Minimum Growth Temperature Research Articles

One-step dynamic analysis of growth kinetics of Bacillus cereus from spores in simulated fried rice – Model development, validation, and Marko Chain Monte Carlo simulation

Bacillus cereus is a spore-forming pathogen capable of producing an emetic toxin and several diarrheal enterotoxins that may cause outbreaks of foodborne illness often associated with rice-based and other farinaceous foods. Therefore, the objective of this study was to investigate the growth kinetics of B. cereus from spores in simulated egg fried rice.The growth of B. cereus was observed under dynamic conditions. Three independent growth curves were analyzed simultaneously using a one-step dynamic analysis (OSDA) to determine the kinetic parameters. The results showed that the minimum, optimum, and maximum growth temperatures were 11.8, 40.8, and 50.6 °C, respectively, with an optimum specific growth rate of 2.4 per h. The root-mean-square-error (RMSE) of model development was 0.4 log CFU/g. Deterministic validation with another 3 independent dynamic temperature profiles showed a RMSE of 0.5 log CFU/g. With Markov Chain Monte Carlo simulation, the RMSE of prediction was only 0.3 log CFU/g.This study proved that OSDA is an effective and efficient method for quickly developing integrated predictive models and estimating kinetic parameters. The resulting integrated model can be used to accurately predict the growth of B. cereus and for managing its risks associated with egg fried rice. The developed kinetic models also can be used to guide restaurant owners and catering establishments to properly prepare and store egg fried rice and other related products to prevent the growth of B. cereus. According to the model, the growth of mesophilic B. cereus is unlikely to occur if the food is stored below 10 °C.

In Vitro Thermal Requirements of Some Beauveria sp. Isolates Under Constant Conditions

The thermal tolerance of four isolates of Beauveria bassiana and one isolate of Beauveria pseudobassiana was evaluated in vitro, by measuring the colonial diameters, on PDA medium, at temperatures between 5 and 35 ° C, during 14 days. The data obtained were used to calculate the growth rate of fungal colonies (mm / day), using linear regression. The representation of the values corresponding to the minimum, optimal and maximum temperature for vegetative growth was a curve described by a modified beta (ß) mathematical function. The minimum growth temperature of these isolates varied between 3.4 and 4.5 °C, the optimum temperature varied between 21.8 and 22.9 °C, except for one isolate of which optimal temperature was 26.8 °C, while the maximum temperature was varied for all isolates between 35.0 and 35.7 °C.

Analysis and mathematical modeling of the survival kinetics of Staphylococcus aureus in raw pork under dynamic and static temperature conditions.

The incidence of frequent foodborne disease outbreaks due to Staphylococcus aureus contamination necessitates the urgent searching for effective methods to monitor S. aureus. This research aims to construct model with a dynamic survival curve and some static growth curves to predict the behavior of S. aureus in raw pork. Lack of research about S. aureus kinetics in pork under fluctuating temperature conditions across freezing and thawing necessitates this study. One‐step analysis was used to determine the model parameters, which was more efficient than conventional model analysis with two steps. The results of kinetic analysis showed that Tmin (minimum growth temperature) was 6.85°C, which is close to the estimated values in previous reports. Subsequently, validation results indicated the integrated model can accurately predict the behavior of S. aureus regardless of isothermal or nonisothermal conditions with the root‐mean‐square errors (RMSE < 0.44 log CFU/g, 73.9% of the errors of prediction falls within ±0.5 log CFU/g), accuracy factors Af and bias factors Bf were both close to 1. This work may offer an effective method for the assessment of microbial security related to S. aureus in pork.

