Survival kinetics of Salmonella enterica serotype senftenberg (S. senftenberg) after heat and acid stress

The survival kinetics of two clinical isolates of Salmonella senftenberg were studied after heat and acid stress. The strains survived better at 53 and 55 °C after heat shock of 30 min at 50 °C or overnight heat adaptation at 45 °C. An increase in the decimal reduction time, D, of heat-shocked [10.2 min (53 °C) and 9.37 min (55 °C)] and heat-adapted [8.12 min (53 °C) and 7.8 min (55 °C)] cells was observed compared with the non-stressed cells [6.87 min (53 °C), 6.56 min 55 °C)]. A significant difference was also observed in the survival of acid-adapted to acid non-adapted S. senftenberg bacteria.     

Production of a thermostable ATPase by the facultative thermophile,Bacillus coagulans

The properties of the ATPase in the facultative thermophile, Bacillus coagulans, grown at thermophilic or mesophilic temperatures were similar. Arrhenius plots did not show discontinuities indicative of thermoadaptation. Magnesium stimulation of the enzyme was dependant on the assay temperature but independant of the growth temperature. The ATPase in cells grown at 35°C or 55°C was equally thermostable at 65°C. In contrast, the ATPase from the mesophile, Bacillus megaterium (T _max=42°C) was completely inactivated at 55°C in 5 min.     

Upper temperature limits for growth and diazotrophy in the thermophilic cyanobacterium HTF Chlorogloeopsis

The effect of temperature and oxygen on diazotrophic growth of the thermophilic cyanobacterium HTF (High Temperature Form) Chlorogloeopsis was investigated using cells grown in light-limited continuous culture at a dilution rate of 0.02 h^-1. Diazotrophy was more sensitive to elevated temperatures than growth with combined nitrogen. The maximum temperature for growth of cultures gassed with CO₂-enriched air was more than 55 °C but less than 60 °C with N₂ as the sole nitrogen source, but between 60°C and 65°C when nitrate was present in the medium. The effect of temperature on nitrogenase activity, photosynthesis and respiration in the dark was determined using cells grown at 55°C. Maximal rates of all three processes were observed at 55°C and rates at 60°C during shortterm incubations were not less than 75% of the maximum. However, nitrogenase activity at 60°C was unstable and decayed at a rate of 2.2 h^-1 under air and at 0.3 h^-1 under argon. Photosynthesis and respiration were more stable at 60°C than anoxic nitrogen fixation. The upper temperature limits for diazotrophic growth thus seem to be set by the stability of nitrogenase.Abbreviations chl chlorophyll a - DCMU N-(3,4-dichlorophenyl) N,N-dimethylurea - Taps N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid     

Inactivation of Alicyclobacillus acidoterrestris vegetative cells in model system,apple, orange and tomato juices by high hydrostatic pressure

The objective of this study is to determine the effect of high hydrostatic pressure (HHP) on inactivation of Alicyclobacillus acidoterrestris vegetative cells in a model system (BAM broth) and in orange, apple and tomato juices. The shelf-life stability of pressurized juices is also studied. In general the viability loss was enhanced significantly as the level of pressure and temperature were increased (P < 0.05). 4.70 log cycle reduction was obtained after pressurization at 350 MPa at 50 °C for 20 min in BAM broth whereas thermal treatment at 50 °C for 20 min caused only 1.13 log cycle inactivation showing the effectiveness of HHP treatment on inactivation. The D values for pressure (350 MPa at 50 °C) and temperature (50 °C) treatments were 4.37 and 18.86 min in BAM broth, respectively. All juices were inoculated with A. acidoterrestris cells to 10⁶ c.f.u./ml and were pressurized at 350 MPa at 50 °C for 20 min. More than 4 log cycle reduction was achieved in all juices studied immediately after pressurization. The pressurized juices were also stored up to 3 weeks at 30 °C and the viable cell numbers of A. acidoterrestris in orange, apple and tomato juices were 3.79, 2.59 and 2.27 log cycles, respectively after 3 weeks. This study has indicated that A. acidoterrestris vegetative cells can be killed by HHP at a predictable rate even at temperatures at which the microorganism would normally grow.     

