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PubMed2003

Inter-population differences in Cd, Cr, Se, and Zn accumulation by the green mussel Perna viridis acclimated at different salinities.

Trace metal (Cd, Cr, Se, and Zn) uptake from the dissolved phase, assimilation efficiency from the dietary phase, and metal body burden, as well as the clearance rate, apparent water permeability and gill surface area were measured in the green mussel Perna viridis collected from two contrasting salinity sites in Hong Kong coastal waters with following acclimation in the laboratory at different salinities. The concentrations of metals were 1.2-6.4x greater in mussels collected from the low salinity site, i.e. Tai O, as compared with Tap Mun (high salinity) mussels. Influx of Cd and Zn from the dissolved phase increased with decreased salinity. Furthermore, Cr(VI) and Se (selenite) influx were also affected by decreased salinity, in particular below 17 psu, suggesting that speciation was not the only factor to effect metal uptake. Long-term acclimation to different salinity also had an effect on metal uptake. Mussels collected from Tap Mun (high salinity) accumulated metals 1.2-2.2x faster than mussels from Tai O (low salinity) at intermediate and high experimental salinities >17 psu. Metal assimilation efficiencies were unaffected by salinity variation, but gut passage times were significantly longer at low (10 psu) salinities, indicating some effect of lowered salinity on mussels gut physiology. Gill surface area, which was similar in both populations of mussels, and filtration rate, which was generally similar or higher in those groups with low metal uptake, could not explain the inter-population difference in metal accumulation. Although there was no significant difference, due to high inter-individual variability, the apparent water permeability of the Tap Mun population was on average about 1.6x greater compared with Tai O mussels, and may partially account for the difference in metal uptake between these two populations acclimated at salinity >17 psu. Thus, the effect of salinity on metal uptake is dependent on metal biogeochemistry as well as a range of physiological responses. There was a clear effect of acclimation to lowered salinity on metal uptake, which may have important implications for metal accumulation modelling, biomonitoring, and toxicity studies.

Animals↗
PubMed1976

Adaptations with respect to salinity.

Amino acids contribute up to about 50% of the intracellular osmotic pressure of aquatic invertebrates. Since their concentration varies according to the salinity of the medium (high in sea water, low in fresh water) euryhaline invertebrates are good models for studying the mechanisms involved in the control of amino acid metabolism. During hyperosmotic stress CO2 production and O2 consumption decrease whereas the reverse is true when the animal is submitted to a hypo-osmotic stress. Nitrogen excretion (as NH3) increases in media of low salinity and the concentration of cyclic AMP increases during hyperosmotic stress. Moreover, blood proteins and haemocyanin are more concentrated in individuals adapted to media of low salinity. To explain the situation, three main mechanisms can be considered: (a) hydrolysis and synthesis of blood proteins; (b) transport of amino acids across the cell membrane; (c) control of the turnover rate of some amino acids. Results obtained on whole animals as well as on isolated tissues indicate that some amino acids are released from the cells and carried via the haemolymph to the posterior pairs of gills where they are oxidized (mechanisms b) or to an organ (hepatopancreas ?) Where they are used for blood protein synthesis (mechanism a). The use of labelled substrates demonstrates that the turnover rate of amino acids is controlled by the salinity of the environment (mechanism c). It is suggested that inorganic ions trigger the metabolic response by directing reducing equivalents toward oxygen or 2-oxo acids through control of the catalytic activity of dehydrogenases.

