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USGS2014

Extracellular enzyme kinetics scale with resource availability

Microbial community metabolism relies on external digestion, mediated by extracellular enzymes that break down complex organic matter into molecules small enough for cells to assimilate. We analyzed the kinetics of 40 extracellular enzymes that mediate the degradation and assimilation of carbon, nitrogen and phosphorus by diverse aquatic and terrestrial microbial communities (1160 cases). Regression analyses were conducted by habitat (aquatic and terrestrial), enzyme class (hydrolases and oxidoreductases) and assay methodology (low affinity and high affinity substrates) to relate potential reaction rates to substrate availability. Across enzyme classes and habitats, the scaling relationships between apparent V max and apparent K m followed similar power laws with exponents of 0.44 to 0.67. These exponents, called elasticities, were not statistically distinct from a central value of 0.50, which occurs when the K m of an enzyme equals substrate concentration, a condition optimal for maintenance of steady state. We also conducted an ecosystem scale analysis of ten extracellular hydrolase activities in relation to soil and sediment organic carbon (2,000–5,000 cases/enzyme) that yielded elasticities near 1.0 (0.9 ± 0.2, n = 36). At the metabolomic scale, the elasticity of extracellular enzymatic reactions is the proportionality constant that connects the C:N:P stoichiometries of organic matter and ecoenzymatic activities. At the ecosystem scale, the elasticity of extracellular enzymatic reactions shows that organic matter ultimately limits effective enzyme binding sites. Our findings suggest that one mechanism by which microbial communities maintain homeostasis is regulating extracellular enzyme expression to optimize the short-term responsiveness of substrate acquisition. The analyses also show that, like elemental stoichiometry, the fundamental attributes of enzymatic reactions can be extrapolated from biochemical to community and ecosystem scales.

Biogeochemistry↗

USGS1969

Ion association in natural brines

Natural brines, both surface and subsurface, are highly associated aqueous solutions. Ion complexes in brines may be ion pairs in which the cation remains fully hydrated and the bond between the ions is essentially electrostatic, or coordination complexes in which one or more of the hydration water molecules are replaced by covalent bonds to the anion. Except for Cl − , the major simple ions in natural brines form ion pairs; trace and minor metals in brines form mainly coordination complexes. Limitations of the Debye-Hückel relations for activity coefficients and lack of data on definition and stability of all associated species in concentrated solutions tend to produce underestimates of the degree of ion association, except where the brines contain a very high proportion of Cl − . Data and calculations on closed basin brines of highly varied composition have been coupled with electrode measurements of single-ion activities in an attempt to quantify the degree of ion association. Such data emphasize the role of magnesium complexes. Trace metal contents of closed basin brines are related to complexes formed with major anions. Alkaline sulfo- or chlorocarbonate brines (western Great Basin) carry significant trace metal contents apparently as hydroxides or hydroxy polyions. Neutral high chloride brines (Bonneville Basin) are generally deficient in trace metals. With a knowledge of the thermodynamic properties of a natural water, many possible reactions with other phases (solids, gases, other liquids) may be predicted. A knowledge of these reactions is particularly important in the study of natural brines which may be saturated with many solid phases (silicates, carbonates, sulfates, etc.), which may have a high pH and bring about dissolution of other phases (silica, amphoteric hydroxides, CO 2 , etc.), and which because of their high density may form relatively stable interfaces with dilute waters.

Chemical Geology↗

USGS1988

Methane hydrate - A major reservoir of carbon in the shallow geosphere?

Methane hydrates are solids composed of rigid cages of water molecules that enclose methane. Sediment containing methane hydrates is found within specific pressure-temperature conditions that occur in regions of permafrost and beneath the sea in outer continental margins. Because methane hydrates are globally widespread and concentrate methane within the gas-hydrate structure, the potential amount of methane present in the shallow geosphere at subsurface depths of < ???2000 m is very large. However, estimates of the amount are speculative and range over about three orders of magnitude, from 2 ?? 103 to 4 ?? 106 Gt (gigatons = 1015 g) of carbon, depending on the assumptions made. The estimate I favor is ??? 1 ?? 104 Gt of carbon. The estimated amount of organic carbon in the methane-hydrate reservoir greatly exceeds that in many other reservoirs of the global carbon cycle - for example, the atmosphere (3.6 Gt); terrestrial biota (830 Gt); terrestrial soil, detritus and peat (1960 Gt); marine biota (3 Gt); and marine dissolved materials (980 Gt). In fact, the amount of carbon may exceed that in all fossil fuel deposits (5 ?? 103 Gt). Because methane hydrates contain so much methane and occur in the shallow geosphere, they are of interest as a potential resource of natural gas and as a possible source of atmospheric methane released by global warming. As a potential resource, methane hydrates pose both engineering and production problems. As a contributor to a changing global climate, destabilized methane hydrates, particularly those in shallow, nearshore regions of the Arctic Ocean, may have some effect, but this effect will probably be minimal, at least during the next 100 years. ?? 1988.

Chemical Geology↗

USGS1970

The diffusion of ions in unconsolidated sediments

Diffusion in unconsolidated sediments generally proceeds at rates ranging from half to one twentieth of those applying to diffusion of ions and molecules in free solution. Diffusion rates are predictable with respect to porosity and path tortuosity in host sediments, and can be conveniently measured by determinations of electrical resistivity on bulk sediment samples. Net ion flux is further influenced by reactions of diffusing species with enclosing sediments, but such influences should not be confused with or lumped with diffusion processes.

Earth and Planetary Science Letters↗

USGS1969

Pyrolysis of humic and fulvic acids

Pyrolysis of humic and fulvic acids isolated from a North Carolina soil yields a variety of aromatic, heterocyclic and straight chain organ compounds. The pyrolysis products identified by gas chromatography and mass spectrometry indicate that humic and fulvic acids have aromatic and polysaccharide structures in their molecules.

Geochimica et Cosmochimica Acta↗

USGS1983

An interpretation of carbon and sulfur relationships in Black Sea sediments as indicators of environments of deposition

Syngenetic iron sulfides in sediments are formed from dissolved sulfide resulting from sulfate reduction and catabolism of organic matter by anaerobic bacteria. It has been shown that in recent marine sediments deposited below oxygenated waters there is a constant relationship between reduced sulfur and organic carbon which is generally independent of the environment of deposition. Reexamination of data from recent sediments from euxinic marine environments ( e.g. , the Black Sea) also shows a linear relationship between carbon and sulfur, but the slope is variable and the line intercepts the S axis at a value between 1 and 2 percent S. It is proposed that the positive S intercept is due to watercolumn microbial reduction of sulfate using metabolizable small organic molecules and the sulfide formed is precipitated and accumulates at the sediment-water interface. The variation in slope and intercept of the C to S plots for several cores and for different stratigraphic zones for the Black Sea can be interpreted in relation to thickness of the aqueous sulfide layer or thinness of the oxygen containing layer and to deposition rate, but also may be influenced by availability of iron, and perhaps the type of organic matter (Leventhal, 1979).

Geochimica et Cosmochimica Acta↗

USGS1983

A method of calculating quartz solubilities in aqueous sodium chloride solutions

The aqueous silica species that form when quartz dissolves in water or saline solutions are hydrated. Therefore, the amount of quartz that will dissolve at a given temperature is influenced by the prevailing activity of water. Using a standard state in which there are 1,000 g of water (55.51 moles) per 1,000 cm 3 of solution allows activity of water in a NaCl solution at high temperature to be closely approximated by the effective density of water, p e , in that solution, i.e. the product of the density of the NaCl solution times the weight fraction of water in the solution, corrected for the amount of water strongly bound to aqueous silica and Na + as water of hydration. Generally, the hydration of water correction is negligible. The solubility of quartz in pure water is well known over a large temperature-pressure range. An empirical formula expresses that solubility in terms of temperature and density of water and thus takes care of activity coefficient and pressure-effect terms. Solubilities of quartz in NaCl solutions can be calculated by using that equation and substituting p e , for the density of pure water. Calculated and experimentally determined quartz solubilities in NaCl solutions show excellent agreement when the experiments were carried out in non-reactive platinum, gold, or gold plus titanium containers. Reactive metal containers generally yield dissolved silica concentrations higher than calculated, probably because of the formation of metal chlorides plus NaOH and H 2 . In the absence of NaOH there appears to be no detectable silica complexing in NaCl solutions, and the variation in quartz solubility with NaCl concentration at constant temperature can be accounted for entirely by variations in the activity of water. The average hydration number per molecule of dissolved SiO 2 in liquid water and NaCl solutions decreases from about 2.4 at 200°C to about 2.1 at 350°C. This suggests that H 4 SiO 4 may be the dominant aqueous silica species at 350°C, but other polymeric forms become important at lower temperatures.

Geochimica et Cosmochimica Acta↗

USGS1994

An experimental study of zinc chloride speciation from 300 to 600 °C and 0.5 to 2.0 kbar in buffered hydrothermal solutions

The solubility of sphalerite (ZnS) was measured in KCl-HCl-H 2 O solutions at 300–600°C and 0.5–2.0 kbar. The silicate assemblage K-feldspar-muscovite (or andalusite)-quartz was used to buffer the solution to acid conditions, resulting in the total solubility reaction 2 K + + KAl 2 AlSi 3 O 10 ( OH ) 2 + 6 SiO 2 + ZnS + nCl − = ZnCl n (2− n ) + 3 KAlSi 3 O 8 + H 2 S . (muscovite) (quartz) (sphalerite) (K-feldspar) A computer retrieval technique was used to derive average chloride ligand numbers for chlorozinc species at 0.25–2.0 molal total chloride. This technique mathematically solves for the average ligand number using a series of pertinent chemical relations at P and T . Mono- and di-chlorozinc species were found to predominate throughout the pressure-temperature-composition range investigated. The logarithms of the first and second dissociation constants for ZnCl 2 0 were evaluated over the P - T range; for example, at 1 kbar, the values −0.41 and −1.42 were computed for the logarithm of the first dissociation constant, while −7.62 and −10.57 were computed for the logarithm of the second dissociation constant, for 400 and 500°C, respectively. Results are compared to past studies conducted at subcritical conditions and differ in that we find no evidence for more highly coordinated chloro-zinc species except possibly for ZnCl 3 − at 600°C, 1 and 2 kbar. Our results are consistent with electrostatic theory, which favors lower charged to neutral molecules in low dielectric-constant media.

Geochimica et Cosmochimica Acta↗

USGS1996

Mechanism of molybdenum removal from the sea and its concentration in black shales: EXAFS evidence

Molybdenum K-edge EXAFS (extended X-ray absorption fine structure) spectra yield new structural information about the chemical environment of Mo in high-Mo black shales and sediments. Two spectral types are found. The less common one, associated with Mo ores developed in shale in China, is that of a MoS2 phase, possibly X-ray amorphous jordisite. The other, associated with Cretaceous deep sea sediments and with other black shales, is characterized by short Mo-O distances (1.69-1.71 A??), by Mo-S distances of 2.30-2.38 A??, and in some cases by second shell Mo and Fe interactions, which suggests that some Mo resides in transition metal-rich phases. EXAFS spectra of synthetic amorphous materials, prepared by scavenging Mo from HS solutions with Fe(II), FeOOH, and humic acid, suggest that the second spectral type arises from Mo present chiefly in two forms. One is a compact, Mo-Fe-S "cubane" type compound with Mo-S distances of ???2.36 A?? and Mo-Fe distances of ???2.66 A??, while the other is probably an organic form containing some Mo-O double bonds (???1.69 A??). Laboratory products, that were prepared by scavenging dissolved Mo from sulfidic solutions with humic acid, yield spectra quite similar to the second spectral type observed in shales and sediments, including unexpected indications of Mo-Fe interactions. Molybdenum L-edge spectra indicate that the mean oxidation state in the sediments and shales lies between IV and VI. This work demonstrates the merit of EXAFS for obtaining structural information on natural materials containing X-ray amorphous components which defeat conventional mineralogical characterization. The implications of these findings regarding Mo scavenging from sulfidic natural waters are considered. We introduce the concept of a geochemical switch, in which HS- transforms the marine behavior of Mo from that of a conservative element to that of a particle reactive element. The action point of the HS- switch is calculated to be, aHS- = 10-3.6 - 10-4.3. When aHS- approaches the action point, Mo becomes reactive to particles containing transition metals (e.g., Fe). We conjecture that thiols, including humic-bound thiol groups, also switch Mo behavior. In contrast to previous ideas, our model for Mo scavenging deemphasizes the role of reduction from Mo(VI) to Mo(V) as the initial step in scavenging; instead, we emphasize the ease with which Mo forms covalent bonds to transition metals and organic molecules via S bridges.

Geochimica et Cosmochimica Acta↗

USGS1992

Pesticide residues in ground water of the San Joaquin Valley, California

A regional assessment of non-point-source contamination of pesticide residues in ground water was made of the San Joaquin Valley, an intensively farmed and irrigated structural trough in central California. About 10% of the total pesticide use in the USA is in the San Joaquin Valley. Pesticides detected include atrazine, bromacil, 2.4-DP, diazinon, dibromochloropropane, 1,2-dibromoethane, dicamba, 1,2-dichloropropane, diuron, prometon, prometryn, propazine and simazine. All are soil applied except diazinon. Pesticide leaching is dependent on use patterns, soil texture, total organic carbon in soil, pesticide half-life and depth to water table. Leaching is enhanced by flood-irrigation methods except where the pesticide is foliar applied such as diazinon. Soils in the western San Joaquin Valley are fine grained and are derived primarily from marine shales of the Coast Ranges. Although shallow ground water is present, the fewest number of pesticides were detected in this region. The fine-grained soil inhibits pesticide leaching because of either low vertical permeability or high surface area; both enhance adsorption on to solid phases. Soils of the valley floor tend to be fine grained and have low vertical permeability. Soils in the eastern part of the valley are coarse grained with low total organic carbon and are derived from Sierra Nevada granites. Most pesticide leaching is in these alluvial soils, particularly in areas where depth to ground water is less than 30m. The areas currently most susceptible to pesticide leaching are eastern Fresno and Tulare Counties. Tritium in water molecules is an indicator of aquifer recharge with water of recent origin. Pesticide residues transported as dissolved species were not detected in non-tritiated water. Although pesticides were not detected in all samples containing high tritium, these samples are indicative of the presence of recharge water that interacted with agricultural soils.

Journal of Hydrology↗

USGS1973

Coexisting cummingtonite and aluminous hornblende from garnet amphibolite, Boehls Butte area, Idaho, USA

Electron microprobe analyses of green hornblende and coexisting cummingtonite from garnet amphibolite show identical Fe/Mg ratios ( = 0.9). Cummingtonite is iron-magnesium silicate with very little calcium and aluminum and practically no alkalies. In contrast, the hornblende has 1.5 tetrahedral Al, 0.9 octahedral Al and a considerable amount of Ca and alkalies. Comparison with the hornblendes from the Sierra Nevada shows a higher relative amount of tschemakite molecule in the hornblendes from Idaho where pressures during the recrystallization were higher.

Idaho↗

USGS1995

A review of the geochemistry of methane in natural gas hydrate

The largest accumulations on Earth of natural gas are in the form of gas hydrate, found mainly offshore in outer continental margin sediment and, to a lesser extent, in polar regions commonly associated with permafrost. Measurements of hydrocarbon gas compositions and of carbon-isotopic compositions of methane from natural gas hydrate samples, collected in subaquatic settings from around the world, suggest that methane guest molecules in the water clathrate structures are mainly derived by the microbial reduction of CO 2 from sedimentary organic matter. Typically, these hydrocarbon gases are composed of > 99% methane, with carbon-isotopic compositions (δ 13 C PDB ) ranging from − 57 to − 73‰. In only two regions, the Gulf of Mexico and the Caspian Sea, has mainly thermogenic methane been found in gas hydrate. There, hydrocarbon gases have methane contents ranging from 21 to 97%, with δ 13 C values ranging from − 29 to − 57‰. At a few locations, where the gas hydrate contains a mixture of microbial and thermal methane, microbial methane is always dominant. Continental gas hydrate, identified in Alaska and Russia, also has hydrocarbon gases composed of > 99% methane, with carbon-isotopic compositions ranging from − 41 to − 49‰. These gas hydrate deposits also contain a mixture of microbial and thermal methane, with thermal methane likely to be dominant.

Organic Geochemistry↗

USGS1987

Calculation of solar radiation in mountainous terrain

A study was performed to assess the accuracy of a daily solar radiation model for horizontal or sloping sites in terrain where surrounding ridges and tall trees block both direct beam and diffuse sky short wave radiation. To simulate adequately the major effects of these environments on radiation, the model incorporated (1) standard treatment of solar geometry (after Harris, 1983); (2) separation of direct and diffuse radiation by considering scattering and absorption due to aerosols, water vapor, air molecules and ozone (after Iqbal, 1983); (3) anisotropy of diffuse radiation modeled as a circumsolar component (15–50% of the total clear sky diffuse) plus an isotropic background; and (4) proper calculation of the proportions of sky radiation and ground reflected radiation sensed by both horizontal and inclined sensors. The model was calibrated using data from both horizontal and inclined pyranometers at six sites over four years. Values for the Ångstrom turbidity coefficient and the percentage of circumsolar diffuse radiation were determined using an iterative best fit technique. Mean monthly values of these coefficients and mean monthly ozone and water vapor concentrations from nearby weather service stations could be used for predicting total, cloud free, daily radiation with acceptable accuracy. Required site measurements include slope, aspect, latitude, longitude, date, time, effective horizon for the site, and an assessment of albedo for the surrounding terrain (including vegetation).

Agricultural and Forest Meteorology↗

USGS1995

Mechanism of formation of humus coatings on mineral surfaces 1. Evidence for multidentate binding of organic acids from compost leachate on alumina

Measurements of the infrared linear dichroism of carboxylate groups of organic acids from compost leachate adsorbed to an alumina surface and the enthalpy of adsorption of this reaction have been made. The linear dichroism measurements indicated that the carboxylate groups are not free to rotate. This limited rotation probably results from bidentate binding of the carboxylate groups. The molar enthalpy of adsorption of the acids is approximately −100 kJ mol −1 . This high value for enthalpy of adsorption may best be explained by assuming that two or more carboxylate groups on a single dissolved organic carbon (DOC) molecule coordinate to the surficial aluminium ions.

Colloids and Surfaces A: Physicochemical and Engin↗

USGS2014

Assessing the solubility controls on vanadium in groundwater, northeastern San Joaquin Valley, CA

The solubility controls on vanadium (V) in groundwater were studied due to concerns over possible harmful health effects of ingesting V in drinking water. Vanadium concentrations in the northeastern San Joaquin Valley ranged from <3 μg/L to 70 μg/L with a median of 21 μg/L. Concentrations of V were highest in samples collected from oxic groundwater (49% > 25 μg/L) and lowest in samples collected from anoxic groundwater (70% < 0.8 μg/L). In oxic groundwater, speciation modeling (SM) using PHREEQC predicted that V exists primarily as the oxyanion H 2 VO 4 − . Adsorption/desorption reactions with mineral surfaces and associated oxide coatings were indicated as the primary solubility control of V 5+ oxyanions in groundwater. Environmental data showed that V concentrations in oxic groundwater generally increased with increasing groundwater pH. However, data from adsorption isotherm experiments indicated that small variations in pH (7.4–8.2) were not likely as an important a factor as the inherent adsorption capacity of oxide assemblages coating the surface of mineral grains. In suboxic groundwater, accurate SM modeling was difficult since Eh measurements of source water were not measured in this study. Vanadium concentrations in suboxic groundwater decreased with increasing pH indicating that V may exist as an oxycationic species [e.g. V(OH) 3 + ]. Vanadium may complex with dissolved inorganic and organic ligands under suboxic conditions, which could alter the adsorption behavior of V in groundwater. Speciation modeling did not predict the existence of V-inorganic ligand complexes and organic ligands were not collected as part of this study. More work is needed to determine processes governing V solubility under suboxic groundwater conditions. Under anoxic groundwater conditions, SM predicts that aqueous V exists as the uncharged V(OH) 3 molecule. However, exceedingly low V concentrations show that V is sparingly soluble in anoxic conditions. Results indicated that V may be precipitating as V 3+ - or mixed V 3+ /Fe 3+ -oxides in anoxic groundwater, which is consistent with results of a previous study. The fact that V appears insoluble in anoxic (Fe reducing) redox conditions indicates that the behavior of V is different than arsenic (As) in aquifer systems where the reductive dissolution of Fe-oxides with As adsorbed to the surface is a well-documented mechanism for increasing As concentrations in groundwater. This hypothesis is supported by the relation of V to As concentrations in oxic versus anoxic redox conditions. Sequential extraction procedures (SEP) applied to aquifer material showed that the greatest amount of V was recovered by the nitric acid (HNO 3 ) extract (37–71%), followed by the oxalate-ascorbic acid extract (19–60%) and the oxalate extract (3–14%). These results indicate that V was not associated with the solid phase as an easily exchangeable fraction. Although the total amount of V recovered was greatest for the HNO 3 extract that targets V adsorbed to sorption sites of crystalline Al, Fe and Mn oxides, the greatest V saturation of sorption sites appeared to occur on the amorphous and poorly crystalline oxide solid phases targeted by the oxalate and oxalate-ascorbic acid extracts respectively. Adsorption isotherm experiments showed no correlation between V sorption and any of the fractions identified by the SEP. This lack of correlation indicates the application of an SEP alone is not adequate to estimate the sorption characteristics of V in an aquifer system.

