large desert-dwelling herbivore.

Generally, young growing mammals have resting metabolic rates (RMRs) that are proportionally greater than those of adult animals. This is seen in the red kangaroo (Macropus rufus), a large (>20 kg) herbivorous marsupial common to arid and semi-arid inland Australia. Juvenile red kangaroos have RMRs 1.5–1.6 times those expected for adult marsupials of an equivalent body mass. When fed high-quality chopped lucerne hay, young-at-foot (YAF) kangaroos, which have permanently left the mother's pouch but are still sucking, and recently weaned red kangaroos had digestible energy intakes of 641±27 kJ kg^–0.75 day^–1 and 677±26 kJ kg^–0.75 day^–1, respectively, significantly higher than the 385±37 kJ kg^–0.75 day^–1 ingested by mature, non-lactating females. However, YAF and weaned red kangaroos had maintenance energy requirements (MERs) that were not significantly higher than those of mature, non-lactating females, the values ranging between 384 kJ kg^–0.75 day^–1 and 390 kJ kg^–0.75 day^–1 digestible energy. Importantly, the MER of mature female red kangaroos was 84% of that previously reported for similarly sized, but still growing, male red kangaroos. Growth was the main factor affecting the proportionally higher energy requirements of the juvenile red kangaroos relative to non-reproductive mature females. On a good quality diet, juvenile red kangaroos from permanent pouch exit until shortly after weaning (ca. 220–400 days) had average growth rates of 55 g body mass day^–1. At this level of growth, juveniles had total daily digestible energy requirements (i.e. MER plus growth energy requirements) that were 1.7–1.8 times the MER of mature, non-reproductive females. Our data suggest that the proportionally higher RMR of juvenile red kangaroos is largely explained by the additional energy needed for growth. Energy contents of the tissue gained by the YAF and weaned red kangaroos during growth were estimated to be 5.3 kJ g^–1, within the range found for most young growing mammals.Abbreviations BMR basal metabolic rate - DEI digestible energy intake - MER maintenance energy requirement - MER_g maintenance plus growth energy requirement - PPE permanent pouch exit - RMR resting metabolic rate - YAF young-at-foot Communicated by I.D. Hume     

Effects of saturated fatty acids on amylase release from exocrine pancreatic segments of sheep,rats, hamsters,field voles and mice

 Stimulatory effects of saturated fatty acids consisting of 4 (butyrate), 8 (octanoate), 12 (laurate) and 16 (palmitate) carbon atoms, as well as acetylcholine on pancreatic amylase release were assessed in tissue segments isolated from sheep, rats, hamsters, field voles and mice. The amount of amylase release induced by the fatty acids (1 μmol ⋅ l^-1 to 10 mml ⋅ l^-1) and by acetylcholine (10 nmol ⋅ l^-1 to 100 μmol ⋅ l^-1) increased in a concentration-dependent manner, and the maximum response in response to the fatty acids was obtained at the maximal dose used. The maximum increase in amylase release in response to butyrate or octanoate was highly and significantly (r=0.974, P<0.001) dependent on the log value of the mean body mass in the following order: sheep>rats>hamsters>field voles>mice. On the other hand, the response to laurate and palmitate was variable among animal species. Addition of atropine (1.4 μmol ⋅ l^-1) to the medium did not reduce the responses to octanoate stimulation, but significantly reduced acetylcholineinduced responses, implying that the effects of the fatty acids were not mediated through activation of muscarinic acetylcholine receptors. Reduction of calcium ion concentration in the medium significantly inhibited the responses induced by the fatty acids and acetylcholine, suggesting that amylase release depends on extracellular calcium ions. Accepted: 14 May 1996     

Octanoate increases cytosolic Ca2+ concentration and membrane conductance in ovine pancreatic acinar cells

