The quantitative relationship of lethality between extracellular protease and extracellular haemolysin of Aeromonas salmonicida in Atlantic salmon (Salmo salar L.)

An additive relationship of lethality between purified protease and haemolysin of the extracellular products (ECP) of Aeromonas salmonicida was demonstrated by i.p. injection in Atlantic salmon (Salmo salar L.). The lethal toxicity of the combinations of protease and haemolysin follow a linear regression line y = -54.54x + 2400. The LD50 of protease and haemolysin when injected separately was 2400 ng/g fish and 44 ng protein/g fish, respectively.     

Distinct effects of different low temperatures on the induction of NAD-sorbitol dehydrogenase activity in diapause eggs of the silkworm,Bombyx mori

Summary Diapause eggs of the silkworm, Bombyx mori, exposed to 5°C and 0.5°C from 2 or 30 days after oviposition, were examined for changes in contents of glycogen, sorbitol and glycerol. Cold acclimation did not alter the profile of accumulation of sorbitol from that in eggs kept continuously at 25°C. However, acclimation at 5°C resulted in conversion of sorbitol to glycogen, while acclimation at 0.5°C was not accompanied by the utilization of sorbitol. NAD-sorbitol dehydrogenase (NAD-SDH; EC 1.1.1.14) activity was examined in the cold-acclimated eggs. The activity was induced by acclimation at 5°C but not at 0.5°C. Incubation at 0.5°C suppressed any further increase in the activity that had been induced. Temperature-directed changes in NAD-SDH activity paralleled those in sorbitol content. Hatching of the diapause eggs was monitored after cold acclimation for various periods of time and subsequent transfer to 25°C. Incubation at 0.5°C was less effective than 5°C at breaking diapause. The time required for the eggs to hatch in synchrony after acclimation at 5°C coincided with that required for the induction of NAD-SDH activity. These results show that different effects result from acclimation at 5°C and near 0°C with respect to the control of NAD-SDH activity, that utilization of sorbitol is controlled by NAD-SDH activity, and that induction of this activity is temperature-dependent. Furthermore, induction of NAD-SDH activity is involved in the termination of diapause in B. mori.Abbreviations DH diapause hormone - NAD nicotinamide-adenine-dinucleotide - NAD-SDH NAD-sorbitol-dehydrogenase     

变温对两种昆虫发育速率的影响

报道了松毛虫赤眼蜂和瓜螟在多组恒温、交替变温下的发育历期。对结果的分析表明,温度交替对这两种昆虫在任一温度下的瞬时发育率无明显影响,恒温下和变温下完成发育所需的热量无显著差异或基本相似。     

Round-cell mutants of Salmonella typhimurium produced by transposition mutagenesis: Lethality of rodA and mre mutations

Summary Thirty-three insertions of transposon Tn10l6l7 into genes involved in the control of rod cell shape were isolated in Salmonella typhimurium by the characteristic glossy appearance of colonies composed of spherical cells. Genetic tests demonstrated that 25 (76%) were insertions in the rodA gene, 7 (21 %) were mre mutants, and 1 (3%) was a divD mutant. No insertion in the pbpA gene were found. Insertions in cell shape genes only appeared when strains displaying resistance to mecillinam (not caused by -lactamase production) were employed. Neither rodA nor mre insertions could be transduced to wild-type strains but they were normally accepted by mecillinam-resistant derivatives and by cya and crp mutants, which, unlike the corresponding Escherichia coli strains, did not display resistance to mecillinam. On the other hand, the divD insertion could be efficiently transduced to any strain. It is concluded that the rodA, mre, and divD genes are involved in the control of rod cell shape but, in addition, the RodA and Mre products perform some function(s) that is essential for wild-type cells but dispensable for some mecillinam-resistant strains, and for cya and crp mutants.     

