Continuous production of l(+)-lactic acid by Lactobacillus casei in two-stage systems

A two-stage two-stream chemostat system and a two-stage two-stream immobilized upflow packed-bed reactor system were used for the study of lactic acid production by Lactobacillus casei subsp casei. A mixing ratio of D ₁₂/D ₂= 0.5 (D = dilution rate) resulted in optimum production, making it possible to generate continuously a broth with high lactic acid concentration (48 g l⁻¹) and with a lowered overall content of initial yeast extract (5  g l⁻¹), half the concentration supplied in the one-step process. In the two-stage chemostat system, with the first stage at pH 5.5 and 37 °C and a second stage at pH 6.0, a temperature change from 40 °C to 45 °C in the second stage resulted in a 100% substrate consumption at an overall dilution rate of 0.05 h⁻¹. To increase the cell mass in the system, an adhesive strain of L. casei was used to inoculate two packed-bed reactors, which operated with two mixed feedstock streams at the optimal conditions found above. Lactic acid fermentation started after a lag period of cell growth over foam glass particles. No significant amount of free cells, compared with those adhering to the glass foam, was observed during continuous lactic acid production. The extreme values, 57.5 g l⁻¹ for lactic acid concentration and 9.72 g l⁻¹ h⁻¹ for the volumetric productivity, in upflow packed-bed reactors were higher than those obtained for free cells (48 g l⁻¹  and 2.42 g l⁻¹ h⁻¹) respectively and the highest overall l(+)-lactic acid purity (96.8%) was obtained in the two-chemostat system as compared with the immobilized-cell reactors (93%). Received: 4 December 1997 / Received revision: 23 February 1998 / Accepted: 14 March 1998     

Cardiorespiratory responses to underwater treadmill walking in healthy females

This study compared the cardiorespiratory responses of eight healthy women (mean age 30.25 years) to submaximal exercise on land (LTm) and water treadmills (WTm) in chest-deep water (Aquaciser). In addition, the effects of two different water temperatures were examined (28 and 36°C). Each exercise test consisted of three consecutive 5-min bouts at 3.5, 4.5 and 5.5 km · h⁻¹. Oxygen consumption (V˙O₂) and heart rate (HR), measured using open-circuit spirometry and telemetry, respectively, increased linearly with increasing speed both in water and on land. At 3.5 km · h⁻¹ V˙O₂ was similar across procedures [χ = 0.6 (0.05) l · min⁻¹]. At 4.5 and 5.5 km · h⁻¹ V˙O₂ was significantly higher in water than on land, but there was no temperature effect (WTm: 0.9 and 1.4, respectively; LTm: 0.8 and 0.9 l · min⁻¹, respectively). HR was significantly higher in WTm at 36°C compared to WTm at 28°C at all speeds, and compared to LTm at 4.5 and 5.5 km · h⁻¹ (P ≤ 0.003). The HR-V˙O₂ relationship showed that at a V˙O₂ of 0.9 l · min⁻¹, HR was higher in water at 36°C (115 beats · min⁻¹) than either on land (100 beats · min⁻¹) or in water at 28°C (99 beats · min⁻¹). The Borg scale of perceived exertion showed that walking in water at 4.5 and 5.5 km · h⁻¹ was significantly harder than on land (WTm: 11.4 and 14, respectively; LTm: 9.9 and 11, respectively; P ≤ 0.001). These cardiorespiratory changes occurred despite a slower cadence in water (the mean difference at all speeds was 27 steps/min). Thus, walking in chest-deep water yields higher energy costs than walking at similar speeds on land. This data has implications for therapists working in hydrotherapy pools. Accepted: 3 September 1997     

High alcohol production by repeated batch fermentation using an immobilized osmotolerant Saccharomyces cerevisiae