Adaptation, Physiological↗
PubMed1998

Confocal laser scanning and electron microscopical studies on osmoregulatory epithelia in the branchial cavity of the lobster homarus gammarus

The adult lobster Homarus gammarus is a weak hyper-regulator at low salinity. The objective of this study was to locate the ion-transporting tissues in the branchial chamber of this species, using electron microscopy and confocal laser scanning microscopy with a fluorescent vital stain for mitochondria, DASPMI, which is widely used to locate mitochondria-rich cells in ion-transporting epithelia of fish. A thick mitochondria-rich epithelium is present on the inner side of the branchiostegite and over the entire surface of the epipodites. Ultrastructural observations confirm that this tissue has features typical of an ion-transporting epithelium. When the lobster is transferred to low salinity, these epithelia undergo marked ultrastructural changes, such as an increase in thickness related to the development of basolateral infoldings, the appearance of numerous vesicles and an increase in height of the apical microvilli. In the gills, the branchial filaments are lined by a thin and poorly differentiated epithelium, containing numerous mitochondria; no significant ultrastructural changes were observed in the gills of animals acclimated to low salinity. In summary, in H. gammarus, no evidence of osmoregulatory structures was found in the gills. Differentiated ion-transporting epithelia are present in the branchial cavity, on the inner side of the branchiostegite and on the epipodites; these organs are probably involved in osmoregulation.

Journal Article↗
PubMed2006

Prolactin gene expression and gill chloride cell activity in fugu Takifugu rubripes exposed to a hypoosmotic environment.

To evaluate a possible involvement of prolactin (PRL) in low-salinity tolerance of a marine pufferfish Takifugu rubripes, or fugu, gene-expression profiles of PRL in the pituitary and PRL receptor (PRLR) in the osmoregulatory organs were investigated in fish exposed to 25%-dilute seawater (SW). Following transfer from full-strength (100%) SW to 25% SW, plasma osmolality and Na(+) and Cl(-) levels were slightly decreased on day 1, which were restored on days 3 and 7. Expression levels of PRL mRNA in the pituitary was significantly increased in response to 25% SW transfer, which was in sharp contrast with a remarkable decrease in growth hormone (GH) mRNA levels. These profiles suggest that PRL and GH are involved in hyper- and hypoosmoregulation, respectively, as is the case with euryhaline teleosts. Expression levels of PRLR mRNA in the gill and intestine were not significantly different from the initial levels, whereas, PRLR mRNA expression in the kidney was significantly higher on day 7 than the initial levels. Although transfer to 25% SW did not affect the average size of Na(+)/K(+)-ATPase-immunoreactive chloride cells in the gills, both size and density of apical openings of chloride cells became significantly smaller after transfer to 25% SW. These findings suggest that the possible hypoosmotic action of PRL is mediated by PRLR expressed in the osmoregulatory organs, and that low-salinity tolerance of fugu may involve reduction of an ion-secreting function of gill chloride cells. To further evaluate long-term effects of the low-salinity environment on growth and osmoregulation, fugu were raised in 25% and 100% SW for a prolonged period of 8 weeks. They grew similarly in 25% and 100% SW, and there was no significant difference in body weight and standard length at any weekly sampling point. The plasma osmolality was maintained at about 345mOsm/kg.H(2)O in both media, whereas the gill Na(+)/K(+)-ATPase activity was significantly lower in 25% SW than 100% SW. Gene expression of PRL in the pituitary was higher in 25% SW than in 100% SW; conversely, expression levels of GH were lower in 25% SW than in 100% SW. These findings support a hyperosmotic action of PRL and a hypoosmotic, rather than growth-promoting, action of GH in this marine teleost.

Animals↗
PubMed2005

Molecular analysis of halophilic bacterial community for high-rate denitrification of saline industrial wastewater.

A denitrification system for saline wastewater utilizing halophilic denitrifying bacteria has not been developed so far. In this study, denitrification performance and microbial community under various saline conditions were investigated using denitrifying sludge acclimated under low-salinity condition for a few years as seed sludge. A continuous denitrification experiment showed that denitrification performance and microbial community at 10% salinity was higher than that at 1% salinity. The microbial community in the denitrification sludge that was acclimated under low salinity was monitored by terminal-restriction fragment length polymorphism (T-RFLP) analysis during acclimation to high-salinity condition. T-RFLP profiles and clone analysis based on 16S rRNA-encoding genes in the sludge of the denitrification system with 10% salinity indicated that the gamma-Proteobacteria, particularly Halomonas spp., were predominant species, suggesting that these bacterial members were possibly responsible for a high denitrification activity under high-salinity conditions. Furthermore, the investigation of denitrification performance under various saline conditions revealed that 4-10% salinity results in the highest denitrification rate, indicating that this salinity was optimal for predominant bacterial species to exhibit denitrification activity. These results indicate the possibility that an appropriate denitrification system for saline wastewater can be designed using acclimated sludge with a halophilic community.