The effect of pH on the growth rate of Bacillus cereus sensu lato: Quantifying strain variability and modelling the combined effects of temperature and pH

In this study, the effect of pH, alone or in combination with temperature, on the maximum growth rate (μmax) of B. cereus sensu lato was investigated. In phase 1, the effect of pH at 30 °C was studied for 16 mesophilic strains and 2 psychrotrophic strains of Bacillus cereus sensu lato. The μmax vs. pH relationship was found to show a similar pattern for all the strains. Several pH models from literature were evaluated and the best performing ‘growth rate vs. pH’ model selected. A stochastic model was then developed to predict the maximum specific growth rate of mesophilic B. cereus at 30 °C as a function of pH, the intra-species variability being incorporated via considering the model parameters (e.g. pHmin) randomly distributed. The predicted maximum specific growth rates were acceptably close to independent published data. In phase 2, the combined effects of temperature and pH were studied. Growth rates were also generated at 15, 20 and 40 °C for a selection of strains and the pH model was fitted at each temperature. Interestingly, the results showed that the estimates for the pHmin parameter for mesophilic strains were lower at 20–30 °C than near the optimum temperature (40 °C), suggesting that experiments for the determination of this parameter should be conducted at lower-than-optimum temperatures. New equations were proposed for the relationship between temperature and the minimum pH-values, which were also consistent with the experimental growth boundaries. The parameters defining this equation quantify the minimum temperature for growth observed experimentally, the temperature of maximum enzyme stability and the maximum temperature for growth. Deviations from the Gamma hypothesis (multiplicative effects of environmental factors on the maximum specific growth rate) were observed near the growth limits, especially at 40 °C. To improve model performance, two approaches, one based on a minimum pH-term (doi: https://doi.org/10.3389/fmicb.2019.01510) and one based on an interaction term (doi: http://dx.doi.org/10.1016/S0168-1605(01)00640-7) were evaluated.

Phylogeny and Pathogenicity of Phytophthora Species Associated with Artichoke Crown and Root Rot and Description of Phytophthora marrasii sp. nov.

Field surveys conducted on nine farms over a 2-year period showed the widespread presence of Phytophthora-related diseases on globe artichoke plants in the main growing area in Sardinia (Italy). Characteristic symptoms included wilting and necrosis of the outermost leaves and dark brown discoloration of stem tissues, as well as root rot. A total of 18 Phytophthora colonies belonging to three species were isolated and characterized. Based on morphological features and ITS sequence data, Phytophthora isolates were identified as P. crassamura (eight isolates) and P. cactorum (four isolates). Six isolates could not be assigned to any formally described species of Phytophthora and are therefore described here as Phytophthora marrasii sp. nov. The ITS phylogeny places P. marrasii in a terminal clade basal to the sister taxa (P. foliorum, P. hibernalis, P. lateralis, and P. ramorum) of the clade 8c. In particular, P. marrasii is phylogenetically related to P. foliorum, a species from which it differs in 62 nucleotides in the ITS region. At the same time, it can easily be distinguished morphologically from P. foliorum mainly because of the low minimum temperature for growth, the bigger and persistent non-papillate sporangia, and smaller oogonia. Pathogenicity tests confirmed that all three Phytophthora species are pathogenic on globe artichokes, which represent a new host for these pathogens.

Isolation and Molecular Identification of the Native Microflora on Flammulina velutipes Fruiting Bodies and Modeling the Growth of Dominant Microbiota (Lactococcus lactis)

The objectives of this study were to isolate and identify the dominant microorganism in Flammulina velutipes fruiting bodies (FVFB) and to develop kinetic models for describing its growth. The native microflora community on FVFB was isolated and identified using morphological examination and high-throughput sequencing analysis. FVFB presented complex microbial communities with dominant microorganisms being Lactococcus lactis. Irradiated FVFB were inoculated with the isolated strain of L. lactis and cultivated at various temperatures (4, 10, 16, 20, 25, 32, and 37°C). Three primary models, namely the Huang, Baranyi and Roberts, and reparameterized Gompertz models, and three secondary models, namely the Huang square-root, Ratkowsky square-root, and Arrhenius-type models, were developed and evaluated. With the lowest values of mean square error (MSE, 0.023–0.161) and root mean square error (RMSE, 0.152–0.401) values, the reparameterized Gompertz model was more suitable to describe the growth of L. lactis on FVFB than both Huang and Baranyi and Roberts models. The Ratkowsky square-root model provided more accurate estimation for the effect of temperature on the specific growth rate of L. lactis. The minimum growth temperature predicted by the Ratkowsky square-root model was −7.1°C. The kinetic models developed in this study could be used to evaluate the growth behavior of L. lactis on FVFB and estimate the shelf-life of FVFB.

