Reappraisal of the effect of temperature on the growth kinetics of Aeromonas salmonicida

The effect of temperature (1–34 °C ) on the maximum specific growth rate of Aeromonas salmonicida could not be described by the classical growth models ; for some strains, two optimal temperatures at 23 °C and 30 °C were observed, as well as an unexpected increase in the pseudolag time above 27 °C. This could be explained by the presence of two subsets, notably S-layer⁺ and S-layer⁻ sub-populations. The A⁻ cells had higher growth parameters (T_opt and μ_opt) than the A⁺ cells and were selected by subcultures above 30 °C. Yet the relative proportion of A⁺ cells did not explain all the variation of μ_max versus temperature, and the growth kinetics of an Aer. salmonicida isolate remained unpredictable.     

The effect of incubation temperature, sodium chloride and ascorbic acid on the growth kinetics of Aeromonas hydrophila

The effects of temperature, sodium chloride and ascorbic acid on the aerobic growth kinetics of a clinical strain of Aeromonas hydrophila were evaluated. At 5°C, ascorbic acid (1 mmol l^-1) and sodium chloride (3% w/v) inhibited the growth of the organism. At 10°C, ascorbic acid depressed only the maximum population densities (A) by approximately 2 log cycles, but not maximum specific growth rate (μ_m) or the lag time (Λ). On the contrary, NaCl caused A to increase, with the effect being greatest when the NaCl content was 1.5%. Temperature increase from 10 to 15°C resulted in an approximate doubling of μ_m and unexpectedly an apparent increase in Λ However, this apparent increase resulted from the particular manner in which the lag phase was mathematically calculated.     

Effect of temperature on sulphate reduction, growth rate and growth yield in five psychrophilic sulphate-reducing bacteria from Arctic sediments

Five psychrophilic sulphate-reducing bacteria (strains ASv26, LSv21, PSv29, LSv54 and LSv514) isolated from Arctic sediments were examined for their adaptation to permanently low temperatures. All strains grew at −1.8°C, the freezing point of sea water, but their optimum temperature for growth ( T _opt) were 7°C (PSv29), 10°C (ASv26, LSv54) and 18°C (LSv21, LSv514). Although T _opt was considerably above the in situ temperatures of their habitats (−1.7°C and 2.6°C), relative growth rates were still high at 0°C, accounting for 25–41% of those at T _opt. Short-term incubations of exponentially growing cultures showed that the highest sulphate reduction rates occurred 2–9°C above T _opt. In contrast to growth and sulphate reduction rates, growth yields of strains ASv26, LSv54 and PSv29 were almost constant between −1.8°C and T _opt. For strains LSv21 and LSv514, however, growth yields were highest at the lowest temperatures, around 0°C. The results indicate that psychrophilic sulphate-reducing bacteria are specially adapted to permanently low temperatures by high relative growth rates and high growth yields at in situ conditions.     

Mutation of rpoS gene decreased resistance to environmental stresses, synthesis of extracellular products and virulence of Vibrio anguillarum

Vibrio anguillarum is a gram-negative halophilic bacterium that causes vibriosis in marine fish, freshwater fish and other aquatic animals. Bacteria have developed strategies to survive in harsh environments. The alternative σ factor, RpoS (σ^S), plays a key role in surviving under stress conditions in some gram-negative bacteria. An rpoS mutant of pathogenic V. anguillarum W-1 was constructed by homologous recombination. The sensitivity of the rpoS mutant to osmotic stress [2.4 M NaCl in artificial seawater (ASW)] did not change obviously, but the sensitivity of the rpoS mutant to high temperature (45 °C in ASW), UV-irradiation and oxidative stress (5 mM H₂O₂ in ASW) increased 33-fold, sixfold and 10-fold, respectively. The production of extracellular phospholipase, diastase, lipase, caseinase, hemolysin, catalase and protease of the rpoS mutant decreased markedly compared with those of the wild-type strain. Virulence of the rpoS mutant strain was also decreased when it was inoculated intraperitoneally into zebra fish; the lethal dose 50% of the wild type and the mutant was 8.66 × 10⁴ and 2.55 × 10⁶ CFU per fish, respectively. These results indicated that the RpoS of V. anguillarum plays important roles in bacterial adaptation to environmental stresses and its pathogenicity.     

Modelling the growth of Weissella cibaria as a function of fermentation conditions

Aims:  To investigate the effect of pH, water activity ( a _w) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs.
Methods and Results:  The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), a _w (0·935–0·994) and temperature (10–45°C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol 23, 277–294). The effect of pH, a _w and temperature on maximum specific growth rate (μ_max) were estimated by fitting a cardinal model. μ_max under optimal conditions (pH = 6·6, a _w = 0·994, T  = 36·3°C) was estimated to be 0·93 h⁻¹. Minimum and maximum estimated pH and temperature for growth were 3·6 and 8·15, and 9·0°C and 47·8°C, respectively, while minimum a _w was 0·918 (equivalent to 12·2% w/v NaCl).
Conclusions:  Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study:  This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations.     

Ontogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia

Knowledge of how the optimum temperature for growth ( T °_opt) varies during ontogeny, and how close it is to the temperatures that induce phenotypic masculinization is fundamental to the understanding of the evolution of thermolabile sex determinism (TSD) in fishes. In blue tilapia Oreochromis aureus , T °_opt is 32·6° C at the start of exogenous feeding (10mg fish) and it decreases by c . 1° C each time that the fish body mass increases by an order of magnitude. Temperatures <35° C are not sufficient to induce complete phenotypic masculinization. Based on a multiple-regression model ( r ²=0·938) plotting growth against body mass and water temperature, genotypically female tilapia living at high temperatures during the thermosensitive period (21–28 days) and being reversed into phenotypic males would incur an initial growth disadvantage over fish living at T °_opt, but not over those living at slightly colder temperatures (27–29° C). This initial disadvantage would be later compensated for by faster growth because of between-sex growth dimorphism to the detriment of phenotypic females. These arguments suggest that there is no definite pressure against the selection of TSD in blue tilapia and probably other Oreochromis spp.     

Polygalacturonase biosynthesis by Lactobacillus plantarum: effect of cultural conditions on enzyme production

Lactobacillus plantarum was found to produce extracellular polygalacturonase (EC 3.2.1.15.). Maximum enzyme production was obtained in a medium containing 0.5% glucose and 1.5% low methyl-pectin as inducer at 27°C at an initial pH of 6.8. Enzyme production was strongly inhibited by 5 μmol/l NiCl₂, 5 μmol/l CoCl₂, 5 μmol/l CuSO₄, and 10 μmol/l ZnCl₂. MnSO₄ and MgSO₄ at 200 μmol/l and 50 μmol/l respectively seemed to enhance enzyme biosynthesis. The optimal pH and temperature for enzyme activity were 4.5 and 30°C respectively. Enzyme production in batch culture accompanied growth.     

Vibrio anguillarum: Influence of temperature, pH, NaCl concentration and incubation time on growth

An analysis of the effect of growth conditions on the growth (O.D. values) of five Vibrio anguillarum strains showed that the optima were as follows: pH 7, temperature 25°C, NaCl concentration 2%, and O.D. estimates increased with the incubation time. The independent parameters, as well as their interactions significantly influenced the growth of Vibrio anguillarum ( P 0<0001). Only the strain-salinity interaction was not always statistically significant. A restriction of the parameters to a level relevant for Danish marine recipients showed that pH and NaCl concentration (salinity) might be of minor importance while the temperature was always of high significance. The possible impact of these observations on local conditions is discussed.     

Kinetics of leaf oxygen uptake represent in planta activities of respiratory electron transport and terminal oxidases

We present, for the first time, the oxygen response kinetics of mitochondrial respiration measured in intact leaves (sunflower and aspen). Low O₂ concentrations in N₂ (9–1500 ppm) were preset in a flow-through gas exchange measurement system, and the decrease in O₂ concentration and the increase in CO₂ concentration as result of leaf respiration were measured by a zirconium cell O₂ analyser and infrared-absorption CO₂ analyser, respectively. The low O₂ concentrations little influenced the rate of CO₂ evolution during the 60-s exposure. The initial slope of the O₂ uptake curve on the dissolved O₂ concentration basis was relatively constant in leaves of a single species, 1.5 mm s⁻¹ in sunflower and 1.8 mm s⁻¹ in aspen. The apparent K _0.5(O₂) values ranged from 0.33 to 0.67 μ M in sunflower and from 0.33 to 1.1 μ M in aspen, mainly because of the variation of the maximum rate, V _max (leaf temperature 22°C). The initial slope of the O₂ response of respiration characterizes the catalytic efficiency of terminal oxidases, an important parameter of the respiratory machinery in leaves. The plateau of the response characterizes the activity of the mitochondrial electron transport chain and is subject to regulations in accordance with the necessity for ATP production. The relatively low oxygen conductivity of terminal oxidases means that in leaves, less than 10% of the photosynthetic oxygen can be reassimilated by mitochondria.     