Acclimation of potassium influx in rye (Secale cereale) to low root temperatures

The influx of K⁺(⁸⁶Rb⁺) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K⁺-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K⁺ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K⁺ influx into the apical (0–2 cm) region of the seminal root which is associated with a compensatory increase in K⁺ influx into the more mature, basal regions of the root. Values of V _max and apparent K _m for K⁺ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent K _m at 8° C. The influx of K⁺ from solutions containing 0.6 mol·m^-3 K⁺ into both WG and DT plants was found to be linearly related to assay temperature over the range 2–27° C, and the temperature sensitivity of K⁺ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K⁺ influx at 20° C:K⁺ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K⁺ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K⁺ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K⁺]int). This result indicates some change in the regulation of K⁺ influx by [K⁺]int in plants exposed to low root temperatures. We suggest that K⁺ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K⁺ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.Abbreviations DT differential temperature pretreatment - [K⁺]int root potassium concentration - [K⁺]ext potassium concentration of nutrient medium - WG warm-grown pretreatment     

Recovery of photosynthetic reactions after high-temperature treatments of a heat-tolerant cactus

Inhibition and recovery of net CO₂ uptake and three photosynthetic electron transport reactions as well as plant survival following high-temperature treatments were investigated for Opuntia ficus-indica. For plants maintained at 30°C/20°C day/night air temperatures, treatment at 60°C for 1 h irreversibly inhibited net CO₂ uptake and photosynthetic electron transport, resulting in plant death in about 60 days. When a plant maintained at 30°C/20°C was treated at 55°C for 1 h, net CO₂ uptake was completely inhibited 1 d after the treatment but fully recovered in 60 d. Differential inactivation of photosystem (PS) I, PSII, and whole chain electron transport activities occurred; PSI was the most tolerant of 55°C and took the least time (45 d) for total recovery. All 30°C/20°C plants survived a 1-h treatment at 55°C, although some pale green areas were observed on the cladode surfaces. In contrast to growing at 30°C/20°C, plants acclimated to 45°C/35°C survived 60°C for 1 h without showing any necrotic or pale green areas on the cladode surfaces. When such a plant was transferred to 30°C/20°C following the high-temperature treatment, recovery in net CO₂ uptake began in 1 d and progressed to complete recovery by 30 d. Growth temperatures thus influence the possibility for recovery of photosynthetic reactions and ultimately the survival of O. ficus-indica following a high-temperature exposure.Abbreviations DCPIP 2,6-dichlorophenol indophenol - MV methyl viologen - PAR photosynthetically active radiation - PSI or PSII photosystem I or II - WC whole chain     

New Thermophilic Methanotrophs of the Genus Methylocaldum

Two pure cultures of obligate methanotrophs, strains H-11 and O-12, growing in the temperature range from 30 to 61°C with a optimum at 55°C were isolated from samples of silage and manure. Based on the results of analysis of the 16S rRNA genes and genes of membrane-bound methane monooxygenase, as well as on phenotypic properties, the isolates were assigned to the genus Methylocaldum. Significant temperature-dependent variations in morphology and phospholipid and fatty acid composition were revealed. Both strains assimilated methane carbon via the ribulose monophosphate, serine, and ribulose bisphosphate pathways. The activity of hexulosephosphate synthase was independent of the cultivation temperature; however, the activities of hydroxypyruvate reductase and ribulose bisphosphate carboxylase were higher in cells grown at 55°C than in cells grown at 37°C, indicating the important roles of the serine and ribulose bisphosphate pathways in the thermoadaptation of the strains under study. NH₄ ⁺ assimilation occurred through reductive amination of -ketoglutarate and via the glutamate cycle. The relationship between the physiological and biochemical peculiarities of the isolates and their thermophilic nature is discussed.     

Elevating intracellular free Mg2+ preserves sensitivity of Na+−K+ pump to ATP at reduced temperatures in guinea pig red blood cells

Red cells of hibernating species have a higher relative rate of Na⁺–K⁺ pump activity at low temperature than the red cells of a mammal with a typical sensitivity to cold. The kinetics of ATP stimulation of the Na⁺–K⁺ pump were determined in guinea pig and ground squirrel red cells at different temperatures between 5 and 37°C by measuring ouabain-sensitive K⁺ influx at different levels of ATP. In guinea pig cells, elevation of intracellular free Mg²⁺ to 2 mmol·l^-1 by use of the divalent cation ionophore A23187 caused the apparent affinity of the pump for ATP to increase with cooling to 20°C, rather than to decrease, as occurs in cells not loaded with Mg²⁺. In ground squirrel cells raising intracellular free Mg²⁺ had little effect on apparent affinity of the pump for ATP at 20°C. ATP affinity rose slightly with cooling both in Mg²⁺-enriched and in control ground squirrel cells. Increased intracellular free Mg²⁺ in guinea pig cells stimulated Na⁺–K⁺ pump activity so that at 20°C the pump rate was the same in the Mg²⁺-enriched guinea pig and control ground squirrel cells. Pump activity in Mg²⁺-enriched guinea pig cells at 5°C was significantly improved but still lower than pump activity in control cells from ground squirrel. Thus, loss of affinity of the Na⁺–K⁺ pump for ATP that occurs with cooling in cold-sensitive guinea pig red cells can be, at least partially, prevented by elevating cytoplasmic free Mg²⁺. Conversely, in ground squirrel red cells natural rise of free Mg²⁺ may in part account for the preservation of the ATP affinity of their Na⁺–K⁺ pump with cooling.Abbreviations K _m Michaelis-Menten constant for apparent affinity - MOPS 3-(N-morpholino)-propanesulphonic acid - [Mg²⁺]_i intracellular concentration of free Mg²⁺ - OD optical density - RBC red blood cell(s) - T _b body temperature     