A stochastic approach for modelling the effects of temperature on the growth rate of Bacillus cereus sensu lato

A stochastic model that predicts the maximum specific growth rate (μmax) of Bacillus cereus sensu lato as a function of temperature was developed. The model integrates the intra-species variability by incorporating distributions of cardinal parameters (Tmin, Topt, Tmax) in the model. Growth rate data were generated for 22 strains, covering 5 major phylogenetic groups of B. cereus, and their cardinal temperatures identified. Published growth rate data were also incorporated in the model fitting, resulting in a set of 33 strains. Based on their cardinal temperatures, we identified clusters of Bacillus cereus strains that show similar response to temperature and these clusters were considered separately in the stochastic model. Interestingly, the μopt values for psychrotrophic strains were found to be significantly lower than those obtained for mesophilic strains. The model developed within this work takes into account some correlations existing between parameters (μopt, Tmin, Topt, Tmax). In particular, the relationship highlighted between the b-slope of the Ratkowsky model and Tmin (doi: https://doi.org/10.3389/fmicb.2017.01890) was adapted to the case of the popular Cardinal Temperature Model. This resulted in a reduced model in which μopt is replaced by a function of Tmin, Topt and 2 strain-independent parameters. A correlation between the Tmin parameter and the experimental minimal growth temperature was also highlighted and integrated in the model for improved predictions near the temperature growth limits. Compared to the classical approach, the model developed in this study leads to improved predictions for temperatures around Tmin and more realistic tails for the predicted distributions of μmax. It can be useful for describing the variability of the Bacillus cereus Group in Quantitative Microbial Risk Assessment (QMRA). An example of application of the stochastic model to Reconstituted Infant Formulae (RIF) was proposed.

Sonication treatment of pomegranate juice containing Saccharomyces cerevisiae and Byssochlamys fulva: Thermodynamic and predictive modeling after treatment and during shelf life.

The effect of ultrasound treatment (100 W, 30 kHz; 50 and 100% amplitudes) on inactivation of Saccharomyces cerevisiae and Byssochlamys fulva in pomegranate juice and shelf life of the juice during storage at different temperatures (5, 15 and 30 °C) for 30 days was modeled using predictive and thermodynamics models. The Baranyi and square root type models were implemented to determine the growth rate of microorganisms. It was predicted that the minimum growth temperature (Tmin) of B. fulva increased by increasing sonication amplitude, however, the Tmin of S. cerevisiae was not function of sonication amplitude. The predicted shelf life was shown to be in good agreement with the measured sensorial shelf life. Increasing the temperature from 5 to 35 °C, reduced the shelf life from 17.5 to 3.5 days for B. fulva and from 15 to 5 days for S. cerevisiae. Moreover, for B. fulva, the activation energy (Ea) decreased from 43.4 to 27.5 kJ/mol by increasing the amplitude, while no significant change was observed for S. cerevisiae. Besides, thermodynamics properties of the shelf life such as enthalpy (), entropy () and Gibbs free energy ( were proven to be suitable measures to determine the microbial spoilage reaction.

