Partial purification and characterization of phospholipase C from Yersinia enterocolitica

About 34% of the strains of Yersinia enterocolitica isolated from raw milk were found to produce lecithinase. A selected strain produced phospholipase C at 22°C and 37°C; production was optimum at 37°C in the stationary phase (14–16 h). A decrease in phospholipase C activity at various storage temperatures (—5°C, 4°C, 37°C) was also observed, although the enzyme was active over a wide range of temperature (5–65°C) and pH (3mD5–7mD5). The phospholipase C was partially purified by ammonium sulphate precipitation and Sephadex column chromatography, and characterized.     

Use of a commercial gene probe assay kit for rapid MPN enumeration of Escherichia coli in drinking water

A commercial gene probe assay kit for presence/absence determination of Escherichia coli in food samples has been used in the standard UK six tube format most probable number (MPN) method for enumerating E. coli in drinking water samples. Presence/absence analysis with the gene probe kit (requiring 3 h) of all MPN tubes after a 21–24 h incubation (minerals modified glutamate; 37°C) enumerated confirmed E. coli in 24–27 h which offered an improvement of up to 48 h over the standard UK MPN method. MPNs determined by the gene probe method and the standard UK method agreed in nine of the 16 water samples which were analysed and for which E. coli concentrations were within the detection limits of the six tube MPN format. This was consistent with the gene probe method detecting one E. coli in a tube. For the other seven water samples, the gene probe method registered positive only 20 of the 30 tubes which the standard UK method determined to be positive. The sensitivity of the gene probe method for drinking water samples, although encouraging, needs improvement perhaps through kit quality control procedures.     

Survival, development and food energy partitioning of nase larvae and early juveniles at different temperatures

Survival was generally high, 94–100%, for newly hatched larvae of the nase Chondrostoma nasus held at 10, 13, 16, 19, 22, 25 and 28° C up to day 66 post-fertilization. The developmental rate decreased with age and increased with temperature. Specific growth rates increased with temperature; within one temperature range growth rate decreased with ontogenetic development. Food consumption and respiration increased with temperature and body size. A temperature increase from 25 to 28° C resulted in slightly reduced survival, minor acceleration of developmental growth and respiration rates, and impeded skeleton formation. Growth efficiency of consumed energy decreased throughout the larval period from 55 to 67% at the first larval stage (L1) to 36–48% at the first juvenile stage (J₁). A similar trend for assimilation efficiency and its utilization for growth was observed. The constant temperatures required by larval nase ranged from a minimum 8–10° C to a maximum 25–28° C. A shift of optimum temperatures, 8–12, 13–16, 15–18, 19 and 22° C for nase spawning, embryonic development, yolk feeding larvae, early externally feeding larvae and, late larvae and juveniles, respectively, paralleled the spring rise in the river water temperature. Larval and juvenile nase show high survival, growth and energy conversion efficiencies compared with other fish species. On the other hand, low survival rates and growth can be attributed to external perturbations; thus, young nase may be considered a good indicator of the environmental and ecological integrity of river systems.     

Viability of heat-stressed cells of micro-organisms as influenced by pre-incubation and post-incubation temperatures

The viability of heat-stressed cells of Escherichia coli was influenced by the temperature of incubation prior and subsequent to heat treatment. The effect of pre-incubation temperature on the viability of heated cells was almost constant regardless of heating temperature in the range 48–54°C. The involvement of the change in fluidity of the membrane was suggested as a cause of the effects of pre-incubation and post-incubation. These phenomena were observed with other Gram negative and positive bacteria, and yeasts.     

Factors affecting the production of an antimicrobial agent, plantaricin F, by Lactobacillus plantarum BF001

Lactobacillus plantarum BF001 produced plantaricin F in MRS broth but it was detected only after ca a 50-fold concentration. Growth on MRS broth and appearance of plantaricin F were similar under aerobic and anaerobic conditions. No growth occurred at pH 3 or at 4°C. Plantaricin F appeared first at early stationary growth phase (24 h) and was stable thereafter (pH 2). Amounts found in liquid cultures were ca 2–3 times higher than those from solidified MRS medium, and specific activities were ca 6 times higher in liquid culture (48 h). Maximal amounts of plantaricin F were found (48 h) when medium had an initial pH of 4 and growth was at 30°C. Under these conditions, cell growth and fermentation were partially uncoupled. Plantaricin F was not produced endogenously, organic nutrients were necessary. A molecular weight range of 500–3500 Da was indicated. Plantaricin F appears to be a secondary metabolite.     

