Examining the Osmotic Response of Acidihalobacter aeolianus after Exposure to Salt Stress

Acidihalobacter aeolianus is an acidophilic, halo-tolerant organism isolated from a marine environment near a hydrothermal vent, an ecosystem whereby levels of salinity and total dissolved salts are constantly fluctuating creating ongoing cellular stresses. In order to survive these continuing changes, the synthesis of compatible solutes—also known as organic osmolytes—is suspected to occur, aiding in minimising the overall impact of environmental instability. Previous studies on A. aeolianus identified genes necessary for the accumulation of proline, betaine and ectoine, which are known to act as compatible solutes in other halophilic species. In this study, the impact of increasing the osmotic stress as well as the toxic ion effect was investigated by subjecting A. aeolianus to concentrations of NaCl and MgSO4 up to 1.27 M. Exposure to high concentrations of Cl- resulted in the increase of ectC expression in log-phase cells with a corresponding accumulation of ectoine at stationary phase. Osmotic stress via MgSO4 exposure did not trigger the same up-regulation of ectC or accumulation of ectoine, indicating the transcriptionally regulated response against osmotic stress was induced by chloride toxicity. These findings have highlighted how the adaptive properties of halo-tolerant organisms in acidic environments are likely to differ and are dependent on the initial stressor.

Osmoregulation and the Anthozoan-Dinoflagellate Symbiosis

<p>This study investigated the responses of the temperate anemone Anthopleura aureoradiata, and the tropical coral Acropora aspera to osmotic stress and the role that free amino acids (FAAs) may play in the osmoregulatory mechanism of these anthozoan-dinoflagellate symbioses. Specimens were exposed to a range of hypo- and hyper-saline conditions for durations of 1, 12, 48 and 96 hours, whereupon respiration and photosynthetic rates were measured as physiological indicators of osmotic stress. High performance liquid chromatography was used to quantify 15 FAAs within the anthozoan host tissues to establish the response of FAA pools to osmotic stress and whether FAAs are used in an osmoregulatory capacity. Aposymbiotic specimens of A. aureoradiata were similarly tested to establish if the presence of symbiotic dinoflagellates alters the host’s capacity to respond to osmotic stress given that the symbionts are known to release FAAs into the host cytoplasm. In A. aureoradiata, significant changes in respiration were only observed with exposure to the extreme hypo-osmotic salinity of 12‰, with respiration decreasing by 67% after 1 hour of exposure. No significant changes in respiration were seen at 25, 43 or 50‰, despite a 52% decrease in respiration seen at the hyper-saline treatment of 50‰. The response of the coral A. aspera was markedly different, showing an increase in respiration in response to hypo-salinity (22 and 28‰). Interestingly, the most pronounced respiratory increase of up to 460% occurred in the less extreme hypo-saline treatment of 28‰. The response of photosynthesis also showed differences between the two species. In the symbiotic A. aureoradiata, photosynthesis declined by 61% after the 1 hour exposure to 12‰ and further decreased to 72% below control rates after 96 hours. While in A. aspera, photosynthesis showed no significant deviation from control levels at any of the treatment salinities. FAA pools in both A. aureoradiata and A. aspera showed significant responses to osmotic stress. In symbiotic A. aureoradiata, exposure to 12‰ caused total FAA pools to decline by 50% after 1 hour, after which a seemingly stable state was reached. A hyper-osmotic treatment of 50‰ resulted in a similar trend with a more than 50% decrease after 1 hour of exposure. In A. aspera, the response of the FAA pool was markedly different, with the concentration increasing by up to 200% with exposure to 22‰ and by more than 260% at 28‰. Interestingly, one on the main constituents of FAA pools in A. aureoradiata, Taurine (15% of FAA pools at 35‰), was not present in measurable quantities within A. aspera host tissue. In aposymbiotic individuals of A. aureoradiata exposed to extreme hypo- and hyper-saline treatments of 12 and 50‰ a significant impact on respiration was only observed at 12‰, with a 77% decrease in respiration after 96 hours. Changes in FAA pools of aposymbiotic A. aureoradiata were only seen after 12 hours exposure to 50‰ with a significant 26% decrease. However, the direct comparison between symbiotic and aposymbiotic A. aureoradiata did serve to highlight the contribution of symbiont-derived FAAs to the host pool of FAAs, with FAA pools in aposymbiotic anemones up to 41% lower than those found in symbiotic anemones. The results seen here were not suggestive of FAAs being regulated for the explicit use as compatible organic osmolytes. Rather, changes in FAA pools showed changes consistent with other stress responses. Moreover, the response of anthozoan-dinoflagellate symbioses to osmotic stress appears to be species specific, or at least taxa specific, as the responses of respiration, photosynthesis and FAA pools were very different between the temperate anemone A. aureoradiata and the tropical coral A. aspera. Nevertheless, differences in the respiratory response between symbiotic and apo-symbiotic anemones did indicate some influence of the dinoflagellate symbionts on the ability of the anthozoan host to mediate osmotic stress. It may therefore be that other symbiont-derived compounds are utilised as compatible organic osmolytes (COOs), with a primary candidate being glycerol. This warrants further investigation.</p>