Critical temperatures controlling the phenology and radial growth of Pinus sylvestris var. Mongolica on the southern margin of a cold temperate coniferous forest

Temperature plays a key role in phenology and growth of dominant tree species and hence in the structure and function of coniferous forests in cold temperate zones. We used a dendrochronological method to determine the critical temperatures of Pinus sylvestris var. mongolica (Mongolian pine) radial growth and the xylem growing season. Results showed that Mongolian pine radial growth is sensitive to daily mean temperatures of 4.0–5.5 °C in early spring, 14.0 °C in summer and 2.0–2.5 °C in autumn. A temperature of 4 °C might be the initial temperature required for sap flow, photosynthesis and tree germination in this area in early spring, and 5.5 °C is the most critical temperature for earlywood onset growth. The advance and extension of temperature 14.0 °C in summer can exacerbate water stress for trees and inhibit earlywood growth under the condition of insufficient precipitation. In autumn, 2.0–2.5 °C may be the minimum temperature for the xylem growth. These critical temperatures are important in predicting the changes in the phenology of cambial activity and the growth of conifers in cold temperate regions under a scenario of a warming climate. We defined the mean xylem growing season of pines in this region as 151 days from early May to early October. With the increase in temperatures during 1972–2015, the start date of the xylem growing season advanced by 0.24 days/year, the duration of the xylem growing season increased by 0.27 days/year and the basal area increment of Mongolian pine increased significantly (P < 0.01). The influence of the earlier and longer xylem growing season compensated the negative effect of high initial temperature (14.0–15.0 °C) in some months, resulting in an increase in tree radial increment in this area. The warmer climate will lead to a longer xylem growing season, resulting in greater wood production with an adequate supply of water available.

Dynamic kinetic analysis of growth of Listeria monocytogenes in pasteurized cow milk

The objective of this study was to develop a dynamic model for predicting the growth of Listeria monocytogenes in pasteurized cow milk under fluctuating temperature conditions during storage and temperature abuse. Six dynamic temperature profiles that simulated random fluctuation patterns were designed to change arbitrarily between 4 and 30°C. The growth data collected from 3 independent temperature profiles were used to determine the kinetic parameters and construct a growth model combining the primary and secondary models using a 1-step dynamic analysis method. The results showed that the estimated minimum growth temperature and maximum cell concentration were 0.6 ± 0.2°C and 7.8 ± 0.1 log cfu/mL (mean ± standard error), with the root mean square error (RMSE) only 0.3 log cfu/mL for model development. The model and the associated kinetic parameters were validated using the data collected under both dynamic and isothermal conditions, which were not used for model development, to verify the accuracy of prediction. The RMSE of prediction was approximately 0.3 log cfu/mL for fluctuating temperature profiles, and it was between 0.2 and 1.1 log cfu/mL under certain isothermal temperatures (2-30°C). The resulting model and kinetic parameters were further validated using 3 growth curves at 4, 7, and 10°C arbitrarily selected from ComBase (www.combase.cc). The RMSE of prediction was 0.8, 0.4, and 0.5 log cfu/mL, respectively, for these curves. The validation results indicated the predictive model was reasonably accurate, with relatively small RMSE. The model was then used to simulate the growth of L. monocytogenes under a variety of continuous and square-wave temperature profiles to demonstrate its potential application. The results of this study showed that the model developed in this study can be used to predict the growth of L. monocytogenes in contaminated milk during storage.

Investigation of the biotechnological properties of Zygosaccharomyces kombuchaensis and Gluconacetobacter xylinus as promising microorganisms for the production of functional drinks

The issues of biological conversion of products of processing plant raw materials remain invariably relevant. The development of processing secondary resources allows to increase the efficiency of food production, solving environmental problems and to contribute to ensuring food security. The paper presents data on the results of studies of biotechnological properties of yeast cultures Zygosaccharomyces kombuchaensis sp. and bacteria Gluconoacetobacter xylinus (Brown 1886) Yamada et al 1998, constituting a symbiotic culture called SCOBY (symbiotic culture of bacreties and yeasts), adapted and cultivated in the Krasnodar Territory with the aim of their further use for biological conversion of fruit and berry raw materials and secondary raw materials for the production of functional drinks. The optimal values for the cultivation of the studied cultures were established: pH – 6.5, temperature – for Zygosaccharomyces kombuchaensis sp. minimum growth temperature t = +15-20 °С, maximum – t = +45-50 °С, for Gluconoacetobacter xylinus (Brown 1886) Yamada et al 1998 minimum growth temperature t = +10- 25 °С, maximum – t = +45-50 °C; the content of reducing substances is 10-15 %. The data obtained will be used to develop biotechnological processes for the production of functional drinks.

