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PubMed2004

Demonstration of antifreeze protein activity in Antarctic lake bacteria.

Antifreeze proteins (AFPs) are a structurally diverse group of proteins that have the ability to modify ice crystal structure and inhibit recrystallization of ice. AFPs are well characterized in fish and insects, but very few bacterial species have been shown to have AFP activity to date. Thirty eight freshwater to hypersaline lakes in the Vestfold Hills and Larsemann Hills of Eastern Antarctica were sampled for AFPs during 2000. Eight hundred and sixty six bacterial isolates were cultivated. A novel AFP assay, designed for high-throughput analysis in Antarctica, demonstrated putative activity in 187 of the cultures. Subsequent analysis of the putative positive isolates showed 19 isolates with significant recrystallization inhibition (RI) activity. The 19 RI active isolates were characterized using ARDRA (amplified rDNA restriction analysis) and 16S rDNA sequencing. They belong to genera from the alpha- and gamma-Proteobacteria, with genera from the gamma-subdivision being predominant. The 19 AFP-active isolates were isolated from four physico-chemically diverse lakes. Ace Lake and Oval Lake were both meromictic with correspondingly characteristic chemically stratified water columns. Pendant Lake was a saline holomictic lake with different chemical properties to the two meromictic lakes. Triple Lake was a hypersaline lake rich in dissolved organic carbon and inorganic nutrients. The environments from which the AFP-active isolates were isolated are remarkably diverse. It will be of interest, therefore, to elucidate the evolutionary forces that have led to the acquisition of functional AFP activity in microbes of the Vestfold Hills lakes and to discover the role the antifreezes play in these organisms.

Antarctic Regions↗

PubMed2002

Accelerated molecular evolution in halophilic crustaceans.

In contrast to the stable ionic composition of the oceans, inland waters show striking diversity, possessing salt concentrations varying from I mM to 5 M. Although species diversity is highest in fresh water, some lineages have colonized hypersaline environments where they encounter elevated levels of both ultraviolet (UV) radiation and osmotic stress. This study compares rates of evolution in halophilic and freshwater taxa for two groups of microcrustaceans, anostracans and daphniids, from Australia and North America. The results establish that halophilic species show consistent rate acceleration, involving elevated levels of both insertion/deletion events and of nucleotide substitutions. The elevated pace of molecular evolution does not appear to be linked to selection or to other agents that are known to influence the supply rate of mutations, such as UV exposure, generation length, or shifts in metabolic rate. However, variance in ionic strength, which is known to have potent effects on DNA-protein interactions as well as on the structural properties of DNA and proteins, might account for the lowered fidelity of DNA replication in life from hypersaline settings. Regardless of its cause, the consistent rate acceleration in halophiles suggests that past efforts to employ sequence divergences to date events, such as the age of asexual lineages in Artemia, have resulted in serious overestimates. More generally, the results indicate that coordinated shifts in rates of molecular evolution may occur in lineages exposed to extreme environmental conditions.

Animals↗

PubMed2004

Isolation and cultivation of Walsby's square archaeon.

In 1980, A. E. Walsby described a square halophilic archaeon. This archaeon is of specific interest because of its unique shape and its abundance in hypersaline ecosystems, which suggests an important ecophysiological role. Ever since its discovery, the isolation and cultivation of 'Walsby's square archaeon' has been a holy grail for many microbiologists working on halophiles. Despite their abundance and easy recognition by microscopy, all cultivation attempts have failed up to now, marking the organism as one of the unculturables. Cultivation of the square archaeon is essential to understand their ecophysiological role and the nature of their unique morphologically features. Here, we report the isolation and cultivation of the enigmatic square archaeon that we propose to name Haloquadratum walsbyi. Pure cultures are easily maintained in simple artificial hypersaline media. Initial growth experiments revealed a tolerance to high concentrations of MgCl(2) (>2 M) in the presence of 3.3 M NaCl. Fresh cultures contained extraordinary large cells (>40 x 40 microm) without any visible division structures, ranking them among the largest prokaryotes known to date. The genome was estimated to contain approximately three million basepairs.