 In order to investigate the cellular mechanisms involved in amylase release in response to stimulation with short-chain fatty acids, changes in intracellular calcium concentration ([Ca²⁺]_i), membrane current and amylase release were measured in pancreatic acinar cells of sheep. Both octanoate and acetylcholine raised [Ca²⁺]_i in acinar cells in a concentration-dependent manner. The rise in [Ca²⁺]_i in response to the stimulation with octanoate (10 mmol ⋅ l^-1) was reduced in a medium without CaCl₂, but was markedly enhanced by reintroduction of CaCl₂ into the medium up to 2.56 mmol ⋅ l^-1. Perfusion of the cells with a medium containing octanoate (5 mmol ⋅ l^-1) or acetylcholine (0.5 μmol ⋅ l^-1) immediately raised inward current across the cell membrane at a holding-membrane potential of −30 mV. The inward current became greater as the holding potential became more negative. The equilibrium potential was 1.8 mV and 3.9 mV for octanoate and acetylcholine, respectively, being consistent with that for Cl^-. Although intracellular application of octanoate through a patch-clamp pipette also raised inward current after several minutes in some cells (4 out of 12), this possibility was significantly smaller than that for extracellular application. In other cells, even though the intracellular application of octanoate did not cause an increase in current, it always caused responses immediately after introduction of the fatty acid into the medium. Stimulation with fatty acid as well as acetylcholine raised amylase release in a concentration-dependent manner in cells dispersed from tissue segments with crude collagenase and trypsin inhibitor. Without trypsin inhibitor, crude collagenase significantly and selectively reduced the octanoate (10 mmol ⋅ l^-1)-induced amylase release. Dispersion with crude collagenase and trypsin significantly reduced both responses induced by octanoate and acetylcholine (5.5 μmol ⋅ l^-1). We conclude that fatty acids and acetylcholine increase [Ca²⁺]_i, which consequently evokes a rise in transmembrane ion (Cl^-) conductance and amylase release, and that trypsin-sensitive protein(s) in the cell membrane are involved in secretory processes activated by stimulation with fatty acids in ovine pancreatic acinar cells. Accepted: 14 May 1996     

Decomposition of aboveground and belowground organs of wild rice (Zizania latifolia): mass loss and nutrient changes

Decomposition of aboveground and belowground organs of the emergent macrophyte Z.latifolia was investigated using a litterbag technique for a period of 359 days in a freshwater marsh in Japan. Aboveground parts were classified into: leaves, sheaths and stems. Belowground parts were classified into: horizontal rhizomes (new rhizome, hard rhizome, soft rhizome) and vertical rhizome (stembase). The decay rate (k) was 0.0036 day⁻¹, 0.0033 day⁻¹ and 0.0021 day⁻¹ for leaves, sheaths and stems, respectively. For belowground parts, the decay rate varied considerably from 0.0018 day⁻¹ to 0.0079 day⁻¹, according to differences in the initial chemical compositions of rhizomes. After 359 days of decay, new rhizomes lost 94% of their original dry mass, compared with a loss of 48–84% for the other rhizomes. There was a significant positive relationship between litter quality and decay rate for horizontal rhizomes. For the new rhizomes, which had an internal nitrogen content of 24.2 mg N g⁻¹ dry mass, the mass loss was 40% higher than that of soft rhizomes, which had an internal N content of 9.8 mg N g⁻¹ dry mass. Over the period of 359 days, the nitrogen concentration in all rhizome types decreased to levels lower than initial values, but the phosphorus concentration remained constant after an initial leaching loss. Most nitrogen and phosphorus were lost during the first 45 days of decay. Changes in carbon to nitrogen (C:N) and carbon to phosphorus (C:P) ratios basically followed inversed trends of the nitrogen and phosphorus concentrations.     

Shake-flask culture of Laccaria laccata,an ectomycorrhizal basidiomycete

 Large-scale exploitation of the potential benefits of ectomycorrhizal fungi in improving plantation yields means that fermentation techniques for these fungi will be required. Starting with a base performance on a rich, complex medium, the effect of variations in some physicochemical culture parameters on biomass yield was studied. It was possible to reduce the amount of phosphate salts (to 1/9th) and other ingredients (to 1/3rd) in the medium. A shaking speed of either 100 rpm or 200 rpm in an orbital incubator was satisfactory and biomass yield responded to an increase in carbon substrate (glucose, from 10 g l^-1 and 20 g l^-1) though Y _x/s declined. An increase in inoculum size shortened culture time but decreased biomass yield. The upper limit of the incubation temperature was between 25°C and 30°C. Biomass yields were about 12 g l^-1 dry weight (Y _x/s=0.63) when 20 g l^-1 glucose was supplied, and about 7 g l^-1 (Y _x/s=0.74) when 10 g l^-1 glucose was supplied. Received: 9 October 1995/Accepted: 4 December 1995     

Continuous production of pediocin by immobilized Pediococcus acidilactici PO2 in a packed-bed bioreactor

