The metabolic and biochemical responses of tropical whitespotted bamboo shark Chiloscyllium plagiosum to alterations in environmental temperature

The capacity of tropical whitespotted bamboo sharks Chiloscyllium plagiosum to metabolically compensate, at both the whole‐animal and biochemical levels, to prolonged exposure to temperatures higher (30° C) and lower (20 and 15° C) than their native temperature (24·5° C) was examined. As expected, whitespotted bamboo shark oxygen consumption increased upon exposure to 30° C and decreased at 20 and 15° C. Initial changes in oxygen consumption were maintained even after months at the experimental temperature, indicating that whitespotted bamboo sharks did not compensate metabolically to the experimental temperatures. Maximal activities and thermal sensitivity of citrate synthase and lactate dehydrogenase from whitespotted bamboo shark white locomotor muscle were similar between control animals maintained at 24·5° C and those maintained at 15° C, indicating that cold‐exposed animals did not compensate at the biochemical level. Similarly, lactate dehydrogenase activity did not change following prolonged exposure to 30° C. White muscle from whitespotted bamboo sharks maintained at 30° C had significantly lower citrate synthase activity than did control animals. This result was surprising given the lack of metabolic compensation at the whole‐animal level. Overall, whole‐animal oxygen consumption measurements supported the hypothesis that animals from thermally stable environments lacked the capacity to metabolically compensate to altered temperatures. Enzymatic results, however, suggested that the metabolic potential of muscle could change following temperature acclimation even in the absence of metabolic compensation at the whole‐animal level.     

Laboratory studies of egg development and diapause in Isoperla obscura (Plecoptera) from a mountain stream in Norway

SUMMARY 1. A laboratory study of egg development of the stonefly Isoperla obscura (Zetterstedt) collected from the stream Flybekken (southern Norway, 61°25'N, 8°48'E, 1373 m a.s.l.) showed a short diapause followed by a prolonged period of postdiapause quiescence.
2. Diapause occurred over a wide range of temperatures (−20°C to +8°C), but 0–1°C was the most favourable for fast diapause development and successful hatching. Diapause development required temperatures below 12°C, but sub-zero diapause temperatures increased mortality during the postdiapause phase, as well as reducing hatching success.
3. The threshold for initiation of postdiapausal development was about 1–2°C. Development rate increased and variation in development time decreased at higher water temperatures. These may be important characteristics to ensure seasonal and geographical synchrony of development in individual populations. Low postdiapausal temperatures were unfavourable, despite a subsequent increase in water temperature. No response to postdiapausal photoperiod was detected.
4. The results agreed well with conditions noted in the natural environment, and with the abundance of this species at high altitudes and latitudes in Fennoscandia. Nevertheless, Isoperla obscura also occurs in streams in the maritime parts of western Norway. The results of the present study suggest that egg development in these populations will prove to be different.     

Temperature control of germination and its possible role in the survival of a non-dormant population of Avena fatua

Germination of freshly harvested seeds of a non-dormant (ND) line (Stonehouse 319) of wild oats ( Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo-inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo-dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub-optimal temperatures of 5 to 15°C. This thermo-dormancy would appear to be 'restrictive' in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo-inhibition and thermo-dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319.     

Developmental strategies of Koenigia islandica, a high-arctic annual plant

Seed germination, growth and flowering of the arctic-alpine annual Koenigia islandica were studied in controlled environment. Intact (unabraded) seeds germinated poorely at temperatures up to 18°C, with an optimum at 24°C (89% in 10 d). Scarified seeds germinated rapidly, and reached 100% germination in 3 d at 21°C, but no >40% germination occurred at 9 and 12°C, The seeds had no light requirement for germination, nor did fluctuating temperatures improve germination
Dry matter production was optimal at 12°C in both short day (SD) and long day (LD) conditions, but was markedly higher in LD than in SD at identical fluences at all temperatures except 21°C where the plants showed symptoms of severe heat stress. The temperature compensation point for net productivity was estimated to 24°C, and negative carbon balance at higher temperatures might be an important physiological mechanism limiting the distribution of K. islandica in Scandinavia.
Flowering was extremely rapid and independent of daylength, even in a high-arctic population from 79°N, In full summer daylight anthesis was reached 24 d after germination and seeds ripened after 36 d at 15°C, Days to anthesis varied little across the temperature range from 6 to 21°C, giving a linear decrease in the heat-sum requirement for the attainment of flowering with decreasing temperature.
It is concluded that conservative seed germination strategy, tininess and rapid development, low temperature optima for growth and reproduction, and daylength indifference of flowering are important adaptations for success of an annual plant in high-arctic and high-alpine environments, Daylength neutrality has facilitated the wide-latitudinal distribution of K. islandica. including the penetration of the species to the southern hemisphere.     