Archaea↗

PubMed2026

Genome-scale insights into metabolic streamlining and photosynthetic energy balance in the extremophile green alga Picocystis salinarum (Picocystophyceae, Chlorophyta).

Picocystis salinarum is an early-diverging chlorophyte and the sole described member of the Picocystophyceae, frequently dominating hypersaline and alkaline lakes despite extreme physicochemical constraints. To elucidate the genomic foundations of its ecological success, we generated a fully annotated, chromosome-scale nuclear genome assembly of the type strain originally isolated from a saline pond in San Francisco Bay. The 18.5-Mb genome comprises 30 chromosomal assemblies, exhibits clear diploidy, and contains multiple copies of intact Ty3/Gypsy and Ty1/Copia long terminal repeat retrotransposons encoding polyproteins with atypical accessory domains. Phylogenomic analyses reveal strong affinity with the Nephroselmidophyceae. Comparative analyses reveal extensive metabolic streamlining, including the absence of a queuosine salvage pathway, the 2-methylcitrate cycle, β-oxidation of propionate, and branched-chain amino acid catabolism, traits retained in several marine prasinophyte lineages. In contrast, the genome preserves multiple ancestral bacterial derived systems. Notably, P. salinarum features a complete chloroplast NADH dehydrogenase-like complex, including all membrane, electron binding, and assembly components, a configuration not previously reported in sequenced chlorophyte algae. This retention implies substantial capacity for cyclic electron flow and chlororespiration, processes expected to be critical in chronically low-light and chemically extreme environments. The genome further reveals a distinctive biochemical CO2-concentrating mechanism centered on plastid-targeted phosphoenolpyruvate carboxykinase, complete plastid peptidoglycan biosynthetic and remodeling pathways, and partial retention of lipid-A-related machinery. Conversely, P. salinarum lacks canonical non-photochemical quenching proteins while retaining xanthophyll-cycle enzymes that support slower photoprotective responses. Together, these features define a coordinated genomic architecture that underpins the specialization of P. salinarum to hypersaline, alkaline, and persistently low-light ecosystems.

3‐deoxy‐D‐manno‐octulo↗

PubMed2003

Melt inclusions in veins: linking magmas and porphyry Cu deposits.

At a porphyry copper-gold deposit in Bajo de la Alumbrera, Argentina, silicate-melt inclusions coexist with hypersaline liquid- and vapor-rich inclusions in the earliest magmatic-hydrothermal quartz veins. Copper concentrations of the hypersaline liquid and vapor inclusions reached maxima of 10.0 weight % (wt %) and 4.5 wt %, respectively. These unusually copper-rich inclusions are considered to be the most primitive ore fluid found thus far. Their preservation with coexisting melt allows for the direct quantification of important oreforming processes, including determination of bulk partition coefficients of metals from magma into ore-forming magmatic volatile phases.

Journal Article↗

PubMed2000

Extremely halophilic bacteria in crystallizer ponds from solar salterns.

It is generally assumed that hypersaline environments with sodium chloride concentrations close to saturation are dominated by halophilic members of the domain Archaea, while Bacteria are not considered to be relevant in this kind of environment. Here, we report the high abundance and growth of a new group of hitherto-uncultured Bacteria in crystallizer ponds (salinity, from 30 to 37%) from multipond solar salterns. In the present study, these Bacteria constituted from 5 to 25% of the total prokaryotic community and were affiliated with the Cytophaga-Flavobacterium-Bacteroides phylum. Growth was demonstrated in saturated NaCl. A provisional classification of this new bacterial group as "Candidatus Salinibacter gen. nov." is proposed. The perception that Archaea are the only ecologically relevant prokaryotes in hypersaline aquatic environments should be revised.