Effects of Temperature on Germination of Peronospora parasitica Conidia and Infection of Brassica oleracea

The effect of temperature on germination of a South African isolate of Peronospora parasitica , and infection of Brassica oleracea was studied. The optimum condition for germination was 20° C at 100% relative humidity. The percentage germination obtained was 80–98% and 70–80% between 15 and 25° C at 100% relative humidity, after a 12 and 6h incubation period, respectively. Optimum temperature for germ tube growth was also 20° C. The temperature range for maximum infection of seedlings of a highly susceptible cabbage cultivar and subsequent disease development in vitro was 15–25° C and 90–100% infection was achieved after 48 h of incubation. At<15°C and 26–30° C infection percentage was decreased to 40–50% and 35–40%, respectively. No disease incidence was recorded at temperatures above 35° C. A scanning electron microscope study of the infection process showed that penetration of cotyledons by germ tubes was mostly via stomata and occasionally directly through the cuticle. Results are discussed in relation to the need for future studies of P. parasitica in South Africa.     

Growth of Listeria monocytogenes at refrigeration temperatures

The growth of three strains of Listeria monocytogenes at refrigeration temperatures (-0.5 to 9.3°C) in chicken broth and/or UHT milk was determined using a rocking temperature gradient incubator. Minimum growth temperatures ranged from -0.1 to -0.4°C for the three strains. Lag times of 1–3 d and 3 to >34 d were observed with incubation at 5 and 0°C respectively. Corresponding generation times ranged from 13–24 h at 5°C and 62–131 h at 0°C. The type of culture medium had an influence on both the rate and extent of growth. Incubation of cultures at 4°C before inoculation caused a marked reduction in the lag time when compared with cultures which had been previously incubated at 30°C.     

Influence of ambient and thoracic temperatures upon sexual behaviour of the gypsy moth, Lymantria dispar

ABSTRACT. In an ambient temperature ( T _a) range of 18–28°C, thoracic temperatures ( T _th) of individual male Lymantria dispar (L.), caught at flight in the field, ranged from 21 to 36.5°C, with a correlation coefficient of 0.63 between T _th and ambient temperature ( T _a). Ambient temperature (and insolation) altered the insect's body temperature and the probabilities, latencies, and durations of preflight responses to pheromone. In a wind tunnel at 16 and 20°C, quiescent males exposed to pheromone raised their T _th by sustained wing fanning from 17 and 21°C, respectively, to c. 24°C before takeoff. At 24 and 28°C ambient, T _th rose by takeoff to 28 and 31°C, respectively. The latencies of male wing fanning in response to pheromone decreased from 1.44 min at 16°C ambient, to 0.58 min at 20°C, to 0.26 min at 24°C, and to 0.16min at 28°C. The components of behaviour (antennal twitch, body jerk, step and wing tremor) that occurred between quiescence and wing fanning were more frequent at ambients of 16 and 20°C than at 24 and 28°C.     

The Effects on Temperature on Growth in vitro of Pseudomonas syringae and Xanthomonas pruni

Growth rates in vitro of Pseudomonas syringae and Xanthomonas pruni were measured over the temperature range 0–36 °C. The estimated temperature optimum for X. pruni was 31 °C, with a doubling time of 1.53 h. The estimated temperature optimum for P. syringae was 28 °C with a doubling time of 1.27 h, although analysis showed no significant difference in the doubling times over the range 23–33 °C, indicating an unusual plateau at the maximum rate of growth of this organism. P. syringae and related plant pathogenic Pseudomonas spp. grew well at low temperatures, but X. pruni did not. Cultures of P. syringae and X. pruni had a very short lag phase after their incubation temperature was changed from 4 °C to a temperature close to their optimum (29 °C). When the incubation temperature of these organisms was changed from 11.5–29 °C, X. pruni grew without a lag phase at the rate expected for the higher temperature. However, the initial growth rate of P. syringae at the higher temperature was significantly greater than that at which the organism subsequently developed. The ecological significance of these points is discussed. The usefulness of the Arrhenius coefficients as characteristics of these organisms is discussed.     

