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PubMed1986

Molecular aspects of adaptation to extreme cold environments.

Here are reviewed and summarized the strategies adopted by living organisms to survive low temperatures, from a molecular and membrane point of view. The presentation is aimed at a wide variety of readers. Two prime examples of connections between biological cold adaptation and the molecular level are (1) antifreeze proteins in fish from cold sea water, (the DNA sequence of the protein gene is now known) (2) the fluidity characteristics of cell membranes in a wide variety of organisms. In model membranes of phospholipids, stabler "s-phases" have recently been found to form at low temperatures. Antarctic endolithic organisms, living just under the surface of rocks, are exposed to long periods of low temperatures, and may develop such phases in their membranes. In the saturated phosphatidyl cholines, only lipids with a restricted range of acyl chain lengths show simultaneously s-phases and a main transition : This restricted range is about the restricted range found in natural membranes. The s-phases also form in the presence of natural cryoprotectants, and may be connected with botanical vernalization.

Acclimatization↗
PubMed2003

Characterisation of intestinal peptide transporter of the Antarctic haemoglobinless teleost Chionodraco hamatus.

H(+)/peptide cotransport was studied in brush-border membrane vesicles (BBMV) from the intestine of the haemoglobinless Antarctic teleost Chionodraco hamatus by monitoring peptide-dependent intravesicular acidification with the pH-sensitive dye Acridine Orange. Diethylpyrocarbonate-inhibited intravesicular acidification was specifically achieved in the presence of extravesicular glycyl-L-proline (Gly-L-Pro) as well as of glycyl-L-alanine (Gly-L-Ala) and D-phenylalanyl-L-alanine (D-Phe-L-Ala). H(+)/Gly-L-Pro cotransport displayed saturable kinetics, involving a single carrier system with an apparent substrate affinity (K(m,app)) of 0.806+/-0.161 mmol l(-1). Using degenerated primers from eel and human (PepT1) transporter sequence, a reverse transcription-polymerase chain reaction (RT-PCR) signal was detected in C. hamatus intestine. RT-PCR paralleled kinetic analysis, confirming the hypothesis of the existence of a PepT1-type transport system in the brush-border membranes of icefish intestine. Functional expression of H(+)/peptide cotransport was successfully performed in Xenopus laevis oocytes after injection of poly(A)(+) RNA (mRNA) isolated from icefish intestinal mucosa. Injection of mRNA stimulated D-Phe-L-Ala uptake in a dose-dependent manner and an excess of glycyl-L-glutamine inhibited this transport. H(+)/peptide cotransport in the Antarctic teleost BBMV exhibited a marked difference in temperature optimum with respect to the temperate teleost Anguilla anguilla, the maximal activity rate occurring at approximately 0 degrees C for the former and 25 degrees C for the latter. Temperature dependence of icefish and eel intestinal mRNA-stimulated uptake in the heterologous system (oocytes) was comparable.

Amino Acid Sequence↗
PubMed2002

Metabolic labelling of membrane microdomains/rafts in Jurkat cells indicates the presence of glycerophospholipids implicated in signal transduction by the CD3 T-cell receptor.

Cell membranes contain sphingolipids and cholesterol, which cluster together in distinct domains called rafts. The outer-membrane leaflet of these peculiar membrane domains contains glycosylphosphatidylinositol-anchored proteins, while the inner leaflet contains proteins implicated in signalling, such as the acylated protein kinase p56(lck) and the palmitoylated adaptator LAT (linker for activation of T-cells). We present here an approach to study the lipid composition of rafts and its change upon T-cell activation. Our method is based on metabolic labelling of Jurkat T-cells with different precursors of glycerophospholipid synthesis, including glycerol and fatty acids with different lengths and degrees of saturation as well as phospholipid polar head groups. The results obtained indicate that lipid rafts isolated by the use of sucrose density-gradient centrifugation after Triton X-100 extraction in the cold, besides sphingolipids and cholesterol, contain unambiguously all classes of glycerophospholipids: phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine and phosphatidylcholine. Fatty acid labelling shows that lipid rafts are labelled preferentially with saturated fatty acids while the rest of the plasma membrane incorporates mostly long-chained polyunsaturated fatty acids. To see whether the raft composition as measured by metabolic labelling of phospholipids is involved in T-cell activation, we investigated the production of sn-1,2-diacylglycerol (DAG) in CD3-activated cells. DAG production occurs within rafts, confirming previous demonstration of protein kinase C translocation into membrane microdomains. Our data demonstrate that raft disorganization by methyl-beta-cyclodextrin impairs both CD3-induced DAG production and changes in cytosolic Ca(2+) concentration. These lines of evidence support the conclusion that the major events in T-cell activation occur within or due to lipid rafts.