Bacteroides↗

PubMed2026

The halophilic archaeon Halogranum roseipondis sp. nov. is susceptible to a virus carrying an exceptionally high number of viral tRNA genes.

UNLABELLED: Archaea constitute a diverse group of organisms, many of which inhabit extreme environments, such as haloarchaea that dominate hypersaline ecosystems, like solar salterns. Sampling of solar salterns and other hypersaline environments has resulted in numerous haloarchaeal isolates, including 3 classified and 27 uncharacterized Halogranum species. However, no complete genome has so far been reported for any member of this genus. Here, we present the first comprehensive study of Halogranum sp. SS5-1 isolated from a solar saltern in Samut Sakhon, Thailand. Hgn. SS5-1 is a pleomorphic, aerobic heterotroph that thrives in high salinity and moderate temperature and is capable of hydrolyzing starch. Its genome consists of a 3.6 Mbp chromosome and seven additional plasmids. Based on our phylogenetic analyses, which establish Hgn. SS5-1 as a distinct species, we propose that it will be classified as the novel species Halogranum roseipondis sp. nov. SS5-1T. Additionally, we report that Hgn. roseipondis sp. nov. SS5-1T is infected by Hagravirus capitaneum (HGTV-1), the only virus known to infect a Halogranum host. HGTV-1 exhibits a unique head-tailed morphology and encodes the largest archaeal virus double-stranded DNA genome known to date, including 34 tRNA-encoding genes. Codon usage analysis of the viral genome suggests partial alignment with host preferences, yet the abundance of viral tRNA genes hints at broader roles, potentially including roles in translation and host regulation. This study establishes Hgn. roseipondis and HGTV-1 as a novel virus-host system, opening avenues to explore infection dynamics and the roles of virus-encoded tRNA in archaea. IMPORTANCE: Archaea that thrive in high-salinity environments are key players in geochemical cycles and important contributors to ecosystem productivity. Despite their ecological significance and importance for the development of novel methodologies in synthetic biology, haloarchaea remain poorly studied. Further exploration of haloarchaea is required to obtain valuable information on the evolution of cellular complexity and the molecular mechanisms that allow cells to thrive in harsh environmental conditions. Here, we present the characterization of a novel archaeon, Halogranum roseipondis sp. SS5-1T, alongside the infection cycle of its associated virus, Hagravirus capitaneum. This tailed myovirus carries an extraordinary set of 34 viral tRNA genes, a feature that opens intriguing questions about virus-host interactions and translational control. Our findings lay the groundwork for future investigations into the expression and function of viral tRNAs in an archaeal model system, thereby opening a new frontier for studying archaeal translation and virus-driven modulation of host cellular processes.

Halobacteriaceae↗

PubMed2005

A hundred years of Dunaliella research: 1905-2005.

A hundred years have passed since the description of the genus Dunaliella, the unicellular green alga which is responsible for most of the primary production in hypersaline environments worldwide. The present paper provides an historical survey of research on Dunaliella, from the early work in the 19th century to the thorough taxonomic studies by Teodoresco, Hamburger, Lerche and others from the beginning of the 20th century onwards. It attempts to trace the origin of some of the most important breakthroughs that have contributed to our present understanding of this alga that plays such a key role in many hypersaline environments.

Journal Article↗

PubMed2002

Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia.