Use of Local Raw Materials for the Production of Bacillus sphaericus Insecticide in Ghana

Locally available raw materials were used as fermentation media for the preparation of an effective bacterial insecticide of Bacillus sphaericus in Ghana. The choice of materials for media production was based on their availability, their cost and how well they supported growth and sporulation of the bacterium. The materials used were anchovy (Engraulis encrasicolus), spent grain from breweries, bambara beans (Vigna subterranea), sprout maize (Zea mays) and B. sphaericus strain IAB 881. The larvicidal activities of each final whole culture of the insecticides prepared were evaluated against third and fourth instar larvae of the mosquito species Culex quinquefasciatus. The levels of larvicidal activity exhibited by preparations using the raw materials were similar to those where the bacterium was cultured in a synthetic medium, with median lethal concentrations ranging from 0.30 10- 5 to 0.68 10-6. Cell counts were in the range 11 108 - 36 108 colony-forming units ml-1, and spore counts were between 29 107 and 61 107 ml-1.     

Shoot regeneration after fire or freezing temperatures and its relation to plant life-form for some heathland species

Shoot regeneration after prescribed burning or following the freezing temperatures of winter was monitored for nineteen heathland species present in an Arctostaphyleto-Callunetum community in northeast Scotland. Species whose renewal buds were near the surface of the ground started to grow earlier in the spring than species with renewal buds above the surface, but grouping species according to the position of their renewal bud (i.e. their life-form) did not account for all of the interspecific variation apparent. In the case of shoot regeneration after fire, species whose renewal buds were destroyed by fire because they were above-ground started to regenerate about the same time as species with belowground buds, protected from fire, but reached their maximum frequency of occurrence later. Grouping species by life-form was of limited value as a means of interpreting this interspecific variation in the timing of shoot regeneration after fire. It would be unwise to use plant life-form as the sole basis for interpreting or predicting a species' response to temperature stress when extreme temperatures occur regularly, as they do in heathland. The possible use of other plant traits to interpret and predict interspecific variation in the regeneration rate of heathland plants is discussed.Nomenclature follows Tutin et al. (1964–1980) for vascular plants. Acknowledgements. The Nature Conservancy Council and Mr J. J. Humphries kindly allowed Dinnet Moor to be used for the work presented here. One of us (RJR) received financial support for field work from the Natural Sciences and Engineering Research Council of Canada.     

Acclimation to temperature and death at changing lethal temperatures in the freshwater fish Chalcalburnues chalcoides

1. 1.|In the freshwater fish Chalcalburnus chalcoides, an increase in the body (standard) size caused decreases in the upper LT-50 from 36.6° to 36.0°C and lower LT-50 from 6.3° to 5.3°C

2. 2.|The fish acclimated to constant temperatures between 10°C and 30°C showed reasonable heat acclimation and also reasonable cold acclimation. Thus, an increase in the acclimation temperature from 10°C to 30°C caused increases in the upper LT-50 from 34° to 36.2°C and the lower LT-50 from 1.25 to 6.5°C.

3. 3|The mean survival time — temperature curves of 10°, 20° and 30°C acclimated fish at various constant temperatures showed decreased in the survival tim ewith increasing lethal temperatures. Furthermore, an increase in the acclimation temperature causes a shift in the survival duration-temperature curve to the right, i.e., the fish become more heat resistant. Thus, the mean survival duration of 10°, 20° and 30°C acclimated fish at 35°C were 7.5, 79.6 and 530 minutes, respectively.

4. 4.|The effect of the thermal experience to changing lethal temperatures depends on the first lethal temperature to which the fish were exposed as well as the sequence of temperature changes. In the experiments in which the first lethal temperatures were between 32° and 34°C and the temperature was varied in an ascending order, their thermal resistance was increased and the fish required 114 to 174% of the expected lethal doses to die while in the experiments in which the starting temperature were between 38° and 40°C and the temperature varied in descending order, the fish become more sensitive to the upper lethal temperature and they died after receiving only 62 to 81% of the expected lethal doses. Thus, with a gradual increase in the lethal temperature, the fish show additional acclimation in the zone of resistance which in turn causes an increase in the thermal resistance. This may have ecological significance in nature.