Arachidonic Acid↗
PubMed1999

Pleiotropic defects caused by loss of the proteasome-interacting factors Rad23 and Rpn10 of Saccharomyces cerevisiae.

Rad23 is a member of a novel class of proteins that contain unprocessed ubiquitin-like (UbL) domains. We showed recently that a small fraction of Rad23 can form an interaction with the 26S proteasome. Similarly, a small fraction of Rpn10 is a component of the proteasome. Rpn10 can bind multiubiquitin chains in vitro, but genetic studies have not clarified its role in vivo. We report here that the loss of both Rad23 and Rpn10 results in pleiotropic defects that are not observed in either single mutant. rad23Delta rpn10Delta displays slow growth, cold sensitivity, and a pronounced G2/M phase delay, implicating overlapping roles for Rad23 and Rpn10. Although rad23Delta rpn10Delta displays similar sensitivity to DNA damage as a rad23Delta single mutant, deletion of RAD23 in rpn10Delta significantly increased sensitivity to canavanine, a phenotype associated with an rpn10Delta single mutant. A mutant Rad23 that is unable to bind the proteasome ((DeltaUbL)rad23) does not suppress the canavanine or cold-sensitive defects of rad23Delta rpn10Delta, demonstrating that Rad23/proteasome interaction is related to these effects. Finally, the accumulation of multiubiquitinated proteins and the stabilization of a specific proteolytic substrate in rad23Delta rpn10Delta suggest that proteasome function is altered.

Canavanine↗
PubMed2004

Nitric oxide in early ischaemia reperfusion injury during human orthotopic liver transplantation.

BACKGROUND: Altered nitric oxide (NO) metabolism has been shown to contribute to ischemia-reperfusion (IR) injury in animal models. However, similar studies have not been performed in human liver transplantation (LT). In this study, we examined nitrate, nitrite, and nitrosothiols (NOx), NO synthases (endothelial [constitutive] nitric oxide synthase [eNOS] and inducible nitric oxide synthase [iNOS]), and nitrotyrosine in early IR injury after human LT. METHODS: Paired biopsies were obtained from nine donor livers before cold ischemia (retrieval biopsy) and after reimplantation (reperfusion biopsy). Sections were graded for reperfusion injury using the Suzuki score. NO was detected by chemiluminescence after reduction of NOx. Expression of eNOS and iNOS was by Western blot and reverse transcriptase polymerase chain reaction and peroxynitrite by immunodetection of 3-nitrotyrosine. RESULTS: Reperfusion biopsies showed histologic evidence of injury (median Suzuki score: retrieval 2, reperfusion 6, P=0.008) and neutrophil infiltration. NOx was reduced after reperfusion from 5.41 microM/100 mg (median, range 2.17-13.39 microM) to 3.51 microM (1.45-5.66 microM, P=0.05). eNOS protein was reduced after reperfusion from 0.6 units (median, range 0.45-1 unit) in retrieval biopsies to 0.39 units in reperfusion biopsies (range 0.2-0.79 units, P=0.007). There was no change in eNOS or iNOS mRNA expression or iNOS protein. Western blotting showed increased nitrotyrosine formation after reperfusion, median 0.42 (range 0.16-0.87) units in retrieval biopsies and 0.68 (0.29-1.06) units in reperfusion samples (P=0.007) and localized to periportal regions. CONCLUSIONS: iNOS protein may not contribute to early reperfusion injury during human LT. However, reduced NO bioavailability caused by reduced eNOS may contribute significantly to damage at this time point.