Development and characterization of cell lines from heart, liver, spleen and head kidney of sea perch Lateolabrax japonicus

Five cell lines (LJHK, LJS, LJL, LJH-1 and LJH-2) were established from the head kidney, spleen, liver and heart of sea perch Lateolabrax japonicus . The cell lines LJHK, LJS, LJL, LJH-1 and LJH-2 were subcultured 46, 32, 32, 36 and 34 times in minimum essential medium (MEM) supplemented with foetal bovine serum (FBS), sea perch serum and 10 ng ml⁻¹ basic fibroblast growth factor (bFGF). Morphology of primary cultures and subcultures of the five cell lines were observed continuously by microscopy. The suitable temperature for growth was 18 to 30° C for all of these cell lines with the optimum growth at 24° C and a reduced growth rate <18° C. The optimum concentration of FBS was found to be 10% and addition of bFGF to the medium significantly increased the growth rate of the cells. The doubling time of LJS, LJH-1, LJL, LJH-2 and LJHK cells was determined to be 52·7, 54·9, 57, 58·7 and 66 h at a plating density of 1 × 10⁵ cells ml⁻¹ at 24° C, respectively. Chromosome analysis revealed that 42, 48, 38, 43 and 45% cells maintained normal diploid chromosome number (48) in the LJH-1, LJH-2, LJHK, LJL and LJS cell lines, respectively. The LJHK cells were successfully transfected with green fluorescent protein (GFP) reporter plasmids and the expression of GFP gene in the cells indicated the possible utility of the cells in gene expression studies. Furthermore, treatment of the LJHK cells with lipopolysaccharide led to increased expression of IL-1β, demonstrating that LJHK cells might be a valuable tool for studying the expression and function of immunomodulatory gene in fishes.     

Bioemulsifier production by Bacillus stearothermophilus VR-8 isolate

Bacillus stearothermophilus produced an extracellular bioemulsifier during growth in a medium containing 4% crude oil. Over the temperature range of 45° to 70°C, maximum recovery (0·6 g 1^-1) occurred at 50°C. The emulsifier had its greatest activity on benzene, among the hydrocarbons tested. Acetone precipitated, dialysed emulsifier contained 46% protein, 16% carbohydrate and 10% lipid. The emulsification activity was stable over a broad range of temperature (50–80°C), pH (2–8) and salt concentration (5% NaCl, 5% CaCl₂ and 1% MgCl₂). Thus, this emulsifier was found to be better than liposan (showing emulsifying activity between pH 2–5 and stable up to 70°C) in terms of pH and temperature stability. Additionally, it was also salt tolerant, suggesting its potential use in crude oil tank clean-up and enhanced oil recovery.     

Photoperiodic control of flowering in Dactylis glomerata, a true short-long-day plant

Flowering requirements of three Scandinavian cultivars of Dactylis glomerata L. have been studied in controlled environments. At temperatures ranging from 9 to 21°C optimal flowering required 10 weeks of exposure to short days (SD) followed by exposure to long days (LD). Only a few plants flowered in continuous LD and no primary induction took place in any daylength at 24 or 27°C. However, at a temperature of 3°C primary induction occurred also in 24 h LD, but more than 20 weeks of treatment were required for 100% flowering. The critical photoperiod for secondary induction was about 12–13 h, depending on the latitude of origin of the cultivar. A critical number of 12 to 16 LD cycles was required for 100% flowering, although some plants flowered after only 4 LD. A high proportion of viviparous proliferation resulted from marginal LD induction. Initiation of floral primordia did not take place in SD but required a transition from SD to LD. These results demonstrate that D. glomerata is a true short-long-day plant.     

Growth responses of Matteuccia struthiopteris plants from northern and southern Norway exposed to different temperature and photoperiod treatments

Plants of the fern Matteuccia struthiopteris from northern and southern populations in Norway were studied in a phytotron. Relative growth rate (RGR), growth period, and sporophyll production were measured under different photoperiod (12–24 h) day-length and temperature (9–21 °C) treatments. For the southern plants, there were no significant differences between the different light treatments, but for the northern plants there was a significant (p<0.01) linear increase in the mean maximum RGR with increasing day-length. Small, but statistically significant (p<0.01) differences were found between northern and southern plants when the mean maximum RGR-values were compared. When plants from different origin were exposed to different treatment, there were major differences between the populations in the production of sporophylls (p<0.0001). Southern plants produced in average three times more sporophylls than the northern plants, and they had also higher proportions of fertile plants. Diurnal alternating temperature treatments gave no significant (p>0.05) effect on the mean maximum RGR compared with constant temperatures, but they gave significantly higher production of sporophylls. In general, the northern plants had a higher temperature threshold (approximately 12 °C) for sporophyll production than the southern plants (approximately 9 °C). Plants exposed to 24 h with natural light were generally more often fertile than plants exposed to a shorter photoperiod. The mean maximum RGR-values and time needed to develop the fronds at the 9 °C treatment were fairly equal to those found under natural conditions close to the altitudinal distribution limit of M.struthiopteris in W Norway. In general, the investigation showed that the applied temperature and light treatments affected sporophyll production more than vegetative growth.     

