Supraoptimal Growth Temperatures Research Articles

Genotypic variation in growth, single leaf physiology, and acclimation potential of thylakoid processes in cotton exposed to high temperature extremes

The cotton crop already experiences yield-limiting high temperatures during the growing season, which are predicted to worsen in a changing climate. This makes the identification of heat tolerant cultivars that can acclimate to high temperature conditions a necessity. The objective of this study was to assess the effects of growth temperature and genotype on plant growth, single-leaf physiology, and thermotolerance of thylakoid processes for cotton exposed to optimal and supra-optimal temperature conditions. A diverse collection of cotton cultivars was selected based on previously documented differences in thylakoid-specific thermotolerance, and they were exposed to optimal (30/20 C) and two supra-optimal growth temperatures (35/25 and 40/30 °C). There was a significant interaction between genotype (G) and growth temperature (T) for all growth measures (leaf area, mainstem node production, and plant dry weight), photosynthetic rates, nighttime respiration and stomatal conductance, and thermotolerance of photosystem II. Greater relative growth (plant dry matter) under high temperature was strongly and positively correlated with leaf area and strongly and negatively correlated with nighttime respiration and stomatal conductance. In contrast, photosynthetic parameters were not significantly associated with genotypic variation in growth-specific thermotolerance. Thermotolerance of the thylakoid reactions was not consistently associated with more thermotolerant growth. We conclude that genotypes with heat tolerant vegetative growth have higher relative leaf area and lower relative values for nocturnal respiration and stomatal conductance under high temperature conditions.

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Hydrogen peroxide (H2O2) and glutathione (GSH) are involved in the stress response in plants. To elucidate the role of H2O2 in the acclimation of CO2 assimilation under sub- or supra-optimal growth temperatures, we examined the effect and interaction of H2O2 manipulation on the photosynthetic metabolism of cucumber plants (Cucumis sativus L.) grown under five temperature regimes spanning above and below the optimal growth temperature; 11/9, 18/15, 25/20, 32/27, and 39/33 °C (day/night), with or without dimethylthiourea (DMTU) or H2O2 treatment. As expected, exposure to sub- or supra-optimal growth temperatures resulted in decreased plant growth, associated with a decline in CO2 assimilation (Asat), Rubisco content, and activities of enzymes involved in the CO2 assimilation, as well as a decrease in the ratio of reduced (GSH) to oxidized (GSSG) glutathione (GSH/GSSG). Foliar application of H2O2 promoted, whilst DMTU retarded the capacity of plants to acclimate to non-optimal growth temperatures; this was consistently shown in altered activity of redox-sensitive enzymes involved in CO2 assimilation. These results strongly suggest that the influence of growth temperature on CO2 assimilation was primarily targeted at the activities of the redox-sensitive enzymes of CO2 assimilation. Meanwhile, the data suggest that the cellular H2O2 level is an important signal for the glutathione-dependent regulation of redox-sensitive enzymes of CO2 assimilation in cucumber plants.

Temperature-Dependent Alkyl Glycerol Ether Lipid Composition of Mesophilic and Thermophilic Sulfate-Reducing Bacteria

The occurrence of non-isoprenoid alkyl glycerol ether lipids in Bacteria and natural environments is increasingly being reported and the specificity and diagenetic stability of these lipids make them powerful biomarkers for biogeochemical and environmental studies. Yet the environmental controls on the biosynthesis of these peculiar membrane lipids remain poorly documented. Here, the lipid content of two mesophilic (Desulfatibacillum aliphaticivorans and Desulfatibacillum alkenivorans) and one thermophilic (Thermodesulfobacterium commune) sulfate-reducing bacteria—whose membranes are mostly composed of ether lipids—was investigated as a function of growth temperature (20–40°C and 54–84°C, respectively). For all strains, the cellular lipid content was lower at sub- or supra-optimal growth temperature, but the relative proportions of dialkyl glycerols, monoalkyl glycerols and fatty acids remained remarkably stable whatever the growth temperature. Rather than changing the proportions of the different lipid classes, the three strains responded to temperature changes by modifying the average structural composition of the alkyl and acyl chains constitutive of their membrane lipids. Major adaptive mechanisms concerned modifications of the level of branching and of the proportions of the different methyl branched lipids. Specifically, an increase in temperature induced mesophilic strains to produce less dimethyl branched dialkyl glycerols and 10-methyl branched lipids relative to linear structures, and the thermophilic strain to decrease the proportion of anteiso relative to iso methyl branched compounds. These modifications were in agreement with a regulation of the membrane fluidity. In one mesophilic and the thermophilic strains, a modification of the growth temperature further induced changes in the relative proportions of sn-2 vs sn-1 monoalkyl glycerols, suggesting an unprecedented mechanism of homeoviscous adaptation in Bacteria. Strong linear correlations observed between different ratios of alkyl glycerols and temperature allow to hypothesize the use of these specific lipids as indicators of temperature changes in the environment.