Adolescent↗
PubMed1999

CNS origins of the sympathetic nervous system outflow to brown adipose tissue.

Brown adipose tissue (BAT) plays a critical role in cold- and diet-induced thermogenesis. Although BAT is densely innervated by the sympathetic nervous system (SNS), little is known about the central nervous system (CNS) origins of this innervation. The purpose of the present experiment was to determine the neuroanatomic chain of functionally connected neurons from the CNS to BAT. A transneuronal viral tract tracer, Bartha's K strain of the pseudorabies virus (PRV), was injected into the interscapular BAT of Siberian hamsters. The animals were killed 4 and 6 days postinjection, and the infected neurons were visualized by immunocytochemistry. PRV-infected neurons were found in the spinal cord, brain stem, midbrain, and forebrain. The intensity of labeled neurons in the forebrain varied from heavy infections in the medial preoptic area and paraventricular hypothalamic nucleus to few infections in the ventromedial hypothalamic nucleus, with moderate infections in the suprachiasmatic and lateral hypothalamic nuclei. These results define the SNS outflow from the brain to BAT for the first time in any species.

Adipose Tissue, Brown↗
PubMed1988

Occurrence of three distinct molecular species of chondroitin sulfate proteoglycan in the developing rat brain.

More than 60% of brain chondroitin sulfate proteoglycans were extracted from 10-day-old rat brains by homogenization in ice-cold phosphate-buffered saline containing protease inhibitors. Although the soluble proteoglycan preparation was a mixture of chondroitin sulfate proteoglycans with a different hydrodynamic size as well as a different molecular density, each subfraction of the proteoglycans contained chondroitin sulfate side chains with virtually identical molecular weight (approximately 15,000) and chondroitin sulfate disaccharide composition (high content of 4-sulfate unit). Digestion of the purified proteoglycan preparation with protease-free chondroitinase ABC produced five core proteins with Mr = 250,000 (designated as 250K protein), 220,000 (220K), 150,000 (150K), 130,000 (130K), and 93,000 (93K). All these core proteins were obtained from chondroitin sulfate proteoglycan preparations extracted from various regions of the brain, but their composition varied among different brain regions. Analysis for amino acid composition of these core proteins and two-dimensional mapping of their proteolytic peptides revealed that three major core proteins (250K, 220K, and 150K proteins) were structurally different. These observations indicate that at least three distinct types of chondroitin sulfate proteoglycan occur in the developing rat brain.

Amino Acids↗
PubMed1993

VH4.21-encoded natural autoantibodies with anti-i specificity mirror those associated with cold hemagglutinin disease.

The Ig VH regions of virtually all human pathogenic cold agglutinin (CA) anti-i/l autoantibodies are encoded by a single Ig VH gene segment, VH4.21, in conjunction with a highly variable CDR3 structure. The anti-I specificity is often associated with V kappa III-encoded L chains, whereas anti-i autoantibodies appear to use a broader array of kappa and lambda VL gene segments. B cells expressing VH4.21 are abundantly present in adult lymphoid tissues from healthy individuals but their relationship with B cells secreting pathogenic CA is unknown. Herein we have analyzed the distribution of VH4.21-expressing B cells in fetal, neonatal, and adult B cell populations using the monoclonal anti-VH4.21 antibody 9G4. In addition, we have analyzed the anti-i and anti-I binding capacity and V regions of 19 VH4.21-encoded mAb secreted by cord and adult blood-derived cell lines from healthy individuals. The results show that VH4.21 expressing B cells are overrepresented in all repertoires studied and are evenly distributed over cord blood CD5+ and CD5- B cell populations. VH4.21-encoded H chains strongly predispose for anti-i binding capacity, regardless of the VL regions or H chain CDR3 structure. The avidity of some of these antibodies was similar to those of pathogenic CA. In addition, we found evidence for monospecific anti-I binding in antibodies encoded by other members of the VH4 gene family. We conclude that VH4.21-encoded antibodies with anti-i specificity from the normal B cell repertoire mirror their pathogenic counterparts and that naturally occurring anti-I antibodies may be encoded by a more diverse array of VH4 genes.

