Large populations (200 to 5,000 cells ml(-1) in snowmelt) of bacteria were present in surface snow and firn from the south pole sampled in January 1999 and 2000. DNA isolated from this snow yielded ribosomal DNA sequences similar to those of several psychrophilic bacteria and a bacterium which aligns closely with members of the genus Deinococcus, an ionizing-radiation- and desiccation-resistant genus. We also obtained evidence of low rates of bacterial DNA and protein synthesis which indicates that the organisms were metabolizing at ambient subzero temperatures (-12 to -17 degrees C). (+info)
NMR analysis of type III antifreeze protein intramolecular dimer. Structural basis for enhanced activity.
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The structure of a new antifreeze protein (AFP) variant, RD3, from antarctic eel pout (Rhigophila dearborni) with enhanced activity has been determined for the first time by nuclear magnetic resonance spectroscopy. RD3 comprises a unique translational topology of two homologous type III AFP globular domains, each containing one flat, ice binding plane. The ice binding plane of the N domain is located approximately 3.5 A "behind" that of the C domain. The two ice binding planes are located laterally with an angle of 32 +/- 12 degrees between the planes. These results suggest that the C domain plane of RD3 binds first to the ice [1010] prism plane in the <0001> direction, which induces successive ice binding of the N domain in the <0101> direction. This manner of ice binding caused by the unique structural topology of RD3 is thought to be crucial for the significant enhancement of antifreeze activity, especially at low AFP concentrations. (+info)
Aerobic endospore-forming bacteria from geothermal environments in northern Victoria Land, Antarctica, and Candlemas Island, South Sandwich archipelago, with the proposal of Bacillus fumarioli sp. nov.
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Aerobic endospore-forming bacteria were isolated from soils taken from active fumaroles on Mount Rittmann and Mount Melbourne in northern Victoria Land, Antarctica, and from active and inactive fumaroles on Candlemas Island, South Sandwich archipelago. The Mt Rittmann and Mt Melbourne soils yielded a dominant, moderately thermophilic and acidophilic, aerobic endospore-former growing at pH 5.5 and 50 degrees C, and further strains of the same organism were isolated from a cold, dead fumarole at Clinker Gulch, Candlemas Island. Amplified rDNA restriction analysis, SDS-PAGE and routine phenotypic tests show that the Candlemas Island isolates are not distinguishable from the Mt Rittmann strains, although the two sites are 5600 km apart, and 16S rDNA sequence comparisons and DNA relatedness data support the proposal of a new species, Bacillus fumarioli, the type strain of which is LMG 17489T. (+info)
Description of Cellulophaga algicola sp. nov., isolated from the surfaces of Antarctic algae, and reclassification of Cytophaga uliginosa (ZoBell and Upham 1944) Reichenbach 1989 as Cellulophaga uliginosa comb. nov.
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A group of strains with potent extracellular enzymic activity were isolated from the surfaces of the chain-forming sea-ice diatom Melosira and from an unidentified macrophyte collected from the Eastern Antarctic coastal zone. 16S rDNA sequence analysis indicated that the strains belonged to the genus Cellulophaga and showed greatest similarity to the species Cellulophaga baltica (sequence similarity 97%). Phenotypic characteristics, DNA base composition and DNA-DNA hybridization values clearly separate the Antarctic strains from Cellulophaga baltica and other Cellulophaga species. Thus, the strains form a distinct and novel species and have the proposed name Cellulophaga algicola sp. nov. (type strain IC166T = ACAM 630T). In addition, it was recognized that the species Cytophaga uliginosa (ZoBell and Upham 1944) Reichenbach 1989, a species phylogenetically remote from the type species of the genus Cytophaga, possessed 16S rDNA sequences and phenotypic and chemotaxonomic traits similar to those of other Cellulophaga species. Thus, it was proposed that the species Cytophaga uliginosa be renamed as Cellulophaga uliginosa comb. nov. (+info)
Psychrophilic enzymes: revisiting the thermodynamic parameters of activation may explain local flexibility.