Osmoregulation and the Anthozoan-Dinoflagellate Symbiosis

<p>This study investigated the responses of the temperate anemone Anthopleura aureoradiata, and the tropical coral Acropora aspera to osmotic stress and the role that free amino acids (FAAs) may play in the osmoregulatory mechanism of these anthozoan-dinoflagellate symbioses. Specimens were exposed to a range of hypo- and hyper-saline conditions for durations of 1, 12, 48 and 96 hours, whereupon respiration and photosynthetic rates were measured as physiological indicators of osmotic stress. High performance liquid chromatography was used to quantify 15 FAAs within the anthozoan host tissues to establish the response of FAA pools to osmotic stress and whether FAAs are used in an osmoregulatory capacity. Aposymbiotic specimens of A. aureoradiata were similarly tested to establish if the presence of symbiotic dinoflagellates alters the host’s capacity to respond to osmotic stress given that the symbionts are known to release FAAs into the host cytoplasm. In A. aureoradiata, significant changes in respiration were only observed with exposure to the extreme hypo-osmotic salinity of 12‰, with respiration decreasing by 67% after 1 hour of exposure. No significant changes in respiration were seen at 25, 43 or 50‰, despite a 52% decrease in respiration seen at the hyper-saline treatment of 50‰. The response of the coral A. aspera was markedly different, showing an increase in respiration in response to hypo-salinity (22 and 28‰). Interestingly, the most pronounced respiratory increase of up to 460% occurred in the less extreme hypo-saline treatment of 28‰. The response of photosynthesis also showed differences between the two species. In the symbiotic A. aureoradiata, photosynthesis declined by 61% after the 1 hour exposure to 12‰ and further decreased to 72% below control rates after 96 hours. While in A. aspera, photosynthesis showed no significant deviation from control levels at any of the treatment salinities. FAA pools in both A. aureoradiata and A. aspera showed significant responses to osmotic stress. In symbiotic A. aureoradiata, exposure to 12‰ caused total FAA pools to decline by 50% after 1 hour, after which a seemingly stable state was reached. A hyper-osmotic treatment of 50‰ resulted in a similar trend with a more than 50% decrease after 1 hour of exposure. In A. aspera, the response of the FAA pool was markedly different, with the concentration increasing by up to 200% with exposure to 22‰ and by more than 260% at 28‰. Interestingly, one on the main constituents of FAA pools in A. aureoradiata, Taurine (15% of FAA pools at 35‰), was not present in measurable quantities within A. aspera host tissue. In aposymbiotic individuals of A. aureoradiata exposed to extreme hypo- and hyper-saline treatments of 12 and 50‰ a significant impact on respiration was only observed at 12‰, with a 77% decrease in respiration after 96 hours. Changes in FAA pools of aposymbiotic A. aureoradiata were only seen after 12 hours exposure to 50‰ with a significant 26% decrease. However, the direct comparison between symbiotic and aposymbiotic A. aureoradiata did serve to highlight the contribution of symbiont-derived FAAs to the host pool of FAAs, with FAA pools in aposymbiotic anemones up to 41% lower than those found in symbiotic anemones. The results seen here were not suggestive of FAAs being regulated for the explicit use as compatible organic osmolytes. Rather, changes in FAA pools showed changes consistent with other stress responses. Moreover, the response of anthozoan-dinoflagellate symbioses to osmotic stress appears to be species specific, or at least taxa specific, as the responses of respiration, photosynthesis and FAA pools were very different between the temperate anemone A. aureoradiata and the tropical coral A. aspera. Nevertheless, differences in the respiratory response between symbiotic and apo-symbiotic anemones did indicate some influence of the dinoflagellate symbionts on the ability of the anthozoan host to mediate osmotic stress. It may therefore be that other symbiont-derived compounds are utilised as compatible organic osmolytes (COOs), with a primary candidate being glycerol. This warrants further investigation.</p>