Orthophosphate influx and efflux rates of Chlorella fusca measured in a continuous turbidostat culture with 32P under various conditions

The main objective of the experiments with Chlorella fusca strain 211-8b was to measure, with adequate time resolution, the unidirectional influx rates of phosphate into non-phosphate-starved algae under different steady state conditions (light, temperature, 3-phosphoglycerate influence) or following the addition of several photosynthesis and phosphate transport inhibitors (phenylmercuric acetate, p-chloromercuribenzoate, arsenate). the algae were cultivated in a phosphate rich medium in a continuous turbidostat culture. The phosphate exchange experiments with carrier-free ³²PO ₄ ^3- were performed directly in the continuous culture. The sampling intervals after the tracer addition were 15 s.For a continuous steady state culture grown in the light (25° C) the unidirectional influx rate measured with ³²P is 260 times higher than the net uptake rate (=influx minus efflux rate) calculated from the mass balance using the data of this culture. In all experiments, except the control experiment with trichloroacetic acid killed cells, the specific activity of the intracellular inorganic orthophosphate compartment oscillates around a constant mean value which never reaches the specific activity of the nutrient medium within the duration of the short-term experiments (7.5 min). The inhibitors strongly affect the characteristics of the oscillations. The unidirectional influx rates are constant. Oscillating flushing rates with unlabelled phosphate from a storage compartment have been postulates to explain the oscillations. Oscillating rates from the individual cells are apparently synchronized by an unknown mechanism.     

Geobacillus uralicus,a New Species of Thermophilic Bacteria

The K^T ₂ strain of thermophilic spore-forming bacteria was isolated from a biofilm on the surface of a corroded pipeline in an extremely deep well (4680 m, 40–72°C) in the Urals. The cells are rod-shaped, motile, gram-variable. They grow on a complex medium with tryptone and yeast extract and on a synthetic medium with glucose and mineral salts without additional growth factors. The cells use a wide range of organic substances as carbon and energy sources. They exhibit a respiratory metabolism but are also capable of anaerobic growth on a nitrate-containing medium. Growth occurs within the 40–75°C temperature range (with an optimum of 65°C) and at pH 5–9. The minimum generation time (15 min) was observed at pH 7.5. Ammonium salts, nitrates, and arginine are used as nitrogen sources. The G+C content of the DNA is 54.5 mol %. From the morphological, physiological, and biochemical properties and the nucleotide sequence of the 16S rRNA gene, it was concluded that the isolate K^T ₂ represents a new species of the genus Geobacillus, Geobacillus uralicus.     

The respiratory chain of the facultative thermophile,Bacillus coagulans

Two oxidases were found to be present in membranes from the facultative thermophile Bacillus coagulans grown at 55°C, compared to one in cells grown at 37°C. Cytochrome spectra and inhibitors of the respiratory chain identified them as cytochrome oxidases aa ₃ and d. Both were present in membranes from 55°C grown cells, but only cytochrome oxidase aa ₃ was found in membranes from 37°C grown cells. The presence of cytochrome d in 55°C grown cultures was found to be due to decreased oxygen tension and not to the high growth temperature. This was confirmed by (a) induction of cytochrome d at 37°C under conditions of oxygen limitation and (b) its repression at 55°C under conditions of high aeration and its subsequent induction on lowering the dissolved oxygen concentration in chemostat cultures. Two cytochromes b (_max 558 and _max 562) were present in both 37°C and 55°C grown cells. Results from the inhibition of substrate oxidation by membranes suggested different pathways of electron transport by the respiratory chain.     

