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.     

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.     

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.     

Effect of Some Environmental Factors on Psychrophilic Microbacteria

S ummary . The growth of three psychrophilic strains of Microbacterium isolated from meat was studied at 10 temperatures between 0° and 35° and at 6 water activity (a_w) levels between 0.99 and 0.94. The temperature and water relations of the three strains were similar. For all strains the rate of growth was fastest at 25° and a_w 0.99, and growth did not occur at 35°.
Further experiments on one strain showed that under aerobic conditions the range of water activities permitting growth was independent of temperature, but under anaerobic conditions the minimum water activity increased from about 0.94—0.96 as the temperature was reduced from 25° to 0°. Growth was inhibited by low concentrations of undissociated nitrous acid, and inhibition was greater at 0° than at 10° or 25°.     

The effect of pH, acidulant and temperature on the survival of Yersinia enterocolitica

The survival of Yersinia enterocolitica at sub-optimal temperatures (0–23°C) and growth inhibitory pH values, achieved using a range of acidulants, was investigated. At a given pH, survival was greater the lower the temperature. Sulphuric and citric acids had lower bactericidal activity than acetic and lactic acids and in nearly all cases where the four acids could be compared at the same pH the order of bactericidal activity was acetic > lactic > citric > sulphuric. Attempts to model this behaviour by a negative square root relationship gave good correlation coefficients for plots of the square root of death rate against temperature at different combinations of pH and acidulant but so too did several other functions of death rate. The high coefficient of variation for T ₀ determined from square root plots prevented construction of a combined temperature/pH model similar to that already described for growth.     

Utility of phenomenological models for describing temperature dependence of bacterial growth.

We compared three unstructured mathematical models, the master reaction, the square root, and the damage/repair models, for describing the relationship between temperature and the specific growth rates of bacteria. The models were evaluated on the basis of several criteria: applicability, ease of use, simple interpretation of model parameters, problem-free determination of model parameters, statistical evaluation of goodness of fit (chi 2 test), and biological relevance. Best-fit parameters for the master reaction model could be obtained by using two consecutive nonlinear least-square fits. The damage/repair model proved to be unsuited for the data sets considered and was judged markedly overparameterized. The square root model allowed nonproblematical parameter estimation by a nonlinear least-square procedure and, together with the master reaction model, was able to describe the temperature dependence of the specific growth rates of Klebsiella pneumoniae NCIB 418, Escherichia coli NC3, Bacillus sp. strain NCIB 12522, and the thermotolerant coccobacillus strain NA17. The square root and master reaction models were judged to be equally valid and superior to the damage/repair model, even though the square root model is devoid of a conceptual basis.     

Effect of growth temperature on several exported enzyme activities in the psychrotrophic bacterium Pseudomonas fluorescens.

In accordance with previous results, the activity of extracellular proteases from Pseudomonas fluorescens MF0 is maximal at a growth temperature of 17.5 degrees C, well below the optimal growth temperature. In addition, the activities of three periplasmic phosphatases display the same growth temperature optimum. Chemostat experiments have shown that it is the growth temperature itself and not the value of the growth rate that regulates these activities. In contrast, a foreign periplasmic phosphatase, expressed under the control of its own promoter, displays a different sensitivity toward temperature. We conclude that in the psychrotrophic strain P. fluorescens MF0, growth temperature exerts a specific control upon the activity of certain enzymes. The critical temperature (17.5 degrees C) is within the range of normal growth, suggesting that this control is probably different from a cold shock or heat shock response.     

Utility of phenomenological models for describing temperature dependence of bacterial growth.

We compared three unstructured mathematical models, the master reaction, the square root, and the damage/repair models, for describing the relationship between temperature and the specific growth rates of bacteria. The models were evaluated on the basis of several criteria: applicability, ease of use, simple interpretation of model parameters, problem-free determination of model parameters, statistical evaluation of goodness of fit (chi 2 test), and biological relevance. Best-fit parameters for the master reaction model could be obtained by using two consecutive nonlinear least-square fits. The damage/repair model proved to be unsuited for the data sets considered and was judged markedly overparameterized. The square root model allowed nonproblematical parameter estimation by a nonlinear least-square procedure and, together with the master reaction model, was able to describe the temperature dependence of the specific growth rates of Klebsiella pneumoniae NCIB 418, Escherichia coli NC3, Bacillus sp. strain NCIB 12522, and the thermotolerant coccobacillus strain NA17. The square root and master reaction models were judged to be equally valid and superior to the damage/repair model, even though the square root model is devoid of a conceptual basis.     