Modulation of salt-induced stress impact in Gladiolus grandiflorus L. by exogenous application of salicylic acid

Salinity is challenging threats to the agricultural system and leading cause of crop loss. Salicylic acid (SA) is an important endogenous signal molecule, which by regulating growth and physiological processes improves the plant ability to tolerate salt stress. Considering the prime importance of Gladiolus grandiflorus (L.) in the world’s cut-flower market, the research work was undertaken to elucidate salinity tolerance in G. grandiflorus by exogenous application of SA irrigated with saline water. Results revealed that increasing salinity (EC: 2, 4 and 6 dS m–1) considerably altered morpho-growth indices (corm morphology and plant biomass) in plants through increasing key antioxidants including proline content and enzymes activity (superoxide dismutase, catalase and peroxidase), while negatively affected the total phenolic along with activity of defense-related enzymes (phenylalanine ammonia lyase, and polyphenol oxidase activity). SA application (50–200 ppm) in non-saline control or saline conditions improved morpho-physiological traits in concentration-dependent manners. In saline conditions, SA minimized salt-stress by enhancing chlorophyll content, accumulating organic osmolytes (glycine betaine and proline content), total phenolic, and boosting activity of antioxidant and defense-related enzymes. Principle component analysis based on all 16 morphological and physiological variables generated useful information regarding the classification of salt tolerant treatment according to their response to SA. These results suggest SA (100 or 150 ppm) could be used as an effective, economic, easily available and safe phenolic agent against salinity stress in G. grandiflorus.

Alleviation of Cadmium Toxicity in Zea Mays L. through Up-Regulation of Antioxidant Defense System and Organic Osmolytes under Supplemental Calcium

Calcium (Ca) is a macronutrient and work as a modulator to mitigate oxidative stress induced by heavy metals. Present work was conducted to elucidate the role of Ca in modulating growth, physio-biochemical traits, and cellular antioxidant defense system in Zea mays L. seedlings under Cd stress. The experiment was designed in a complete randomized design with two levels of Cd (0 and 150 µM) and six levels of Ca (0, 0.5, 1, 2.5, 5 and 10 mM). Maize seedlings exposed to Cd at150 µM concentration showed a notable decrease in growth, biomass, anthocyanins, chlorophylls, and antioxidant enzymes activities. Higher level of Cd (150 µm) also caused an upsurge in oxidative damage observed as higher electrolyte leakage (increased membrane permeability), H2O2 production and MDA accumulation. Supplementation of Ca notably improved growth traits, photosynthetic pigments, cellular antioxidants (APX, POD and ascorbic acid), anthocyanins and level of osmolytes. The significant improvement in the osmolytes (proteins and amino acids), and enzymatic antioxidative defense system enhanced the membrane stability and mitigated the damaging effects of Cd. The present results concluded that exogenously applied Ca can potentially improve growth by regulating antioxidants and enable maize plants to withstand the Cd toxicity.