Temperature dependency of induction of sexual agglutinability by α pheromone in the yeast Saccharomyces cerevisiae

When pheromone-pretreated cells of an inducible a strain of Saccharomyces cerevisiae carrying the inducible gene saa1 were incubated in a growth medium at 28°C, induction of sexual agglutinability began after a 10 min lag period. If the cells were incubated at 38°C during the lag period, no induction occurred even after incubation at 28°C. Contrary to this, if the cells were incubated at 28°C during the lag period, almost complete induction occurred, even after transfer to 38°C. Temperature shift experiments revealed that 5 min incubation at 28°C was necessary for the initiation of the temperature-sensitive period and further 5 min incubation for the completion of the period. The temperature-sensitive period was sensitive to phenylmethylsulfonyl fluoride.Non-common abbreviations PBS 10^-2 M phosphate buffer solution, pH 5.5 - PMSF phenylmethylsulfonyl fluoride     

Effects of temperature and holding time on production of renewable fuels from pyrolysis of Chlorella protothecoides

To investigate the influence of temperature andholding time on the pyrolyzate yields of Chlorella protothecoides, the microalgal cells weresubjected to pyrolysis at 200, 300, 400, 500 and 600 ^°Cfor 5, 20, 60 and 120 min, separately. High oil yields above 40% dry weight cells wereobtained both at relatively low temperature (300 ^°C)with relatively long holding times (20–120min) and relatively high temperatures (400–500 ^°C)with relatively short holding times (5–20min). The maximum oil yield of 52.0% was achieved at500 ^°C for 5 min. The gas yield was generallyincreased with the increasing temperature and holdingtime. It could reach 63.3–76.0% at 600 ^°C.High pyrolytic rates of 72–87% were obtained at allexperiments except at 200 ^°C for 5–20 min or300 ^°C for 5 min. Thermogravimetric analysisindicated that the main thermal degradation of thismicroalga occurred at 200–520 ^°C. The resultsimply that C. protothecoides is a good candidatefor the production of renewable fuels by pyrolysis.     

Characterization of the calcium paradox in the isolated perfused frog heart: enzymatic,ionic, contractile and electrophysiological studies

Summary The effect of perfusion temperature and duration of calcium deprivation on the occurrence of the calcium paradox was studied in the isolated frog heart. Loss of electrical and mechanical activity, ion fluxes, creatine kinase and protein release were used to define cell damage. Perfusion was performed at 22, 27, 32, and 37°C, and calcium deprivation lasted 10, 20, 30, or 40 min. At 22°C and 27°C even a prolonged calcium-free perfusion failed to induce a calcium paradox. After 30 min of calcium-free perfusion at 37°C ventricular activity ceased and a major contraction occurred followed by an increase in resting tension. During the 15-min re-perfusion period the release of creatine kinase was 158.24±2.49 IU·g dry wt^-1, and the total amount of protein lost was 70.37±0.73 mg·g dry wt^–1, while lower perfusion temperatures resulted in a decreased loss of protein and creatine kinase. Ion fluxes in the perfusion effluent indicate that during re-perfusion a massive calcium influx accompanied by a potassium and a magnesium efflux, and an apparent sodium efflux, occur at a perfusion temperature of 37°C after 30 min of calcium deprivation. The results suggest that the basic principles and damaging effects of calcium overloading are common to both mammalian and frog hearts.     

Thermophilic amylase-producing bacteria from Vietnamese soils

Of 25 bacterial isolates from Vietnamese soils, two were identified asBacillus stearothermophilus and one asThermoactinomyces thalpophilus, both thermophilic, amylase-producing bacteria. Amylase activity was highest in the presence of cassava starch as carbon source and (NH₄)₂HPO₄ as nitrogen source. The strains exhibit a high amylase productivity within the first 5 to 7 h of cultivation at 55°C. The crude enzyme had optima of pH 6.5 and 70°C.     

Thermus 2S from Thai hot springs: isolation and immobilization

Three strains of thermophilic bacteria producing extracellular protease have been isolated from hot springs in Chiang Mai, Thailand. The bacterium producing the highest amount of protease has been selected and identified as belonging to the genusThermus, and is tentatively calledThermus 2S. The isolate is a Gram-negative, rod shaped bacterium. It exhibited maximum growth around 60°C at pH 7. Entrapment of the microbial cells in calcium alginate maintained the cell viability. Protease production from immobilized cells using 2 g wet cells per 10 ml 3% (w/v) sodium alginate was higher than that from a free-cell system using 2% inoculum.     