Influence of Water Potential on Growth, Enzyme Secretion and In Vitro Enzyme Activities of Trichoderma harzianum at Different Temperatures

The influence of water potential on linear mycelial growth, secretion, and the in vitro activities of enzymes β-glucosidase, cellobiohydrolase, β-xylosidase, exochitinase, and chymotrypsin of Trichoderma harzianum strain T66 was studied at different temperatures. Nearly linear correlation was found between water potential and colony growth rate at both 25°C and 10°C, with higher growth rates at the higher temperature and higher water potentials. The amounts of enzyme secretion depended on the water potential and not on the quality of salt (NaCl or KCl) used as osmoticum. Enzyme activities were significantly affected by water potential. Significant enzyme activities were measured for most of the enzymes even at −14.800 megapascal (MPa), which is below the water potential where mycelial growth ceased. These results suggest the possibility of using mutants with improved xerotolerance for biocontrol purposes in soils with lower water potentials. Received: 5 October 1999 / Accepted: 22 November 1999     

Comparison of temperature effects on soil respiration and bacterial and fungal growth rates

Temperature is an important factor regulating microbial activity and shaping the soil microbial community. Little is known, however, on how temperature affects the most important groups of the soil microorganisms, the bacteria and the fungi, in situ. We have therefore measured the instantaneous total activity (respiration rate), bacterial activity (growth rate as thymidine incorporation rate) and fungal activity (growth rate as acetate-in-ergosterol incorporation rate) in soil at different temperatures (0-45 degrees C). Two soils were compared: one was an agricultural soil low in organic matter and with high pH, and the other was a forest humus soil with high organic matter content and low pH. Fungal and bacterial growth rates had optimum temperatures around 25-30 degrees C, while at higher temperatures lower values were found. This decrease was more drastic for fungi than for bacteria, resulting in an increase in the ratio of bacterial to fungal growth rate at higher temperatures. A tendency towards the opposite effect was observed at low temperatures, indicating that fungi were more adapted to low-temperature conditions than bacteria. The temperature dependence of all three activities was well modelled by the square root (Ratkowsky) model below the optimum temperature for fungal and bacterial growth. The respiration rate increased over almost the whole temperature range, showing the highest value at around 45 degrees C. Thus, at temperatures above 30 degrees C there was an uncoupling between the instantaneous respiration rate and bacterial and fungal activity. At these high temperatures, the respiration rate closely followed the Arrhenius temperature relationship.     

Soil temperature and flooding effects on two species of citrus

Summary Rough lemon (Citrus jambhiri Lush.) and sour orange (C. aurantium L.) seedlings were grown at constant soil temperatures of 16, 24, and 33 C for 3 months. Shoot and root growth of rough lemon was greatest at 33 C while growth of sour orange was greatest at 24 C. There were no significant effects of soil temperature on shoot: root ratio, leaf water potential or stomatal conductance. The hydraulic conductivity of intact root systems of both species was highest when seedlings were grown at 16 C. Thus, acclimation through greater root conductivity at low soil temperature may have compensated for decreased root growth at 16 C and negated effects of soil temperature on plant water relations. Half the plants growing at each soil temperature were subsequently flooded. Within 1 week, the soil redox potential (Eh) dropped below zero mV, reaching a minimum Eh of –250mV after 3 weeks of flooded conditions. Flooded plants exhibited lower root conductivity, a cessation of shoot growth, lower leaf water potentials, lower stomatal conductances, and visual sloughing of fibrous roots. Decreases in root conductivity in response to flooding were large enough to account for the observed decreases in stomatal conductance.Florida Agricultural Experiment Stations Journal Series No. 4080.     

Comparison of a quadratic response surface model and a square root model for predicting the growth rate of Yersinia enterocolitic

Polynomial equations, relating the growth rate of Yersinia enterocolitica to temperature (0–25°C) and pH (4.5–6-5) in a liquid medium were constructed for four different acidulants. The logarithm of the time for a 100-fold increase in bacterial numbers could be represented by a quadratic response surface function of pH and temperature. The interactions between pH and temperature on growth rate were found to be additive. Values for a 2 log cycle increase in growth derived from the model were in good agreement with experimental values. Predictions from the quadratic model and from a square root model were compared with experimental values in laboratory media and UHT milk. The mean square error (MSE) for the quadratic response surface model was smaller than that for the square root model in 81% of cases. In UHT milk the square root model increasingly underestimated growth rate, as the temperature decreased and would 'fail dangerous' if used for predictive purposes. This indicated that the response surface model is more reliable for predicting the growth of Y. enterocolitica under conditions of sub-optimal temperature and pH.     