A repeated batch fermentation system was used to produce ethanol using an osmotolerant Saccharomyces cerevisiae (VS₃) immobilized in calcium alginate beads. For comparison free cells were also used to produce ethanol by repeated batch fermentation. Fermentation was carried for six cycles with 125, 250 or 500 beads using 150, 200 or 250 g glucose L⁻¹ at 30°C. The maximum amount of ethanol produced by immobilized VS₃ using 150 g L⁻¹ glucose was only 44 g L⁻¹ after 48 h, while the amount of ethanol produced by free cells in the first cycle was 72 g L⁻¹. However in subsequent fed batch cultures more ethanol was produced by immobilized cells compared to free cells. The amount of ethanol produced by free cells decreased from 72 g L⁻¹ to 25 g L⁻¹ after the fourth cycle, while that of immobilized cells increased from 44 to 72 g L⁻¹. The maximum amount of ethanol produced by immobilized VS₃ cells using 150, 200 and 250 g glucose L⁻¹ was 72.5, 93 and 87 g ethanol L⁻¹ at 30°C. Journal of Industrial Microbiology & Biotechnology (2000) 24, 222–226. Received 16 September 1999/ Accepted in revised form 22 December 1999     

Biodegradation of propanol and isopropanol by a mixed microbial consortium

The aerobic biodegradation of high concentrations of 1-propanol and 2-propanol (IPA) by a mixed microbial consortium was investigated. Solvent concentrations were one order of magnitude greater than any previously reported in the literature. The consortium utilized these solvents as their sole carbon source to a maximum cell density of 2.4 × 10⁹ cells ml⁻¹. Enrichment experiments with propanol or IPA as carbon sources were carried out in batch culture and maximum specific growth rates (μ_max) calculated. At 20 °C, μ _max values were calculated to be 0.0305 h⁻¹ and 0.1093 h⁻¹ on 1% (v/v) IPA and 1-propanol, respectively. Growth on propanol and IPA was carried out between temperatures of 10 °C and 45 °C. Temperature shock responses by the microbial consortium at temperatures above 45 °C were demonstrated by considerable cell flocculation. An increase in propanol substrate concentration from 1% (v/v) to 2% (v/v) decreased the μ _max from 0.1093 h⁻¹ to 0.0715 h⁻¹. Maximum achievable biodegradation rates of propanol and IPA were 6.11 × 10⁻³% (v/v) h⁻¹ and 2.72 × 10⁻³% (v/v) h⁻¹, respectively. Generation of acetone during IPA biodegradation commenced at 264 h and reached a maximum concentration of 0.4% (v/v). The results demonstrate the potential of mixed microbial consortia in the bioremediation of solvent-containing waste streams. Received: 14 December 1999 / Received revision: 3 April 2000 / Accepted: 7 April 2000     

The effect of growth conditions on the biodegradation of tributyl phosphate and potential for the remediation of acid mine drainage waters by a naturally-occurring mixed microbial culture

The biodegradation of tributyl phosphate (Bu₃-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu₃-P biodegradation by growing cells is described. Growth at the expense of Bu₃-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu₃-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited, and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu₃-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h⁻¹ mg protein⁻¹ and 37 μmol h⁻¹ mg protein⁻¹ respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate precipitation at the expense of Bu₃-P hydrolysis in the presence of 35 mM SO₄ ²⁻. At pH 4.5, 79% of the UO₂ ²⁺ was removed at a flow rate of 1.4 ml/h on a 7-ml test column. Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997     

Effects of temperature on photosynthesis of two morphologically contrasting plant species along an altitudinal gradient in the tropical high Andes