The Osmolyte Ties That Bind: Genomic Insights Into Synthesis and Breakdown of Organic Osmolytes in Marine Microbes

The production and consumption of organic matter by marine organisms plays a central role in the marine carbon cycle. Labile organic compounds (metabolites) are the major currency of energetic demands and organismal interaction, but these compounds remain elusive because of their rapid turnover and concomitant minuscule concentrations in the dissolved organic matter pool. Organic osmolytes are a group of small metabolites synthesized at high intracellular concentrations (mM) to regulate cellular osmolarity and have the potential to be released as abundant dissolved substrates. Osmolytes may represent an essential currency of exchange among heterotrophic prokaryotes and primary and secondary producers in marine food webs. For example, the well-known metabolite dimethylsulfoniopropionate (DMSP) is used as an osmolyte by some phytoplankton and can be subsequently metabolized by 60% of the marine bacterial community, supplying up to 13% of the bacterial carbon demand and 100% of the bacterial sulfur demand. While marine osmolytes have been studied for decades, our understanding of their cycling and significance within microbial communities is still far from comprehensive. Here, we surveyed the genes responsible for synthesis, breakdown, and transport of 14 key osmolytes. We systematically searched for these genes across marine bacterial genomes (n = 897) and protistan transcriptomes (n = 652) using homologous protein profiles to investigate the potential for osmolyte metabolisms. Using the pattern of gene presence and absence, we infer the metabolic potential of surveyed microbes to interact with each osmolyte. Specifically, we identify: (1) complete pathways for osmolyte synthesis in both prokaryotic and eukaryotic marine microbes, (2) microbes capable of transporting osmolytes but lacking complete synthesis and/or breakdown pathways, and (3) osmolytes whose synthesis and/or breakdown appears to be specialized and is limited to a subset of organisms. The analysis clearly demonstrates that the marine microbial loop has the genetic potential to actively recycle osmolytes and that this abundant group of small metabolites may function as a significant source of nutrients through exchange among diverse microbial groups that significantly contribute to the cycling of labile carbon.

The red alga Tsunamia transpacifica (Stylonematophyceae) from plastic drift shows adaptation to its uncommon habitat in ultrastructure and soluble low molecular weight carbohydrate composition

The recently described red alga Tsunamia transpacifica (Stylonematophyceae) was previously isolated from plastic drift found at the pacific coast, but the natural habitat remains unknown. Here, we investigate ultrastructural details and the low molecular weight soluble carbohydrate composition to get further insight into the adaptation to this uncommon habitat. By means of high pressure freeze fixation, followed by freeze substitution, we could detect an up to 2-µm-thick cell wall surrounded by a distinct layer of extracellular polymeric substances (EPS), likely responsible for the adhering capacities of Tsunamia. The central position of the nucleus and multilobed parietal chloroplast, already observed by light microscopy, could be confirmed. The ultrastructure revealed large electron-dense bodies (EB) in the central cytoplasm, likely resembling degradation products of the chloroplast. Interestingly, these structures contained phosphorous and cobalt, and iron was found in smaller rounded electron-dense bodies by electron energy loss spectroscopy (EELS). Accumulation of these elements suggests a high biosorption activity of Tsunamia. Liquid chromatography-mass spectrometry (LC–MS) data showed the presence of two heterosides (floridoside and digeneaside) together with the polyol sorbitol, which are known as organic osmolytes and compatible solutes. Taken together, these are the first observations on ultrastructural details, element storage and accumulation of protective compounds are contributing to our understanding of the ultrastructural and osmotic solute basis for the ability of Tsunamia to thrive on plastic surfaces.

