Model for combined effect of temperature and salt concentration/water activity on the growth rate of Staphylococcus xylosus

The combined effect of temperature and NaCl concentration/water activity on the growth rate of a strain of halotolerant Staphylococcus is described by the square-root models which had been used previously to model temperature dependence only. The model square root r = b(T-T min) is shown to be a special case of the B?lehrádek temperature function which is given by r = a(T-alpha)d. The constant alpha is the socalled 'biological zero' and equivalent to T min in the square-root models. This and the exponent d = 2 were unaffected by changing NaCl concentration/water activity. The B?lehrádek-type equations are preferable to the Arrhenius equation in that their parameters do not change with temperature. The constancy of T min allows derivation of a simple expression relating growth rate of strain CM21/3 to temperature and salt concentration/water activity within the range of linear response to temperature predicted by the square-root model.     

Combined effect of temperature and salt concentration/water activity on the growth rate of Halobacterium spp.

Growth responses of the halophilic bacteria, Halobacterium sp. strain HB9 and Halobacterium salinarium strain CM42/12, to temperature and water activity/sodium chloride concentration were described by the square root model and T _min (the theoretical minimum temperature for growth) was fixed. Little change in growth rate was observed in response to added NaCl at water activities below which cell lysis was avoided. Hence, growth of halobacteria on products such as salted, dried fish at water activities below 0.85 may be based on the square root temperature response without the need to incorporate a water activity term.     

Modelling the growth response of Staphylococcus xylosus to changes in temperature and glycerol concentration/water activity

The growth response of Staphylococcus xylosus strain CM21/3 to changes in temperature and water activity (glycerol concentration) was similar to that observed when water activity was adjusted by added NaCl. At each water activity level the effect of temperature on bacterial growth rate was described well by the square root model. T _MIN (the notional minimum temperature for growth) was found to be constant and was similar to the value obtained for the same organism grown in media containing NaCl. Growth rate was proportional to glycerol concentration/water activity allowing the combined effect of this factor and temperature to be modelled by substitution of the constant b in the basic square root model by a term for water activity. The observed minimum water activity for growth at the optimum temperature was close to that predicted by the model.     

Ecological relevance of minimum seasonal water potentials

The minimum seasonal water potential a plant experiences, ψ_min, provides an important measure of plant water status, as it reflects the maximum water deficit that leaves and xylem must tolerate to maintain physiological activity. ψ_min also acts as a selective force on xylem structure which, in turn, generates correlations between ψ_min and numerous hydraulic traits. This review focuses on the ecological relevance of ψ_min as a reflection of overall plant hydraulic strategy. The focus is on plant functional strategies with respect to soil drought, but we conclude with preliminary findings on the role of atmospheric drought.     

The effect of incubation temperature and sodium chloride concentration on the growth kinetics of Vibrio anguillarum and Vibrio anguillarum-related organisms

The effect of temperature and NaCl concentration on the growth kinetics of Vibrio anguillarum and V. anguillarum -related (VAR) strains was studied.
For one wild VAR strain, NaCl concentration interfered with growth temperature parameters, in particular, with the maximum growth temperature but also with the optimum temperature (defined as the temperature at which μ_max equals its maximal value μ_opt), and with μ_opt itself. For the same strain, optimal growth required the adding of NaCl to the medium to a final concentration of 1·5%. These results were not confirmed by tests on a V. anguillarum collection strain.
When the NaCl concentration in the culture media was 1.5%, the optmum temperature for the nine strains studied ranged from 29.7°C to 34°C whereas the maximum temperature ranged between 35.3°C and 38.5°C.
Hence, antbiotic susceptibility testing as well as biochemical identification might be carried out at 30°C in the presence of 1.5% NaCl, which corresponded to a suboptimal growth.     

A note on Aeromonas spp. from chickens as possible food-borne pathogens

The possible role of Aeromonas spp. as potential food-borne psychrotrophic pathogens was investigated by examining organisms isolated from processed raw chicken for their biochemical characteristics, ability to produce exotoxins and to grow at chill temperatures. These strains, in particular A. sobria , with identical characteristics to human diarrhoea-associated aeromonads were readily found. Chicken, and human and environmental (water) strains characterized in a previous study, were investigated for their ability to grow at refrigeration temperatures (5 ± 2°C) and, for selected strains, the theoretical minimum temperature for growth ( T _min) was determined from the growth pattern in a temperature gradient incubator. All enterotoxigenic chicken strains tested were typical mesophiles, with an optimal growth temperature of ˜37°C and T _min values ˜4.5°C. They were rapidly outgrown by a psychrotrophic Pseudomonas sp. typical of spoilage biota found on food. Enterotoxin was not produced below 15°C by any of the toxigenic food strains tested. The Aeromonas strains isolated from chickens in this study seem unlikely therefore to be a significant health risk, provided the chickens are properly stored and cooked. This would appear to be substantiated by the lack of reports of food-associated outbreaks of illness from these sources.     