Elevated temperature reduces the respiratory scope of coral reef fishes

The capacity for marine fishes to perform aerobically (aerobic scope) is predicted to control their thermal tolerance and, thus, the impact that rapid climate change will have on their populations. We tested the effect of increased water temperatures on the resting and maximum rates of oxygen consumption in five common coral reef fishes at Lizard Island on the northern Great Barrier Reef, Australia. All species exhibited a decline in aerobic capacity at elevated water temperatures (31, 32 or 33 °C) compared with controls (29 °C); however, the response was much stronger in two cardinalfishes, Ostorhinchus cyanosoma and O. doederleini , compared with three damselfishes, Dascyllus anuarus, Chromis atripectoralis and Acanthochromis polyacanthus . Aerobic scope of the two cardinalfishes was reduced by nearly half at 31 °C compared with 29 °C, and virtually all capacity for additional oxygen uptake was exhausted by 33 °C. In contrast, the three damselfishes retained over half their aerobic scope at 33 °C. Such differences in thermal tolerance between species, and possibly families, suggest that the community structure of reef fish assemblages might change significantly as ocean temperatures increase. Populations of thermally tolerant species are likely to persist at higher temperatures, but populations of thermally sensitive species could decline on low-latitude reefs if individual performance falls below levels needed to sustain viable populations.     

The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides

Abstract. Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14–20 m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1°–30.0°C in mean increments of 0.4±0.1°C (±SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5°C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4°–27.7°C, and were smallest and had the lowest population densities at 25.8°C and 28.8°C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1°C and 30°C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatio-temporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase.     

Flowering requirements of Scandinavian Festuca pratensis

Flowering requirements of three Scandinavian cultivars of Festuca pratensis Huds, have been studied in controlled environments. At 3 and 6°C, primary induction was independent of photoperiod, while short days (8 h) were more effective than long days (24 h) at higher temperatures. The critical temperature for induction was about 15°C in short days and about 12°C in long days. Saturation of induction required 18–20 weeks of exposure to optimal conditions. At temperatures below 12°C both induction and initiation of inflorescence primordia took place in long days, while a transition to long days was required for inflorescence initiation after primary induction in short days. A minimum of 8 long-day cycles were required for flowering of plants primary induced in short days and saturation of flowering required more than 16 cycles. The critical photoperiod for secondary induction was about 13 h. High temperature (21°C) had some devernalization effect in primary induced plants, suppressing flowering compared with 15°C.     

The effect of environmental temperature on the production of ultrasounds by isolated non-handled albino mouse pups

Albino mouse pups develop homoiothermy during the first 19 days of their life and show three distinct stages during this period. From day 1 to day 6 they are almost completely poikilothermic at low ambient temperatures; from day 7 to day 14 or 15 is a transitional period during which they develop homoiothermy at medium temperatures (e.g. 22°C); from day 15 or 16 to day 19 or 20 is the final stage when homoiothermy at very low ambient temperatures is developed. These changes are very closely correlated with changes in the ultrasounds produced by isolated pups within the 19 day period. Thus their acoustic response to cold is weak from day 1 to day 5 or 6 and very strong from day 6 or 7 to day 12 or 13, on exposure even to medium temperatures. From day 14 onwards the pups progressively stop producing ultrasounds depending on the ambient temperatures, and there is complete cessation of calling after day 19 or 20 even on exposure to temperatures as low as 2°C. In general, decreasing the ambient temperatures increases the rate and intensity of ultrasounds produced but very low ambient temperatures have an inhibiting effect and at 2–3°C breathing and calling cease completely after a time which varies with age of the pups.     

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD-induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high-latitude population from 70°N ('Alta') had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high-latitude population.     

