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At least 217 records · Page 12Linked to original sources
PubMed1988

A possible role for taurine in osmoregulation within the brain.

Intracranial microdialysis was used to measure changes in extracellular amino acids within the rat brain during local osmotic alteration of the extracellular microenvironment or during systemic water intoxication. Increased cellular hydration produced by either of these methods was accompanied by a marked increase in extracellular taurine levels without affecting the other amino acids measured. With local osmotic alteration, this increase was osmolarity dependent and reversible. The specificity, sensitivity, and reversibility of the increase in extracellular taurine strongly suggest a functional role in osmoregulation in the brain under normal as well as pathological conditions.

Animals↗
PubMed1989

Influence of osmoregulation processes on starvation survival of Escherichia coli in seawater.

The adaptation of enteric bacteria in seawater has previously been described in terms of nutrient starvation. In the present paper, we bring experimental arguments suggesting that survival of these microorganisms could also depend on their ability to overcome the effects of osmotic stress. We analyzed the influence of osmoregulatory mechanisms (potassium transport, transport and accumulation of organic osmolytes) on the survival of Escherichia coli in seawater microcosms by using mutants lacking components of the osmotic stress response. Long-term protection was afforded to cells by growth in a medium whose osmotic pressure was increased by either NaCl, LiCl, or saccharose. Achievement of the protection state depended at least partly on osmoregulatory mechanisms, but differed when these were activated or induced during prior growth or in resting cells suspended in phosphate buffer or in seawater. When achieved during growth, K+ transport, glycine-betaine (GBT) synthesis or transport, and trehalose synthesis helped increase the ability to survive in seawater. Protection by GBT was also obtained with resting cells in a phosphate buffer at high osmotic pressure. However, when added only to the seawater, GBT did not change the survival ability of cells no matter what their osmoregulation potential. These results showed that the survival of E. coli cells in seawater depends, at least partly, on whether they possess certain genes which enable them to regulate osmotic pressure and whether they can be stimulated to express those genes before or after their release into the environment. This expression requires nutrients as the substrates from which the corresponding gene products are made.

Culture Media↗
PubMed1990

Detection of the osmoregulator betaine in methanogens.

Trimethyl glycine (glycine betaine) was detected by 13C nuclear magnetic resonance spectroscopy at high intracellular concentrations in several methanogens (Methanogenium cariaci, "Methanogenium anulus" AN9, Methanohalophilus zhilinae, Methanohalophilus mahii, and Methanococcus voltae) grown on marine media containing yeast extract. 13C labeling studies with Methanogenium cariaci suggested that the betaine which accumulated inside the cells was not synthesized de novo but was transported in from the medium. Proof of such a transport system was provided by growing Methanogenium cariaci on yeast-free medium supplemented with betaine. Under these conditions, betaine was the dominant osmoregulator.

Betaine↗
PubMed1994

In vivo nuclear magnetic resonance study of the osmoregulation of phosphocholine-substituted beta-1,3;1,6 cyclic glucan and its associated carbon metabolism in Bradyrhizobium japonicum USDA 110.

A phosphocholine-substituted beta-1,3;1,6 cyclic glucan (PCCG), an unusual cyclic oligosaccharide, has been isolated from Bradyrhizobium japonicum USDA 110 (D. B. Rolin, P. E. Pfeffer, S. F. Osman, B. S. Swergold, F. Kappler, and A. J. Benesi, Biochim. Biophys. Acta 1116:215-225, 1992). Data presented here suggest that PCCG synthesis is dependent on the carbon metabolism and that osmotic regulation of its biosynthesis parallels regulation of membrane-derived oligosaccharide biosynthesis observed in Escherichia coli (E. P. Kennedy, M. K. Rumley, H. Schulman, and L. M. G. van Golde, J. Biol. Chem. 251:4208-4213, 1976) and Agrobacterium tumefaciens (G. A. Cangelosi, G. Martinetti, and E. W. Nester, J. Bacteriol. 172:2172-2174, 1990). Growth of B. japonicum USDA 110 cells in the reference medium at relatively low osmotic pressures (LO) (65 mosmol/kg of H2O) caused a large accumulation of PCCG and unsubstituted beta-1,3;1,6 cyclic glucans (CG). Sucrose and polyethylene glycol, nonionic osmotica, reduce all growth rates and inhibit almost completely the production of PCCG at high osmotic pressures (HO) above 650 and 400 mosmol/kg of H2O), respectively. We used in vivo 13C nuclear magnetic resonance spectroscopy to identify the active osmolytes implicated in the osmoregulation process. The level of alpha,alpha-trehalose in B. japonicum cells grown in autoclaved or filter-sterilized solutions remained constant in HO (0.3 M sucrose or 250 g of polyethylene glycol 6000 per liter) medium. Significant amounts of glycogen and extracellular polysaccharides were produced only when glucose was present in the autoclaved HO 0.3 M sucrose media. The results of hypo- and hyperosmotic shocking of B. japonicum USDA 110 cells were monitored by using in vivo 31P and 13C nuclear magnetic resonance spectroscopy. The first observed osmoregulatory response of glycogen-containing cells undergoing hypoosmotic shock was release of P(i) into the medium. Within 7 h, reabsorption of P(i) was complete and production of PCCG was initiated. After 12 h, the PCCG content had increased by a factor of 7. Following the same treatment, cells containing little or no glycogen released trehalose and failed to produce PCCG. Thus the production of PCCG/CG in response to hypoosmotic shocking of stationary-phase cells was found to be directly linked to the interconversion of stored glycogen. Hyperosmotic shocking of LO-grown stationary-phase cells with sucrose had no effect on the content of previously synthesized CG/PCCG. The PCCG/CG content and its osmotically induced biosynthesis are discussed in terms of carbon metabolism and a possible role in hypoosmotic adaptation in B. japonicum USDA 110.

Carbon↗
PubMed2002

Osmoregulation and fungicide resistance: the Neurospora crassa os-2 gene encodes a HOG1 mitogen-activated protein kinase homologue.

Neurospora crassa osmosensitive (os) mutants are sensitive to high osmolarity and therefore are unable to grow on medium containing 4% NaCl. We found that os-2 and os-5 mutants were resistant to the phenylpyrrole fungicides fludioxonil and fenpiclonil. To understand the relationship between osmoregulation and fungicide resistance, we cloned the os-2 gene by using sib selection. os-2 encodes a putative mitogen-activated protein (MAP) kinase homologous to HOG1 and can complement the osmosensitive phenotype of a Saccharomyces cerevisiae hog1 mutant. We sequenced three os-2 alleles and found that all of them were null with either frameshift or nonsense point mutations. An os-2 gene replacement mutant also was generated and was sensitive to high osmolarity and resistant to phenylpyrrole fungicides. Conversely, os-2 mutants transformed with the wild-type os-2 gene could grow on media containing 4% NaCl and were sensitive to phenylpyrrole fungicides. Fludioxonil stimulated intracellular glycerol accumulation in wild-type strains but not in os-2 mutants. Fludioxonil also caused wild-type conidia and hyphal cells to swell and burst. These results suggest that the hyperosmotic stress response pathway of N. crassa is the target of phenylpyrrole fungicides and that fungicidal effects may result from a hyperactive os-2 MAP kinase pathway.

Dioxoles↗
PubMed1983

Osmoregulation of alkaline phosphatase synthesis in Escherichia coli K-12.

Alkaline phosphatase, the phoA product, is synthesized constitutively in phoR mutants. This constitutive synthesis, which is independent of phosphate control, varies with changes in the osmolarity of the growth medium; phoA expression increases with increasing osmolarity. Maximum expression of the osmoregulated genes phoA, ompC, and ompF was achieved by osmotic manipulation of minimal medium; complex media repressed their expression.

Alkaline Phosphatase↗
PubMed1985

Identification of osmoresponsive genes in Escherichia coli: evidence for participation of potassium and proline transport systems in osmoregulation.

Mu d1(Ap lac)-generated operon fusions were used in the identification of genes in Escherichia coli whose transcriptional expression is altered by changes in the osmolarity of the growth medium. One such osmoresponsive gene, designated osrA, was induced 400-fold when the osmolarity of the medium was increased with the addition of either ionic or neutral impermeable solutes but was not induced with glycerol, which is freely permeable across the cell membrane. osrA was mapped to 57.5 min and was shown to be transcribed clockwise on the E. coli chromosome. The ability of small concentrations of L-proline to promote the growth of E. coli in high-osmolar medium was shown to have been specifically lost in osrA mutants; other lines of evidence were also obtained to support the notion that osrA codes for an osmoresponsive L-proline transport system and is homologus to proU in Salmonella typhimurium. A second osmoresponsive operon identified was kdp, which codes for an inducible K+-transport system in E. coli. kdp expression was elevated 12-fold when the osmolarity of the growth medium was increased with the addition of impermeable ionic solutes but not neutral solutes; furthermore, osmoresponsivity of kdp expression was demonstrable only in K+-limiting media. kdp mutants were able to grow normally in high-osmolar media, but strains defective in both kdp and trkA (a gene for a second major K+-transport system) displayed an osmosensitive phenotype. The results suggest that transport systems for L-proline and K+, specified by osrA (proU) and kdp, respectively, play independent and important roles in osmoregulation in E. coli. A third osmoresponsive gene that was identified was lamB, which codes for an outer membrane protein for maltodextrin transport and lambda phage adsorption; its expression was reduced fourfold with increase in the osmolarity of the growth medium.

Biological Transport↗
PubMed1985

Osmoregulation of gene expression in Salmonella typhimurium: proU encodes an osmotically induced betaine transport system.

Previous evidence has indicated that a gene, proU, is involved in the response of bacterial cells to growth at high osmolarity. Using Mu-mediated lacZ operon fusions we found that transcription of the proU gene of Salmonella typhimurium is stimulated over 100-fold in response to increases in external osmolarity. Our evidence suggests that changes in turgor pressure are responsible for these alterations in gene expression. Expression of proU is independent of the ompR gene, known to be involved in osmoregulation of porin expression. Thus, there must be at least two distinct mechanisms by which external osmolarity can influence gene expression. We show that there are relatively few genes in the cell which are under such osmotic control. The proU gene is shown to encode a high-affinity transport system (Km = 1.3 microM) for the osmoprotectant betaine, which is accumulated to high concentrations in response to osmotic stress. Even when fully induced, this transport system is only able to function in medium of high osmolarity. Thus, betaine transport is regulated by osmotic pressure at two levels: the induction of expression and by modulation of activity of the transport proteins. We have previously shown that the proP gene encodes a lower-affinity betaine transport system (J. Cairney, I. R. Booth, and C. F. Higgins, J. Bacteriol., 164:1218-1223, 1985). In proP proU strains, no saturable betaine uptake could be detected although there was a low-level nonsaturable component at high substrate concentrations. Thus, S. typhimurium has two genetically distinct pathways for betaine uptake, a constitutive low-affinity system (proP) and an osmotically induced high-affinity system (proU).

Betaine↗
PubMed1986

proP-mediated proline transport also plays a role in Escherichia coli osmoregulation.

The growth of Escherichia coli strains in media having elevated osmolarity was promoted in the presence of low concentrations of the L-proline analog 5-hydroxy-L-pipecolic acid. The osmoprotective ability of this compound was correlated with the presence in these strains of a functional proP+ gene. The results suggest that the proP-mediated transport of L-proline (in addition to that by proU) is important in osmoregulation. proP::lac operon fusions were used to demonstrate that this gene shows limited induction of expression upon growth in media having elevated osmolarity and that it is transcribed clockwise on the chromosome.

Biological Transport↗
PubMed1989

Osmoregulation in Escherichia coli: complementation analysis and gene-protein relationships in the proU locus.

The proU locus in Escherichia coli encodes an osmotically inducible transport system for two substrates, glycine betaine and L-proline, whose intracellular accumulation represents an important component in the physiology of osmoregulation. Several osmoresponsive proU::lac mutants were isolated and tested for complementation with plasmids carrying different functional regions of proU. Three classes of mutations were identified which were physically mapped to distinct regions of DNA from this locus. Tn1000-insertion mutagenesis of cloned proU DNA also yielded three phenotypic classes of mutations whose physical distribution approximately corresponded with those of the chromosomal mutants above. Three proteins, of Mr 44,000, 35,000, and 33,000, were shown to be products of proU, and the last of these was localized to the periplasmic space. The data indicate that proU is an operon with three genes, designated in order proV, proW, and proX, encoding respectively the gene products above. All three genes were shown to be necessary for exhibition of the proU-mediated osmoprotective effects of both glycine betaine and L-proline in E. coli.

Bacterial Proteins↗
PubMed1989

An osmoregulated dipeptide in stressed Rhizobium meliloti.

One common mechanism of cellular adaptation to osmotic stress is the accumulation of organic solutes in the cytosol. We have used natural-abundance 13C nuclear magnetic resonance to identify all organic solutes that accumulate to significant levels in Rhizobium meliloti. Our studies led to the discovery of a new dipeptide, N-acetylglutaminylglutamine amide (NAGGN), which is accumulated during osmotic stress. Only rarely have peptides been shown to function in bacteria, and furthermore, this is the first example of a peptide playing a role in osmoregulation. Evidence for the biological role of NAGGN in osmotic-stress protection is presented.

Chromatography, High Pressure Liquid↗
PubMed1995

Modulation of flagellar expression in Escherichia coli by acetyl phosphate and the osmoregulator OmpR.

During the search for unknown factors involved in motility, we have found that expression of the flagellar master operon flhDC is affected by mutations of the pta and ackA genes, encoding phosphotransacetylase and acetate kinase, respectively (S. Shin, J. Sheen, and C. Park, Korean J. Microbiol. 31:504-511, 1993). Here we describe results showing that this effect is modulated by externally added acetate, except when both pta and ackA are mutated, suggesting the role of acetyl phosphate, an intermediate of acetate metabolism, as a regulatory effector. Furthermore, the following evidence indicates that the phosphorylation of OmpR, a trans factor for osmoregulation, regulates flagellar expression. First, in a strain lacking ompR, the expression of flhDC is no longer responsive to a change in the level of acetyl phosphate. Second, an increase in medium osmolarity does not decrease flhDC expression in an ompR mutant. It is known that such an increase normally enhances OmpR phosphorylation. Third, OmpR protein binds to the DNA fragment containing the flhDC promoter, and its affinity is increased with phosphorylation by acetyl phosphate. DNase I footprinting revealed the regions of the flhDC promoter protected by OmpR in the presence or absence of phosphorylation. Therefore, we propose that the phosphorylated OmpR, generated by either osmolarity change or the internal level of acetyl phosphate, negatively regulates the expression of flagella.

Acetates↗
PubMed1997

Topological analysis of the membrane-bound glucosyltransferase, MdoH, required for osmoregulated periplasmic glucan synthesis in Escherichia coli.

The MdoH protein is essential for synthesis of the osmoregulated periplasmic glucans, known as membrane-derived oligosaccharides (MDOs), in Escherichia coli. Mutants lacking MdoH are deficient in a glucosyltransferase activity assayed in vitro. The MdoH protein is the product of the second gene of an operon, and it has been shown to span the cytoplasmic membrane. The MdoH protein comprises 847 amino acids and is poorly expressed as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We have experimentally measured the topological organization of MdoH within the membrane by construction of fusions to beta-lactamase as a reporter. Analysis of 51 different MdoH-beta-lactamase fusions suggested that the MdoH protein crosses the cytoplasmic membrane eight times, with the N and C termini in the cytoplasm. Moreover, a 310-amino-acid domain is present in the cytoplasm between the second and third transmembrane segments. It was deduced from the measurement of the MDO biosynthetic activity of truncated or fused MdoH proteins that almost all the C-terminal residues are necessary for this activity. The model of the MdoH protein in the membrane suggests that this protein could be directly involved in the translocation of nascent polyglucose chains to the periplasmic space.

Amino Acid Sequence↗
PubMed1999

The mdoC gene of Escherichia coli encodes a membrane protein that is required for succinylation of osmoregulated periplasmic glucans.

Osmoregulated periplasmic glucans (OPGs) of Escherichia coli are anionic oligosaccharides that accumulate in the periplasmic space in response to low osmolarity of the medium. Their anionic character is provided by the substitution of the glucosidic backbone by phosphoglycerol originating from the membrane phospholipids and by succinyl residues from unknown origin. A phosphoglycerol-transferase-deficient mdoB mutant was subjected to Tn5 transposon mutagenesis, and putative mutant clones were screened for changes in the anionic character of OPGs by thin-layer chromatography. One mutant deficient in succinylation of OPGs was obtained, and the gene inactivated in this mutant was characterized and named mdoC. mdoC, which encodes a membrane-bound protein, is closely linked to the mdoGH operon necessary for the synthesis of the OPG backbone.

Chromatography, Thin Layer↗
PubMed2001

Osmoregulated periplasmic glucan synthesis is required for Erwinia chrysanthemi pathogenicity.

Erwinia chrysanthemi is a phytopathogenic enterobacterium causing soft rot disease in a wide range of plants. Osmoregulated periplasmic glucans (OPGs) are intrinsic components of the gram-negative bacterial envelope. We cloned the opgGH operon of E. chrysanthemi, encoding proteins involved in the glucose backbone synthesis of OPGs, by complementation of the homologous locus mdoGH of Escherichia coli. OpgG and OpgH show a high level of similarity with MdoG and MdoH, respectively, and mutations in the opgG or opgH gene abolish OPG synthesis. The opg mutants exhibit a pleiotropic phenotype, including overproduction of exopolysaccharides, reduced motility, bile salt hypersensitivity, reduced protease, cellulase, and pectate lyase production, and complete loss of virulence. Coinoculation experiments support the conclusion that OPGs present in the periplasmic space of the bacteria are necessary for growth in the plant host.

Bacterial Proteins↗
PubMed2002

Osmoregulation of dimer resolution at the plasmid pJHCMW1 mwr locus by Escherichia coli XerCD recombination.

Xer-mediated dimer resolution at the mwr site of plasmid pJHCMW1 is osmoregulated in Escherichia coli. Whereas under low-salt conditions, the site-specific recombination reaction is efficient, under high-salt conditions, it proceeds inefficiently. Regulation of dimer resolution is independent of H-NS and is mediated by changes in osmolarity rather than ionic effects. The low level of recombination at high salt concentrations can be overcome by high levels of PepA or by mutating the ARG box to a sequence closer to the E. coli ARG box consensus. The central region of the mwr core recombination site plays a role in regulation of site-specific recombination by the osmotic pressure of the medium.

Aspartic Acid Endopeptidases↗
PubMed2003

Negative osmoregulation of the Salmonella ompS1 porin gene independently of OmpR in an hns background.

The ompS1 gene encodes a quiescent porin in Salmonella enterica serovars Typhi and Typhimurium. By using random mariner transposon mutagenesis, mutations that caused derepression of ompS1 expression were isolated, one in S. enterica serovar Typhi and two in S. enterica serovar Typhimurium. All of them mapped in the hns gene in the region coding for the carboxy terminus of the H-NS nucleoid protein. The derepressed ompS1 expression was subject to negative regulation at high osmolarity, both in the presence and in the absence of OmpR. This observation was possible due to the fact that there are two promoters: P1, which is OmpR dependent, and P2, which does not require OmpR for activation (rather, OmpR represses P2). The sequences upstream from position -88, a region previously shown to be involved in the negative regulation of ompS1, can form a static bend, and the integrity of this region was required for function and binding of H-NS and for osmoregulation, as determined with gene reporter fusions of different lengths and with a 31-bp deletion mutant. This is consistent with the notion that this region determines a structure required for repression. Hence, ompS1 shares negative regulation by H-NS with other loci, such as the bgl operon and the ade gene.

Bacterial Outer Membrane Proteins↗
PubMed2004

Identification of mdoD, an mdoG paralog which encodes a twin-arginine-dependent periplasmic protein that controls osmoregulated periplasmic glucan backbone structures.

Osmoregulated periplasmic glucans (OPGs) of Escherichia coli are anionic and highly branched oligosaccharides that accumulate in the periplasmic space in response to low osmolarity of the medium. The glucan length, ranging from 5 to 12 glucose residues, is under strict control. Two genes that form an operon, mdoGH, govern glucose backbone synthesis. The new gene mdoD, which appears to be a paralog of mdoG, was characterized in this study. Cassette inactivation of mdoD resulted in production of OPGs with a higher degree of polymerization, indicating that OpgD, the mdoD product (according to the new nomenclature), controls the glucose backbone structures. OpgD secretion depends on the Tat secretory pathway. Orthologs of the mdoG and mdoD genes are found in various proteobacteria. Most of the OpgD orthologs exhibit a Tat-dependent secretion signal, while most of the OpgG orthologs are Sec dependent.

Amino Acid Sequence↗