The effects of temperature on photosynthesis of a rosette plant growing at ground level, Acaena cylindrostachya R. et P., and an herb that grows 20–50 cm above ground level, Senecio formosus H.B.K., were studied along an altitudinal gradient in the Venezuelan Andes. These species were chosen in order to determine – in the field and in the laboratory – how differences in leaf temperature, determined by plant form and microenvironmental conditions, affect their photosynthetic capacity. CO₂ assimilation rates (A) for both species decreased with increasing altitude. For Acaena leaves at 2900 m, A reached maximum values above 9 μmol m⁻² s⁻¹, nearly twice as high as maximum A found at 3550 m (5.2) or at 4200 m (3.9). For Senecio leaves, maximum rates of CO₂ uptake were 7.5, 5.8 and 3.6 μmol m⁻² s⁻¹ for plants at 2900, 3550 and 4200 m, respectively. Net photosynthesis-leaf temperature relations showed differences in optimum temperature for photosynthesis (A _o.t.) for both species along the altitudinal gradient. Acaena showed similar A _o.t. for the two lower altitudes, with 19.1°C at 2900 m and 19.6°C at 3550 m, while it increased to 21.7°C at 4200 m. Maximum A for this species at each altitude was similar, between 5.5 and 6.0 μmol m⁻² s⁻¹. For the taller Senecio, A _o.t. was more closely related to air temperatures and decreased from 21.7°C at 2900 m, to 19.7°C at 3550 m and 15.5°C at 4200 m. In this species, maximum A was lower with increasing altitude (from 6.0 at 2900 m to 3.5 μmol m⁻² s⁻¹ at 4200 m). High temperature compensation points for Acaena were similar at the three altitudes, c. 35°C, but varied in Senecio from 37°C at 2900 m, to 39°C at 3550 m and 28°C at 4200 m. Our results show how photosynthetic characteristics change along the altitudinal gradient for two morphologically contrasting species influenced by soil or air temperatures. Received: 5 July 1997 / Accepted: 25 October 1997     

Production of Spirulina sp. in sea water supplemented with anaerobic effluents in outdoor raceways under temperate climatic conditions

The use of untreated sea water supplemented with anaerobic effluents from digested pig waste and sodium bicarbonate was evaluated as a low-cost medium for semi-continuous cultivation of a mixed culture of two Spirulina strains in outdoor raceways under temperate climatic conditions (pond temperature in the range 21–26 °C and light intensity in the range 225–957␣μE m⁻² s⁻¹). The mixed culture had a predominant population (86.6 ± 3.9%) of an atypical Spirulina strain consisting of straight filaments, which appeared spontaneously after the strain with helicoidal trichomes had been subcultured. Morphological studies for the identification of the type and size of trichomes of the two strains (HF and SF) were carried out. The proportions of the two strains were observed to be stable during the monitoring period (30 days). Three different sets of semicontinuous cultures were carried out. Sets 1 and 2 were operated under regime 1 (a single addition of anaerobic effluents at time zero and no pH control) during the same season (June and July) of different years. Set 3 was operated under regime 2 (semi-continuous addition of anaerobic effluents and pH control) during the autumn. A minimum productivity of 3.6 g m⁻² day⁻¹ was obtained at one of the lowest temperatures (22.1 °C) and light intensities (245 μE m⁻² s⁻¹) and a maximum productivity of 10.9 g m⁻² day⁻¹ was observed at the highest temperature (25 °C) and highest average light intensity (618 μE m⁻² s⁻¹) registered for sets 1 and 2. The protein content in the Spirulina biomass harvested from these two sets varied from 17% to 65.6%. In set 3, a maximum productivity of 9.0 g m⁻² day⁻¹ was recorded at an average temperature of 24.4 °C and at an average light intensity of 668 μE m⁻² s⁻¹. The protein content in this set under regime 2 varied within a narrower range than in set 1 and set 2 (from 34.8% to 49.1%), apparently because of a continuous availability of ammonia nitrogen at a level of 30–50 mg l⁻¹. However, in terms of the removal of ammonia nitrogen and chemical oxygen demand, regime 1 was more efficient than regime␣2. Received: 3 September 1996 / Received revision: 19 February 1997 / Accepted: 7 March 1997     

Sex-related differences in thermoregulatory responses while wearing protective clothing

This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m² · kg⁻¹ · 10⁻², Dubois surface area 2.01 (0.16) m², %body fatness 14.6 (3.9)%, V˙O_2peak 49.0 (4.8) ml · kg⁻¹ · min⁻¹] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m² · kg⁻¹ · 10⁻², 1.68 (0.13) m², 20.2 (4.8)%, 43.2 (6.6) ml · kg⁻¹ · min⁻¹, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h⁻¹ followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical protective clothing (0.29 m² ·°C · W⁻¹ or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i _m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min⁻¹ at 105 min (n = 13) compared with 145.1 (14.4) beats · min⁻¹ for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T _re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m⁻² for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg⁻¹] compared with M [9.45 (1.26) kJ · kg⁻¹]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg⁻¹ for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness. Accepted: 31 October 1997     

Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects

The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen uptake (V˙O_{2 max} ) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM). Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of the hand on the rim (−30°, 0° and +30°). The results indicate that paraplegic subjects reached a similar V˙O_{2 max} [1.23 (0.34) l · min⁻¹, 1.25 (0.38) l · min⁻¹, 1.22 (0.18) l · min⁻¹ for AC, TM and WE, respectively] and V˙O_{2 max} /body mass [19.7 (5.2) ml · min⁻¹ · kg⁻¹, 19.5 (6.14) ml · min⁻¹ · kg⁻¹, 19.18 (4.27) ml · min⁻¹ · kg⁻¹ for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f _{c max} during the last minute of AC (173 (17) beats · min⁻¹], TM [168 (14) beats · min⁻¹], and WE [165 (16) beats · min⁻¹], were correlated, but f _{c max} was significantly higher for AC than for TM (P<0.03). There were significant correlations between MVF and LAV (P<0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1 (71) N, at −30°, 0° and +30°, respectively]. There was no correlation between V˙O_{2 max} and LAV or MVF. The relatively low values of f _{c max} suggest that V˙O_{2 max} was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the lack of a significant correlation between V˙O_{2 max} and MVF or muscle mass was not in favour of muscle strength being the main factor limiting V˙O_{2 max} in our subjects. Accepted: 31 January 1997     

Inhibition of degradation and aggregation of recombinant human consensus interferon-α mutant expressed in <Emphasis Type="Italic">Pichia pastoris</Emphasis> with complex medium in bioreactor

The methylotrophic yeast Pichia pastoris has been used for the expression of many proteins. However, limitations such as protein degradation and aggregation became obvious when secreting heterologous protein-recombinant human consensus interferon-α mutant. Here, we investigate the effect of induction temperature on the yield and stability of interferon mutant expressed by P. patoris with buffered complex medium. The best results in terms of interferon mutant bioactivity and specific bioactivity were obtained when the microorganism was induced at 15°C, which were 2.91 × 10⁸ ± 0.3 × 10⁸ and 2.26 × 10⁸± 0.23 × 10⁸ IU mg⁻¹, respectively. At the same time, the cells grew fast owing to high AOX1-specific activity, and interferon mutant expression level reached 1.23 g l⁻¹, which was almost 30 times higher than that in the flask. Also, the proteolytic degradation of interferon mutant was inhibited completely because of lower protease bioactivity probably due to a reduced cell death rate at lower temperatures as well as protection of yeast extract and peptone in complex medium. In addition, interferon mutant aggregation was repressed significantly by the addition of Tween-80, and a specific bioactivity of 7.35 × 10⁸ ± 0.56 × 10⁸ IU mg⁻¹ was obtained. These results should be applicable to other low-stability recombinant proteins expressed in P. pastoris.     

Studies on water transport through the sweet cherry fruit surface: characterizing conductance of the cuticular membrane using pericarp segments