Agglutinins↗
PubMed1998

Successful gene transfer to the porcine liver in vivo with an adenoviral vector.

In vivo gene transfer to the porcine liver was tested with adenoviral vector to achieve molecular biological graft modulation. In adult female pigs immunosuppressed with cyclophosphamide, cyclosporine, and prednisolone, the liver was surgically isolated and flushed out with cold lactate Ringer solution (4 degrees C), by means of a pump-controlled bypass of the portal vein and the inferior vena cava in Groups A and D. In Group A (n = 4), 2 x 1011 pfu of the adenoviral vectors (pAdexCALacZ) were injected through the left hepatic artery during cold ischemia. In Group (n = 4), 2 x 1011 pfu of adenovirus vectors were injected through the auricular vein in a one-shot manner without a laparotomy. In Group C (n = 4), 2 x 1011 pfu/ml of adenoviral vectors were injected through the hepatic artery in a one-shot manner, without a surgical isolation of the liver. Group D (n = 4) animals received the same protocol as Group A except for the fact that they did not receive the immunosuppressive regimen. In a polymerase chain reaction, a transfected LacZ sequence was detected until POD 28 in Group A, but not in the other groups. In 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) staining, only the Group A animals revealed apparent staining predominantly in the portal area at POD 2, which then continued to be recognized until POD 28. The in situ perfusion of the liver combined with immunosuppression is thought to provide an ideal environment for the liver-directed adenovirus-mediated gene transfer to the porcine liver, by enabling a long contact with a high titer of the adenoviral vector.

Adenoviridae↗
PubMed2004

Annual evolution of fatty acid profile from muscle lipids of the common carp (Cyprinus carpio) in Madagascar inland waters.

Annual evolution of muscle lipids fatty acid (FA) from common carp (Cyprinus carpio) has been determined in 2001 through monthly samplings in the reserve pond of Sisaony (SIS series) and Itasy Lake (ITA series) of the Madagascar highlands. Total lipids from muscle were extracted and quantified according to the Bligh and Dyer method. FA identification was performed by GC-MS of FA methyl esters and FA pyrrolidides and led to the identification of 41 FA; routine analyses of FA were made by capillary GC. Principal component analysis (PCA) was performed on the data set to compare FA profiles. Lipid content is low, ranging from 0.91 to 1.73% of wet muscle, with a low stage during the hot season (January-April) and a higher stage during the cold season (July-October). Three FA dominated the FA composition: oleic acid (17.0-21.5%), palmitic acid (13.1-16.1%), and linoleic acid (9.6-13.2%). Polyunsaturated fatty acids (PUFA) were present in appreciable amounts: arachidonic acid (AA; 2.9-5.9%), docosahexaenoic acid (DHA; 2.9-6.7%), eicosapentaenoic acid (EPA; 1.9-3.4%), and docosapentaenoic acid (DPA; 1.9-4.3%). Two opposite evolution schemes appear within two groups of FA; on the one hand PUFA (both n-3 and n-6 series) show a maximum in August-October and a minimum in January-April, and, on the other hand, oleic, palmitic, and linoleic acids show the opposite maxima and minima. PCA results give confirmation of these evolution schemes, the two groups of FA giving opposite high factor loadings on axis 1. The SIS and ITA series are differentiated by axis 2 by mean of minor FA, mostly odd- and branched-chain. Results indicate that common carp, the second most abundant freshwater fish in Madagascar highlands waters, may be an interesting source of dietary PUFA.

Animals↗
PubMed2005

Expression analysis of a cold responsive transcript from trifoliate orange by real-time PCR and RT-PCR.