At a field site in Belize, mangrove killifish Rivulus marmoratus inhabit hypersaline waters (up to 48 per thousand containing approximately 1 mmol l(-1) ammonia. We tested the hypotheses that R. marmoratus modify their nitrogen metabolism and excretion (i) by accumulating free amino acids (FAAs) and urea in the tissues during hyperosmotic stress and (ii) by shifting to ureotelism and accumulating FAAs during hyperammonia stress. Urea excretion (J(Urea)) (but not ammonia excretion, J(Amm)) displayed a diurnal pattern, with significantly less (75 %) urea excreted at night than during the day in both laboratory-reared clones and wild-caught killifish. When fish were exposed to hypersaline conditions (45 per thousand sea water), J(Urea) was significantly reduced and tissue urea and FAA levels were elevated compared with those of control fish (15 per thousand sea water). When R. marmoratus were exposed to 0, 1, 2, 5 and 10 mmol l(-1) NH(4)Cl (pH 8) for 48 h, no differences were found in J(Urea). Remarkably, prolonged exposure (10 days) to 5 mmol l(-1) NH(4)Cl (pH 8) did not result in an elevation of tissue ammonia levels. In addition, tissue urea and total FAA levels did not differ between control and ammonia-exposed fish after > or =4 days. We propose that the euryhaline R. marmoratus retain urea and FAAs within their tissues in response to extreme osmotic stress. In contrast to many ammonia-tolerant fishes, R. marmoratus do not shift to ureotelism during prolonged hyperammonia stress, nor do they convert nitrogenous wastes into FAAs. The data suggest that killifish continue to eliminate ammonia despite an unfavourable blood-to-water gradient, thereby avoiding accumulation of ammonia.

Amino Acids↗

PubMed2004

Derivation of a chronic site-specific water quality standard for selenium in the Great Salt Lake, Utah, USA.

The purpose of this study was to develop a site-specific water quality standard for selenium in the Great Salt Lake, Utah, USA. The study examined the bioavailability and toxicity of selenium, as selenate, to biota resident to the Great Salt Lake and the potential for dietary selenium exposure to aquatic dependent birds that might consume resident biota. Because of its high salinity, the lake has limited biological diversity with bacteria, algae, diatoms, brine shrimp, and brine flies being the only organisms present in the main (hypersaline) portions of the lake. To evaluate their sensitivity to selenium, a series of acute and chronic toxicity studies were conducted on brine shrimp (Artemia franiciscana), brine fly (Ephydra cinerea), and a hypersaline alga (Dunaliella viridis). The resulting acute and chronic toxicity data indicated that resident species are more selenium tolerant than many freshwater species. Because sulfate is known to reduce selenate bioavailability, this selenium tolerance is thought to result in part from the lake's high ambient sulfate concentrations (>5,800 mg/L). The acute and chronic test results were compared to selenium concentrations expected to occur in a mining effluent discharge located at the south end of the lake. Based on these comparisons, no appreciable risks to resident aquatic biota were projected. Field and laboratory data collected on selenium bioaccumulation in brine shrimp demonstrated a linear relationship between water and tissue selenium concentrations. Applying a dietary selenium threshold of 5 mg/kg dry weight for aquatic birds to this relationship resulted in an estimate of 27 microg/L Se in water as a safe concentration for this exposure pathway and an appropriate chronic site-specific water quality standard. Consequently, protection of aquatic birds represents the driving factor in determining a site-specific water quality standard for selenium.

Animals↗

PubMed2003

Complexity in natural microbial ecosystems: the Guerrero Negro experience.

The goal of this project is to describe and understand the organismal composition, structure, and physiology of microbial ecosystems from hypersaline environments. One collection of such ecosystems occurs at North America's largest saltworks, the Exportadora de Sal, in Guerrero Negro, Baja California Sur. There, seawater flows through a series of evaporative basins with an increase in salinity until saturation is reached and halite crystallization begins. Several of these ponds are lined with thick (10 cm) microbial mats that have received some biological study. To determine the nature and extent of diversity of the microbial organisms that constitute these ecosystems, we are conducting a phylogenetic analysis using molecular approaches, based on cloning and sequencing of small subunit (SSU) rRNA genes (16S for Bacteria and Archaea, 18S for Eukarya). In addition, we report preliminary results on the microbial composition of a laminated community that occurs in a crystallized gypsum-halite matrix in near-saturated salt water. Exposure of the interior of these large (kilogram) wet, endoevaporite crystals reveals a multitude of colors: layers of yellow, green, pink, and purple microbiota. To date, analyses of these two environments indicate the ubiquitous dominance of uncultured organisms of phylogenetic kinds not generally thought to be associated with hypersaline environments.