Bacteria↗
PubMed1979

Responses of halophytes to high salinities and low water potentials.

The effects of nonsaline polyethylene glycol (PEG)-6000 and saline seawater solutions of comparable osmotic potential on the concentrations of organic solutes and inorganic ions in the tissues of halophytes (Plantago maritima L., Triglochin maritima L., Limonium vulgare Mill., Halimione portulacoides (L.) Aell) have been investigated. Studies were made to determine whether high salinities induce specific ion effects that are absent in plants grown in nonsaline solutions of comparable osmotic potential. Over-all, the responses of each species to the two different treatments (seawater or PEG) are similar; the accumulation of organic solutes (compatible osmotica) in tissues is primarily correlated with a decrease in the osmotic potential of culture solutions. Depending on the species, sorbitol, proline, reducing sugars, quaternary ammonium compounds, and alpha-amino nitrogen accumulate in tissues as the water potential of the tissues falls. Within a species there are differences in the concentrations of inorganic ions and organic solutes between roots and shoots of plants grown at high salinities or at high concentrations of PEG.

Journal Article↗
PubMed1984

Response of toxigenic Vibrio cholerae 01 to physico-chemical stresses in aquatic environments.

The survival and growth of toxigenic Vibrio cholerae 01 in water under various conditions of salinity, pH, temperature and cation composition and concentration were studied in an extensive series of laboratory experiments. Inter- and intra-strain variation in stress response (of 01 and non-01 strains) and the ability of V. cholerae to adapt to stressful environments were also studied. Toxigenic V. cholerae 01 were able to survive for at least 70 days at 25 degrees C in solutions of sea salt. The optimal salt concentration was 2.0% though all solutions in the range 0.25-3.0% gave good support. Substrains with enhanced capacity to persist at sub-optimal salinity (0.1%) were demonstrated. A great degree of inter-strain variation in stress response at low salinity (0.05%) was found among 59 strains, and this variation was unrelated to serogroup (01 or non-01), source (clinical or environmental) or country of origin (Tanzania or Bangladesh). At optimal salinity, inter-strain variation was less and 18 out of 20 strains remained viable at high concentrations for at least 40 months at 25 degrees C. V. cholerae 01 could not survive beyond 45 days at 4 degrees C and optimal salinity, either with or without nutrients. The optimal pH range for survival at 25 degrees C was 7.0-8.5 at optimal salinity, and 7.5-9.0 at low salinity. V. cholerae 01 require Na+ for survival in the absence of nutrients, and for enhanced growth in their presence. The presence of Ca2+ or Mg2+, in addition to Na+, further enhanced survival. These, and other results reported in this paper, suggest that toxigenic V. cholerae 01 are able to survive for extended periods in warm water containing no nutrients but having a salinity of 0.25-3.0% and a pH of around 8.0. With added nutrients and under the same conditions, rapid growth is possible. The implications of these findings for the identification of putative aquatic reservoirs of V. cholerae 01, and for the epidemiology of cholera, are considerable.

Culture Media↗
PubMed2001

Salinity dependence of vanadium toxicity against the brackish water hydroid Cordylophora caspia.

Vanadium, an abundant metal, enters the environment through natural rock weathering or by combustion of oil products. A third pathway is the leaching of vanadium-rich building materials. Stones made from steel industry residual slags, so-called slag stones, contain rather large amounts of vanadium. The increasing use of these slag stones in riverbank reinforcement has therefore led to increased interest in the toxicity of vanadium to aquatic organisms. The aim of the study was to determine the toxicity of vanadium to the brackish water hydroid Cordylophora caspia and the effect of vanadium on the membrane-bound enzyme Na, K-ATPase at various salinities. EC50 values for population growth inhibition were determined from 1.74 to 7.96 mg x L(-1) vanadium, depending on salinity. The maximum inhibition of population growth by vanadium was observed at low salinities. Correspondingly, maximum Na, K-ATPase inhibition was also measured at low salinities and decreased with increasing salinity. The present study suggests that the observed inhibition of population growth of C. caspia caused by vanadium-contaminated rearing water is due to the vanadium-induced inhibition of phosphatases.

Animals↗
PubMed2006

Expression profiles of Na+,K+-ATPase during acute and chronic hypo-osmotic stress in the blue crab Callinectes sapidus.

During acclimation to dilute seawater, the specific activity of Na+,K+-ATPase increases substantially in the posterior gills of the blue crab Callinectes sapidus. To determine whether this increase occurs through regulation of pre-existing enzyme or synthesis of new enzyme, mRNA and protein levels were measured over short (<24 h) and long (18 days) time courses. Na+,K+-ATPase expression, both mRNA and protein, did not change during the initial 24-h exposure to dilute seawater (10 ppt salinity). Thus, osmoregulation in C. sapidus during acute exposure to low salinity likely involves either modulation of existing enzyme or mechanisms other than an increase in the amount of Na+,K+-ATPase enzyme. However, crabs exposed to dilute seawater over 18 days showed a 300% increase in Na+,K+-ATPase specific activity as well as a 200% increase in Na+,K+-ATPase protein levels. Thus, it appears that the increase in Na+,K+-ATPase activity during chronic exposure results from the synthesis of new enzyme. The relative amounts of mRNA for the alpha-subunit increased substantially (by 150%) during the acclimation process, but once the crabs had fully acclimated to low salinity, the mRNA levels had decreased and were not different from levels in crabs fully acclimated to high salinity. Thus, there is transient induction of the Na+,K+-ATPase mRNA levels during acclimation to dilute seawater.

Animals↗
PubMed2006

Effect of estrogen upon methamphetamine-induced neurotoxicity within the impaired nigrostriatal dopaminergic system.

In the present study, we investigated whether estrogen remains effective as a neuroprotectant within an impaired nigrostriatal dopaminergic (NSDA) system of gonadectomized female and male mice. In Experiment 1, mice were treated with four different regimens of methamphetamine (MA) to establish a protocol for an impaired NSDA system to be used in subsequent experiments. Based upon the results of Experiment 1, in Experiment 2 gonadectomized female mice received a treatment with either control (saline), low- or high-dose of MA to produce an initial NSDA impairment. At one week post-MA, mice received either estradiol benzoate (10 microg) or vehicle followed 24 h later with low-MA or saline. Estrogen altered the toxic effects of the second invasion of MA as indicated by a significant decrease in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations. In addition, DA and DOPAC depletion was greater in high- vs. low-dose MA. In gonadectomized male mice (Experiment 3), striatal DA and DOPAC concentrations showed greater decreases following high-, vs. low-doses of MA; however, estrogen did not alter these responses. These results demonstrate that the capacity for estrogen to protect or worsen MA-induced neurotoxicity of dopaminergic neurons is limited to female mice and depends on the condition of the NSDA system.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2006

Following the heart: temperature and salinity effects on heart rate in native and invasive species of blue mussels (genus Mytilus).

The three species of blue mussels, Mytilus trossulus Gould 1850, M. edulis Linnaeus 1758 and M. galloprovincialis Lamarck 1819, have distinct global distribution patterns that are hypothesized to reflect differences in their tolerances of temperature and salinity. We examined effects on heart rate (beats min(-1)) of acute exposure and acclimation to different combinations of temperature and salinity to test this hypothesis and, in the context of the invasive success of M. galloprovincialis, to gain insights into the factors that may explain the replacement of the temperate Pacific native, M. trossulus, by this Mediterranean Sea invader along much of the California coast. Heart rate of M. trossulus was significantly higher than that of M. galloprovincialis, consistent with evolutionary adaptation to a lower habitat temperature (temperature compensation) in the former species. Heart rates of M. trossulus/M. galloprovincialis hybrids were intermediate between those of the parental species. Following acclimation to 14 degrees C and 21 degrees C, heart rates of all species exhibited partial compensation to temperature. Heart rate increased with rising temperature until a high temperature was reached at which point activity fell sharply, the high critical temperature (H(crit)). H(crit) increased with increasing acclimation temperature and differed among species in a pattern that reflected their probable evolutionary adaptation temperatures: M. galloprovincialis is more heat tolerant than the other two congeners. Ability to sustain heart function in the cold also reflected evolutionary history: M. trossulus is more cold tolerant than M. galloprovincialis. Heart rates for all three congeners decreased gradually in response to acute reductions in salinity until a low salinity (S(crit)) was reached at which heart rate dropped precipitously. S(crit) decreased with decreasing salinity of acclimation and was generally lowest for M. galloprovincialis. Mortality during acclimation under common garden conditions was greatest in M. trossulus and was highest at high acclimation temperatures and salinities. These intrinsic differences in basal heart rate, thermal and salinity responses, acclimatory capacity, and survivorship are discussed in the contexts of the species' biogeographic patterning and, for the invasive species M. galloprovincialis, the potential for further range expansion along the Pacific coast of North America.

Acclimatization↗
PubMed2001

Effects of experimental manipulation of pH and salinity on Cd(2+) uptake by the sponge Microciona prolifera and on sponge cell aggregation induced by Ca(2+) and Cd(2+).

Marine sponges (Microciona prolifera) collected in St. Joseph Bay, Florida panhandle, were exposed for 2 h to pH/salinity unit combinations of 7.4/30, 6.3/30, 7.4/11, and 6.3/11. Cell suspensions from these were aggregated with 24 microM of either CaCl(2) or CdCl(2). Cells exposed to the low/low (11/6.3) combination aggregated spontaneously (no added stimulus) in 8/11 experiments, suggesting a significant disturbance of normal function, possibly involving disrupted ion uptake. In all other combinations aggregation proceeded normally and there were no statistically significant differences among the groups. CdCl(2) was as effective an aggregation stimulus as CaCl(2). The calcium channel blocker verapamil (100 microM) reduced calcium-induced aggregation by 15% but had no effect on cadmium (Cd)-induced aggregation, indicating that L-type calcium channels do not play a major role in aggregation induced by these divalent cations. Sponge tissue was exposed for 48 h to the same pH/salinity combinations but containing Cd (15 or 150 microg/ml) and then dried and analyzed for Cd. All sponges concentrated Cd but those exposed to low salinity concentrated it most (in one case x13). Low pH alone had no appreciable effect but appeared to increase the effect of low salinity. One sponge with a native Cd content of 47.2 microg/g dry weight had the highest acquired Cd content. The results of this study indicate that low levels of salinity and pH, similar to those we recorded in the study area, facilitate the accumulation of Cd, but not via L-type calcium channels, and disrupt normal aggregation responses of the cell. These results may help explain a previous observation that cells from M. prolifera from this area, with high native levels of Cd, failed to aggregate in response to CaCl(2)[Philp RB (1999) Comp Biochem Physiol 124C:41-49] and also the frequent die-offs of Microciona that have virtually eliminated this sponge from its local habitat.

Animals↗
PubMedDate not supplied

Preventive effects of dexamethasone on hypoxic-ischemic brain damage in the neonatal rat.

To clarify the preventive effects of glucocorticoid on perinatal hypoxic-ischemic (HI) brain damage, an experiment was carried out on 4-day-old rats pretreated for 4 consecutive days with 3 different regimens; namely, a low dose dexamethasone (Dex) (0.1 mg/kg/day), a high dose Dex (0.5mg/kg/day), and a saline administration. On the 7th postnatal day, after ligation of the left common carotid artery, the rats were exposed to 8% oxygen and decapitated on the 10th, 14th, 21st and 28th postnatal days. Ligated side brain damage was observed in 75, 7 and 3% of the rats in the saline, low and high dose Dex groups, respectively. However, a high mortality rate (42%) was noted in the high dose Dex group. The cumulative number of animals with poor outcome (death or brain damage) was 49 (80%), 13 (33%) and 24 (44%) in the saline, low and high dose Dex groups, respectively. On the 10th and 14th postnatal days, the rats in both the Dex groups showed delayed neuronal maturation and myelination in the non-ligated side motor cortex, however, these maturational differences disappeared on the 21st postnatal days. Otherwise, the number of cortical cells in both the Dex groups were significantly lower than that in the saline group on the 28th postnatal days (P < 0.05 in each). These findings suggest that the pretreatment with Dex protects the developing brain from HI injury through the suppression of the neuronal maturation. However, a decreased number of cortical cells may give rise to psychomotor retardation later.

Animals↗
PubMed1989

The effect of a low pH saline perfusate upon the integrity of the energy-depleted rat blood-brain barrier.

The effect of a low pH perfusate upon the integrity of the rat blood-brain barrier was studied using an in situ supravital brain perfusion technique in which high-energy phosphates are depleted. Control animals were perfused for 10 min with a Ringer's salt solution containing the metabolic inhibitor 2,4-dinitrophenol (DNP) and adjusted to a pH of 7.4. In two separate experimental groups the perfusate, consisting of either the same medium as the controls or with additional buffering from Tris maleate, was switched after 5 min at a pH of 7.4, to a medium adjusted to pH 5.5 with lactic acid. Following a total perfusion time of 10 min, the integrity of the blood-brain barrier was assessed using the small molecular weight tracer [14C]mannitol. The cerebral perfusate flow rates (CPFR) after 10 min of perfusion were also determined in the three groups by perfusing for 40 s with [14C]iodoantipyrine. In each group, mannitol was excluded from the tissue of the brain to the same degree as has been previously reported in vivo, indicating an intact blood-brain barrier. There was also no significant pH-dependent change in CPFR. Ultrastructural examination of animals that had been perfusion fixed following in situ perfusion revealed no obvious differences between the cerebral endothelium of the control and low pH perfused animals. These results demonstrate that in the absence of energy-producing metabolism a perfusate pH of 5.5 is insufficient to disrupt the blood-brain barrier.

2,4-Dinitrophenol↗
PubMed2026

Ecological and evolutionary implications of a mobile genetic element-rich haloarchaeon with unique osmotic resilience.

We isolated a novel halophilic archaeon, strain DSL9, representing the proposed new species Haloliberatus hailidukes gen. nov., sp. nov., from Dishui Lake, China. Unlike most obligate halophiles, DSL9 survives in low salinity, even distilled water, without lysis. Genomic analysis revealed dual salinity adaptation strategies: salt-in and compatible solutes, including a complete trehalose biosynthesis pathway. The strain harbors multiple plasmids, notably a 111,311 bp large plasmid (pHdsl9-3) encoding replication (Orc1/Cdc6, SSB), transcription (TFIIB), transmission (T4SS cluster, ArdC-like protein), and recombination (XerA) modules. pHdsl9-3 provides auxiliary functions such as defense, genome diversification, ion detoxification, and suggests active horizontal gene transfer. Similar elements are widespread in Halobacteriales, highlighting their role in haloarchaeal genetic diversity and plasticity. The encoded XerA hinted at a function beyond DNA dimer resolution, suggesting it may have been adapted by other archaeal mobile genetic elements. These findings underscore the need to investigate plasmid-driven evolution and environmental adaptation mechanisms in haloarchaea.IMPORTANCEThis study reports the isolation and characterization of DSL9, a novel halophilic archaeon from a freshwater lake. Remarkably, DSL9 defies the typical obligate halophilic lifestyle by surviving in low-salinity environments, including distilled water, without cell lysis. A key discovery is the identification of a 111,311 bp large plasmid harboring essential modules for replication, transcription, transmission, and integration. Widespread distribution of similar elements across Halobacteriales suggests their crucial role in haloarchaeal genetic diversity and plasticity, warranting further study of plasmid-mediated evolution and adaptation strategies.

Lakes↗
PubMedDate not supplied

[Relationship between the ionic composition of blood and urine and the salinity of the external environment of the crab Hemigrapsus sanguineus].

Studies have been made on the dependence of sodium, potassium, magnesium and calcium concentrations of the blood and urine on the salinity of the external milieu in the crab H. sanguineus. Effective regulation of sodium and potasssium balance at low salinities was found. Within the salinity range investigated, magnesium level in the blood is maintained at lower level as compared to that in the environment. At low salinities, regulation of potassium and sodium concentrations in the blood is monitored by extrarenal mechanisms. Uber high salinity conditions, regulation of magnesium and potassium concentrations in the blood is accomplished at the expense of the activity of antennal glands. Calcium concentration in the blood is regulated by extra-renal mechanisms. The antennal glands affect regulation of calcium balance.

Animals↗
PubMed2006

Functional evidence for the presence of a carbonic anhydrase repressor in the eyestalk of the euryhaline green crab Carcinus maenas.

Carbonic anhydrase (CA) activity and relative expression of CA mRNA were measured in the gills of the euryhaline green crab Carcinus maenas in response to eyestalk ablation (ESA), injection of eyestalk extract and exposure to low salinity. For crabs acclimated to 32 p.p.t. salinity, ESA alone resulted in an increase in both CA activity and relative mRNA expression in the posterior, ion-transporting gills, but not in the anterior, respiratory gills. The ESA-stimulated increase in CA activity was abolished by injections of extracts of eyestalks taken from crabs acclimated to 32 p.p.t. salinity. Transfer of intact crabs from 32 to 10 p.p.t. salinity for 7 days resulted in an eightfold increase in CA activity and a sixfold increase in mRNA expression in posterior gills. ESA potentiated the normal low salinity-mediated CA induction by 23%. Daily injections of eyestalk extract reduced low salinity-stimulated CA induction by nearly 50% in intact crabs and by almost 75% in eyestalk ablated crabs. A 4-day transfer to 10 p.p.t. salinity also caused significant increases in both CA activity and mRNA expression in posterior gills, and ESA resulted in a 32% increase in the normal degree of CA induction. Daily injections of eyestalk extracts reduced CA induction in a dose-dependent manner over the 4-day time course. When CA induction was reduced by 66%, hemolymph osmotic regulation was also disrupted. These results are functional evidence for the presence of a CA repressor in the major endocrine complex of the crab, the eyestalk. This compound appears to function in keeping CA expression at low, baseline levels in crabs at high salinity. Exposure to low salinity removes the effects of the putative repressor, allowing CA expression, and thus CA activity, to increase.

Acclimatization↗
PubMed2006

HMG-CoA reductase is regulated by salinity at the level of transcription in Haloferax volcanii.

The moderately halophilic archaeon Haloferax volcanii was surveyed for protein profile changes correlated with growth at high and low salinity. A single polypeptide with an approximate mass of 46 kDa was conspicuously more abundant during growth at high salinity. This protein was identified as HMG-CoA reductase (HMGR), encoded by the hmgR gene. HMGR is a key enzyme in the mevalonate pathway of isoprenoid biosynthesis, the sole route in haloarchaea for lipid and carotenoid production. Enzymatic assays confirmed that HMGR activity is more abundant in cells grown at high salinity. Low salt cultures of H. volcanii contained lower amounts of hmgR transcript compared to cells grown in high salt suggesting that the observed regulation occurs at the level of transcription. Paradoxically, both lipid and carotenoid content decreased in H. volcanii grown at high salinity despite the increased levels of HMGR specific activity. To our knowledge, this is the first report demonstrating that the expression of HMGR is regulated in response to non-optimal salinity in a halophilic archaeon.

Adaptation, Physiological↗