A Novel Lens for Cell Volume Regulation: Liquid-Liquid Phase Separation

Cells are constantly exposed to the risk of volume perturbation under physiological conditions. The increase or decrease in cell volume accompanies intracellular changes in cell membrane tension, ionic strength/concentration and macromolecular crowding. To avoid deleterious consequences caused by cell volume perturbation, cells have volume recovery systems that regulate osmotic water flow by transporting ions and organic osmolytes across the cell membrane. Thus far, a number of biomolecules have been reported to regulate cell volume. However, the question of how cells sense volume change and modulate volume regulatory systems is not fully understood. Recently, the existence and significance of phaseseparated biomolecular condensates have been revealed in numerous physiological events, including cell volume perturbation. In this review, we summarize the current understanding of cell volume-sensing mechanisms, introduce recent studies on biomolecular condensates induced by cell volume change and discuss how biomolecular condensates contribute to cell volume sensing and cell volume maintenance. In addition to previous studies of biochemistry, molecular biology and cell biology, a phase separation perspective will allow us to understand the complicated volume regulatory systems of cells.

The PKA-p38MAPK-NFAT5-Organic Osmolytes Pathway in Duchenne Muscular Dystrophy: From Essential Player in Osmotic Homeostasis, Inflammation and Skeletal Muscle Regeneration to Therapeutic Target

In Duchenne muscular dystrophy (DMD), the absence of dystrophin from the dystrophin-associated protein complex (DAPC) causes muscle membrane instability, which leads to myofiber necrosis, hampered regeneration, and chronic inflammation. The resulting disabled DAPC-associated cellular pathways have been described both at the molecular and the therapeutical level, with the Toll-like receptor nuclear factor kappa-light-chain-enhancer of activated B cells pathway (NF-ƘB), Janus kinase/signal transducer and activator of transcription proteins, and the transforming growth factor-β pathways receiving the most attention. In this review, we specifically focus on the protein kinase A/ mitogen-activated protein kinase/nuclear factor of activated T-cells 5/organic osmolytes (PKA-p38MAPK-NFAT5-organic osmolytes) pathway. This pathway plays an important role in osmotic homeostasis essential to normal cell physiology via its regulation of the influx/efflux of organic osmolytes. Besides, NFAT5 plays an essential role in cell survival under hyperosmolar conditions, in skeletal muscle regeneration, and in tissue inflammation, closely interacting with the master regulator of inflammation NF-ƘB. We describe the involvement of the PKA-p38MAPK-NFAT5-organic osmolytes pathway in DMD pathophysiology and provide a clear overview of which therapeutic molecules could be of potential benefit to DMD patients. We conclude that modulation of the PKA-p38MAPK-NFAT5-organic osmolytes pathway could be developed as supportive treatment for DMD in conjunction with genetic therapy.

Simultaneous Biochemical and Physiological Responses of the Roots and Leaves of Pancratium maritimum (Amaryllidaceae) to Mild Salt Stress

Pancratium maritimum (Amaryllidaceae) is a bulbous geophyte growing on coastal sands. In this study, we investigated changes in concentrations of metabolites in the root and leaf tissue of P. maritimum in response to mild salt stress. Changes in concentrations of osmolytes, glutathione, sodium, mineral nutrients, enzymes, and other compounds in the leaves and roots were measured at 0, 3, and 10 days during a 10-day exposure to two levels of mild salt stress, 50 mM NaCl or 100 mM NaCl in sandy soil from where the plants were collected in dunes near Cuma, Italy. Sodium accumulated in the roots, and relatively little was translocated to the leaves. At both concentrations of NaCl, higher values of the concentrations of oxidized glutathione disulfide (GSSG), compared to reduced glutathione (GSH), in roots and leaves were associated with salt tolerance. The concentration of proline increased more in the leaves than in the roots, and glycine betaine increased in both roots and leaves. Differences in the accumulation of organic osmolytes and electron donors synthesized in both leaves and roots demonstrate that osmoregulatory and electrical responses occur in these organs of P. maritimum under mild salt stress.