Bacteria↗

PubMed2002

Salt toxicosis in ruddy ducks that winter on an agricultural evaporation basin in California.

Agricultural evaporation basins are used as a means to dispose of highly saline underground-tile-drainage water in the San Joaquin Valley (California, USA). The hypersaline water conditions encourage high aquatic invertebrate production, primarily brine shrimp (Artemia franciscana), which attract birds to these sites. Cool winter temperatures (< 4 C) and hypersaline water conditions (> 70,000 mumhos/cm) resulted in feather salt encrustation and salt toxicosis in ruddy ducks (Oxyura jamaicensis). During December 1998 and January 1999, approximately 200 dead and sick ruddy ducks were collected from an evaporation basin and five healthy control ruddy ducks were collected from a freshwater wetland. Brains contained > or = 1,890 ppm sodium (wet tissue mass) in seven dead birds and contained < or = 1,150 ppm sodium in the control birds. Liver arsenic, lead, and mercury concentrations were < 1 ppm in all birds examined. Manganese, molybdenum, and copper liver concentrations did not differ significantly (P > 0.05) between the two groups of ducks. The dead ducks had significantly higher liver selenium, cadmium, iron, and zinc than the controls, but the concentrations were not sufficient to cause toxicity. Significant gross and microscopic lesions in most of the dead birds included conjunctivitis, lens opacity and cataract formation, vascular congestion in various organs most notably in the meninges of the brain, and myocardial and skeletal muscle degeneration.

Animals↗

PubMedDate not supplied

[Adaptation strategies of halophilic microorganisms and Debaryomyces hansenii (halophilic yeast)].

The term halophile is used for all those organisms belonging to hypersaline habitats; they constitute an interesting class of organisms able to compete successfully in salt water and to resist its denaturing effects. A wide diversity of microorganisms, prokaryotic and eukaryotic belong to this category. Halophile organisms have strategies allowing them not only to withstand osmotic stress, but also to function better in the presence of salt, in spite of maintaining high intracellular concentrations of salt, partly due to the synthesis of compatible solutes that allow them to balance their osmotic pressure. We describe the characteristics of some halophile organisms and D. hansenii (halophile yeast), that allow them to resist high concentrations of salt. The interest to know the great diversity microorganisms living in hypersaline habitats is growing, and has begun to be the center of recent investigations, since halophile organisms produce an wide variety of biomolecules that can be used for different applications. In this review we describe some mechanisms with which some halophile organisms count to resist the high concentration of salts, mainly NaCl.

Adaptation, Physiological↗

PubMed1998

Osmoregulation and salinity effects on the expression and activity of Na+,K(+)-ATPase in the gills of European sea bass, Dicentrarchus labrax (L.).

The European sea bass, Dicentrarchus labrax, tolerates salinities ranging from freshwater (FW) to hypersaline conditions. In two experiments, we analysed changes in plasma ions, muscle water content (MWC), gill Na+,K(+)-ATPase activity, and alpha-subunit mRNA expression during the course of acclimation from 15 ppt salt water to FW or high salinity seawater (HSSW). In Experiment 1, fish (6.2 +/- 1.1 g) were acclimated from 15 ppt to either FW, 5, 15, 25, 50, or 60 ppt SW and sampled after 10 days. Gill Na+,K(+)-ATPase activity was stimulated in FW- and in 50 and 60 ppt SW-groups relative to the 15 ppt control group. In Experiment 2, subgroups of fish (89 +/- 7 g) were transferred from 15 ppt SW to FW or 50 ppt SW, and sampled 1, 2, 4, and 10 days later. Plasma osmolality, [Na+] and [Cl-] decreased in the FW-group and increased in the HSSW-group one day after transfer and lasting until day 10. This was accompanied by a pronounced increase in MWC in the FW-group and an insignificant decrease in the HSSW-group. The plasma [Na+]:[Cl-]-ratio increased markedly in the FW-group and decreased slightly in the HSSW-group, suggesting acid-base balance disturbances after transfer. Gill Na+,K(+)-ATPase activity was unchanged in 15 ppt SW but doubled in FW- and HSSW-groups after transfer. In both groups, this was preceded by a 2- to 5-fold elevation of the gill alpha-subunit Na+,K(+)-ATPase mRNA level. Thus increased expression of alpha-subunit mRNA is part of the molecular mechanism of both FW and SW acclimation in sea bass. Gill Na+,K(+)-ATPase Na(+)-, K(+)-, and ouabain-affinity were similar in fish acclimated to FW, 15 ppt, and HSSW, suggesting that identical isoforms of the catalytic subunit of the enzyme are expressed irrespective of salinity.

Adaptation, Physiological↗

PubMed1991

Sublethal effects of pentachlorophenol in the abalone (Haliotis rufescens) as measured by in vivo 31P NMR spectroscopy.

The sublethal biochemical effects of pentachlorophenol (PCP) were investigated in live, intact red abalones (Haliotis rufescens), using a flow-through exposure system, by in vivo 31P NMR spectroscopy. Based on rangefinding tests (6-hr LC50 = 1.6 mg/L; 6-hr no-observable-effect-level (NOEL) = 0.8 mg/L), three abalones were separately exposed to a sublethal concentration (1.2 mg/L) for 5 hr, followed by a 13 hr recovery period. Effects in foot muscle included both a decrease in phosphoarginine and an increase in inorganic monophosphate concentrations ([PA] and [Pi], respectively); both foot muscle concentrations of adenosine triphosphate [ATP] and intracellular pH (pHi) also declined. Parallel in vitro experiments revealed that concentrations of glycerol 3-phosphate, lactate, citrate, succinate, malate, and alanine (Ala) all increased, while those of glyceraldehyde 3-phosphate and glutamine (Gln) remained stable. Also, these effects were not evident until 2 hr into exposure, possibly the time required for PCP to attain an effective concentration in foot muscle. During recovery, while Pi declined to pre-exposure levels, [PA] completely recovered in only one individual. Also, realkalinization of pHi was similar to recovery of [Pi], and ATP returned to near-initial levels, as did glycerol 3-phosphate, lactate, succinate, malate, and Ala; glyceraldehyde 3-phosphate, citrate, and Gln levels declined. Recovery responses corresponded to the time for PCP clearance from foot muscle. The effects of PCP were similar to those of hypoxia, fatigue, hypersalinity, and arginine kinase inhibitors, and so sublethal PCP concentrations may also inhibit electron transport and arginine kinase as well as uncouple mitochondrial oxidative phosphorylation in intact molluscs. Thus, the effects of pollutants on key biochemical processes may now be measured in intact aquatic organisms as they occur, improving our ability to accurately assess the environmental effects of pollutants in the laboratory.

Animals↗

PubMed2002

Differential induction of branchial carbonic anhydrase and NA(+)/K(+) ATPase activity in the euryhaline crab, Carcinus maenas, in response to low salinity exposure.