Effect of long-term and rapid cold hardening on the cold torpor temperature of an aphid

Abstract.  The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT _min) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min⁻¹ is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min⁻¹ both produce a significant decrease in CT _min from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT _min of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT _min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.     

Effect of body weight and temperature on the maximum daily food consumption of Gasterosteus aculeatus L. and Phoxinus phoxinus (L.): selecting an appropriate model

The relationships between the maximum, daily food consumption, body weight and water temperature for the stickleback, Gasterosteus aculeatus L. , and the minnow, Phoxinus phoxinus (L.), were studied. The two species occupy the same lakes in mid-Wales, but differ in that G. aculeatus has a true stomach whereas P. phoxinus lacks a true stomach.
For both species, the relationship between food consumption (F) and body weight ( W ) could be described by the model: log_eF=a + b log_e W . The effect of temperature (T) could be incorporated in the form: log_ef= a + b, log_e W+b₂log_e T. These models were selected because they accounted for a high proportion of the variance in the dependent variable, and because an analysis of the residuals obtained after fitting a model showed no trends which would have signalled the inadequacy of the model.     

Using infrared thermography to assess seasonal trends in dorsal fin surface temperatures of free-swimming bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida

The temperature differential (Δ T ) between a body surface and the environment influences an organism's heat balance. In Sarasota Bay, FL, where ambient water temperature ( T _w) ranges annually from 11° to 33°C, Δ T was investigated in a resident community of bottlenose dolphins ( Tursiops truncatus ). Dorsal fin surface temperatures ( T _dfin) were measured on wild, free-swimming dolphins using infrared thermography. Field and laboratory calibration studies were also undertaken to assess the efficacy of this non-invasive technology in the marine environment. The portability of infrared thermography permitted measurements of T _dfin across the entire range of environmental temperatures experienced by animals in this region. Results indicated a positive, linear relationship between T _dfin and T _w ( r ²= 0.978, P < 0.001). On average, T _dfin was 0.9°C warmer than T _w across seasons, despite the 22°C annual range in T _w. Changes in integumentary and vascular insulation likely account for the stability of Δ T _{dfin − w} and the protection of core temperature ( T _core) across seasons. The high thermal conductivity of water may also influence this Δ T . The use of infrared thermography is an effective, non-invasive method of assessing dorsal fin skin surface temperatures (±1°C) across large numbers of wild, free-swimming dolphins throughout their thermally dynamic aquatic environment.     

Water relations of solute accumulation in Pseudomonas fluorescens

When Pseudomonas fluorescens was grown in a glucose salts medium adjusted with NaCl to a water activity (a_w) value of 0.980, the intracellular glutamic acid concentration increased 23-fold and comprised 90% of the total amino acid pool. This increase was not observed when the a_w of the medium was reduced to 0.980 with sorbitol. Sorbitol was taken up rapidly over a 30 min period and accumulated intracellularly to a level approximately two-fold greater than the concentration in the growth medium. In continuous culture, the specific rate of glutamic acid production and glucose uptake was greater at 0.980 (NaCl) than at 0.997 a_w. The maintenance coefficients for glucose uptake were similar at both a_w values but were 2.4-fold greater for glutamic acid production at 0.980 (NaCl) than at 0.997 a_w.     

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.     

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

The hydraulic conductance ( L ₀) of detached, exuding root systems from melon ( Cucumis melo cv. Amarillo oro) was measured. All plants received a half-strength Hoagland nutrient solution, and plants stressed either solely with NaCl (50 mM) or with NaCl (50 mM) following treatment (2 d) with CaCl₂ (10 mM) were compared with controls and CaCl₂-treated (10 mM) plants. The L ₀ of NaCl-treated plants was markedly decreased when compared to control and CaCl₂-treated plants, but the decrease was smaller when NaCl was added to plants previously treated with CaCl₂. A similar effect was observed when the flux of Ca²⁺ into the xylem and the Ca²⁺ concentration in the plasma membrane of the root cells were determined. In control, CaCl₂- and NaCl + CaCl₂-treated plants, HgCl₂ treatment (50 μM) caused a sharp decline in L ₀ to values similar to those of NaCl-stressed roots, but L ₀ was restored by treatment with 5 mM DTT. However, in NaCl roots only a slight effect of Hg²⁺ and DTT were observed. The effect of all treatments on L ₀ was similar to that on osmotic water permeability ( P _f) of individual protoplasts isolated from roots. The results suggest that NaCl decreased the passage of water through the membrane and roots by reducing the activity of Hg-sensitive water channels. The ameliorative effect of Ca²⁺ on NaCl stress could be related to water-channel function.     

