Physiological studies on Biomphalaria alexandrina and Bulinus truncatus,the snail vectors of Schistosommiasis

Summary The Warburg's manometric technique was used to measure the rate of oxygen consumption of the second generation of laboratory-reared snails, Biomphalaria alexandrina and Bulinus truncatus at two temperatures of 25° and 30°C. The individual weight of the experimental snails ranged between 40 and 78 mg for B. alexandrina, between 60 and 90 mg for B. truncatus.At 25°C, the uninfected snails B. alexandrina consumed oxygen at an average rate of 0.096 ± 0.020 ml/g wet wt/hr. The rate of oxygen consumption increased to an average of 0.147 ± 0.008 ml/g wet wt/hr for uninfected snails maintained at 30°C (about 53 per cent increase). The average RW value for uninfected snails maintained at 25°C was 0.80.The snail Bulinus truncatus showed higher oxygen requirements than the snail Biomphalaria alexandrina. At 25°C, it consumed oxygen at an average rate of 0.124 ± 0.016 ml/g wet wt/hr. At 30°C, the rate of oxygen consumption reached a value of 0.220 + 0.006 ml/g wet wt/hr. The average RQ for Bulinus truncatus maintained at 25°C was 0.87.The rate of oxygen consumption of the schistosome — infected Biomphalaria alexandrina snails, maintained at 25°C decreased to an average rate of 0.059 ± 0.010 ml/g wet wt/hr, (an average of 39 per cent decrease). The respiratory quotient (RQ) also decreased to an average value of 0.58. Further research is suggested to clarify the metabolism of both schistosome-infected and uninfected snails.Read at the Ist African Symposium on Bilharziasis, Cairo Egypt, U.A.R., February, 1969.From the Laboratory of Bilharziasis Research, National Research Centre, Dokki, Egypt, U.A.R.     

Measurements of oxygen production rate in flowing Spirulina suspension

Summary The oxygen production rates for a cyanobacterial suspension flowing in straight and coiled tubes were measured to find a way of achieving higher efficiency of light utilization by means of convective mixing. The photosynthetic flow chambers were made of glass tubes and illumination was by fluorescent light. The cyanobacterium used was Spirulina platensis, which has a high growth rate. The oxygen production rate for fluid flow in straight and coiled tubes increase with the increase in Reynolds number. The maximum oxygen production rate was achieved at 30°C for both tube reactors, but the oxygen production rate was higher for the coiled tube unit than the straight tube unit at 30°C. Thus the convective mixing generated in the coiled tube reactor contributed to an increased in light utilization, which played an important part in improving the oxygen production rate. Offprint requests to: K. Tanishita     

Respiratory quotient and ammonia quotient in Tilapia mossambica (Peters) with special reference to hypoxia and recovery

At oxygen concentrations below air saturation, R.Q. and A.Q. values of Tilapia mossambica increase with decrease in ambient oxygen at 30 and 35°C, indicating an increase in anaerobic metabolism and protein utilization. The recovery metabolism indicates that T. mossambica accumulates an oxygen debt at 30°C, which was not obvious at 35°C. The post-hypoxic oxygen consumption at 30°C is quite pronounced and the fish repays almost wholly the oxygen debt accumulated. At 30°C, R.Q. and A.Q. reach prehypoxic level immediately after exposure to high oxygenated water. In contrast to this, during recovery the first high R.Q. which is higher than unity and subsequent low R.Qs., almost as low as 0.5, suggest respectively that, anaerobic energy utilization persists and carbon dioxide is retained. The differences in the recovery metabolism of T. mossambica at the two temperatures may be due to changes in metabolism and pathways due to temperature. The recovery metabolism of T. mossambica suggests that energy derived anaerobically could proceed through other pathways than the conventional glycolytic way. The decrease in random activity during the hypoxic phase at 30 and 35°C may have a special significance for survival.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.     

Regulation of exoprotease production by temperature and oxygen in Vibrio alginolyticus

The production of an extracellular collagenase and an alkaline protease by Vibrio alginolyticus during stationary phase was inhibited by a temperature shift from 30 to 37°C and by a lack of oxygen. The stability of the exoproteases was unaffected by incubation at 37°C and aeration. The optimum growth temperature for the V. alginolyticus strain was 33.5°C Aeration enhanced the rate of growth of exponential phase cells. Temperature and oxygen did not affect the growth of stationary phase cells when the exoproteases were being produced. Macromolecular synthesis in stationary phase cells was not affected by temperature. There was no rapid release of the exoproteases after temperature shift down and chloramphenicol inhibited the production of the enzymes when added at time of temperature shift down from 37 to 30°C. The regulation of exoprotease production by temperature and oxygen was specific and has implications regarding the ecology of V. alginolyticus. Cerulenin, quinacrine and O-phenanthroline inhibited the production of the exoproteases.     