Microbial populations and sludge characteristics in thermophilic aerobic sewage sludge digestion

Summary Estimates of bacterial numbers from raw sewage sludge and sludge treated by thermophilic aerobic digestion were compared with simple indicators of sludge quality and concentrations of potential substrates. Significant differences were found between sludge types for all but one of the variables examined (frequency of dividing cells). During a stable period of digestor operation, the average number of viable obligate thermophiles present in digested sludge (1.63 × 10⁶ ml^–1) was approximately 10²-fold greater than in feed sludge (1.10 × 10⁴ ml^–1). Total numbers of bacteria were slightly greater in digested sludge (3.24 × 10¹⁰ ml^–1) than in feed sludge (2.39 × 10 ml^–10), as were viable counts of bacteria at incubation temperatures of 37°C and 55°C. Significant correlation was found between viable counts of bacteria at 37°C and 55°C for digested sludge, and 65°C and 55°C for feed sludge. The numbers of obligate thermophiles present and the total of bacteria present were related to the temperature and pH of the digested sludge and inversely related to the numbers ofEscherichia coli and coliforms present, which were not detected at temperatures greater than 50°C.     

Using Thermal Inactivation Kinetics to Calculate the Probability of Extreme Spore Longevity: Implications for Paleomicrobiology and Lithopanspermia

Thermal inactivation kinetics with extrapolation were used to model the survival probabilities of spores of various Bacillus species over time periods of millions of years at the historical ambient temperatures (25–40 °) encountered within the 250 million-year-old Salado formation, from which the putative ancient spore-forming bacteriumSalibacillus marismortui strain 2-9-3 was recovered. The model indicated extremely low-to-moderate survivalprobabilities for spores of mesophiles, but surprisingly high survival probabilities for thermophilic spores. The significance of the results are discussed in terms of the survival probabilities of (i) terrestrial spores in ancient geologic samples and (ii) spores transported betweenplanets within impact ejecta.     

Effect of Temperature and Illumination on Growth and Reproduction of the Green Alga Ulva fenestrata

The combined effect of temperature (5, 10, 15, and 20°C) and illumination (40 and 60 mE/(m² s)) on growth and reproduction of the green marine alga Ulva fenestrata P. et R. from the sublittoral zone of Amursky Bay, Sea of Japan, was studied in the laboratory environment in the months April–July, 2000. It was demonstrated that the temperature of 5°C and illumination of 40 mE/(m² s) are the most favorable for maintaining the vegetative mass of the algae. A water temperature of 10°C and illumination of 40 mE/(m² s) are the optimum conditions for vegetative growth of U. fenestrata thalli. A temperature decrease and increase by 5°C reduces the growth rate on average by 30%. Sporo- and gametogenesis in U. fenestrata are the most regular (every 10 days) and occupy the greatest disk area at a water temperature of 15°C and illumination of 40 mE/(m² s). Vegetative growth of thalli is sharply inhibited at the stage of cell preparation to gametogenesis a day before the beginning of gamete formation.     

Reproductive biology of Stictosiphonia hookeri (Rhodomelaceae,Rhodophyta) from Argentina,Chile, South Africa and Australia in laboratory culture

The red alga Stictosiphonia hookeri is epilithic in shaded habitats of the upper intertidal zone from 30 to 55° S. Thalli of this species from Argentina, Chile, South Africa and Australia, usually without reproductive structures when collected, all developed tetrasporangia in culture. Although good vegetative growth occurred in all nine isolates at 20–25 °C, 12:12 light: dark cycle, 10–30 µmol photons m^–2 s^–1, none reproduced in these conditions except one isolate from Australia. At 15 °C the four South African (34 °S) isolates developed tetrasporangial stichidia, and three completed a Polysiphonia-type life history. Gametophytes were unisexual or bisexual. At 15 °C one isolate from Chile (36 °S) formed tetrasporangia, but sporelings were not viable. At 10 °C isolates from Argentina and Chile (53 °S and 54 °S) formed tetrasporangia; however, only the Chile isolate completed a Polysiphonia-type life history with unisexual gametophytes. The temperature required to induce sporogenesis correlates with the range of water and air temperatures in the natural habitats of each isolate. In irradiances >50 µmol m^–2 s^–1 the thalli became yellow- brown within two weeks because of phycobiliprotein loss, but this did not impair growth or reproduction. The Argentina and Chile isolates were resistant to freezing in seawater for at least two days, showing no cell damage. The protein cuticle of the outer cell wall is repeatedly shed in culture. This may serve to minimize the attachment of epiphytes in the field.