The influence of thermal parameters on the acclimation responses of pinfish Lagodon rhomboides exposed to static and decreasing low temperatures

Pinfish Lagodon rhomboides acclimation rates were determined by modelling changes in critical thermal minimum ( T _{crit min}, ° C) estimates at set intervals following a temperature decrease of 3–4° C. The results showed that pinfish gained a total of 3·7° C of cold tolerance over a range of acclimation temperatures ( T _acc, ° C) from (23–12° C), that cold tolerance increased with exposure time to the reduced temperature at all T _acc, but that the rate of cold tolerance accruement (mean 0·14° C day⁻¹) was independent of T _acc. A highly significant ( P < 0·001) multivariate predictive model was generated that described the acclimation rates and thermal tolerance of pinfish exposed to reduction in water temperature: log₁₀ T _{crit min}= 0·41597 − 0·01704 T _acc+ 0·04320 T _plunge− 0·08376[log₁₀ ( t + 1)], where T _plunge is plunge temperature (° C) and t is the time (days). A comparison of the present data, with acclimation rate data for other species, suggests that factors such as latitude or geographic range may play a more important role than ambient temperature in determining cold acclimation rates in fishes.     

A desk study of the relationship between temperature and hatching time for the eggs of five species of salmonid fishes

SUMMARY. Information on temperature (T°C) and time from fertilization to 50% hatch ( D days) for five species of salmonid fishes has been used to assess several mathematical models relating D and T . No single equation gave the best fit to all five data sets. The power law with temperature correction (α), log₁₀₁ D = log₁₀ a + b log₁₀ ( T - α) and the quadratic, log₁₀ D = log₁₀ a + bT + b ₁ T ² (where a, b, b ₁, and α are constants), each accounted for over 97 % of the variance of D and were good fits to the observed data points for all five species. There was little difference between the predictions obtained from these two equations within the range of observed temperatures. Therefore, the simpler power-law model is preferred. However, there were substantial within-species differences between values of D predicted from extrapolations of the two models from 2 or 3°C down to 0°C. When more data for low temperatures become available it will be possible to make a more objective choice of model.     

Effect of oxygen tension, salinity, temperature and organic matter concentration on the growth and nitrifying activity of an estuarine strain of Nitrosomonas

Abstract The effects of O₂ tension, temperature, salt concentration and organic matter concentration on the growth and nitrifying activity of Nitrosomonas N₃ isolated from Tay Estuary sediments have been investigated. Chemostat-grown cultures were able to grow and nitrify at dissolved O₂ concentrations as low as 0.1 mg O₂· 1⁻¹ (cell population densities were 15% of those obtained in fully aerated cultures). This bacterium was sensitive to reduced temperatures as chemostat-grown cultures washed out at growth temperatures below 15°C, at dilution rates > 0.025 · h⁻¹. Batch-grown cultures of Nitrosomonas N₃ were used to study the effects of NaCl and complex organic matter concentration on nitrifying activity. Maximum rates of NH⁺₄ oxidation were recorded at NaCl concentrations of 1% w/v, whilst tryptone soya broth (TSB), nutrient broth (NB), yeast extract broth (YEB) and peptone were inhibitory at concentrations > 10 mg · 1⁻¹.     

Study of the effects of temperature, pH, NaCl, and aw on the proteolytic and lipolytic activities of cheese-related lactic acid bacteria by quadratic response surface methodology

The individual and interactive effects of temperature, pH, NaCl, and a_w on the proteolytic and lipolytic activities of Lactobacillus delbrueckii subsp. bulgaricus B397, Lactococcus lactis subsp. lactis T12, and Lb. plantarum 2739 were studied by quadratic response surface methodology. The effects on enzyme activities depended on the interactions among the independent variables, type of activity, substrate and, especially, species. The proteinase activity of strains B397 and T12 was affected differently by pH as individual or interactive terms depending on the type of substrate _sl- or β-casein. The increase of NaCl concentration (2.5–7.5%) under cheese-like conditions had a negative effect on the proteinase activity of strain T12. The effect of NaCl was related to the corresponding decrease in a_w. Aminopeptidases N and A, iminopeptidase and endopeptidase of Lc. lactis subsp. lactis T12 were strongly inhibited by pH 5–6 and NaCl concentration higher than 3.75%. The negative effects of these independent variables was in several cases enhanced by their interaction and/or by the interaction with the lowest temperatures. In contrast, the same peptidases of Lb. plantarum 2739 retained a high activity under the very hostile environmental conditions. Iminopeptidase and especially endopeptidase activities of strain 2739 were stimulated slightly by NaCl at concentrations up to 5%. Lipase/esterase activity of Lb. delbrueckii subsp. bulgaricus B397 was markedly inhibited under cheese-like conditions.     

Nitrogen fixation (C2H2 reduction) by Medicago nodules and bacteroids under sodium chloride stress

Medicago ciliaris (L.) All., a salt-tolerant legume, was not nodulated by Rhizobium meliloti (2011), a strain commonly used for field inoculation of alfalfas. A strain of Rhizobium meliloti (ABS7) was isolated from saline Algerian soils. It is generally more salt-resistant than strain 2011, exhibits a higher rate of growth and induces the formation of nodules on M. ciliaris . C₂H₂ reduction activity of M. ciliaris nodules was inhibited by 50% in the presence of 200 m M NaCl in the culture medium. whereas 100 m M NaCl was sufficient to inhibit the activity of nodules of M. sativa (L. cv. Europe). C₂H₂ reduction by bacteroids, isolated from nodules of the two species of alfalfa, was directly inhibited by the presence of NaCl in the incubation medium. In both cases, glucose could support bacteroid nitrogen fixation, but only in a narrow range of O₂ tensions. Bacteriods from M. ciliaris were more tolerant to salt than M. sativa ones. The salt resistance of bacteroids from nodules of plants watered with NaCl solutions was not improved in either species. Salt directly added to the incubation mixture of bacteroids or to the culture medium of plants inhibited O₂ uptake of bacteroids isolated from nodules of both M. ciliaris and M. sativa . The depressive effect of NaCl on bacteroid C₂H₂ reduction could be directly related to the drop in bacteroid respiration. The nitrogen fixation capacity of the M. ciliaris-Rhizobium meliloti (ABS7) symbiosis under saline conditions leads us to recommend the introduction of this association in salt-troubled areas.     

Chemostat adaptation of Escherichia coli B/r/1 to low water activity

Chemostat cultures of Escherichia coli B/r/1 under conditions of glucose limitation in a salts medium at high water activity ( a _w of 0.999) and at an a _w of 0.987, controlled by NaCl, have been compared. The system was run at dilution rates above 0.035 h^-1. The results suggested that the organism adapted to the lower a _w of the medium as no significant change was observed in the energy requirement for maintenance, although the maximum molar growth yield for glucose decreased by 23.2%. Such cultures showed also a shorter lag and a higher growth rate in batch at an a _w of 0.987, as compared with cultures initiated with an unadapted ( a _w of 0.999) inoculum.     

Modelling the growth response of Staphylococcus xylosus to changes in temperature and glycerol concentration/water activity

The growth response of Staphylococcus xylosus strain CM21/3 to changes in temperature and water activity (glycerol concentration) was similar to that observed when water activity was adjusted by added NaCl. At each water activity level the effect of temperature on bacterial growth rate was described well by the square root model. TMIN (the notional minimum temperature for growth) was found to be constant and was similar to the value obtained for the same organism grown in media containing NaCl. Growth rate was proportional to glycerol concentration/water activity allowing the combined effect of this factor and temperature to be modelled by substitution of the constant b in the basic square root model by a term for water activity. The observed minimum water activity for growth at the optimum temperature was close to that predicted by the model.     

Prediction, from temperature, of eyeing, hatching and 'swim-up' times for salmonid embryos

SUMMARY. 1. The literature contains a number of curves relating time (days) required for median hatch (=D₂) to water temperature (T,°C) for the eggs of several salmonid fishes. There are relatively few data on the relationships between time to median eyed (= D₁), days) or time to median swim-up (= D₃, days) and temperature.
2. From published data, over most of the range 0-9.5°C, approximate relationships are D,=0.5D₂ for Atlantic salmon (Salmo salar L.) and D3 = 1.7D₂ for eight species of Salmo and Oncorhynchus.
3. Field and hatchery tests suggest that these are useful empirical models for approximate prediction of D₁ and D₃ from D₂ for most salmonids.