 A continuous bioreactor packed with a fibrous matrix was set up. Cells of Pediococcus acidilactici PO2 were inoculated and MRS broth was fed gradually until cell growth and immobilization were achieved. Kinetics of fermentation and production of bacteriocin were investigated at dilution rates ranging from 0.63 day^-1 to 1.58 day^-1 and at pH values that varied between 4.0 and 5.5. A maximum bacteriocin activity of 6400 AU/ml was detected when the medium was fermented at dilution rates of at least 1.19 day^-1 and the pH controlled at 4.5. The maximum bacteriocin productivity was 1.0×10⁷ AUl^-1 day^-1 at a dilution rate of 1.58 day^-1 and pH 4.5. At this high dilution rate, 1.21 g cells/l medium was produced, 95.9% of the glucose in MRS broth was utilized, and 15.1 g lactic acid/l accumulated in the bioreactor effluent. The bioreactor was operated continuously for 3 months without encountering any clogging, degeneration, or contamination problems, indicating good long-term stability of the bioreactor for bacteriocin production. About 94% of the cells in the bioreactor were immobilized, and the remainder were suspended in the medium. According to scanning electron microscopic observations, cell immobilization in the fibrous matrix was attained by natural attachment to fiber surfaces and entrapment in the void volume within the fibrous matrix. In conclusion, conditions for the optimum continuous production of pediocin were defined; this may facilitate the development of large-scale industrial processes for production of this bacteriocin. Received: 25 September 1995/Received revision: 30 November 1995/Accepted: January 1996     

Electrogenic cation transport across leech caecal epithelium

 Electrogenic cation transport across the caecal epithelium of the leech Hirudo medicinalis was investigated using modified Ussing chambers. Transepithelial resistance (R _T ) and potential difference (V _T ) were 61.0±3.5 Ω ⋅ cm² and −1.1±0.2 mV (n=149), respectively, indicating that leech caecal epithelium is a “leaky” epithelium. Under control conditions short circuit current (I _SC ) and transepithelial Na⁺ transport rate (I _Na ) averaged at 22.1±1.5 μA ⋅ cm^-2 and 49.7±2.6 μA ⋅ cm^-2, respectively. Mucosal application of amiloride (100 μmol ⋅ l^-1) or benzamil (50 μmol ⋅ l^-1) influenced neither I _SC nor I _Na . The transport system in the apical membrane showed no pronounced cation selectivity and a linear dependence on mucosal Na⁺ concentration. Removal of mucosal Ca²⁺ increased I _SC by about 50% due to an increase of transepithelial Na⁺ transport. Trivalent cations (La³⁺ and Tb³⁺, 1 mmol ⋅ l^-1 both) added to the mucosal Ringer solution reduced I _Na by more than 40%. Serosal ouabain (1 mmol ⋅ l^-1) almost halved I _SC and I _Na while 0.1% (=5.4 mmol ⋅ l^-1) DNP decreased I _Na to 11.8±5.1% of initial values. Serosal addition of cAMP increased both I _SC and I _Na whereas the neurotransmitters FMRFamide, acetylcholine, GABA, L-dopa, serotonin and dopamine failed to show any effects; octopamine, glycine and L-glutamate reduced I _Na markedly. On the basis of these results we conclude that in leech caecal epithelium apical uptake of monovalent cations is mediated by non-selective cation conductances which are sensitive to extracellular Ca²⁺ but insensitive to amiloride. Basolaterally Na⁺ is extruded via ouabain-sensitive and -insensitive ATPases. cAMP activates Na⁺ transport across leech caecal epithelium, although the physiological stimulus for cAMP-production remains unknown. Accepted: 20 May 1996     

Microbial sensors for naphthalene using Sphingomonas sp. B1 or Pseudomonas fluorescens WW4

 Amperometric biosensors for naphthalene were developed using either immobilized Sphingomonas sp. B1 or Pseudomonas fluorescens WW4 cells. The microorganisms were immobilized within a polyurethane-based hydrogel, which was used for a microbial biosensor for the first time. Both strains were shown to be equally suited for the quantification of naphthalene in aqueous solutions. The biosensors were tested in a flow-through system and a stirred cell (batch method). In both systems a linear response down to the detection limit was obtained. Measurements in the flow-through system gave sensitivities of up to 1.2 nA mg⁻¹ l⁻¹ and a linear range from 0.03 mg/l to 2.0 mg/l. The response time (t ₉₅) was 2 min and the sample throughput six per hour; the repeatability was within ±5 %. With the batch method, sensitivities of between 3 nA mg⁻¹ l⁻¹ and 5 nA mg⁻¹l⁻¹ and a linear range of 0.01–3.0 mg/l were obtained; the response time was between 3 min and 5 min. The sensors reached an operational lifetime of up to 20 days. The sensitivity of both sensors for naphthalene was, in most cases, more than four times higher than for various other substrates. Received: 18 October 1995/Received revision: 22 December 1995/Accepted: 22 January 1996     