CLTa and CLTb are two transcripts produced by the citrus CLT gene. CLTb is constitutively expressed, while CLTa is a low temperature responsive transcript expressed in temperatures below 10 degrees C during the acclimation process of some species of citrus. Real-time PCR was used to study CLTa expression pattern in trifoliate orange during acclimation, gradual deacclimation and abrupt deacclimation. A standard curve of nine dilution series from 10 x 10(6) to 10 x 10(-3) fg was constructed, using part of the CLTa transcript, which enabled us to determine the concentration of the transcript at different temperatures and conditions. It was found that during acclimation, CLTa expression is first detected at 10 degrees C, reaching a maximum after 24 h of exposure at -1 degrees C. During gradual deacclimation, the transcript accumulated at 5 degrees C and after this point it degrades, reaching a low level at 10 degrees C. When the plants were abruptly transferred to room temperature after being acclimated to -1 degrees C, the transcript reduced from 11,303 fg to levels below the threshold 3 h later, indicating a rapid degradation and how the expression of CLTa is dependent on low temperature. Exposure of trifoliate plants to abscisic acid (ABA) and salts indicated that CLTa is not induced by these treatments at the concentrations used. CLTa expression was also verified in other citrus species and was not detected in the acclimated cold-sensitive species "Mexican lime" (Citrus aurantifolia Swing.) and in the cold hardy "Satsuma mandarin (C. unchiu Marc.).

Abscisic Acid↗
PubMed1984

The effects of different thymidine concentrations on DNA replication in pea-root cells synchronized by a protracted 5-fluorodeoxyuridine treatment.

Single-cell and DNA fiber autoradiography, cytophotometry and velocity sedimentation in alkaline sucrose gradients were used to analyse DNA replication and nascent replicon maturation in 5-fluorodeoxyuridine (FUdR)-synchronized cells of Pisum sativum. The replicon size was not significantly changed by the protracted FUdR treatment. When the synchronized cells were released from the inhibitor, labeled with [3H]TdR for 30 min, and chased in medium containing 1 X 10(-6) M or lower concentrations of cold thymidine, DNA replication stopped after approx. 25% of the genome had replicated, and the nascent strands failed to grow above 9 - 12 X 10(6) D single-stranded (ss) DNA. When the cells were chased in medium with 1 X 10(-5) M cold thymidine, the DNA content of the labeled cells steadily increased with time and the size of the nascent molecules grew continuously until replicon size was achieved; then they were accumulated at replicon size until the cells arrived in late S or G2. When the FUdR-synchronized cells were chased in medium containing 1 X 10(-4) M cold thymidine, the size of the nascent strands increased continuously with time, indicating that some neighbouring nascent replicons were joined as soon as they completed their replication. These observations led us to postulate that in FUdR-synchronized cells the rates of chain elongation, cell progression through the S phase and nascent replicon maturation are controlled by thymidine availability.

DNA Replication↗
PubMed1996

Gammopathy-related crystal-storing histiocytosis, pseudo- and pseudo-pseudo-Gaucher cells. Critical commentary and mini-review.

Commenting on a case report of dermal immunocytoma with crystal-storing histiocytes, a short review is given on the phenomena related to crystallization of monoclonal immunoglobulins within plasma cells, in the extracellular space, or within the lysosomal compartment of macrophages. Paraprotein crystallization is supported by hydrophobicity, poor solubility in the cold or at acid pH, and there are few reports on structural defects of crystal-forming myeloma proteins which are supposed to promote either their crystallization or impaired intralysosomal degradation. In the hitherto known cases of crystal histiocytosis, immunoglobulins of light chain type kappa have been exclusively involved in the process of macrophage storage. Accumulation of paraprotein-related crystals in macrophages may mimic the appearance of Gaucher cells or of the so-called pseudo-Gaucher cells seen in chronic myelogeneous leukaemia. With regard to their lightmicroscopical and ultrastructural differences to both, Gaucher cells and pseudo-Gaucher cells, paraproteinaemia-related crystal-storing macrophages may be denoted as pseudo-pseudo-Gaucher cells (PPGC). Human PPGC are similar to constitutive crystal-storing histiocytes known from inbred C57 BL-6 mice. The distribution of PPGC may be limited to the realm of a plasmacytoma or immunocytoma, but there are also cases with systemic involvement of the RES similar to Gaucher disease.