Interactive effects of solutes, potassium sorbate and incubation temperature on growth, heat resistance and tolerance to freezing of Zygosaccharomyces rouxii

The interactive effects of solutes, potassium sorbate and incubation temperature on growth, heat resistance and tolerance to freezing of Zygosaccharomyces rouxii were investigated. Growth rates in media supplemented with glucose, sucrose or NaCl to a _w 0.93 were more rapid than in unsupplemented media ( a _w 0.99). Although growth in unsupplemented medium was lower at 35°C, incubation at 21°C or 35°C had little effect on growth in media supplemented with glucose and sucrose. The addition of 300 μg potassium sorbate/ml to media resulted in reduced growth rates, particularly at 35°C. Heat resistance of Z. rouxii was substantially greater in cultures previously incubated at 35°C than in cultures incubated at 21° in media both with and without 300 μg potassium sorbate/ml. Zygosaccharomyces rouxii was tolerant to freezing at - 18°C for up to 120 d in all test media supplemented with glucose, sucrose or NaCl. The addition of 300 μg potassium sorbate/ml to sucrose-supplemented media resulted in increased resistance to freezing in cultures previously incubated at 21°C. Sensitivity to freezing increased when cultures were incubated at 21°C in media not supplemented with solutes. Glucose and sucrose provided the best protection against inactivation by heating and freezing, regardless of the presence of potassium sorbate in growth media.     

Response of Campylobacter jejuni to combinations of ferrous sulphate and cadmium chloride

On Mueller Hinton (MH) agar, Campylobacter jejuni showed 20.0 and 30.9mm zones of inhibition surrounding discs impregnated with 2.5 and 20 μg CdCl₂ respectively. The minimal inhibitory concentration (MIC) ranged from 0.64 to 3.2 μg CdCl₂/ml of MH agar for four C. jejuni strains. In the presence of 23 μg FeSO₄/ml of MH the MIC increased to a range of 1.5–5.4 μg CdCl₂/ml of MH. Moreover, the numbers of colonies present on MH supplemented with FeSO₄ were greater than on MH without iron. The growth response of C. jejuni in the presence of 0.025% (w/v) FeSO₄ in MH broth was increased about 10000 fold in three of four strains when compared with the growth in unsupplemented MH broth. Zones of inhibition surrounding 20 μg discs of CdCl₂ were 50.6 and 24.4 mm on MH and Campy-BAP media respectively, with cells grown on MH. These results suggest that the blood-containing medium 'neutralized' the biocidal influence of the CdCl₂. In comparison, C. jejuni inoculum from fluid thioglycollate (FT) medium showed smaller zones of inhibition. These decreased from 34.9 mm on MH agar to 19.6 mm on Campy-BAP agar, suggesting that components in the FT growth medium ameliorated the toxic influence of CdCl₂. Atomic absorption spectroscopy analysis indicated mean values (mg/100 g dry weight) of selected metals bound by C. jejuni as: Cu, 10.4; Mg, 146; Na, 2385; Fe, 45.1; Zn, 13.0; and K, 172.     

The interaction of high temperature and elevated CO2 on photosynthetic acclimation of single leaves of rice in situ

Rice ( Oryza sativa L. cv. IR72) was grown at three different CO₂ concentrations (ambient, ambient + 200 μmol mol⁻¹, ambient + 300 μmol mol⁻¹) at two different growth temperatures (ambient, ambient + 4°C) from sowing to maturity to determine longterm photosynthetic acclimation to elevated CO₂ with and without increasing temperature. Single leaves of rice showed a cooperative enhancement of photosynthetic rate with elevated CO₂ and temperature during tillering, relative to the elevated CO₂ condition alone. However, after flowering, the degree of photosynthetic stimulation by elevated CO₂ was reduced for the ambient + 4°C treatment. This increasing insensitivity to CO₂ appeared to be accompanied by a reduction in ribulose-1.5-bisphosphate carboxylase/oxygenase (Rubisco) activity and/or concentration as evidenced by the reduction in the assimilation (A) to internal CO₂ (C₁) response curve. The reproductive response (e.g. percent filled grains, panicle weight) was reduced at the higher growth temperature and presumably reflects a greater increase in floral sterility. Results indicate that while CO₂ and temperature could act synergistically at the biochemical level, the direct effect of temperature on floral development with a subsequent reduction in carbon utilization may change sink strength so as to limit photosynthetic stimulation by elevated CO₂ concentration.     