Exposure of roots of cucumber (Cucumis sativus) to low temperature severely reduces root pressure, hydraulic conductivity and active transport of nutrients

When root temperature dropped below 25°C, there was a sharp drop in the root pressure ( P _r) and hydraulic conductivity of excised roots ( Lp _r) of young cucumber ( Cucumis sativus L.) seedlings as measured with the root pressure probe. A detailed analysis of root hydraulics provided evidence for a larger reduction in the osmotic component of Lp _r (77%) in comparison with the hydrostatic component (34%) in response to the exposure of the root system to 13°C. The activity of the plasma membrane H⁺-ATPase (EC 3.6.1.35) was reduced from 30 to 16 µmol Pi mg⁻¹ protein h⁻¹ upon exposure to 8°C for 1 day. Ultrastructural observations showed no evidence of loosening of the microstructure of endodermal cell walls in low temperature (LT)-treated roots. It is concluded that the rapid drop in the P _r in response to LT is largely caused by a reduction in the activity of the plasma membrane H⁺-ATPase rather than by loosening of the endodermal wall which would cause substantial solute losses. On the other hand, water permeability of root cell membrane at LT was related to changes in the activity (open/closed state) of water channels.     

The effect of root temperature on rose plants in relation to air temperature

Rose plants (Rosa hybrida ‘Sonia’=‘Sweet Promise’) were grown in heated (minimum night temperature 17°C), and unheated greenhouses with or without root heating to 21°C. These trials covered 6 growth cycles extending over two winter seasons. In the heated greenhouse, root heating did not increase yield, flower quality or plant development. In the unheated greenhouse, root-heated plants grew as well as those in the air-heated greenhouse as long as the air temperature did not fall below 6°C. When minimum night temperatures fell below 6°C, growth, yield and quality were reduced, irrespective of root temperature. Daytime plant water relations were studied in plants growing at 6 different root temperatures in the unheated greenhouse. Leaf resistance to water diffusion was lowest at optimal root temperature. Total leaf water potential was not significantly affected by root temperature.     

Estimation of the contribution of halobacterial to the bacterial biomass and activity in solar salterns by the use of bile salts

Abstract Bile salts (deoxycholate, taurocholate) were used to estimate the contribution of bacteria of the Halobacterium group to bacterial community size and activity at different salinities as found in a multi-pond saltern. Low concentrations of bile salts cause lysis of halophilic archaebacteria of the Halobacterium group, while halophilic eubacteria and halococci remain microscopically intact. Upon addition of bile salts, total bacterial numbers (as estimated microscopically) in saltern ponds at salinities below 250 g/l did not decrease, while above this salinity bacterial numbers decreased by 30–50%. To estimate the contribution of halobacteria to overall heterotrophic activity, the effect of bile salt addition was tested on the incorporation of labelled amino acids. In saltern ponds of a salinity below 250 g/l activity was not greatly inhibited by taurocholate, while at salinity above 300 g/l taurocholate completely abolished incorporation of amino acids.     

副溶血性弧菌温度-盐度双因素预测模型的建立

本文以副溶血性弧菌VP BJ1.1997为研究对象, 采用均匀设计试验方法, 建立并验证了温度范围为7°C~43°C, 盐度范围为0.5%~9.5%NaCl的生长动力学模型。结果表明, 所选一级模型的拟合效果优劣依次为Logistic方程>Gompertz方程>Linear方程, 以Logistic方程为一级模型计算生长参数; 二级模型采用平方根模型进行拟合, 得到模型相关系数r为0.9863, 最低生长温度T min为9.0506°C, 最高生长盐度为5.93%NaCl(对应最低生长水分活度Aw min     

Root growth dynamics linked to above-ground growth in walnut (Juglans regia)

Background and Aims Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature.Methods Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia ‘Chandler’) using minirhizotron techniques.Key Results Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production.Conclusions The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.     

Characterization of Salicola sp. IC10, a lipase- and protease-producing extreme halophile

In order to explore the diversity of extreme halophiles able to produce different hydrolytic enzymes (amylase, protease, lipase and DNAse) in hypersaline habitats of South Spain, a screening program was performed. A total of 43 extreme halophiles showing hydrolytic activities have been isolated and characterized. The isolated strains were able to grow optimally in media with 15–20% (w/v) total salts and in most cases, growth was detected up to 30% (w/v) total salts. Most hydrolase producers were assigned to the family Halobacteriaceae , belonging to the genera Halorubrum (22 strains), Haloarcula (nine strains) and Halobacterium (nine strains), and three isolates were characterized as extremely halophilic bacteria (genera Salicola, Salinibacter and Pseudomonas ). An extremely halophilic isolate, strain IC10, showing lipase and protease activities and identified as a Salicola strain of potential biotechnological interest, was further studied. The optimum growth conditions for this strain were 15–20% (w/v) NaCl, pH 8.0, and 37 °C. Zymographic analysis of strain IC10 detected the lipolytic activity in the intracellular fraction, showing the highest activity against p -nitrophenyl-butyrate as a substrate in a colorimetric assay, whereas the proteolytic activity was detected in the extracellular fraction. This protease degraded casein, gelatin, bovine serum albumin and egg albumin.     

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 squareroot models which had been used previously to model temperature dependence only. The model r = b ( T - T _min) is shown to be a special case of the BélehraAdek temperature function which is given by r = a ( T - aL)^d. The constant aL is the so-called '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 Bélehradek-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.