Viability of bacterial spores surviving heat-treatment is lost by further incubation at temperature and pH not suitable for growth

Spores from 21 strains from different genera were heat-treated and stored in different sets of process conditions (4 temperatures and 3 pH levels) defined to prevent growth. In these conditions, spores surviving the heat treatment progressively lost viability during storage. Different inactivation curve shapes (linear, shoulder and tailing) and different sensitivities to storage were observed. B. coagulans showed the fastest inactivation kinetics, with more than 4-log reduction of spore population within 24 h after heating and G. stearothermophilus displayed slower inactivation kinetics, whereas all the anaerobic strains studied (M. thermoacetica and Thermoanaerobacterium spp.) proved resistant to storage conditions, with no destruction detected during 90 days in most cases. Inactivation rates were relatively unaffected by sub-lethal pH but sharply accelerated by temperature: Inactivation became faster as temperature increased (in the 8 °C–55 °C temperature range), with growth blocked by low pH in sub-lethal temperatures.There were changes in surviving spore numbers after the heat-treatment phase. This has implications and applications in canned food industries, as the probability of a retorted sample testing as non-stable, meaning possible spoilage, may decrease with time. In simple terms, a batch of low-acid canned food that tests as non-shelf-stable after an incubation test i.e. positive growth conditions, may later become negative if stored at room temperature (below the minimal growth temperature for thermophilic spores), which may change the marketability of the batch.

Natural Compounds With Antibacterial Activity Against Cronobacter spp. in Powdered Infant Formula: A Review.

Bacteria from the genus Cronobacter are opportunistic foodborne pathogens capable of causing severe infections in neonates, the elderly and immunocompromised adults. The majority of neonatal infections have been linked epidemiologically to dehydrated powdered infant formulas (PIFs), the majority of which are manufactured using processes that do not ensure commercial sterility. Unfortunately, the osmotolerance, desiccation resistance, mild thermotolerance and wide-ranging minimum, optimum and maximum growth temperatures of Cronobacter spp. are conducive to survival and/or growth during the processing, reconstitution and storage of reconstituted PIFs. Consequently, considerable research has been directed at the development of alternative strategies for the control of Cronobacter spp. in PIFs, including approaches that employ antimicrobial compounds derived from natural sources. The latter include a range of phytochemicals ranging from crude extracts or essential oils derived from various plants (e.g., thyme, cinnamon, clove, marjoram, cumin, mint, fennel), to complex polyphenolic extracts (e.g., muscadine seed, pomegranate peel, olive oil, and cocoa powder extracts), purified simple phenolic compounds (e.g., carvacrol, citral, thymol, eugenol, diacetyl, vanillin, cinnamic acid, trans-cinnamaldehyde, ferulic acid), and medium chain fatty acids (monocaprylin, caprylic acid). Antimicrobials derived from microbial sources (e.g., nisin, other antibacterial peptides, organic acids, coenzyme Q0) and animal sources (e.g., chitosan, lactoferrin, antibacterial peptides from milk) have also been shown to exhibit antibacterial activity against the species. The selection of antimicrobials for the control of Cronobacter spp. requires an understanding of activity at different temperatures, knowledge about their mode of action, and careful consideration for toxicological and nutritional effects on neonates. Consequently, the purpose of the present review is to provide a comprehensive summary of currently available data pertaining to the antibacterial effects of natural antimicrobial compounds against Cronobacter spp. with a view to provide information needed to inform the selection of compounds suitable for control of the pathogen during the manufacture or preparation of PIFs by end users.

Impact of the future coastal water temperature scenarios on the risk of potential growth of pathogenic Vibrio marine bacteria

Vibrio (V) , a genus of marine bacteria, are common inhabitants of warm coastal waters and estuaries. Vibrio includes V. parahaemolyticus and V. vulnificus species that can cause human infections through the consumption of contaminated shellfish (as bivalve molluscs). The growth of pathogenic Vibrio is related to ambient water temperature and seems to increase at 15 °C and over. The expansion of Vibrio infection outbreak is increasing worldwide due to the increase of the sea surface temperature as a result of ocean warming. Canada's coast is not an exception to this worldwide Vibrio spread. Faced with this issue, this study focuses on modelling the future potential Vibrio growth risk along the coasts of the St. Lawrence Gulf and Estuary, where the shellfish industry is well developed. This is done using the adequate machine learning model with explanatory variables that include air temperature and wind speed for predicting future water temperatures. Based on the predicted future water temperature scenarios and a threshold of 15 °C to determine the conditions favorable to the growth of Vibrio bacteria, we modelled the Vibrio growth risk indicator, i.e. the number of days exceeding the minimum temperature for Vibrio pathogenic growth (15 °C), in the horizon 2040–2100. Simulations show that the number of days, where the minimum temperature (15 °C) will be reached, will increase spatially and even seasonally and all the shellfish beds would meet the temperature condition for Vibrio growth regardless of the climate scenario (optimistic and pessimistic). • The statistical modelling of the coastal water temperature from air temperature and wind speed. • Future coastal water temperature scenarios were produced under optimistic and pessimistic climate scenarios. • Maps of the future Vibrio growth risk indicator were produced, from the future water temperature scenarios. • Maps show that the Vibrio growth risk will increase spatially and seasonally regardless the climate change scenario.

Growth kinetics of Staphylococcus aureus and background microorganisms in camel milk

Staphylococcus aureus is a common foodborne pathogen that is ubiquitous in nature. Consumption of contaminated foods, such as dairy products, can lead to food poisoning caused by heat-stable staphylococcal toxins that are not easily destroyed during pasteurization. The objective of this study was to investigate the growth kinetics of S. aureus and background microorganisms in camel milk stored at different temperatures between 8 and 43°C using one-step kinetic analysis to estimate the kinetic parameters from the observed growth curves. The growth of S. aureus showed apparent lag, exponential, and stationary phases, whereas no or negligible lag phase was observed for background microorganisms. Data analysis showed that the estimated minimum, optimum, and maximum growth temperatures were 5.9, 42.0, and 49.2°C for S. aureus, and 3.0, 38.6, and 49.2°C for the background microorganisms, respectively. The estimated optimum specific growth rate was higher for S. aureus (1.24 h-1) than for background microorganisms (0.995 h-1). This study found that camel milk may inhibit the growth of S. aureus, as it exhibits a lower specific growth rate than that in cow milk or cooked potato. It also has a longer lag phase than that in cow milk at comparable temperature ranges. This unique property is probably related to the presence of some antimicrobial compounds naturally occurring in camel milk. Validation of kinetic parameters and models showed that the root mean square error of prediction was only 0.5 log cfu/mL for S. aureus and background microorganisms, suggesting that the models are reasonably accurate. These models can be used for conducting risk assessments of S. aureus and predicting the general microbiological shelf life of camel milk to prevent foodborne staphylococcal poisoning.

Predictive Growth Modeling of Listeria monocytogenes in Rice Balls and Its Risk Assessment

This study aimed to investigate the growth of Listeria monocytogenes in rice balls and to conduct its microbial risk assessment based on the Korean dietary pattern. Each tuna or ham rice ball was mixed with mayonnaise, soy sauce, or gochujang, a Korean traditional fermented red peeper paste, which was artificially contaminated with L. monocytogenes and then stored at 7°C–25°C to assess bacterial growth. Growth data were analyzed using three primary models (the Huang, Baranyi, and Gompertz models), and the growth pattern was found to fit well to the Baranyi model based on the following five statistical criteria: root mean square error (0.38–0.56), Akaike’s information criterion (−51.55–−26.99), coefficient of determination (0.72–0.97), bias factor (0.97–1.01), and accuracy factor (1.06–1.18). The effects of temperature on bacterial growth rate and lag time were evaluated using the square root model. The minimum growth temperature for L. monocytogenes in tuna or ham rice balls was the lowest when they were mixed with mayonnaise (−9.44°C or −15.37°C, respectively). Risk assessment using FDA-iRISK showed that tuna or ham rice balls mixed with gochujang exhibited the highest microbial risk among all the rice balls tested, regardless of the storage temperature. Tuna or ham rice balls mixed with gochujang had the highest disability-adjusted life years per year (0.015) followed by ham rice balls mixed with soy sauce (0.011–0.015) or mayonnaise (0.006–0.015) and then tuna rice balls mixed with soy sauce (0.006–0.008) or mayonnaise (&lt;0.001). In conclusion, our results, determined using predictive growth models, allow the assessment of potential risk ranking associated with the consumption of rice balls contaminated with L. monocytogenes based on the number of illnesses experienced per serving and the disease burden.

Crystal growth, structural characteristics and electronic structure of Ba1-xPbxFe12O19 (x = 0.23–0.80) hexaferrites

The formation of (Ba,Pb)Fe12O19 crystals in the ternary system BaO–PbO–Fe2O3 and electronic structure of the crystals at high lead content are considered in the present study. The phase equilibria in the BaO–PbO–Fe2O3 system and related thermophysical parameters were defined. The analysis suggests that the use of lead oxide as a solvent reduces the minimum temperature for the hexaferrite crystal growth in the PbO–BaFe12O19 section to about 960 °C and, at the same time, gives an appropriate temperature range of about Δ500 °C (from 960 to 1465 °C). High-quality single crystals Ba1–xPbxFe12O19 with x = 0.23(2), 0.44(2) and 0.80(3) were grown by the flux technique and the structural properties were studied. The electronic structure of Ba0·2Pb0·8Fe12O19 hexaferrite was evaluated in parallel by X-ray photoelectron spectroscopy and density functional theory calculations to assess the effects of Pb2+ incorporation into the BaFe12O19 lattice. It is obtained by X-ray photoelectron spectroscopy measurements that the electronic parameters of Ba2+, Fe3+ and O2− ions are nearly the same in Ba0·2Pb0·8Fe12O19 and BaFe12O19 hexaferrites, and it indicates that the ionicities of Ba–O and Fe–O bonds are not affected by the presence of Pb2+ ions in the crystal lattice. On the base of density functional theory calculations, it is found that both the top of valence bands (from −10 eV to 0 eV) and bottom of the conduction bands (3 eV–8 eV) are dominantly occupied by Pb 6s 6p, Fe 3d and O 2p orbitals, indicating that the physicochemical properties of Ba0·2Pb0·8Fe12O19 related to the electron transitions across the forbidden bands are determined by Pb2+ cations, FeO4 and FeO6 groups. In particular, the incorporated Pb2+ cations have a more prominent contribution to the electronic states near the Fermi level than Ba2+ ions.

Distinct cold tolerance traits independently vary across genotypes in Drosophila melanogaster.