Intra- and inter-specific variations in egg survival and brood development time for Austrian populations of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda)

SUMMARY. 1. Egg survival (ES, percentage of eggs hatched in vitro ), reproductive success (RS, percentage of live young released from the brood pouch) and brood development lime ( d , days) in four populations of Gammarus fossarum and two populations of Gammarus roeseli were studied, in the laboratory at water temperatures of 2.0–26.1°C. Intraspecific differences between populations were not significant, but interspecific differences were found between the two species.
2. In natural stream populations, the reproductive period of G. fossarum lasted from December to September, that of G. roeseli from March to September.
3. In the experimental temperature range 2–26°C, 73% of the total number (771) of G. fossarum females and 69% of 469 G. roeseli females were ovigerous. Of these, 45% of G. fossarum and 43% of G. roeseli females successfully released live young from their brood pouches.
4. For G. fossarum , the optimum temperatures were 11.4°C for ES, where 76% of the eggs hatched, and 11.8°C for RS, where 77% of the females released live young from their brood pouches. For G. roseli , the optimum temperatures were 13.5°C for ES (51% hatched) and 14.0°C for RS (76% released). Over 50% of eggs hatched at temperatures of 3.6–19.2°C in G. fossarum and at 1 1.9–15.1°C in G. roeseli . Development time increased from 12 days at 21.9°C to 251 days at 2.0°C in G. fossarum , and from 10 days at 24.1°C to 212 days at 4.1°C in G. roeseli .
5. interspecific differences between the effects of water temperature on ES, RS and d are used to explain the different distributional patterns of G. fossarum and G. roeseli in central European running water systems. assuming that other physico-chemical variables are suitable for both species.     

Allocation of carbon to growth, storage and respiration in the vegetative barley plant

Abstract. It is proposed that the growing plant can be divided into three compartments with reference to carbon: soluble, storage and structural. Experiments carried out at 10, 15, 20 and 30°C in the light followed changes in size of these compartments in barley plants 10–24 days old. The redistribution of ^I4C photo-assimilated by 10 day old plants was monitored simultaneously. The soluble and storage compartments are a higher percentage of plant weight at lower temperatures, and are turned over rapidly at all temperatures; they form the source of respired ¹⁴C. About 30% of the ¹⁴C fixed enters structural material; in the first 24 h after labelling, for each unit of ¹⁴C entering the structural compartment, between 0–9 (at 15°C) and 3.2 (at 30°C) units of ¹⁴C are lost by respiration. At 15°C in the dark, respiratory loss of ¹⁴C is initially from soluble and storage compartments; thereafter respiration of ^I4C occurs at the expense of structural material.     

Adaptative significance of a temperature induced diapause in a cosmopolitan parasitoid of Drosophila

Abstract. 1. We have previously demonstrated pre-pupal diapause in a tropical population of Leptopilima boulardi Barbotin, Carton and Kelner-Pillault (Cynipidae, Hymenoptera), a larval parasitoid of Drosophila melanogaster Meigen. Prepupal diapause was induced by low temperature (17.5°C) but absent at 25°C; it was independent of photoperiod.
2. Four populations which originated from different latitudes (4°S to 44°N) exhibit the same response to temperature without any major genetic geographical variation.
3. In temperate areas, this diapause may permit a phenological and temporal coincidence between the parasitoid and its host whose larval growth is only possible for temperatures above 13°C.
4. The significance of the persistence of this diapause in tropical areas is discussed.     

Effects of temperature and photoperiod on vegetative growth of white clover (Trifolium repens) ecotypes

Effects of photoperiod and temperature on vegetative growth of seedling populations and clones of white clover ( Trifolium repens L.) originating from various latitudes (58°48'–69°54'N) and altitudes (up to 1100 m above sea level) were studied in a phytotron. Dry matter production, stolon elongation, petiole elongation and leaf lamina size were enhanced by long photoperiod. The requirement for long photoperiod increased with decreasing temperature. At 6°C the maximum growth was recorded under 24-h daylength. At 18°C already an increase in photoperiod from 12 to 15 h significantly enhanced growth, and maximum growth was obtained at 21-h photoperiod. The studied populations responded similarly to daylength, and the results did not indicate photoperiodic ecotypes in the material. The southernmost clones and populations generally had the highest dry matter production at all temperature treatments (6–18°C). Variation between clones within one location was, however, significant, and rapidly growing clones were found also in high-latitude locations. Dry matter production was poorly correlated with the morphological characters observed, but in some cases significant correlation with leaf lamina size was found.     