Synergistic effect of relative humidity and temperature on the survival of rhizobia in inoculant carrier

Six strains of Rhizobium , three temperature-tolerant (U1, C13 and A19) and three temperature-sensitive strains (U10, C10 and A4) selected on the basis of previous study were used to screen the synergestic effect of different relative humidities (r.h. 50%, 65% and 90%) and temperatures (28°, 35°, 40° and 45°C) on the survival of rhizobia in inoculant carrier. At a particular temperature all the three r.h.'s were maintained. At a storage temperature of 28° and 35°C, the r.h. had little effect on the population of any of the rhizobial strains tested, but at 40° and 45°C, marked differences were observed and it was concluded that higher r.h. in conjunction with higher temperature resulted in low viable counts. The effect was similar but less obvious with the temperature-tolerant strains. It was found that 50% r.h. at different storage temperatures extended shelf life of rhizobial strains of blackgram, cowpea and arhar crops which were tested in this study in inoculant carrier.     

Behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir

This study investigated behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir on the Snake River, Washington, U.S.A. During the summer, temperatures in the reservoir varied from 23° C on the surface to 11° C at 14 m depth. Subyearlings implanted with temperature-sensing radio transmitters were released at the surface at temperatures >20° C during three blocks of time in summer 2004. Vertical profiles were taken to measure temperature and depth use as the fish moved downstream over an average of 5·6–7·2 h and 6·0–13·8 km. The majority of the subyearlings maintained average body temperatures that differed from average vertical profile temperatures during most of the time they were tracked. The mean proportion of the time subyearlings tracked within the 16–20° C temperature range was larger than the proportion of time this range was available, which confirmed temperature selection opposed to random use. The subyearlings selected a depth and temperature combination that allowed them to increase their exposure to temperatures of 16–20° C when temperatures <16 and >20° C were available at lower and higher positions in the water column. A portion of the subyearlings that selected a temperature c. 17·0° C during the day, moved into warmer water at night coincident with an increase in downstream movement rate. Though subyearlings used temperatures outside of the 16–20° C range part of the time, behavioural thermoregulation probably reduced the effects of intermittent exposure to suboptimal temperatures. By doing so, it might enhance growth opportunity and life-history diversity in the population of subyearlings studied.     

Suitability of oven-dried root nodules for Rhizobium strain identification by immunofluorescence and agglutination

Legume root-nodules, dried at oven temperature (70°C for 48 h) were suitable for Rhizobium strain identification by immunofluorescence and agglutination. The fluorescence of bacteroids of R. japonicum, R. leguminosarum, R. meliloti, R. phaseoli , and Rhizobium spp. from oven-dried nodules was the same as those from frozen, desiccated, or nodules dried at room temperature (28°C). Oven-dried nodules did not require further steaming for agglutination. Bacteroid agglutinations gave 2–16 fold lower titres than those of the cultured cells. Fresh and oven-dried soybean rhizobia from a mixed inoculation gave exactly the same results when identified by immunofluorescence or agglutination.     

Effects of environmental factors on survival, growth, and production of American shad larvae

Episodic increases in temperature of 5°C above 20° C, over 48 h or declines in pH of 1·0 unit from pH 7·0 reduced survival of yolk-sac and feeding-stage larvae of American shad Alosa sapidissima . Over 16 days all measures of survival, growth, and production were more favourable at each higher temperature in the 15–25° C range. More favourable responses were also obtained at the higher prey level (500 v . 50 Artemia nauplii l^-1) and at the higher pH (7·5 v . 6·5). Combinations of high temperature and high prey levels, at pH 7·5, led to highest larval production. Little growth or production occurred at 15° C, regardless of pH or prey level. The effect of pH was strong with respect to survival, but weak with respect to growth. In attempts to restore American shad populations by larval stocking, release times and sites can be critical to optimize survival and eventual returns. Releases of larvae potentially will be most effective when made at temperatures >20° C, pH>7·0, and prey levels >50 1^-1. These conditions are most likely to occur in Maryland tributaries of Chesapeake Bay between mid-May and early June.     

Elevation of the heat resistance of Salmonella typhimurium by sublethal heat shock

The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge.