Sublethal Salinity Research Articles

Characterization of the Low-Salinity Stress in Vibrio vulnificus

Vibrio vulnificus is a marine pathogenic bacterium commonly found in seawater or seafood. This organism encounters low-salinity stress in its natural environment and during food processing. This study was designed to investigate the response of V. vulnificus YJ03 to lethal low salinity (0.04% NaCl) and its adaptation to sublethal salinity (0.12% NaCl with 20 amino acids added). A short period in the nonculturable state was induced by lethal low-salinity stress followed by cell death after 30 min of stress. Addition of 1mM glycine betaine or 0.5mM sucrose reduced the damage. Low-salinity adaptation was achieved in the exponential-phase cells but not in the stationary-phase cells. Significant protection against lethal low-salinity stress was attained when the cells were adapted for as little as 1.5 min. The adapted cells were significantly protected against lethal low salinity and 2.4% sodium sorbate but sensitized to the challenge of heat (52°C) and acid (pH 3.2). Nonlethal lowsalinity treatment of seafood should be avoided to prevent stress adaptation of V. vulnificus.

Effects of different ionic compositions on survival and growth of Physa acuta

Most inland saline waters in southern Australia predominantly contain Na+ and Cl− as major ions. The proportions of Ca2+, Mg2+, SO4 2−, HCO3 − and CO3 2− in these waters somewhat vary and might influence salinity tolerance of freshwater organisms. Here the salinity stress of five ionic compositions to the freshwater snail Physa acuta Draparnaud (Gastropoda: Physidae) was compared: commercial sea salt Ocean Nature (ON), synthetic Ocean Nature (ONS) and three saline water types that are common in southern Australia (ONS but without [1]: SO4 2−, HCO3 − and CO3 2−, [2]: Ca2+, HCO3 − and CO3 2−, [3]: Ca2+, Mg2+), Milli-Q water was used as a negative control. The 96-h LC50 values for all treatments did not differ. However in prolonged sub-lethal exposures, results varied depending on the ionic composition. Growth was negative and shell strength reduced in treatments lacking Ca. Though the content of major cationic elements (Ca, Mg, Na and K) did not differ per unit dry weight of snail across the treatments, the total load of these elements per individual snail varied among treatments. Furthermore, at the sub-lethal salinities tested, 1 and 5 mS cm−1, ionic compositions had more effect on the snail’s growth than salinity. The long-term effects on freshwater animals, especially taxa with calcium-based exoskeletons, from exposure to common saline water types with low calcium concentrations will likely be greater than from exposure to saline waters with an ionic composition similar to seawater.

Salinity tolerance of riverine microinvertebrates from the southern Murray - Darling Basin

Concern about the effect of rising salinity on freshwater biodiversity has led to studies investigating the salt tolerance of macroinvertebrates and fish, with less attention given to microinvertebrates. We investigated the acute lethal effects of salinity on 12 microinvertebrate species from rivers in the southern Murray–Darling Basin in central Victoria, Australia. For a subset of these species, sub-lethal salinity effects and the effect of water temperature on salinity tolerance were also investigated. The most sensitive microinvertebrates had broadly similar 72-h LC50 values to the most sensitive macroinvertebrates, reported in other studies. However, the most tolerant microinvertebrates tested were much more sensitive than the most tolerant macroinvertebrates and the microinvertebrates studied were more sensitive than most freshwater fish. Temperature affected the acute lethal toxicity of salinity but only to a small degree. In three of four species (the exception being Hydra viridissima), the effects of salinity on growth, development and/or reproduction at concentrations below their 72-h LC50 values were observed. However, different endpoints responded differently to salinity. The demonstrated effect of salinity on microinvertebrates has the potential to indirectly affect fish and salt-tolerant macroinvertebrates via changes to their prey species or ecological functions performed by microinvertebrates.

Salinity Tolerance and the Role of Cortisol during Osmotic Adjustments of an Air-Breathing Catfish, <i>Clarias batrachus</i>

Sudden transfer of freshwater catfish, Clarias batrachus to media of various salinities ranging from 10-100% sea water (SW) establishes that it is stenohaline fish with upper limit of tolerance up to 30% SW (298 mmol/kg) which gets marginally elevated upon its acclimation in sub-lethal salinities. No appreciable change in plasma osmolarity following transfer of the catfish to 15% SW (132 mmol/kg) even after 14 days reveals that it can actively osmoregulate up to 15% SW. Unlike other teleost, this fish lacks the bimodal adaptive and regulatory phases as evident from the increase in the plasma osmolarity within 0.5 h of transfer to higher salinities which remained elevated throughout the experiment. The changing profile of plasma cortisol following transfer to higher salinities suggests the involvement of this hormone in SW adaptation.