Prolonged and daily torpor in the feathertail glider, Acrobates pygmaeus (Marsupialia: Acrobatidae)

Deep and prolonged torpor in marsupials is only known from the pygmy possums, family Burramyidae. We investigated the pattern of torpor in the feathertail glider Acrobates pygmaeus (Acrobatidae) to determine whether members of other marsupial families also possess the ability of remaining torpid for several days with body temperatures (T_b) approaching 0°C. At high air temperatures (T_a) of 15 and 20°C, A. pygmaeus usually exhibited daily torpor. Torpor bouts at T_a 12°C usually lasted for about 2˙5 days and at T_a 8°C up to 5˙5 days. The metabolic rate during torpor was reduced to about 1% of that in normothermic, resting individuals. The T_b during torpor was regulated at about 2°C when T_a fell below about 0˙8 °C. Arousal from torpor was rapid and the mean fastest rewarming rate was 0˙88°C/min. While A. pygmaeus exhibited deep and prolonged torpor, its pattern differed somewhat from deep hibernation. Acrobates pygmaeus did not show prehibernation fattening and a subsequent prolonged hibernation period and it appears that prolonged torpor is used only in emergency situations.     

Adaptation to sub- and supraoptimal temperatures of inbred maize lines differing in origin with regard to seedling development and photosynthetic traits

Six inbred lines of maize ( Zea mays L.) from cool temperate regions (C) and from warm regions (W) were grown at 14, 22, 30 and 38°C up to the same physiological age, the full expansion of the third leaf. Generally, plants developed smaller shoot dry weights and leaf areas at extreme temperatures. The shoot:root ratio was lowest at 22°C and highest at 30°C. Most lines had a minimum for specific leaf dry weight at 30°C, but W lines had a second lower minimum at 14°C. Phosphofructokinase activity scarcely reacted to temperature between 22° and 38°C; at 14°C one C line and all W lines had rather low activities. Generally, the chlorophyll content increased steeply from 14 to 22°C and decreased somewhat from 30 to 38°C. In C lines the carotenoid level decreased from 14 to 38°C. No uniform temperature response was found for PEP carboxylase activity, but the highest activity was mostly attained at 38°C. RuBP carboxylase activity increased considerably from 14 to 22°C and remained comparatively constant at higher temperatures. The highest activity of NADP malate dehydrogenase was found at 22°C, with a decrease up to 38°C and with second lowest values at 14°C. C lines possessed larger leaf areas, shoot dry weights and higher shoot:root ratios than W lines at 14 and 22°C, and higher specific leaf dry weights over the whole temperature range. The genotypic pattern of shoot dry weight at 14°C corresponded reasonably well with that of phosphofructokinase activity. A better adaptation of C lines to suboptimal temperatures was mostly clearly indicated for photosynthetic traits which have a well proven relationship with the chloroplast membranes: chlorophyll, carotenoids and RuBP carboxylase. The least distinct effects of origin were observed at 38°C; a tendency prevailed for a better performance of C lines with regard to phosphofructokinase, carotenoids, RuBP carboxylase and NADP malate dehydrogenase.     

Embryogenesis of Dinocras cephalotes, Perla grandis and P. marginata (Plecoptera: Perlidae) in different temperature regimes

1. Temperature dependence of embryogenesis of the three perlid stoneflies Dinocras cephalots , Perla grandis and P. marginata was investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).
2. Dinocras cephalotes embryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient. Perla grandis eggs only developed between 9.9 and 18.4 °C. In P. marginata , successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.
3. Embryogenesis of D. cephalotes and P. grandis was significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.
4. D. cephalotes , hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed-moving floods.     

Embryogenesis of Dinocras cephalotes, Perla grandis and P. marginata (Plecoptera: Perlidae) in different temperature regimes

1. Temperature dependence of embryogenesis of the three perlid stoneflies Dinocras cephalots , Perla grandis and P. marginata was investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).
2. Dinocras cephalotes embryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient. Perla grandis eggs only developed between 9.9 and 18.4 °C. In P. marginata , successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.
3. Embryogenesis of D. cephalotes and P. grandis was significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.
4. D. cephalotes , hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed-moving floods.     