Reverse gyrase is essential for microbial growth at 95 °C.

Reverse gyrase is an enzyme that induces positive supercoiling in closed circular DNA in vitro. It is unique to thermophilic organisms and found without exception in all microorganisms defined as hyperthermophiles, that is, those having optimal growth temperatures of 80 °C and above. Although its in vivo role has not been clearly defined, it has been implicated in stabilizing DNA at high temperatures. Whether or not it is absolutely required for growth at these high temperatures has yet to be fully determined. In a previous study with an organism that has an optimal growth temperature of 85 °C, it was shown that the enzyme is not a prerequisite for life at extreme temperatures as disruption of its gene did not result in a lethal phenotype at the supraoptimal growth temperature of 90 °C. Herein we show that the enzyme is absolutely required for microbial growth at 95 °C, which in this case is a suboptimal growth temperature. Deletion of the gene encoding the reverse gyrase of the model hyperthermophilic archaeon Pyrococcus furiosus, which has an optimal growth temperature of 100 °C, revealed that the gene is required for growth at 95 °C, as well as at 100 °C. The results suggest that a temperature threshold above 90 °C exists, wherein the activity of reverse gyrase is absolutely necessary to maintain a correct DNA twist for any organism growing at such temperature extremes.

Temperature Shift Experiments Suggest That Metabolic Impairment and Enhanced Rates of Photorespiration Decrease Organic Acid Levels in Soybean Leaflets Exposed to Supra-Optimal Growth Temperatures.

Elevated growth temperatures are known to affect foliar organic acid concentrations in various plant species. In the current study, citrate, malate, malonate, fumarate and succinate decreased 40 to 80% in soybean leaflets when plants were grown continuously in controlled environment chambers at 36/28 compared to 28/20 °C. Temperature effects on the above mentioned organic acids were partially reversed three days after plants were transferred among optimal and supra-optimal growth temperatures. In addition, CO2 enrichment increased foliar malate, malonate and fumarate concentrations in the supra-optimal temperature treatment, thereby mitigating effects of high temperature on respiratory metabolism. Glycerate, which functions in the photorespiratory pathway, decreased in response to CO2 enrichment at both growth temperatures. The above findings suggested that diminished levels of organic acids in soybean leaflets upon exposure to high growth temperatures were attributable to metabolic impairment and to changes of photorespiratory flux. Leaf development rates differed among temperature and CO2 treatments, which affected foliar organic acid levels. Additionally, we report that large decreases of foliar organic acids in response to elevated growth temperatures were observed in legume species.

Growth temperature-induced changes in biomass accumulation, photosynthesis and glutathione redox homeostasis as influenced by hydrogen peroxide in cucumber.

Hydrogen peroxide (H2O2) and glutathione (GSH) are involved in the stress response in plants. To elucidate the role of H2O2 in the acclimation of CO2 assimilation under sub- or supra-optimal growth temperatures, we examined the effect and interaction of H2O2 manipulation on the photosynthetic metabolism of cucumber plants (Cucumis sativus L.) grown under five temperature regimes spanning above and below the optimal growth temperature; 11/9, 18/15, 25/20, 32/27, and 39/33 °C (day/night), with or without dimethylthiourea (DMTU) or H2O2 treatment. As expected, exposure to sub- or supra-optimal growth temperatures resulted in decreased plant growth, associated with a decline in CO2 assimilation (Asat), Rubisco content, and activities of enzymes involved in the CO2 assimilation, as well as a decrease in the ratio of reduced (GSH) to oxidized (GSSG) glutathione (GSH/GSSG). Foliar application of H2O2 promoted, whilst DMTU retarded the capacity of plants to acclimate to non-optimal growth temperatures; this was consistently shown in altered activity of redox-sensitive enzymes involved in CO2 assimilation. These results strongly suggest that the influence of growth temperature on CO2 assimilation was primarily targeted at the activities of the redox-sensitive enzymes of CO2 assimilation. Meanwhile, the data suggest that the cellular H2O2 level is an important signal for the glutathione-dependent regulation of redox-sensitive enzymes of CO2 assimilation in cucumber plants.

Two Alternative Pathways for the Synthesis of the Rare Compatible Solute Mannosylglucosylglycerate inPetrotoga mobilis

The compatible solute mannosylglucosylglycerate (MGG), recently identified in Petrotoga miotherma, also accumulates in Petrotoga mobilis in response to hyperosmotic conditions and supraoptimal growth temperatures. Two functionally connected genes encoding a glucosyl-3-phosphoglycerate synthase (GpgS) and an unknown glycosyltransferase (gene Pmob_1143), which we functionally characterized as a mannosylglucosyl-3-phosphoglycerate synthase and designated MggA, were identified in the genome of Ptg. mobilis. This enzyme used the product of GpgS, glucosyl-3-phosphoglycerate (GPG), as well as GDP-mannose to produce mannosylglucosyl-3-phosphoglycerate (MGPG), the phosphorylated precursor of MGG. The MGPG dephosphorylation was determined in cell extracts, and the native enzyme was partially purified and characterized. Surprisingly, a gene encoding a putative glucosylglycerate synthase (Ggs) was also identified in the genome of Ptg. mobilis, and an active Ggs capable of producing glucosylglycerate (GG) from ADP-glucose and d-glycerate was detected in cell extracts and the recombinant enzyme was characterized, as well. Since GG has never been identified in this organism nor was it a substrate for the MggA, we anticipated the existence of a nonphosphorylating pathway for MGG synthesis. We putatively identified the corresponding gene, whose product had some sequence homology with MggA, but it was not possible to recombinantly express a functional enzyme from Ptg. mobilis, which we named mannosylglucosylglycerate synthase (MggS). In turn, a homologous gene from Thermotoga maritima was successfully expressed, and the synthesis of MGG was confirmed from GDP-mannose and GG. Based on the measurements of the relevant enzyme activities in cell extracts and on the functional characterization of the key enzymes, we propose two alternative pathways for the synthesis of the rare compatible solute MGG in Ptg. mobilis.

Occurrence of 1-Glyceryl-1-myo-Inosityl Phosphate in Hyperthermophiles

The accumulation of compatible solutes was studied in the hyperthermophilic bacterium Aquifex pyrophilus as a function of the temperature and the NaCl concentration of the growth medium. Nuclear magnetic resonance analysis of cell extracts revealed the presence of alpha- and beta-glutamate, di-mannosyl-di-myo-inositol phosphate, di-myo-inositol phosphate, and an additional compound here identified as 1-glyceryl-1-myo-inosityl phosphate. All solutes accumulated by A. pyrophilus are negatively charged at physiological pH. The intracellular levels of di-myo-inositol phosphate increased in response to supraoptimal growth temperature, while alpha- and beta-glutamate accumulated in response to osmotic stress, especially at growth temperatures below the optimum. The newly discovered compound, 1-glyceryl-1-myo-inosityl phosphate, appears to play a double role in osmo- and thermoprotection, since its intracellular pool increased primarily in response to a combination of osmotic and heat stresses. This work also uncovered the nature of the unknown compound, previously detected in Archaeoglobus fulgidus (L. O. Martins et al., Appl. Environ. Microbiol. 63:896-902, 1997). The curious structural relationship between diglycerol phosphate (found only in Archaeoglobus species), di-myo-inositol phosphate (a canonical solute of hyperthermophiles), and the newly identified solute is highlighted. This is the first report on the occurrence of 1-glyceryl-1-myo-inosityl phosphate in living systems.

Compatible Solutes of the HyperthermophilePalaeococcus ferrophilus: Osmoadaptation and Thermoadaptation in the OrderThermococcales

The effect of salinity and growth temperature on the accumulation of intracellular organic solutes was examined in the hyperthermophilic archaeon Palaeococcus ferrophilus. The genus Palaeococcus represents a deep-branching lineage of the order Thermococcales, which diverged before Thermococcus and Pyrococcus. Palaeococcus ferrophilus accumulated mannosylglycerate, glutamate, and aspartate as major compatible solutes. Unlike members of the genera Pyrococcus and Thermococcus, Palaeococcus ferrophilus did not accumulate di-myo-inositol phosphate, a canonical solute of hyperthermophiles. The level of mannosylglycerate increased in response to both heat and salt stress; glutamate increased at supraoptimal growth temperatures, whereas aspartate increased at supraoptimal salt concentration. Proline, alanine, and trehalose were also found in lesser amounts, but their levels did not respond significantly to any of the stresses imposed. Additionally, the genes involved in the synthesis of mannosylglycerate in Palaeococcus ferrophilus and Thermococcus litoralis were identified. In both organisms the synthesis proceeds via the two-step pathway comprising mannosyl-3-phosphoglycerate synthase (MPGS) (EC 2.4.1.217) and mannosyl-3-phosphoglycerate phosphatase (MPGP) (EC 3.1.3.70). The mpgS and mpgP genes of Palaeococcus ferrophilus were expressed in Escherichia coli and the proteins were characterized. MPGS had maximal activity at 90 degrees C and pH near 7.0, and was strictly dependent on Mg2+. MPGP had optimal activity at 90 degrees C and pH 6.0 and was barely dependent on Mg2+. The half-life values for inactivation of MPGS and MPGP at 83 degrees C were 18 and 25 min, respectively. A comparative discussion of the osmo- and thermoadaptation strategies in these three genera of the Thermococcales is presented.

A variant of the hyperthermophile Archaeoglobus fulgidus adapted to grow at high salinity.

A variant of Archaeoglobus fulgidus VC-16 was isolated from cultures obtained after a stepwise transfer from media containing 1.8-6.3% NaCl by a plating-independent, selected-cell cultivation technique, using a laser microscope. This variant, A. fulgidus VC-16S, had a higher growth rate throughout the salt range of the parental strain, but was also able to grow in media containing NaCl up to 6.3%, whereas the parental strain could not grow above 4.5% NaCl. Diglycerol phosphate (DGP), only encountered in the Archaeoglobales, was the major solute accumulated under supra-optimal salinities, whereas at supra-optimal growth temperatures di-myo-inositol phosphate was the predominant solute. The accumulation of compatible solutes during growth of variant VC-16S was lower than in the parental strain within 1.8-4.5% NaCl, but the levels of compatible solutes, including DGP, increased sharply in the variant at higher salinities (5.5 and 6.0%). This variant represents, at this time, one of the most halophilic hyperthermophiles known, and its ability to grow at high salinity appears to be due to the massive accumulation of DGP.

A variant of the hyperthermophile Archaeoglobus fulgidus adapted to grow at high salinity

A variant of Archaeoglobus fulgidus VC-16 was isolated from cultures obtained after a stepwise transfer from media containing 1.8–6.3% NaCl by a plating-independent, selected-cell cultivation technique, using a laser microscope. This variant, A. fulgidus VC-16S, had a higher growth rate throughout the salt range of the parental strain, but was also able to grow in media containing NaCl up to 6.3%, whereas the parental strain could not grow above 4.5% NaCl. Diglycerol phosphate (DGP), only encountered in the Archaeoglobales, was the major solute accumulated under supra-optimal salinities, whereas at supra-optimal growth temperatures di- myo-inositol phosphate was the predominant solute. The accumulation of compatible solutes during growth of variant VC-16S was lower than in the parental strain within 1.8–4.5% NaCl, but the levels of compatible solutes, including DGP, increased sharply in the variant at higher salinities (5.5 and 6.0%). This variant represents, at this time, one of the most halophilic hyperthermophiles known, and its ability to grow at high salinity appears to be due to the massive accumulation of DGP.