Animals↗
PubMed2001

Expression of multidrug resistance-associated protein (MRP) in human retinal pigment epithelial cells and its interaction with BAPSG, a novel aldose reductase inhibitor.

PURPOSE: The objective of this study was to determine the expression and activity of multidrug resistance-associated protein (MRP) in the retinal pigment epithelial (RPE) cells and to further assess whether BAPSG, a novel anionic aldose reductase inhibitor, interacts with MRP. METHODS: Functional and biochemical evidence for MRP was obtained in a human retinal pigment epithelial (ARPE-19) cell line and primary cultures of human retinal pigment epithelial (HRPE) cells. Fluorescein accumulation and efflux in the presence and absence of MRP inhibitors was used to obtain functional evidence for MRP. Western blots and RT-PCR were used to obtain biochemical evidence for MRP1. The influence of MRP inhibitors on BAPSG accumulation and efflux in ARPE-19 cells was determined to understand its interaction with MRP. RESULTS: MRP inhibitors increased fluorescein accumulation and reduced efflux in RPE cells. Both cell types exhibited a 190-kDa western blot band corresponding to MRP1 protein and a 287 bp RT-PCR band corresponding to MRP1 mRNA. MRP inhibitors reduced BAPSG efflux and increased its accumulation in ARPE-19 cells. CONCLUSIONS: MRP is functionally and biochemically active in human RPE cells. Anionic BAPSG is a likely substrate for MRP.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

The 9-cis-epoxycarotenoid cleavage reaction is the key regulatory step of abscisic acid biosynthesis in water-stressed bean.

Abscisic acid (ABA), a cleavage product of carotenoids, is involved in stress responses in plants. A well known response of plants to water stress is accumulation of ABA, which is caused by de novo synthesis. The limiting step of ABA biosynthesis in plants is presumably the cleavage of 9-cis-epoxycarotenoids, the first committed step of ABA biosynthesis. This step generates the C(15) intermediate xanthoxin and C(25)-apocarotenoids. A cDNA, PvNCED1, was cloned from wilted bean (Phaseolus vulgaris L.) leaves. The 2, 398-bp full-length PvNCED1 has an ORF of 615 aa and encodes a 68-kDa protein. The PvNCED1 protein is imported into chloroplasts, where it is associated with the thylakoids. The recombinant protein PvNCED1 catalyzes the cleavage of 9-cis-violaxanthin and 9'-cis-neoxanthin, so that the enzyme is referred to as 9-cis-epoxycarotenoid dioxygenase. When detached bean leaves were water stressed, ABA accumulation was preceded by large increases in PvNCED1 mRNA and protein levels. Conversely, rehydration of stressed leaves caused a rapid decrease in PvNCED1 mRNA, protein, and ABA levels. In bean roots, a similar correlation among PvNCED1 mRNA, protein, and ABA levels was observed. However, the ABA content was much less than in leaves, presumably because of the much smaller carotenoid precursor pool in roots than in leaves. At 7 degrees C, PvNCED1 mRNA and ABA were slowly induced by water stress, but, at 2 degrees C, neither accumulated. The results provide evidence that drought-induced ABA biosynthesis is regulated by the 9-cis-epoxycarotenoid cleavage reaction and that this reaction takes place in the thylakoids, where the carotenoid substrate is located.

Abscisic Acid↗
PubMed1997

Induction of interferon-gamma inducing factor in the adrenal cortex.