Isolation and preliminary characterisation of twenty-five temperature-sensitive mutants of mouse cytomegalovirus

Abstract To study the pathogenicity of mouse cytomegalovirus (MCMV) and to identify virulence determinants, we have isolated and phenotypically characterised 25 temperature-sensitive ( ts ) mutants. Six of these ( tsm 9, tsm 13, tsm 20, tsm 22, tsm 28 and tsm 30) failed to replicate in mice and were avirulent. Five mutants ( tsm 14, tsm 18, tsm 19, tsm 25 and tsm27 ) were to similar virulence to the parenthal wild-type ( wt ) virus, five ( tsm 7, tsm 15, tsm 24, tsm31 ) were 12–100 fold less virulent, five ( tsm 8, tsm 12, tsm 16, tsm 23 and tsm 29) were 150–1500 fold less virulent and four ( tsm 10, tsm 11, tsm 17 and tsm 21) were between 2,000 and 85,000 fold less virulent than wt . One mutant ( tsm 28) did not plaque or replicate at 39°C while 5 other mutants ( tsm 7, tsm 9, tsm 23, tsm 24 and tsm 27) also failed to plaque at 39°C but only failed to replicate or replicated poorly at 40°C. A further two mutants ( tsm 10 and tsm 13) were able to plaque and replicate at 39°C but not 40°C. Six other mutants ( tsm 14, tsm 15, tsm 16, tsm21 , tsm 22 and tsm 30) failed to form plaques at 40°C and were severely restricted in their replication at 40°C. The remaining 11 mutants exhibited varying degrees of restriction in ability to plaque and/or replicate at non-permissive temperatures. These 25 mutants, together with 6 isolated previously, comprise at least 24 complementation groups.     

Termination and reinduction of reproductive diapause by photo-period and temperature in males of the grasshopper, Oedipoda miniata

ABSTRACT. Previous publications have demonstrated that O.miniata adults exhibit an aestival reproductive diapause during the dry summer in Israel; females do not lay and males show only little mating behaviour. It was also reported previously that photoperiod and temperatures corresponding to autumn in Jerusalem terminate diapause and induce intense male mating behaviour, whereas continuous illumination and high temperatures maintain diapause. In the present study we used mating behaviour as an indicator for investigating the effects of several photoperiod—temperature combinations on reproductive diapause in O.miniata males. Mating behaviour was induced and diapause terminated under the following conditions: LD 10.5:13.5, T = 38-27°C (the temperatures during the photophase and scotophase, respectively); LD 12:12, T=38–27°C; LD 12:12, T=26–13°C; LD 14:10, T = 26–13°C. In contrast, diapause was maintained under LD 14:10, T = 38–27°C and under LL with high but variable temperatures. In further experiments males that were already sexually active, and which had been kept under LD 12:12, T = 38–27°C, were transferred to LL with high variable temperatures. Similarly, postdiapause males which had been kept under LD 14:10 and T=26–13°C were transferred to T = 38–27°C without changing the photoperiod. In both instances mating behaviour declined, then disappeared, thus reinduction of the diapause occurred under such conditions which previously were found to maintain diapause. O.miniata is therefore a 'short day' and/or 'low temperature' insect. This is the first report on complete control of photoperiod—temperature over aestival reproductive diapause and its reversibility in a male insect.     

Significance of temperature and preincubation temperature on survival of Listeriamonocytogenes at pH 4·8

Listeria monocytogenes is a food-borne pathogenic bacterium that can be found in softcheese. At the beginning of cheese ripening, the pH is about 4·85–4·90. The aimof this work was to study the influence of temperature, preincubation temperature (temperature atwhich the inoculum was cultivated) and initial bacterial concentration on the survival of L.monocytogenes (strain Scott A) at pH 4·8. It was demonstrated in an earlier study thatthese factors did influence growth kinetics. Survival studies of L. monocytogenes weredone in a laboratory broth simulating cheese composition. Four test temperatures (2, 6, 10 and14°C) and two preincubation temperatures were studied (30°C or the test temperature). Listeria monocytogenes (strain Scott A) was unable to grow at pH 4·8 under allconditions tested. The time for 10% survival was about 11 and 2 d, at 2°C with preincubationat 2°C and 30°C, respectively; 9 d at 6°C with preincubation at 6°C; 4 d at 6°Cwith preincubation at 30°C; and 1 d at 14°C with preincubation at 14°C or at 30°C.The results show that survival of L. monocytogenes (strain Scott A) at pH 4·8 is notdependent on initial bacterial concentration but on both the test and preincubation temperatures.