Secretion of Free Fatty Acids by Prokaryotic and Eukaryotic Algae at Optimal, Supraoptimal, and Suboptimal Growth Temperatures

The paper describes the composition of extracellular free fatty acids (FFAs) and intracellular fatty acids (FAs) in the enrichment cultures of the prokaryotic alga Spirulina platensisand the eukaryotic alga Chlorella vulgarisgrown at optimal, supraoptimal, and suboptimal growth temperatures. With increasing growth temperature, the degree of unsaturation of the intracellular FAs of both algae decreased, while that of the extracellular FFAs of S. platensisincreased. The composition of the extracellular FFAs of C. vulgarispractically did not depend on the growth temperature.

PHENOTYPIC CHARACTERIZATION OF PSEUDOMONAS AVELLANAE (PSALLIDAS) JANSE ET AL. AND OCCURRENCE OF COLONY VARIANTS

Thirty-seven strains of Pseudomonas avellanae from northern Greece, northern Italy and two different areas of central Italy were assessed for some morphological and physiological properties. Whole-cell protein profile analysis was performed by means of UPGMA. The occurrence and induction of transparent colonies of P. avellanae sometimes observed on nutrient sucrose agar (NSA) isolation plates, is described. P. avellanae strains showed variability in morphological characteristics, gelatin liquefaction and maximum temperature of growth. Cluster analysis of whole-cell protein profiles indicated that strains from northern Italy differ from those from northern Greece and central Italy and that strains from the provinces of Viterbo and Rome clustered in the same group. All strains were negative in icenucleation activity and accumulation of poly-b-hydroxybutyrate, and positive in production acid from sucrose. All strains were copper-sensitive. The production of fluorescent pigments on media was influenced by subculture on NSA, and strains from Italy lost this feature after a number of transfers. The existence of populations of the pathogen seems possible. Transparent colonies of P. avellanae were also frequently obtained by incubation for three days at supraoptimal growth temperature, by adding 7% sucrose to the nutrient agar and by subculturing 30 day-old colonies on NSA. Such P. avellanae colony variants were encapsulated and did not induce hypersensitivity in tobacco leaves.

Effects of temperature, salinity, and medium composition on compatible solute accumulation by thermococcus spp

The effects of salinity and growth temperature on the accumulation of intracellular organic solutes were examined by nuclear magnetic resonance spectroscopy (NMR) in Thermococcus litoralis, Thermococcus celer, Thermococcus stetteri, and Thermococcus zilligii (strain AN1). In addition, the effects of growth stage and composition of the medium were studied in T. litoralis. A novel compound identified as beta-galactopyranosyl-5-hydroxylysine was detected in T. litoralis grown on peptone-containing medium. Besides this newly discovered compound, T. litoralis accumulated mannosylglycerate, aspartate, alpha-glutamate, di-myo-inositol-1,1'(3,3')-phosphate, hydroxyproline, and trehalose. The hydroxyproline and beta-galactopyranosyl-5-hydroxylysine were probably derived from peptone, while the trehalose was derived from yeast extract; none of these three compounds was detected in the other Thermococcus strains examined. Di-myo-inositol-1,1'(3,3')-phosphate, aspartate, and mannosylglycerate were detected in T. celer and T. stetteri, and the latter organism also accumulated alpha-glutamate. The only nonmarine species studied, T. zilligii, accumulated very low levels of alpha-glutamate and aspartate. The levels of mannosylglycerate and aspartate increased in T. litoralis, T. celer, and T. stetteri in response to salt stress, while di-myo-inositol-1,1'(3,3')-phosphate was the major intracellular solute at supraoptimal growth temperatures. The phase of growth had a strong influence on the types and levels of compatible solutes in T. litoralis; mannosylglycerate and aspartate were the major solutes during exponential growth, while di-myo-inositol-1,1'(3,3')-phosphate was the predominant organic solute during the stationary phase of growth. This work revealed an unexpected ability of T. litoralis to scavenge suitable components from the medium and to use them as compatible solutes.