The time course of induction of activity of carbonic anhydrase (CA) and Na/K ATPase, two enzymes that are central to osmotic and ionic regulation in the eyryhaline green crab, Carcinus maenas, was measured in response to a transfer from 32 to 10 ppt salinity. CA activity was low in all gills in crabs acclimated to high salinity. Activity was induced in the posterior three gills (G6-G9) starting at 96 hr following transfer to low salinity, with activity peaking at seven post-transfer. Na/K ATPase activity in posterior gills was already high in crabs acclimated to 32 ppt salinity, and it did not increase as a result of transfer to 10 ppt. Acclimation of crabs to hypersaline (40 ppt) conditions resulted in uniformly low levels of Na/K ATPase activity, and transfer from 40 ppt to 10 ppt stimulated a four-fold induction of activity in the posterior gills that was evident by seven days of low salinity exposure. Low salinity stimulates the activity of both enzymes, but a different degree of salinity change appears to be necessary to cause the induction of each enzyme. The Na/K ATPase activity is already high at a salinity (32 ppt) at which the crab is still an osmotic and ionic conformer. CA activity, however, even when expressed in low levels, is still present in excess of what is needed to supply counterions at a rate adequate to match the rate of active ion transport. It is possible that two strategies exist for the regulation of these two enzymes that coincide with the crab's intertidal and estuarine lifestyle: short-term modulation of activity of highly expressed enzyme (Na/K ATPase) and long-term modulation of enzyme concentration by changes in gene expression (CA). For all ranges of low salinity exposure, crabs undergo hemodilution, cell swelling, and subsequent cell volume readjustment as evidenced by the increase in concentration of TNPS in the hemolymph. This response takes place before the induction of enzyme activity, and it could serve as the initial signal in the induction pathway.

Adaptation, Physiological↗

PubMed2002

Branchial chloride cells in sea bass (Dicentrarchus labrax) adapted to fresh water, seawater, and doubly concentrated seawater.

Branchial chloride cells (CC) were studied in sea bass (Dicentrarchus labrax) maintained in seawater (SW: 35 per thousand) or gradually adapted to and subsequently maintained in fresh water (0.2 per thousand) or doubly concentrated seawater (DSW: 70 per thousand). Changes were observed in the location, number, and structure of CCs, that were discriminated by light, scanning, and transmission electron microscopy, as well as by immunofluorescence on the basis of their high Na(+)/K(+)-ATPase antigen content. The number of CCs increased in both fresh water and doubly concentrated seawater compared to control fish maintained in SW. In both experimental conditions, these cells were found on the gill filament (as in control fish) and even on the lamellae, especially in hypersaline conditions. Structural changes concerned the shapes and sizes of CCs and their apical outcrops and particularly the structures of their functional complexes (mitochondria, tubular system, and endoplasmic reticulum), which developed significantly in DSW adapted fish. The changes in the expression of the Na(+)/K(+)-ATPase were evaluated by assessing the enzyme's density at the ultrastructural level following immunogold labeling. This parameter was significantly higher in doubly concentrated seawater. The adaptative significance of the quantitative and morphofunctional changes in branchial chloride cells is discussed in relation to the original osmoregulatory strategy of this marine euryhaline teleost.

Adaptation, Physiological↗

PubMed1985

Amino acid metabolism in euryhaline bivalves: regulation of glycine accumulation in ribbed mussel gills.

Glycine levels in isolated ribbed mussel (Modiolus demissus) gill tissue increased slightly and decreased markedly when incubated at high and low salinities, respectively. Low levels of the enzymes involved in the biosynthesis of serine from triose phosphate intermediates, the serine hydroxymethyltransferase, and serine dehydrase were detected in gill tissue homogenates. Experiments using gill tissue incubated with (U-14C)-glycine and (U-14C)-serine indicated interconversion between serine and glycine and transfer of label to alanine, asparate, glutamate, CO2, organic acids, and protein. Glyoxylate was metabolized more slowly than glycine and was probably converted to glycine for catabolism. Studies using (1-14C)-glycine and (2-14C)-glycine with isolated gill tissue and mitochondria indicated that the mitochondrial glycine cleavage enzyme was the major route of glycine catabolism. Metabolic controls activating or inhibiting the glycine cleavage enzyme regulate tissue glycine accumulation and catabolism during hypersalinity or hyposalinity stress.

Amino Acids↗