Species and population variation to salinity stress in Panicum hemitomon, Spartina patens, and Spartina alterniflora: morphological and physiological constraints

Panicum hemitomon, Spartina patens, and Spartina alterniflora are wide-spread dominant grasses of fresh, brackish, and salt marsh plant communities, respectively. Our previous research identified significant intraspecific variation in salt tolerance and morphology among populations within each species. In this study our objectives were to determine shorter-term physiological/biochemical responses to salinity stress and identify potential indicators of salt tolerance, with the ultimate goal of discerning similarities and differences in the mechanisms of salinity stress resistance. We subjected a subset of six populations within each species, ranging from high to low salt tolerance, to sublethal salinity levels (4, 20, and 30 ppt, respectively, for species) and monitored physiological and growth responses after 1 week (early harvest) and 5 weeks (late harvest). In all three species sublethal salinity levels generally resulted in significantly reduced net CO 2 assimilation, leaf expansion, midday leaf xylem pressure, water use efficiency, and live and total biomass; and significantly increased leaf Na +/K + ratio, leaf proline, leaf glycine betaine, leaf sucrose, root-to-shoot ratio, and dead:total aboveground biomass ratio. All three species displayed significant population (intraspecific) variation in net CO 2 assimilation, leaf expansion, water use efficiency, midday leaf xylem pressure, leaf proline, leaf glycine betaine (except Panicum, where it could not be accurately determined), leaf Na +/K + ratio, leaf sucrose, total plant biomass, dead:total aboveground biomass ratio, and root-to-shoot ratio. General indicators of salt tolerance (regardless of species) included high net CO 2 assimilation rates and water use efficiencies, and low ratios of root-to-shoot and dead:total aboveground biomass. Factor analysis and a-priori linear contrasts revealed some unique differences between species in terms of the relative importance of morphology and physiology in explaining intraspecific variation in salt tolerance. Plant morphology (size attributes) were strongly associated with salt tolerance in P. hemitomon, weakly associated with salt tolerance in S. patens, and not associated with salt tolerance in S. alterniflora. Highly salt-tolerant populations of Spartina alterniflora displayed the greatest ion selectivity (lower leaf Na +/K + ratios), which was not displayed by the other two species. These results suggest that plant size attributes can be very important in explaining population differences in salt tolerance in glycophytes, but may be independent of salt tolerance in halophytes, which have specialized physiological (and/or anatomical) adaptations that can confer salinity stress resistance through mechanisms such as selective ion exclusion and secretion.

Transmission of acquired adjustments to salinity in Sorghum bicolor

Previous studies showed that exposure of eight-day-old Sorghum bicolor for three weeks to sublethal salinity induces an increase in salinity tolerance, called physiological adaptation (A). During A, plants of a same population differ in reaction and tolerance to salinity. Tolerance levels of the reaction types depend on environmental conditions besides salinity. Reactions observed most frequently in an experiment have generally highest tolerance levels. This phenomenon is defined adaptive determinism (AD). In this study, the relationship between a potential source of the information subjacent to AD and AD itself is analysed in plants first exposed to salt-inducing A. When the reaction types are close variations of one reaction mode, AD is highest. This relationship is inversed in progeny of adapted plants. Results suggest that information relevant to AD is transmitted to the progeny of adapted plants, and that adaptive information is created during A in plants first exposed to adaptation inducing treatment.

A comparison of indicators of sublethal salinity stress in the salt marsh grass, Spartina patens (Ait.) Muhl.

Wetland plant communities in coastal Louisiana are degrading, resulting in the loss of live emergent vegetation and subsequent succession to open water. Saltwater intrusion has resulted from the construction of navigation canals through the marshes; the subsequent salinity increase is one of the potential sources of sublethal stress on plants. Greenhouse experiments were conducted on Spartina patens (Ait.) Muhl. to compare the usefulness of several indicators for the detection of salinity stress. CO 2 uptake, leaf expansion, proline concentration and live aboveground biomass displayed significant responses to the salinity levels employed as treatments (0, 7, 14, 21 and 28 ppt.). CO 2 exchange was the only indicator showing a significant response within 7 days of the initiation of treatments (measurements were made at 7, 14 and 42 days).

Responses of A Stenohaline Freshwater Teleost (Catostomus Commersoni) to Hypersaline Exposure: I. The Dependence of Plasma Ph and Bicarbonate Concentration on Electrolyte Regulation

ABSTRACT The effects of exposure to 0·94% (300mosmoll−1) sodium chloride on plasma electrolyte and acid-base status were examined in the freshwater stenohaline teleost Catostomus commersoni (Lacépède), the white sucker. Four days’ exposure to this maximum sublethal salinity resulted in an increase in plasma concentrations of both sodium and chloride but a decrease in the Na+/Cl− ratio. Since the plasma concentrations of free amino acids and other strong ions - Ca2+, Mg2+ and K+ - remained unchanged, plasma strong ion difference (SID) decreased. Additionally, plasma pH and bicarbonate concentration decreased at constant. The changes in electrolyte and acid-base status that occurred after the 96 h were not appreciably altered after a further 2–3 weeks of saline exposure. The ambient calcium concentration had no influence on these results. Haemolymph non-bicarbonate buffer capacity (β) calculated as Δ[HCO3−]/ ΔpH, increased in saline-exposed fish. Consequently ΔH+, the apparent proton load, was zero despite the apparent change in acid-base status. Although β was directly proportional to the haemoglobin concentration in both control and experimental fish, this could not account for the increase in β since haemoglobin remained at control values. These results can be explained solely by the change in plasma SID and serve to illustrate the dependence of plasma acid-base status on the prevailing electrolyte characteristics, weak acid concentration and .