Accumulation of Mannosylglycerate and Di-myo-Inositol-Phosphate by Pyrococcus furiosus in Response to Salinity and Temperature

(sup13)C and (sup1)H nuclear magnetic resonance spectroscopy was used to identify and quantify organic solutes accumulated by the hyperthermophilic archaeon Pyrococcus furiosus in response to temperature and salinity. Di-myo-inositol-phosphate and 2-O-(beta)-mannosylglycerate were the major organic solutes accumulated in these cells. The total intracellular organic solutes increased significantly in response either to an increase in temperature or to an increase in salinity, but (beta)-mannosylglycerate accumulated mainly at high salinities, whereas the concentration of di-myo-inositol-phosphate increased dramatically at supraoptimal growth temperatures. Glutamate was present at concentrations detectable by nuclear magnetic resonance only in cells grown in low-salinity media. The intracellular levels of K(sup+) are clearly dependent on the salinity of the medium, and the concentrations of this cation are high enough to counterbalance the negative charges of (beta)-mannosylglycerate and di-myo-inositol-phosphate in the cell. The results presented here together with those previously reported for Pyrococcus woesei (S. Scholz, J. Sonnenbichler, W. Schafer, and R. Hensel, FEBS Lett. 306:239-242, 1992) strongly support a role for di-myo-inositol-phosphate in thermoprotection.

Characterization of a metalloprotease inhibitor protein (SmaPI) of Serratia marcescens.

As suggested by Y. Suh and M.J. Benedik (J. Bacteriol. 174: 2361-2366, 1992), Serratia marcescens ATCC 27117 produced very small amounts (0.8 U ml-1) of an inhibitor protein (SmaPI) that shows an inhibitory activity against extracellular 50-kDa metalloprotease (SMP) of S. marcescens and that is localized in the periplasm of cells at the optimal growth temperature of 25 degrees C. A recombinant S. marcescens harboring plasmid pSP2 encoding SMP and SmaPI genes produced 20 U of SmaPI ml-1 that is also localized in the periplasm of cells at 25 degrees C. However, a large amount of SmaPI (86 Uml-1) was extracellularly produced at the supraoptimal growth temperature 37 degrees C from the recombinant S. marcescens (pSP2). We purified SmaPI from the culture supernatant of S. marcescens (pSP2) grown at 37 degrees C, and some biochemical properties were characterized. SmaPI had a pI value of about 10.0 and was a monomeric protein with a molecular mass of 10,000. SmaPI was produced from a precursor SmaPI by cleavage of a signal peptide (26 amino acid residues). The inhibitor was stable in boiling water for up to 30 min. The thermostability of SmaPI can be attributed to its reversible denaturation. SmaPI inhibited SMP by formation of a noncovalent complex with a molar ratio of 1:1 and showed a high protease specificity, which inhibited only SMP among the various proteases we examined.

Effect of temperature on the physiology and cytology of the methylotrophic yeastCandida boidinii growing in methanol-limited chemostat

All deviations from optimum cultivation temperature affect strongly the physiology and morphology of cells ofCandida boidinii strain 2 during growth in methanol-limited chemostat. The optimum cultivation temperature was 28–30 °C at which maximum cell concentration and maximum cell yield (Y S 0.4 g/g) were achieved. At suboptimal growth temperatures the cells were rich in cell protein, RNA, alcohol oxidase (AO) and in peroxisomes. Formation of cubic peroxisomes and a 20 % decrease of budding cells in the population was observed. At supraoptimal growth temperatures (>30 °C) a sharp decrease in AO activity was accompanied by degradation of peroxisomes in the cells. The culture forms pseudomycelium: at 34 °C the cells stop growing and they are washed out of the bioreactor.