Interferon-gamma inducing factor (IGIF) is a recently identified cytokine also called interleukin-1gamma (IL-1gamma) or interleukin-18 (IL-18). Its biological activity is pleiotropic, and, so far, it has been shown to induce interferon-gamma production in Th1 cells, to augment the production of granulocyte-macrophage-CSF, and to decrease that of interleukin-10 (IL-10). We first detected newly synthesized IGIF mRNA by differential display in the adrenal gland of reserpine-treated rats and then isolated two transcripts by reverse transcription polymerase chain reaction. They were identified as rat IGIF on the basis of the high homology with mouse: 91% at both the nucleotide and the amino acid level. Subsequently, we investigated the effects of stress on IGIF mRNA levels and found that acute cold stress strongly induced IGIF gene expression. In situ hybridization analysis showed that IGIF is synthesized in the adrenal cortex, specifically in the zona reticularis and fasciculata that produce glucocorticoids. The presence of IGIF mRNA was also detected in the neurohypophysis although induction by stress was not significant. Our results call for more attention to the role of the adrenal gland as a potential effector of immunomodulation and suggest that IGIF itself might be a secreted neuroimmunomodulator and play an important role in orchestrating the immune system following a stressful experience.

Adrenal Cortex↗
PubMed2003

Isolation and characterization of new strains of methanogens from cold terrestrial habitats.

Five strains of methanogenic archaea (MT, MS, MM, MSP, ZB) were isolated from permanently and periodically cold terrestrial habitats. Physiological and morphological studies, as well as phylogenetic analyses of the new isolates were performed. Based on sequences of the 16S rRNA and methyl-coenzyme M reductase a-subunit (mcrA) genes all new isolates are closely related to known mesophilic and psychrotolerant methanogens. Both, phylogenetic analyses and phenotypic properties allow to classify strains MT, MS, and MM as members of the genus Methanosarcina. Strain MT is a new ecotype of Methanosarcina mazei, whereas strains MM and MS are very similar to each other and can be assigned to the recently described psychrotolerant species Methanosarcina lacustris. The hydrogenotrophic strain MSP is a new ecotype of the genus Methanocorpusculum. The obligately methylotrophic strain ZB is closely related to Methanomethylovorans hollandica and can be classified as new ecotype of this species. All new isolates, including the strains from permanently cold environments, are not true psychrophiles according to their growth temperature characteristics. In spite of the ability of all isolates to grow at temperatures as low as 1-5 degrees C, all of them have their growth optima in the range of moderate temperatures (25-35 degrees C). Thus, they can be regarded as psychrotolerant organisms. Psychrotolerant methanogens are thought to play an important role in methane production in both, habitats under seasonal temperature variations or from permanently cold areas.

Animals↗
PubMed1976

Periodic variations in the ratio of free to thylakoid-bound chloroplast ribosomes during the cell cycle of Chlamydomonas reinhardtii.

The ratio of free to thylakoid-bound chloroplast ribosomes in Chlamydomonas reinhardtii undergoes periodic changes during the synchronous light-dark cycle. In the light, when there is an increase in the chlorophyll content and synthesis of thylakoid membrane proteins, about 20-30% of the chloroplast ribosomes are bound to the thylakoid membranes. On the other hand, only a few or no bound ribosomes are present in the dark when there is no increase in the chlorophyll content. The ribosome-membrane interaction depends not only on the developmental stage of the cell but also on light. Thus, bound ribosomes were converted to the free variety after cultures at 4 h in the light had been transferred to the dark for 10 min. Conversely, a larger number of chloroplast ribosomes became attached to the membranes after cultures at 4 h in the dark had been illuminated for 10 min. Under normal conditions, when there was slow cooling of the cultures during cell harvesting, chloroplast polysomal runoff occurred in vivo leading to low levels of thylakoid-bound ribosomes. This polysomal runoff could be arrested by either rapid cooling of the cells or the addition of chloramphenicol or erythromycin. Each of these treatments prevented polypeptide chain elongation on chloroplast ribosomes and thus allowed the polyosomes to remain bound to the thylakoids. Addition of lincomycin, an inhibitor of chain initiation on 70S ribosomes, inhibited the assembly of polysome-thylakoid membrane complex in the light. These results support a model in which initiation of mRNA translation begins in the chloroplast stroma, and the polysome subsequently becomes attached to the thylakoid membrane. Upon natural chain termination, the chloroplast ribosomes are released from the membrane into the stroma.

Cell Division↗