Water conductance of the cuticular membrane (CM) of mature sweet cherry fruit (Prunus avium L. cv. Sam) was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit. Segments consisted of epidermis, hypodermis and several cell layers of the mesocarp. Segments were mounted in stainless-steel diffusion cells with the mesocarp surface in contact with water, while the outer cuticular surface was exposed to dry silica (22 ± 1 °C). Conductance was calculated by dividing the amount of water transpired per unit area and time by the difference in water vapour concentration across the segment. Conductance values had a log normal distribution with a median of 1.15 × 10⁻⁴ m s⁻¹ (n=357). Transpiration increased linearly with time. Conductance remained constant and was not affected by metabolic inhibitors (1 mM NaN₃ or 0.1 mM carbonylcyanide m-chlorophenylhydrazone) or thickness of segments (range 0.8–2.8 mm). Storing fruit (up to 42 d, 1 °C) used as a source of segments had no consistent effect on conductance. Conductance of the CM increased from cheek (1.16 ± 0.10 × 10⁻⁴ m s⁻¹) to ventral suture (1.32 ± 0.07 × 10⁻⁴ m s⁻¹) and to stylar end (2.53 ± 0.17 × 10⁻⁴ m s⁻¹). There was a positive relationship (r²=0.066**; n=108) between conductance and stomatal density. From this relationship the cuticular conductance of a hypothetical astomatous CM was estimated to be 0.97 ± 0.09 × 10⁻⁴ m s⁻¹. Removal of epicuticular wax by stripping with cellulose acetate or extracting epicuticular plus cuticular wax by dipping in CHCl₃/methanol increased conductance 3.6- and 48.6-fold, respectively. Water fluxes increased with increasing temperature (range 10–39 °C) and energies of activation, calculated for the temperature range from 10 to 30 °C, were 64.8 ± 5.8 and 22.2 ± 5.0 kJ mol⁻¹ for flux and vapour-concentration-based conductance, respectively. Received: 23 March 2000 / Accepted: 28 July 2000     

CO2 exchange of the endolithic lichen Verrucaria baldensis from karst habitats in northern Italy

CO₂ exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO₂ concentration. The species had low CO₂ exchange rates (maximum net photosynthesis: c. 0.45 μmol CO₂ m⁻² s⁻¹; maximum dark respiration: c. 0.3 μmol CO₂ m⁻² s⁻¹) and a very low light compensation point (7 μmol photons m⁻² s⁻¹ at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9–15°C. Photosynthetic activity was affected only after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant. Low photosynthetically active radiation (normally below 40 μmol photons m⁻² s⁻¹), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO₂ assimilation were often measured in the absence of condensation phenomena. Received: 22 September 1996 / Accepted: 26 April 1997     

Temperature dependence of habituation of the initial responses to cold-water immersion

The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water at 10°C, with smaller responses being observed following immersion in water at 15°C. Habituation of the initial responses can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10°C wearing swimming trunks. These immersions took place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15°C. Respiratory rate (f _R), inspiratory minute volume (V˙ _I) and heart rate (f _H) were measured continuously throughout each immersion. Following repeated immersions in water at 15°C, the f _R, V˙ _I and f _H responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths · min⁻¹, 50.5 l · min⁻¹ and 114 beats · min⁻¹ respectively, to 19.8 breaths · min⁻¹, 26.4 l · min⁻¹ and 98 beats · min⁻¹, respectively. In water at 10°C these responses were reduced (P < 0.01) from 47.3 breaths · min⁻¹, 67.6 l · min⁻¹ and 128 beats · min⁻¹ to 24.0 breaths · min⁻¹, 29.5 l · min⁻¹ and 109 beats · min⁻¹, respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions. The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation. Accepted: 6 February 1998     

Synergistic effect of high-light and low temperature on cell growth of the Δ12 fatty acid desaturase mutant in Synechococcus sp. PCC 7002

The effect of polyunsaturated fatty acids on photosynthesis and the growth of the marine cyanobacterium Synechococcus sp. PCC 7002 was examined using wild-type and Δ12 fatty acid desaturase mutant strains. Under a light intensity of 250 μmol m⁻² s⁻¹, wild-type cells could grow exponentially in a temperature range of 20–38 °C, but growth was non-exponential below 20 °C and ceased at 12 °C. The Δ12 desaturase mutant cells lacking polyunsaturated fatty acids had the same growth rate as wild-type cells in a temperature range of 25–38 °C but grew slowly at 22 °C, and no cell growth took place below 18 °C. Under a very high-light intensity of 2.5 mmol m⁻² s⁻¹, wild-type cells could grow exponentially in a temperature range of 30–38 °C, although the high-light grown cells became chlorotic because of nitrogen limitation. The temperature sensitive phenotype in the Δ12 desaturase mutant was enhanced in cells grown under high-light illumination; the mutant cells could grow at 38 °C, but were killed at 30 °C. The decrease of oxygen evolution and nitrate consumption by whole cells as a function of temperature was similar in both wild type and the Δ12 desaturase mutant. No differences were observed in either light-induced damage of oxygen evolution or recovery from this damage. No inactivation of oxygen evolution took place at 22 °C under the normal light intensity of 250 μmol m⁻² s⁻¹. These results suggest that growth of the Δ12 desaturase mutant at low temperature is not directly limited by the inactivation of photosynthesis, and raise new questions about the functions of polyunsaturated membrane lipids on low temperature acclimation in cyanobacteria. This revised version was published online in June 2006 with corrections to the Cover Date.     