Ca2+sensitivity and caffeine-induced changes in skinned cardiac muscle fibers of the carp,Cyprinus carpio

 Ca²⁺ sensitivity and caffeine-induced sensitivity changes in skinned carp heart fibers were compared with those of guinea pig and rat heart. The Ca²⁺ concentration-response curves of saponin-treated left atrial skinned fibers obtained from guinea pig and rat were almost identical. Doses of 5 and 20 mmol ⋅ l^-1 caffeine shifted this curve to the left. However, when a relatively high concentration (50 mmol ⋅ l^-1) of caffeine was used, the left-ward shift was reduced. Caffeine reduced the peak of the Ca²⁺ concentration-response curve. The Ca²⁺ concentration-response curve of carp atrial skinned fiber is almost identical to that of guinea pig and rat. However, a further increase in Ca²⁺ sensitivity was observed even when 50 mmol ⋅ l^-1 caffeine was added. Similarly, a decrease in the response curve peak was also observed. Ca²⁺ sensitivity in ventricular skinned fibers obtained from carp was almost the same as that observed for the atrial, but the increase in Ca²⁺ sensitivity due to caffeine was larger. In addition, a further increase was also observed when 50 mmol ⋅ l^-1 caffeine was added. These results indicate that the Ca²⁺ sensitivity of contractile proteins in atrial muscles from carp heart is the same as that of guinea pig and rat. It is, however, assumed that there are some differences in properties in the contractile proteins. It is also assumed that there are some differences between the atrial and ventricular muscles of carp heart. Accepted: 17 May 1996     

Osmotic stress effects on the freezing tolerance of the antarctic nematodePanagrolaimus davidi

 The freezing and freezing survival of the Antarctic nematode Panagrolaimus davidi after exposure to solutions of different osmotic concentrations has been examined using a thermoelectric cooling stage and multi-specimen cooling block to see if there is any evidence that freeze-induced desiccation prevents inoculative freezing. The nematodes froze in all the test solutions used (up to 1138 mosmol ⋅ l^-1) and at all cooling rates and nucleation temperatures tested. Freezing survival was at its maximum in 0.1 mol ⋅ l^-1 NaCl in artificial tap water after 1 h exposure to the test solution and in artificial tap water after 24 h exposure. Hyperosmotic and hyposmotic stress adversely affected the nematodes’ ability to survive freezing. In non-frozen controls survival declined with increasing osmolality of the test solution. Measurements of the osmolality of water extracted from a variety of moss samples indicate that the nematodes are exposed to an osmotic concentration of about 9 mosmol ⋅ l^-1 in their natural habitat. This is close to that of artificial tap water. Our experiments, and measurements of freeze concentration effects in the literature, indicate that freeze-induced desiccation is unlikely to prevent inoculative freezing and the survival of nematodes over the winter. Accepted: 5 May 1996     

Long-term stability of a biofilter treating dimethyl sulphide

 The biofiltration of dimethyl sulphide (Me₂S) and other volatile sulphur compounds results in the accumulation of the metabolite sulphuric acid in the carrier material. Regeneration of an acidified (pH 4.7), Hyphomicrobium-MS3-inoculated compost biofilter degrading Me₂S was not possible by trickling tap water (days 0–28) or a KH₂PO₄/K₂HPO₄ buffer solution (1.26 g PO^3- ₄ l^-1, pH 7) (days 29–47) over the bioreactor at a superficial liquid flow rate of 34 lm^-2 day^-1. Since the protons produced displaced nutrient cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH⁺ ₄) from the cation-exchange sites on the compost material, 95% of the SO^2- ₄ was leached as the corresponding sulphate salts and not as sulphuric acid. Concomitantly, the pH of the compost material decreased from 4.7 to 3.9 over the 47 days rinsing period. Moreover, the rinsing procedure resulted in the leaching of essential microbial nutrients from the compost material, such as NH⁺ ₄ (22.3% wash-out over the 47-day rinsing period) and PO^3- ₄ (39.3% washout over the 28-day tap-water rinsing period). However, mixing limestone powder into the Me₂S-degrading compost biofilter was a successful approach to controlling the pH in the optimal range for the inoculum Hyphomicrobium MS3 (pH 6–7). A stoichiometric neutralisation reaction (molar ratio CaCO₃/H₂SO₄=1.1) was observed between the CaCO₃ added and the metabolite of the Me₂S degradation, while high elimination capacities (above 100 g Me₂S m^-3 day^-1) were obtained over a prolonged (more than 100 days) period. Received: 1 December 1995/Received revision: 26 April 1995 Accepted: 29 April 1996     