California↗

USGS2006

Adsorption site analysis of impurity embedded single-walled carbon nanotube bundles

Bundle morphology and adsorptive contributions from nanotubes and impurities are studied both experimentally and by simulation using a computer-aided methodology, which employs a small physisorbed probe molecule to explore the porosity of nanotube samples. Grand canonical Monte Carlo simulation of nitrogen adsorption on localized sites of a bundle is carried out to predict adsorption in its accessible internal pore volume and on its external surface as a function of tube diameter. External adsorption is split into the contributions from the clean surface of the outermost nanotubes of the bundle and from the surface of the impurities. The site-specific isotherms are then combined into a global isotherm for a given sample using knowledge of its tube-diameter distribution obtained by Raman spectroscopy. The structural parameters of the sample, such as the fraction of open-ended nanotubes and the contributions from impurities and nanotube bundles to total external surface area, are determined by fitting the experimental nitrogen adsorption data to the simulated isotherm. The degree of closure between experimental and calculated adsorption isotherms for samples manufactured by two different methods, to provide different nanotube morphology and contamination level, further strengthens the validity and resulting interpretations based on the proposed approach. The average number of nanotubes per bundle and average bundle size, within a sample, are also quantified. The proposed method allows for extrapolation of adsorption properties to conditions where the purification process is 100% effective at removing all impurities and opening access to all intrabundle adsorption sites. ?? 2006 Elsevier Ltd. All rights reserved.

Carbon↗

USGS2006

Conservation of Toll-like receptor signaling pathways in teleost fish

In mammals, toll-like receptors (TLR) recognize ligands, including pathogen-associated molecular patterns (PAMPs), and respond with ligand-specific induction of genes. In this study, we establish evolutionary conservation in teleost fish of key components of the TLR-signaling pathway that act as switches for differential gene induction, including MYD88, TIRAP, TRIF, TRAF6, IRF3, and IRF7. We further explore this conservation with a molecular phylogenetic analysis of MYD88. To the extent that current genomic analysis can establish, each vertebrate has one ortholog to each of these genes. For molecular tree construction and phylogeny inference, we demonstrate a methodology for including genes with only partial primary sequences without disrupting the topology provided by the high-confidence full-length sequences. Conservation of the TLR-signaling molecules suggests that the basic program of gene regulation by the TLR-signaling pathway is conserved across vertebrates. To test this hypothesis, leukocytes from a model fish, rainbow trout ( Oncorhynchus mykiss ), were stimulated with known mammalian TLR agonists including: diacylated and triacylated forms of lipoprotein, flagellin, two forms of LPS, synthetic double-stranded RNA, and two imidazoquinoline compounds (loxoribine and R848). Trout leukocytes responded in vitro to a number of these agonists with distinct patterns of cytokine expression that correspond to mammalian responses. Our results support the key prediction from our phylogenetic analyses that strong selective pressure of pathogenic microbes has preserved both TLR recognition and signaling functions during vertebrate evolution.

Comparative Biochemistry and Physiology, Part D: G↗

USGS2007

Gene expression in the liver of rainbow trout, Oncorhynchus mykiss , during the stress response

To better appreciate the mechanisms underlying the physiology of the stress response, an oligonucleotide microarray and real-time RT-PCR (QRT-PCR) were used to study gene expression in the livers of rainbow trout ( Oncorhynchus mykiss ). For increased confidence in the discovery of candidate genes responding to stress, we conducted two separate experiments using fish from different year classes. In both experiments, fish exposed to a 3 h stressor were compared to control (unstressed) fish. In the second experiment some additional fish were exposed to only 0.5 h of stress and others were sampled 21 h after experiencing a 3 h stressor. This 21 h post-stress treatment was a means to study gene expression during recovery from stress. The genes we report as differentially expressed are those that responded similarly in both experiments, suggesting that they are robust indicators of stress. Those genes are a major histocompatibility complex class 1 molecule ( MHC1 ), JunB , glucose 6-phosphatase ( G6Pase ), and nuclear protein 1 ( Nupr1 ). Interestingly, Nupr1 gene expression was still elevated 21 h after stress, which indicates that recovery was incomplete at that time.

Comparative Biochemistry and Physiology, Part D: G↗