Plasma arginine vasotocin and angiotensin II responses to body temperature elevation in the Pekin duck

The relationship between body temperature (T _b) and the plasma concentrations of arginine vasotocin (AVT) and angiotensin II (AII) was examined in conscious, adult Pekin ducks. Exposure of birds to an ambient temperature of 40 °C for 3 h increased T _b by about 1.5 °C and increased breathing rate five-fold. Plasma osmolality was elevated from the normothermic value of 294.9 ± 1.4 mosmol kg⁻¹ by about 8 mosmol kg⁻¹ Circulating AVT levels increased by about 2 pg ml⁻¹ from a basal concentration of 4.98 ± 0.15 pg ml⁻¹, a rise which could be accounted for by the change in osmotic status. Plasma AII concentrations were unchanged from the pre-heat exposure value of 31.8 ± 3.4 pg ml⁻¹. Time control birds, exposed only to an ambient temperature of 22 °C demonstrated no significant changes in any of the measured variables. The results suggest that an increased T _b has no direct effect on the circulating concentrations of AVT or AII in ducks. Accepted: 2 June 1997     

A neutral carrier-based liquid membrane microelectrode for divalent putrescine cations

A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described that shows the dependence of EMF on the activity of divalent putrescine cations a _Put, with the linear slope s _Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10⁻⁴–10⁻¹ M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK ^Pot _{Put j} (mean ± SD, N) are obtained by the separate solution method for the ions K⁺ (1.0 ± 0.4, 10), Na⁺ (−1.2 ± 0.4, 8), Ca²⁺ (−2.3 ± 0.5, 10) and Mg²⁺ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine cations in the range 5 × 10⁻⁴ to 10⁻¹ M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine the total concentration of the derivatives of free and bound putrescine. Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999     

Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures

Temperature requirements for growth, photosynthesis and dark respiration were determined for five Antarctic red algal species. After acclimation, the stenothermal species Gigartina skottsbergii and Ballia callitricha grew at 0 or up to 5 °C, respectively; the eurythermal species Kallymenia antarctica, Gymnogongrus antarcticus and Phyllophora ahnfeltioides grew up to 10 °C. The temperature optima of photosynthesis were between 10 and 15 °C in the stenothermal species and between 15 and 25 °C in the eurythermal species, irrespective of the growth temperature. This shows that the temperature optima for photosynthesis are located well below the optima from species of other biogeographical regions, even from the Arctic. Respiratory rates rose with increasing temperatures. In contrast to photosynthesis, no temperature optimum was evident between 0 and 25 °C. Partial acclimation of photosynthetic capacity to growth temperature was found in two species. B. callitricha and Gymnogongrus antarcticus acclimate to 0 °C, and 5 and 0 °C, respectively. But acclimation did in no case lead to an overall shift in the temperature optimum of photosynthesis. B. callitricha and Gymnogongrus antarcticus showed acclimation of respiration to 5 °C, and P. ahnfeltioides to 5 and 10 °C, resulting in a temperature independence of respiration when measured at growth temperature. With respect to the acclimation potential of the species, no distinction can be made between the stenothermal versus the eurythermal group. (Net)photosynthetic capacity:respiration (P:R) ratios showed in all species highest values at 0 °C and decreased continuously to values lower than 1.0 at 25 °C. In turn, the low P:R ratios at higher temperatures are assumed to determine the upper temperature growth limit of the studied species. Estimated daily carbon balance reached values between 4.1 and 30.7 mg C g⁻¹ FW day⁻¹ at 0 °C, 16:8 h light/dark cycle, 12–40 μmol m⁻² s⁻¹. Received: 4 November 1999 / Accepted: 7 March 2000     