Response of methanotrophs and methane oxidation on ammonium application in landfill soils

To test the dose effect of ammonium (NH₄ ⁺) fertilization on soil methane (CH₄) oxidation by methanotrophic communities, batch incubations were conducted at a wide scale of NH₄ ⁺ amendments: 0, 100, 250, 500, and 1,000 mg N kg_dry soil ⁻¹. Denaturing gradient gel electrophoresis and real-time quantitative PCR analysis were conducted to investigate the correlation between the CH₄ oxidation capacity and methanotrophic communities. Immediately after the addition of NH₄ ⁺, temporal inhibition of CH₄ oxidation occurred, and this might have been due to the non-specific salt effect (osmotic stress). After a lag phase, the CH₄ oxidation rates of the soils with NH₄ ⁺ fertilization were promoted to levels higher than those of the controls. More than 100 mg N kg_dry soil ⁻¹ of NH₄ ⁺ addition resulted in the reduction of type II/type I MOB ratios and an obvious evolution of type II MOB communities, while less than 100 mg N kg_dry soil ⁻¹ of NH₄ ⁺ addition induced nearly no change of methanotrophic community compositions. The NH₄ ⁺-derived stimulation after the lag phase was attributed to the improvement of N availability for type I MOB. Compared with the controls, 100 mg N kg_dry soil ⁻¹ of NH₄ ⁺ addition doubled the CH₄ oxidation peak value to more than 20 mg CH₄ kg_dry soil ⁻¹ h⁻¹. Therefore, an appropriate amount of leachate irrigation on the landfill cover layer might efficiently mitigate the CH₄ emissions.     

Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata ) pups from the Gulf of St Lawrence, Canada

In this study we measured growth and milk intake and calculated energy intake and its allocation into metabolism and stored tissue for hooded seal (Cystophora cristata) pups. In addition, we measured mass loss, change in body composition and metabolic rate during the first days of the postweaning fast. The mean body mass of the hooded seal pups (n = 5) at the start of the experiments, when they were new-born, was 24.3 ± 1.3 kg (SD). They gained an average of 5.9 ± 1.1. kg · day⁻¹ of which 19% was water, 76% fat and 5% protein. This corresponds to an average daily energy deposition of 179.8 ± 16.0 MJ. The pups were weaned at an average body mass of 42.5 ± 1.0 kg 3.1 days after the experiment was initiated. During the first days of the postweaning fast the pups lost an average of 1.3 ± 0.5␣kg of body mass daily, of which 56% was water, 16% fat and 28% protein. During the nursing period the average daily water influx for the pups was 124.6 ± 25.8 ml · kg⁻¹. The average CO₂ production during this period was 1.10 ± 0.20 ml · g⁻¹ · h⁻¹, which corresponds to a field metabolic rate of 714 ± 130 kJ ·  kg⁻¹ · day⁻¹, or 5.8 ± 1.1 times the predicted basal metabolic rate according to Kleiber (1975). During the postweaning fast the average daily water influx was reduced to 16.1 ± 6.6 ml · kg⁻¹. The average CO₂ production in␣this period was 0.58 ± 0.17 ml · g⁻¹ · h⁻¹ which corresponds to a field metabolic rate of 375 ± 108 kJ · kg⁻¹ · day⁻¹ or 3.2 ± 0.9 times the predicted basal metabolic rate. Average values for milk composition were 33.5% water, 58.6% fat and 6.2% protein. The pups drank an average of 10.4 ± 1.8␣kg of milk daily, which represents an energy intake of 248.9 ± 39.1 MJ · day⁻¹. The pups were able to store 73.2 ± 7.7% of this energy as body tissue. Accepted: 15 August 1996