Cold tolerance, the ability to cope with low temperature stress, is a critical adaptation in thermally variable environments. An individual's cold tolerance comprises several traits including minimum temperatures for growth and activity, ability to survive severe cold, and ability to resume normal function after cold subsides. Across species, these traits are correlated, suggesting they were shaped by shared evolutionary processes or possibly share physiological mechanisms. However, the extent to which cold tolerance traits and their associated mechanisms covary within populations has not been assessed. We measured five cold tolerance traits-critical thermal minimum, chill coma recovery, short- and long-term cold tolerance, and cold-induced changes in locomotor behavior-along with cold-induced expression of two genes with possible roles in cold tolerance (heat shock protein 70 and frost)-across 12 lines of Drosophila melanogaster derived from a single population. We observed significant genetic variation in all traits, but few were correlated across genotypes, and these correlations were sex-specific. Further, cold-induced gene expression varied by genotype, but there was no evidence supporting our hypothesis that cold-hardy lines would have either higher baseline expression or induction of stress genes. These results suggest cold tolerance traits possess unique mechanisms and have the capacity to evolve independently.

Tropical seagrass Halophila stipulacea shifts thermal tolerance during Mediterranean invasion.

Exotic species often face new environmental conditions that are different from those that they are adapted to. The tropical seagrass Halophila stipulacea is a Lessepsian migrant that colonized the Mediterranean Sea around 100 years ago, where at present the minimum seawater temperature is cooler than in its native range in the Red Sea. Here, we tested if the temperature range in which H. stipulacea can exist is conserved within the species or if the exotic populations have shifted their thermal breadth and optimum due to the cooler conditions in the Mediterranean. We did so by comparing the thermal niche (e.g. optimal temperatures, and upper and lower thermal limits) of native (Saudi Arabia in the Red Sea) and exotic (Greece and Cyprus in the Mediterranean Sea) populations of H. stipulacea. We exposed plants to 12 temperature treatments ranging from 8 to 40°C for 7 days. At the end of the incubation period, we measured survival, rhizome elongation, shoot recruitment, net population growth and metabolic rates. Upper and lower lethal thermal thresholds (indicated by 50% plant mortality) were conserved across populations, but minimum and optimal temperatures for growth and oxygen production were lower for Mediterranean populations than for the Red Sea one. The displacement of the thermal niche of exotic populations towards the colder Mediterranean Sea regime could have occurred within 175 clonal generations.

Mathematical modeling Pseudomonas spp. growth and microflora composition variation in Agaricus bisporus fruiting bodies during chilled storage

The objective of this study was to determine the dominant microorganism in Agaricus bisporus fruiting bodies (ABFB) and to develop kinetic models to describe its growth. The variation in microflora composition in ABFB stored at 4 °C during storage was studied using 16S rDNA sequence analyses. ABFB presented complex microbial communities at the initial stage of storage (day 0), with the dominant microorganisms being Pseudomonas spp. along with small proportions of Pedobacter, Sphingobacterium, Bacillus, Corynebacterium, Lactobacillus, Sphingomonas, and Staphylococcus. On day 12, an increase of Pseudomonas spp. and a significant decrease of Pedobacter were observed. As the dominant spoilage microorganism during the storage, the relative abundance of Pseudomonas spp. showed an increasing trend. Additionally, samples inoculated with a cocktail of Pseudomonas spp., i.e., P. fluorescens, P. migulae, P. tolaasii, and P. agarici, were incubated at temperatures of 4, 10, 16, 20, 25, and 32 °C to assess their growth kinetics. Three primary models (Huang, Baranyi, and Reparameterized Gompertz model) and three secondary models (Huang square-root, Ratkowsky square-root, and Arrhenius-type model) were compared to evaluate the effect of temperature on bacterial growth using the Integrated Pathogen Modeling Program. The Reparameterized Gompertz model was a better fit than the Huang and Baranyi models to describe the growth of Pseudomonas spp., and had the lowest mean square error (MSE) and sum of squared errors (SSE) values, ranging from 0.012 to 0.291 and 0.059–1.783, respectively. Huang square-root model MSE and SSE values were 0.002 and 0.007, respectively, and its predicted minimum growth temperature was -0.72 °C. Therefore, the Huang square-root model was more suitable for describing the effect of temperature on growth of Pseudomonas spp. on ABFB. The models developed in this study can be used to evaluate the growth behavior of Pseudomonas spp. on ABFB and assess their shelf-life.