Isolation and properties of sarcoplasmic reticulum from the fast muscles of plaice Pleuronectes platessa L.

This paper describes a method for the isolation of highly purified sarcoplasmic reticulum from plaice fast muscle. The interrelationships of pH, KCL, Ca²⁺, Mg²⁺, ADP and temperature have been investigated. Protein composition of plaice white muscle sarcoplasmic reticulum was found to be comparable to that described for rabbit fast muscle, with a major component of 100 000 daltons. Arrhenius plots of the Ca²⁺-AT Pase are linear over the range 0–30°C. Activation enthalpy (60±1.5 kJ/mol) was found to be independent of KCl concentration. The calcium concentration required to give half maximal activation of the AT Pase (K_Ca) was found to decrease with increasing temperature, from a maximum of 1.7 μm at 0°C to 0.55 at 20°C.     

Purification and characterization of xylanase from alkali-tolerant Aspergillus fischeri Fxn1

Abstract Alkali-tolerant Aspergillus fischeri Fxn1 produced two extracellular xylanases. The major xylanase ( M _r 31000) was purified to electrophoretic homogeneity by ammonium sulfate precipitation, anion exchange chromatography and preparatory PAGE. Xylose was the major hydrolysis product from oat spelt and birch wood xylans. It was completely free of cellulolytic activities. The optimum pH and temperature were 6.0 and 60 °C, respectively. pH stability ranged from 5 to 9.5 and the t_{1 / 2} at 50 °C was 490 min. It had a K _m of 4.88 mg ml⁻¹and a V _max of 588 μmol min⁻¹ mg⁻¹. The activity was inhibited (95%) by AlCl₃ (10 mM). This enzyme appears to be novel and will be useful for studies on the mechanism of hydrolysis of xylan by xylanolytic enzymes.     

Balancing carboxylation and regeneration of ribulose-1,5- bisphosphate in leaf photosynthesis: temperature acclimation of an evergreen tree, Quercus myrsinaefolia

Changes in the temperature dependence of the photosynthetic rate depending on growth temperature were investigated for a temperate evergreen tree, Quercus myrsinaefolia . Plants were grown at 250 μ mol quanta m^–2 s^–1 under two temperature conditions, 15 and 30 °C. The optimal temperature that maximizes the light-saturated rate of photosynthesis at 350 μ L L^–1 CO₂ was found to be 20–25 and 30–35 °C for leaves grown at 15 and 30 °C, respectively. We focused on two processes, carboxylation and regeneration of ribulose-1,5-bisphosphate (RuBP), which potentially limit photosynthetic rates. Because the former process is known to limit photosynthesis at lower CO₂ concentrations while the latter limits it at higher CO₂ concentrations, we determined the temperature dependence of the photosynthetic rate at 200 and 1000 μ L L^–1 CO₂ under saturated light. It was revealed that the temperature dependence of both processes varied depending on the growth temperature. Using a biochemical model, we estimated the capacity of the two processes at various temperatures under ambient CO₂ concentration. It was suggested that, in leaves grown at low temperature (15 °C), the photosynthetic rate was limited solely by RuBP carboxylation under any temperature. On the other hand, it was suggested that, in leaves grown at high temperature (30 °C), the photosynthetic rate was limited by RuBP regeneration below 22 °C, but limited by RuBP carboxylation above 22 °C. We concluded that: (1) the changes in the temperature dependence of carboxylation and regeneration of RuBP and (2) the changes in the balance of these two processes altered the temperature dependence of the photosynthetic rate.     

The affect of temperature on the metabolism and behaviour of an endemic amphipod, Hyalella montezuma, from Montezuma Well, Arizona, U.S.A.

1. Hyalella montezuma is endemic to Montezuma Well, Arizona, and is exposed to minimal diel and seasonal temperature fluctuations in the pelagic zone (21 ± 4 °C). Juvenile H . montezuma feed in the pelagic zone during the day and migrate into the littoral vegetation at night, while adults remain primarily in the littoral vegetation.
2. Oxygen consumption ( V O₂) of adult and juvenile H . montezuma was measured at 20, 25 and 30 °C. The V O₂ of both adult and juvenile H . montezuma increased with temperature. However, the V O₂ of juveniles was significantly greater than that of adults at all temperatures, with greatest divergence at 30 °C where mean juvenile V O₂ (6.31 μl mg^–1 dry weight (DW) h^–1) was almost twice that of adults (3.60 μl mg^–1 DW h^–1).
3. Survivorship of juveniles was significantly lower (54%) at 30 °C than at 27.5 °C (95%) after 4 h, whereas adults showed at least a 93% survivorship at both temperatures.
4. Our data suggest that temperature may have been the proximate cue that elicited the diel horizontal migration of juvenile H . montezuma in Montezuma Well, with the behaviour maintained and enhanced by intensive invertebrate predation in the pelagic and littoral zones.     

The affect of temperature on the metabolism and behaviour of an endemic amphipod, Hyalella montezuma, from Montezuma Well, Arizona, U.S.A.

1. Hyalella montezuma is endemic to Montezuma Well, Arizona, and is exposed to minimal diel and seasonal temperature fluctuations in the pelagic zone (21 ± 4 °C). Juvenile H . montezuma feed in the pelagic zone during the day and migrate into the littoral vegetation at night, while adults remain primarily in the littoral vegetation.
2. Oxygen consumption ( V O₂) of adult and juvenile H . montezuma was measured at 20, 25 and 30 °C. The V O₂ of both adult and juvenile H . montezuma increased with temperature. However, the V O₂ of juveniles was significantly greater than that of adults at all temperatures, with greatest divergence at 30 °C where mean juvenile V O₂ (6.31 μl mg^–1 dry weight (DW) h^–1) was almost twice that of adults (3.60 μl mg^–1 DW h^–1).
3. Survivorship of juveniles was significantly lower (54%) at 30 °C than at 27.5 °C (95%) after 4 h, whereas adults showed at least a 93% survivorship at both temperatures.
4. Our data suggest that temperature may have been the proximate cue that elicited the diel horizontal migration of juvenile H . montezuma in Montezuma Well, with the behaviour maintained and enhanced by intensive invertebrate predation in the pelagic and littoral zones.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

Growth, respiration and survival of Legionella pneumophila at high temperatures

The optimum temperature for multiplication of legionella strains in culture media is around 37°C. The effect of high temperatures on the growth of strains isolated from various environments is poorly known. We studied the growth (cell multiplication, respiration) of clinical and environmental Legionella pneumophila strains in liquid media at intervals of 0.5°C in the temperature range from 41.6 to 51.6°C using a temperature gradient incubator. Cell multiplication and CO₂ production decreased markedly with all the strains at temperatures above 44–45°C. CO₂ continued to be produced up to 51.6C even if cell multiplication generally stopped at around 48.4–50.0C. Thus, legionella retained its metabolic activity beyond the maximum temperature for cell multiplication. The CO₂ production per bacterial cell (metabolic quotient, qCO₂) increased with increasing temperature up to 45°C, whereafter it decreased, the turning point being almost at the same at which the rate of cell multiplication decreased. The difference in qCO₂ between the strains may reflect their different physiological capacities for tolerating high temperatures.     

The protective effect of some food ingredients on Staphylococcus aureus MF31

The upper limiting temperature of growth of Staphylococcus aureus MF31 in heart infusion broth (HI) was about 44°C but addition of monosodium glutamate (MSG) and soy sauce permitted the organism to grow above this temperature. This effect is similar to that of NaCl. Tomato ketchup, Worcestershire and HP sauces added to HI did not allow growth at the non-permissive temperature of 46°C but death was delayed. Staphylococcus aureus died in unsupplemented chicken meat slurry at 46°C but grew at 48°C in slurry supplemented with 5.8% NaCl and survived incubation for 18 h at 50°C in slurry supplemented with 5.8% NaCl and 5% MSG. Cultures grown at 37°C had a D ₆₀ value of 2 min in 50 mmol/l Tris (pH 7.2) buffer. Cultures grown at 46°C in HI containing 5.8% NaCl had a D ₆₀ value of 8 min in Tris buffer. Addition of 5.8% NaCl plus 5% MSG to the buffer increased the D ₆₀ by a factor of about 7 for both cultures. In storage experiments at room temperature, the culture grown at 37°C and at 46°C plus 5.8% NaCl died at about the same rate in salami. In milk powder, however, the count of 37°C culture decreased from 10⁹/g to 10⁶/g in 5 weeks while the count of 46°C culture remained unchanged. In cottage cheese, freeze-dried rice and macaroni, the 37°C cultures also died more rapidly. It is suggested that cultures grown at 46°C plus 5.8% NaCl may be suitable for experiments with artificially contaminated foods.