Use of chitin for controlling plant-parasitic nematodes

Cabbage plants were grown in soil amended with Clandosan (CLA) prepared from crustacean chitin (0.3% w/w). The plants were maintained in constant temperature tanks set to 15° or 30°C, in soils naturally infested with cyst nematodeHeterodera schachtii, or inoculated with the root-knot nematode,Meloidogyne javanica, respectively. At 30°C, after the first month following inoculation, CLA caused an increase in top fresh weight of plants but no reduction in nematode—induced root galling was recorded. However, when fresh plants were planted, CLA induced a large reduction in gall formation and caused an increase in top fresh weight of nematode-inoculated plants. At 15°C, CLA significantly affected the plants only after 60 days: an increase in top fresh weight and a reduction in the number of eggs per cyst were recorded. Ammonium was not detected in soil after 30 days, at 30°C, whereas at 15°C, CLA-treated soil contained twice as much ammonium as non-treated soil. After 60 days, ammonium was not detected at all. After 30 days nitrate concentrations in soil attained higher values at 30°C than at 15°C, whereas after 60 days high levels were detected only at 15°C. At 30°C, CLA induced an increase in the number of fungi, chitinolytic bacteria, and total amount of bacteria; at 15°C, such an increase was detected only with the chitinolytic microorganisms.Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel No. 2196-E, 1987 series.     

Growth and hyoscyamine production of ‘hairy root’ cultures of Datura stramonium in a modified stirred tank reactor

Summary The growth and hyoscyamine production of transformed roots of Datura stramonium have been examined in a modified 14-1 stirred tank reactor in both batch and continuous fermentations on media containing half or full strength Gamborg's B5 salts and at three different temperatures. Under a range of conditions, roots grown on half strength B5 salts with 3% w/v sucrose had a higher dry matter content (up to 8.3% w/w) and a higher hyoscyamine content (up to 0.52 mg·g^–1 wet weight) than roots grown on full strength B5 salts with the same level of sucrose (up to 4.6% w/w dry matter and up to 0.33 mg hyoscyamine g^–1 wet weight). Growth at 30°C was initially faster than at either 25°C or 35°C and by day 12, the drained weight of roots in the fermentor at 30°C was about fourfold greater than at 25°C and twice that at 35°C. The ultimate hyoscyamine levels attained (approximately 0.5 mg·g^–1 wet weight) were similar at both 25°C and 30°C but some 40% lower at 35°C. Final packing densities of 70% w/v were achieved for roots after 37 days growth at 25°C and the highest production rate of 8.2 mg hyoscyamine l^–1 per day was obtained for roots grown at 30°C. In continuous fermentation at 25°C, the release of hyoscyamine into the culture medium was low (less than 0.5% w/w of the total) but was up to sevenfold higher in fermentors operated at 30°C or 35°C. Offprint requests to: M. G. Hilton     

Respiratory energy losses in the protozoan predator Didinium nasutum Müller (Ciliophora)

Summary Respiration in Didinium nasutum, an active protozoan predator, was investigated in relation to cell weight at 10, 15, and 20° C by means of cartesian diver microrespirometry. Oxygen uptake increased progressively over the 10–20° C temperature range; a table of Q ₁₀ related to weight is presented. Regression coefficients of log weight versus log oxygen uptake (b) were 0.96 at 10° C, 0.98 at 15° C and 1.00 at 20° C. D. nasutum was shown to expend very much higher levels of respiratory energy than a mainly sedentary carnivorous ciliate of comparable weight.     

Respiratory metabolism of Cyclops bicuspidatus (sensu stricta) (Claus) (Copepoda: Cyclopoida) from Esthwaite Water,Cumbria

Summary The respiration rate of all stages of Cyclops bicuspidatus (s. str.) (Claus), a benthic copepod, from Esthwaite Water in the English Lake District, was determined at a range of field temperatures, 4° C–12° C, using cartesian diver microrespirometry. The population of C. bicuspidatus in Esthwaite Water was found to be adapted to low temperatures, with an optimum rate of metabolism at 8° C. Weight varied with temperature, in general the largest weights occurred at the lower temperatures. Adult males had higher rates of respiration than adult females, which were on average twice the size of males. Gravid and non-gravid females had similar levels of metabolism. Regression coefficients (b), derived from regressions of log oxygen consumption against log dry weight were low, ranging between 0.25–0.51 according to temperature.     

Aerial and aquatic oxygen uptake by freely-diving snapping turtles (Chelydra serpentina)

Summary Aerial oxygen consumption of unrestrained, freely-diving warm-and cold-acclimated snapping turtles, Chelydra serpentina, was measured at 10, 20, and 30°C. Also, simultaneous determinations of aerial and aquatic oxygen uptake by voluntarilydiving animals were made at 4 and 20°C. The standard rates of aerial oxygen consumption are equivalent in cold-and warm-acclimated animals in water and in cold-acclimated ones in air; these rates are all lower than those of warm-acclimated animals in air. Thus either cold acclimation or voluntary submergence reduces the standard metabolic rate of snapping turtles but the effects are not additive. Aquatic oxygen uptake during voluntary submergence is more important at low than at moderate temperatures and probably contributes significantly to gas exchange in these animals as they overwinter beneath the ice of ponds and streams.     

The effects of temperature on the respiration and production of the freshwater nematode Anonchus sp.

Summary Growth and respiration were measured in a species of Anonchus (Nematoda: Plectidae) at 5°C, 10°C, 15°C, 20°C and 25°C. At 5°C no growth was measurable but the organisms remained active. Maximum production occurred at 15°C, but the highest rate of growth occurred at 20°C. Thus, adult size attained is dependent on the temperature of growth. Respiratory energy losses derived from Cartesian diver microrespirometry, increased with temperature up to 25°C. Regression coefficients (b values) derived from a log log linear regression of weight against oxygen consumption varied between 0.574–1.793, the lowest value being attained at 5°C, the highest at 20°C. Based on Q₁₀, production and respiratory energy losses the optimum temperatures for Anonchus appears to lie between 10°C–15°C.     

Bionomics and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum, at constant temperatures

Development, survival, reproduction and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) at constant temperatures of 10, 13, 15, 20, 25, 30 and 32°C are reported. The developmental times of all life stages were inversely related to temperature ranging from 10 to 30°C. Span of total development (time from birth to adulthood) decreased from 57.8 days at 10°C to 11.7 days at 30°C and increased to 16.8 days at 32°C. A good linear model fit (R²>0.96) between developmental rate and temperature in the range 10–25°C was observed for all life stages. The lower developmental threshold was estimated at 5.8°C for instar I, 4.8°C for instar II, 4.9° for instar III and 4.4°C for instar IV. The lower temperature threshold for total development was estimated at 5.2°C. The upper developmental limit was found to be 32°C. Mean degree-day accumulations required for completion of instars I, II, III, IV and total development were: 125.6, 51.0, 47.7, 50.7 and 267.6, respectively. Fecundity, larviposition period and adult longevity were reduced with increasing temperature. Net reproductive rate was greatest at 15°C whereas intrinsic rate of increase peaked at 25°C. Optimal performance, as measured by fecundity, survival and intrinsic rate of increase, ocurred in the range 13–25°C.     

Oxygen consumption rates of adults and chicks during brooding in king quail (Coturnix chinensis)

Oxygen consumption rates were measured in chicks (0–7 days of age), and in non-brooding and brooding adults. Brooded chicks maintained a constant oxygen consumption rate at a chamber ambient temperature of 10–35°C (0–5 days of age: 2.95ml O₂·g^-1·h^-1 and 6–17 days of age: 5.80 ml O₂·g^-1·h^-1) while unbrooded chicks increased oxygen consumption rate at ambient temperature below 30°C to double the brooded oxygen consumption rate at 25 and 15°C for chicks < 5 days of age and>5 days of age, respectively. The massspecific oxygen consumption rate of breeding male and females (non-brooding) were significantly elevated within the thermoneutral zone thermal neutral zone (28–35°C) in comparison to non-breeding adults. Below the thermal neutral zone, oxygen consumption rate was not significantly different. The elevation in oxygen consumption rate of breeding quail was not correlated with the presence of broodpatches, which developed only in females, but is a seasonal adjustment in metabolism. Male and females that actively brooded one to five chicks had significantly higher oxygen consumption rate than non-brooding quail at ambient temperature below 30°C. Brooding oxygen consumption rate was constant during day and night, indicating a temporary suppression of the circadian rhythm of metabolism. Brooding oxygen consumption rate increased significantly with brood number, but neither adult body mass nor adult sex were significant factors in the relationship between brooding oxygen consumption rate and ambient temperature. The proportion of daylight hours that chicks were brooded by parents was negatively correlated with ambient temperature. After chicks were 5 days old brooding time was reduced but brooding oxygen consumption rate was unchanged. Heat from the brooding parent appeared to originate mainly from the apteria under the wings and legs rather than the broodpatch. The parental heat contribution to chick temperature regulation below the chicks' thermal neutral zone is achieved by increasing parental thermal conductance by a feedback control similar to that suggested for the control of egg temperature via the brood-patch. It is concluded that the brooding period is an energetic burden to parent quail, and the magnitude of the cost increases directly with brood number and inversely with ambient temperature during this period. The oxygen consumption rate of brooding parents was 5.80–6.90 ml O₂·g^-1·h^-1 (ambient temperature 10–15°C) at night and up to 5.10 ml O₂·g^-1·h^-1 (ambient temperature 18°C) during the day, which are 100 and 40% higher than non-brooding birds, respectively.Abbreviations bm body mass - SMR standard metabolic rate - T _a ambient temperature - T _b body temperature - I/O₂ oxygen consumption rate - C _wet wet thermal conductance - TNZ thermal neutral zone - ANOVA analysis of variance - ANCOVA analysis of covariance     

The respiration of sclerotia of Sclerotium rolfsii

Summary The respiration of sclerotia ofS. rolfsii was investigated using the Warburg constant-volume respirometer to measure oxygen uptake. The effects of age of sclerotia, pH, and temperature were studied. Sclerotia produced on prune agar were ideal for respirometric studies, being uniformly round and of approximately equal size. On a dry weight basis, the respiration rates of sclerotia were considerably less than those of vegetative mycelium. Sclerotia showed a decrease in respiration with increasing age. This was accompanied by morphological changes in the outer hyphal rind of the sclerotium during maturation. The respiration rate of sclerotia was approximately the same at 30° and 40° C, but was significantly lower at 45° C. Respiration of sclerotia was not markedly affected by normally encountered hydrogen-ion concentrations. However, a pH of 8.0 markedly repressed oxygen uptake. Sclerotia produced in rye grain cultures were chemically analyzed. The nitrogen content was 4.7 %, the petroleum-ether-soluble lipid content was 0.7 %, and the crude glycogen content was 14.2 % of the oven dry weight of the sclerotia.Contribution No. 345 from The Department of Botany. Portion of a thesis presented by the senior author in partial fullfillment for the M.S. degree.     

Temperature and the biology and predation of Ilione albiseta (Diptera: Sciomyzidae) — Potential biological control agent of liver fluke

The effect of temperature on predation by Ilione albiseta (Diptera: Sciomyzidae) on Lymnaea peregra was investigated at 14°, 17°, 20°, 23° and 26°C. The mean dry weight of snail tissue (Lymnaea peregra) attacked and consumed per day by first and second instar I. albiseta larvae was highest at 20°C while for third instar and total larval duration period it was greatest at 23°C. The mean number of snails killed per day during the third instar was also highest at 23°C. The total amount of snail tissue consumed by I. albiseta larvae increased significantly from first to second instar and from second to third instar at each constant temperature. Mean survival period of unfed first instar larvae decreased from 28.4 days at 14°C to 11 days at 26°C and the mean length of the second instar cephalopharyngeal skeleton decreased with increasing temperatures. As temperature increased the rate of consumption of oxygen (dissolved in water) by first and third instar larvae rose.     

Temperature effects on solute accumulation by Candida utilis

Summary A study was made of the effect of temperature on accumulation of glucosamine and 2-aminoisobutyrate by Candida utilis NCYC 321 grown at 30° C or 10° C. Exponential-phase cells contained greater proportions of C_16:1 and C_18:3 acids, and smaller proportions of C_13:1 and C_18:2 acids, when grown in a defined medium at 10° C compared with 30° C. Cells grown at 30° C or 10° C were able to accumulate extracellular (10 mM) glucosamine and 2-aminoisobutyrate against concentration gradients. 2-Aminoisobutyrate was not metabolised by the cells; glucosamine was accumulated probably as a mixture of glucosamine 1- and 6-phosphates. Rates of accumulation of glucosamine and 2-aminoisobutyrate by cells grown at 30° C or 10° C decreased markedly when the test temperature was decreased from 30° C to 15° C. The rate of accumulation of glucosamine by cells grown at 10° C was considerably lower at each of the test temperatures compared with the corresponding rates for cells grown at 30° C; the rate of accumulation of 2-aminoisobutyrate was much less affected by the temperature at which the cells were grown and then only when measured at temperatures below about 20° C. Apparent K _m values for accumulation of glucosamine by cells grown at 30° C or 10° C decreased considerably when the test temperature was lowered from 20° C to 15° C. The extent of the decrease in K _m value was approximately the same for cells grown at 30° C or 10° C. Apparent K _m values for accumulation of 2-aminoisobutyrate were hardly affected by test temperature. Apparent V _max values for accumulation of glucosamine or 2-aminoisobutyrate were much lower when measured at 15° C than at 30° C. When measured at 30° C, apparent V _max values for accumulation of either solute were slightly lower with cells grown at 10° C compared with cells grown at 30° C; when measured at 15° C, the values were slightly greater with cells grown at 10° C. Net accumulation of glucosamine, at 30° C or 20° C, by cells grown at 30° C or 10° C ceased after 4–6 h. Cells grown at either temperature continued to accumulate 2-aminoisobutyrate at 30° C or 20° C for at least 12 h. The rate of efflux of glucosamine by cells grown at 30° C was slower when measured at 20° C compared with 30° C. With cells grown at 10° C, the rate of efflux at 30° C was slower than with cells grown at 30° C; when measured at 20° C, the rates were about equal. The temperature at which the cells were grown did not affect the ability of d-glucose, d-mannose or d-ribose to compete with d-glucosamine, or with the ability of l-alanine to compete with 2-aminoisobutyrate, when tested at 30° C or 20° C. Cells grown 30° C or 10° C had very similar ATP contents. The results are discussed in relation to the effect of temperature on the rate of solute accumulation by micro-organisms.Abbreviation AIB 2-Aminoisobutyrate     

Respiration of Cytherissa lacustris (Ostracoda) at different temperatures and its tolerance towards temperature and oxygen concentration

Summary The ostracod species Cytherissa lacustris was investigated with respect to its temperature and oxygen tolerance limits. In laboratory experiments the tolerance limits were found to be much wider than expected from field data. Hatching of first instars was observed in cultures up to 20° C. The tolerance limit for oxygen concentrations was less than 1 mg O₂·l^-1 at 10° C and 20 h exposure. The distribution pattern of C. lacustris along a depth profile in lake Attersee showed a maximum density between 10 and 20 m depth coinciding with temperatures between 4 and 15°C throughout the year. The size dependence of respiration rates of well adapted C. lacustris is within the normal range of small metazoans. Its weight specific rates of oxygen uptake indicate an adaptation plateau in the range between 10 and 15°C. Possible reasons and advantages of such an adaptation for C. lacustris are discussed.     

Effect of rearing temperature and larval density on larval survival, age at pupation and adult size of Anopheles gambiae

The effects of temperature and larval density on survival of larvae, growth rate, age at pupation, and adult size (measured as wing length and dry weight) of laboratory-reared Anopheles gambiae (Diptera: Culicidae) were studied. Larvae were reared at three temperatures (24, 27 and 30°C) and three densities (0.5, 1 and 2 larvae/cm²). The effects of density and temperature strongly interacted to determine the mosquitoes' life-history parameters. Survival was highest at the intermediate temperature of 27°C. The differences between the temperatures increased with increasing density. At 30°C survival decreased as density increased, but at 27°C increasing density led to higher survival. Age at pupation increased as temperature decreased from 30°C to 24°C and as density decreased from 2 to 0.5 larvae/cm². Adult size also increased as temperature decreased, but showed a negative correlation with density only at 27°C. In contrast, at 24°C and 30°C a decrease in density led to a decrease in adult size. Growth rate showed a similar pattern. At 27°C growth rate decreased as density increased, but at other temperatures the opposite trend was observed.     

The predatory mite Hypoaspis miles: temperature dependent life table characteristics on a diet of sciarid larvae, Bradysia paupera and B. tritici

Life table characteristics of Hypoaspis miles Berlese (Acarina: Hypoaspidae) fed on a mixture of Bradysia paupera Tuomikoski (Diptera: Sciaridae) and B. tritici Coquillet larvae were investigated in laboratory experiments at 4 temperatures (15, 20, 25, 30 °C) for development time, juvenile mortality, sex ratio, preoviposition period, oviposition period, postoviposition period, age-specific fecundity, and adult longevity. Juvenile development time decreased with increasing temperature from 46 days at 15 °C to 10 days at 30 °C. The lower temperature threshold was 9.9 °C and development required 205 °D. Juvenile mortality decreased from 52% at 15 °C to 3% at 25 °C and then increased to 24% at 30 °C. Preoviposition period varied with temperature from 12 days at 15 °C to 3 days at 25 °C and then increased to about 4 days at 30 °C. Oviposition period decreased with increasing temperature from 58 days at 15 °C to 25 days at 30 °C. The mean number of eggs per female per day increased from 0.4 at 15 °C to 2.3 at 25 °C and decreased to 1.3 at 30 °C. Age-specific fecundity was described by a temperature dependent model from which the maximum daily fecundity rate could be estimated to be attained at 25.6 °C. Female longevity was significantly shorter than for males, and decreased from 90 days at 15 °C to 34 days at 30 °C. Sex ratio was female-biased at all 4 temperatures and increased with temperature up to 25 °C, decreasing at 30 °C. Estimates of net reproductive rate, intrinsic rate of increase, finite rate of increase, mean generation time and doubling time were obtained. The r _m -value increased with temperature from 0.031 day^-1 at 15 °C to 0.133 day^-1 at 25 °C, after which it decreased to 0.112 day^-1 at 30 °C. The study showed that H. miles can develop and reproduce at temperatures between 15 and 30 °C. H. miles and sciarids have approximately the same optimum temperature and thresholds for development and reproduction and H. miles can be used for biological control of sciarids within the temperature range where the pest occurs.     

Assimilation efficiencies of slugs on different food materials

Summary The relative assimilation efficiencies of two common British species of slug, Limax flavus (L.) and Arion hortensis (Fér.), were studied in the laboratory using a gravimetric method. Results are given for adult slugs feeding on carrot root and potato tuber at 5°, 10°, 15°, and 20° C, and for L. flavus juveniles of known age feeding on potato at 10° and 15° C. A few results are also provided for Agriolimax reticulatus (Müller) feeding on both potato and carrot at 15° C.High mean assimilation efficiencies of 76.94 and 76.87% were obtained for L. flavus feeding on carrot and potato respectively. The equivalent results for A. hortensis were 88.60 and 89.42%. For A. reticulatus at 15° C the figures were 76.1 and 71.9%. Ingestion rates and assimilation rates are given for the first two species at all temperatures. Assimilation efficiency was found to be independent of temperature for L. flavus but not for A. hortensis. Ingestion rate and assimilation rate were temperature dependent in all cases except for A. hortensis feeding on potato. A. hortensis was more efficient at consuming both carrot and potato per gram live weight. All species consumed more potato than carrot per gram live weight.Juvenile L. flavus were found to have higher assimilation efficiencies and ingestion rates than the adults per gram live weight.Linear regression equations were determined from the relationship between dry weight of food consumed, and dry weight of faeces produced from that food for L. flavus.It is concluded that food quality and age of slug may be the factors most strongly influencing assimilation efficiency in this group.     

Oxygen and temperature effects on acetaldehyde-induced catabolite inactivation in Pichia pastoris

Summary Exposure of methylotrophic yeasts to other carbon sources after growth on methanol results in catabolite inactivation. As a result, peroxisomes are rapidly degraded effectively disabling the metabolic pathway initiated by alcohol oxidase in favour of a more energetically favourable route. A model equation has been developed to describe the effect of temperature, dissolved oxygen concentration and acetaldehyde (catabolite) concentration on catabolite inactivation in Pichia pastoris. When pre-exposed to 4 g/l acetaldehyde at 30°C, the rate of conversion of ethanol to acetaldehyde decreased by 75%. Inactivation was reduced to 45% at 30°C by reducing the dissolved oxygen concentration. At high dissolved oxygen concentration, enzyme function was only inactivated by 20% if the temperature during the period of exposure to acetaldehyde was reduced to 5°C. The influence of acetaldehyde can be eliminated completely by operating at 5°C and low dissolved oxygen concentrations. Application of these findings to process design has enabled us to conduct preliminary reactions in laboratory-scale reactors that have yielded acetaldehyde concentrations greater than 3 M (130 g/l) in 4 h. Offsprint requests to: S. J. B. Duff