Comparative metabolism, thermoregulation and morphology in two populations of vlei rats (Otomys irroratus)

The Hogsback (32°33S 26°57E) and Alice (32°47S 26°50E), Eastern Cape, South Africa, are separated by only 24 km but by 1000 m in altitude and fall into different climatic regions. Thermal responses (energy expenditure and body temperature) to ambient temperature were measured in a population of vlei rats (Otomys irroratus) from each of the two localities. We predicted that animals from the colder Hogsback would show differences in their thermal physiology and morphology consistent with better cold-resistance. Basal metabolic rates of the Hogsback population were slightly, but not significantly, higher than the Alice population (23.9 J g⁻¹ h⁻¹ vs 22.3 J g⁻¹ h⁻¹), but the slope of the regression between energy expenditure and ambient temperature below the thermal neutral zone was significantly lower (−1.28 vs −1.60). Body temperature, although quite variable in both populations, was not significantly influenced by ambient temperature in the Hogsback population, whereas that of Alice animals was. Fur length was longer and relative size of the ears and tail was smaller in the Hogsback population, which probably accounted for the slightly lower minimum thermal conductance (1.79 J g⁻¹ h⁻¹ °C⁻¹ vs 1.91 J g⁻¹ h⁻¹ °C⁻¹) in the Hogsback population. Vlei rats from the two sites also have different karyotypes that correlate with climate but there is insufficient evidence at present to suggest that the different karyotypes and the physiological parameters measured are adaptive. Accepted: 15 October 1998     

Enumeration of bacteria from a Trichodesmium spp. bloom of the Eastern Arabian Sea: elucidation of their possible role in biogeochemistry

The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E) coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 10⁶ trichomes L⁻¹ was recorded. Total bacterial counts (TBC) varied between 94.09 × 10⁸ cells L⁻¹ in the bloom to 1.34 × 10⁸ cells L⁻¹ in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m⁻¹ (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m⁻¹ in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship of TBC with Chlorophyll a (R ² = 0.65, p < 0.01) and CDOM concentrations (R ² = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid palythene (λ _max = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea.     

Palm oil mill effluent (POME) cultured marine microalgae as supplementary diet for rotifer culture

Malaysia is the world’s leading producer of palm oil products that contribute US$ 7.5 billion in export revenues. Like any other agro-based industries, it generates waste that could be utilized as a source of organic nutrients for microalgae culture. Present investigation delves upon Isochrysis sp. culture in POME modified medium and its utilization as a supplement to Nanochloropsis sp. in rotifer cultures. The culture conditions were optimized using a 1 L photobioreactor (Temp: 23°C, illumination: 180 ∼ 200 μmol photons m⁻²s⁻¹, n = 6) and scaled up to 10 L outdoor system (Temp: 26–29°C, illumination: 50 ∼ 180 μmol photons m⁻²s⁻¹, n = 3). Algal growth rate in photobioreactor (μ = 0.0363 h⁻¹) was 55% higher compared to outdoor culture (μ = 0.0163 h⁻¹), but biomass production was 1.3 times higher in outdoor culture (Outdoor = 91.7 mg m⁻²d⁻¹; Photobioreactor = 69 mg m⁻²d⁻¹). Outdoor culture produced 18% higher lipid; while total fatty acids (FA) was not significantly affected by the change in culture systems as both cultures yield almost similar concentrations of fatty acids per gram of sample (photobioreactor = 119.17 mg g⁻¹; outdoor culture = 104.50 mg g⁻¹); however, outdoor cultured Isochrysis sp. had 26% more polyunsaturated fatty acids (PUFAs). Rotifers cultured in Isochrysis sp./ Nanochloropsis sp. (1:1, v/v) mixture gave similar growth rate as 100% Nanochoropsis sp. culture (μ = 0.40 d⁻¹), but had 45% higher counts of rotifers with eggs (t = 7, maximum). The Isochrysis sp. culture successfully lowered the nitrate (46%) and orthophosphate (83%) during outdoor culture.