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Basic theoretical and practical aspects of activation parameters are briefly reviewed in the context of cold-adaptation. In order to reduce the error impact inherent to the transition state theory on the absolute values of the free energy (DeltaG(#)), enthalpy (DeltaH(#)) and entropy (DeltaS(#)) of activation, it is proposed to compare the variation of these parameters between psychrophilic and mesophilic enzymes, namely Delta(DeltaG(#))(p-m), Delta(DeltaH(#))(p-m) and Delta(DeltaS(#))(p-m). Calculation of these parameters from the available literature shows that the main adaptation of psychrophilic enzymes lies in a significant decrease of DeltaH(#), therefore leading to a higher k(cat), especially at low temperatures. Moreover, in all cases including cold-blooded animals, DeltaS(#) exerts an opposite and negative effect on the gain in k(cat). It is argued that the magnitude of this counter-effect of DeltaS(#) can be reduced by keeping some stable domains, while increasing the flexibility of the structures required to improve catalysis at low temperature, as demonstrated in several cold-active enzymes. This enthalpic-entropic balance provides a new approach explaining the two types of conformational stability detected by recent microcalorimetric experiments on psychrophilic enzymes. (+info)
L-Glutamate dehydrogenase from the antarctic fish Chaenocephalus aceratus. Primary structure, function and thermodynamic characterisation: relationship with cold adaptation.
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In order to study the molecular mechanisms of enzyme cold adaptation, direct amino acid sequence, catalytic features, thermal stability and thermodynamics of the reaction and of heat inactivation of L-glutamate dehydrogenase (GDH) from the liver of the Antarctic fish Chaenocephalus aceratus (suborder Notothenioidei, family Channichthyidae) were investigated. The enzyme shows dual coenzyme specificity, is inhibited by GTP and the forward reaction is activated by ADP and ATP. The complete primary structure of C. aceratus GDH has been established; it is the first amino acid sequence of a fish GDH to be described. In comparison with homologous mesophilic enzymes, the amino acid substitutions suggest a less compact molecular structure with a reduced number of salt bridges. Functional characterisation indicates efficient compensation of Q(10), achieved by increased k(cat) and modulation of S(0.5), which produce a catalytic efficiency at low temperature very similar to that of bovine GDH at its physiological temperature. The structural and functional characteristics are indicative of a high extent of protein flexibility. This property seems to find correspondence in the heat inactivation of Antarctic and bovine enzymes, which are inactivated at very similar temperature, but with different thermodynamics. (+info)
One year in Antarctica: mucosal immunity at three Australian stations.
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The effect of a year's isolation in Antarctica on the human mucosal immune system was assessed during the winter of 1992 at three Australian Antarctic stations: Casey, Davis and Mawson. Saliva samples were collected from each expeditioner prior to their departure from Australia and during each month in Antarctica. The concentrations of salivary immunoglobulins IgA and IgG were significantly different between the three stations, but there were no differences for salivary IgM and albumin. The mean concentrations of IgA were higher at Mawson (P < 0.008), and the mean concentrations of IgG were lower at Davis (P < 0.001) compared with the other stations. Ranges of values observed at the stations over the 12-13 months were similar. The variability of values within individuals showed station differences for salivary IgM and IgG only. The study revealed significant changes in salivary immunoglobulin values over the period in Antarctica, with similar patterns at the three Australian stations. The salivary IgA and IgM levels were lower in the first 4 months in Antarctica (January-April) and increased to maximum values in July-August, before returning to mean levels when isolation was broken in October-November. The patterns of salivary IgA and IgM suggest that stressors due to isolation may play a role in alterations of mucosal immunity in expeditioners in Antarctica. (+info)
Salmonella in sub-Antarctica: low heterogeneity in Salmonella serotypes in South Georgian seals and birds.
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The number of human visitors to Antarctica is increasing rapidly, and with it a risk of introducing infectious organisms to native animals. To study the occurrence of salmonella serotypes in sub-Antarctic wildlife, faecal samples were collected from gentoo penguins, macaroni penguins, gray-headed albatrosses, black-browed albatrosses and Antarctic fur seals on Bird Island in the South Georgian archipelago during the austral summer of 1996 and 1998. In 1996, S. havana, S. typhimurium and S. enteritidis were isolated from 7% of gentoo penguins and 4% of fur seals. In 1998, however, 22% of fur seals were found to be infected with S. havana, S. enteritidis and S. newport. All isolates, except one, showed identical pulsed-field gel electrophoresis-patterns within each serotype, irrespective of sampling year and animal reservoir. No significant antibiotic resistance was found. The very low heterogeneity in the salmonella isolates found could either indicate a high genetic adaptation of the bacteria to the environment or a recent introduction of salmonella into the area. (+info)