Sister-chromatid exchange formation at supra-optimal growth temperatures

The present research was mainly focused on characterizing the formation of sister-chromatid exchanges at both optimal and supra-optimal growth temperatures. Under these conditions (25, 30 and 35°C) meristem cells of Allium cepa L. exhibited a roughly constant cell-cycle time, and modifications in other cell-cycle parameters were negligible. Second-division chromosomes of cells incubated at 30 and 35°C showed increased SCE yields as compared with those detected in cells maintained at the optimal temperature (25°C). When cells with unifilarly BrdUrd-substituted DNA were damaged by irradiation with visible light, we obtained almost the same SCE yields at the various temperatures tested. We suggest that this production of SCEs could be the result of a reduced number of lesions produced by light (perhaps as a consequence of reduced intracellular free oxygen at high temperature) and/or of an increased efficiency in the repair capacity of the cells at these temperatures. The analysis of SCE formation in undamaged cells incubated at different temperatures. during BrdUrd treatment has shown that the optimal growth temperature appears to be the experimental condition in which the cells are able to exhibit the lowest frequency of SCE.

Effects of growth temperature on maximal specific growth rate, yield, maintenance, and death rate in glucose-limited continuous culture of the thermophilic Bacillus caldotenax

The influence of temperature on the growth of the theromophilic Bacillus caldotenax was investigated using chemostat techniques and a chemically defined minimal medium. All determined growth constants, that is maximal specific growth rate, yield and maintenance, were temperature dependent. It was striking that the very large maintenance requirement was about 10 times higher than for mesophilic cells under equivalent conditions. A death rate, which was very substantial at optimal and supraoptimal growth temperatures, was estimated by comparing the maintenance for substrate and oxygen. There was no indication for a thermoadaptation as postulated by Haberstich and Zuber (1974).

Joint destruction and chondrocalcinosis in patients with generalised osteoarthrosis.

<h3>Abstract</h3> Microbial acclimation to different temperature conditions can involve broad changes in cell composition and metabolic efficiency. A systems-level view of these metabolic responses in non-mesophilic organisms, however, is currently missing. In this study, thermodynamically-constrained genome-scale models were applied to simulate the metabolic responses of a deep-sea psychrophilic bacterium, <i>Shewanella psychrophila</i> WP2, under suboptimal (4°C), optimal (15°C), and supraoptimal (20°C) growth temperatures. The models were calibrated with experimentally determined growth rates of WP2. Gibbs free energy change of reactions (<i>Δ_rG’</i>), metabolic fluxes, and metabolite concentrations were predicted using random simulations to characterize temperature-dependent changes in the metabolism. The modeling revealed the highest metabolic efficiency at the optimal temperature, and it suggested distinct patterns of ATP production and consumption that could lead to the lower metabolic efficiency under suboptimal or supraoptimal temperatures. The modeling also predicted rearrangement of fluxes through multiple metabolic pathways, including the glycolysis pathway, Entner-Doudoroff pathway, tricarboxylic acid (TCA) cycle, and the electron transport system, and these predictions were corroborated through comparisons to WP2 transcriptomes. Furthermore, predictions of metabolite concentrations revealed the potential conservation of reducing equivalents and ATP in the suboptimal temperature, consistent with experimental observations from other psychrophiles. Taken together, the WP2 models provided mechanistic insights into the metabolism of a psychrophile in response to different temperatures. <h3>Importance</h3> Metabolic flexibility is a central component of any organism’s ability to survive and adapt to changes in environmental conditions. This study represents the first application of thermodynamically-constrained genome-scale models in simulating the metabolic responses of a deep-sea psychrophilic bacterium to varying temperatures. The models predicted differences in metabolic efficiency that were attributed to changes in metabolic pathway utilization and metabolite concentration during growth under optimal and non-optimal temperatures. Experimental growth measurements were used for model calibration, and temperature-dependent transcriptomic changes corroborated the model-predicted rearrangement of metabolic fluxes. Overall, this study highlights the utility of modeling approaches in studying the temperature-driven metabolic responses of an extremophilic organism.