Antarctic Dry Valley mineral soils contain unexpectedly high levels of microbial biomass

We have applied bioluminescent ATP detection methods to microbial enumeration in Antarctic Dry Valley mineral soils, and validated our ATP data by two independent methods. We have demonstrated that ATP measurement is a valid means of determining microbial biomass in such sites, and that the desiccated surface mineral soils of the Antarctic Dry Valleys contain cell numbers over four orders of magnitude higher than previously suggested.     

Occurrence and preservation of ATP in Antarctic rocks and its implications in biomass determinations

The low temperature and moisture availability in Antarctic rocks would seem to preclude the existence of any sizeable algal biomass. The very high levels of ATP associated with endplithic algal communities have led to speculation that the measured ATP largely represents accumulated exogenous material as well as living biomass. A method was developed to selectively hydrolyze free, extracellular ATP without affecting intracellular ATP. Use of this technique on Antarctic rock samples has led to the conclusion that the ATP found in endolithic communities exclusively reflects living material and not preserved, free ATP.

From these measurements we concluded that the ATP biomass in a gram of rock is equivalent to that found in more temperate and favorable environments.     

Aromatic hydrocarbon-degrading bacteria from soil near Scott Base, Antarctica

Hydrocarbons persist in Antarctic soils when fuel oils such as JP8 jet fuel are spilled. For clean-up of hydrocarbon-contaminated soils in Antarctica, bioremediation has been proposed using hydrocarbon-degrading microbes indigenous to Antarctic soils. A number of alkane-degrading bacteria have been isolated previously from Antarctic soils. In this paper we describe the direct isolation of aromatic hydrocarbon-degrading bacteria from oil-contaminated Antarctic soil. Isolates that grew on JP8 jet fuel were characterised for their ability to degrade aromatic and aliphatic hydrocarbons and for growth at a range of temperatures. All isolates were gram-negative, oxidase-positive, rod-shaped bacteria. Representative strains were identified using 16S rDNA sequence analysis as either Sphingomonas spp. or Pseudomonas spp. Aromatic-degrading bacteria from Antarctic soils were psychrotolerant and appear similar to those found worldwide. Accepted: 27 September 1999     

Bacterial Diversity in Three Different Antarctic Cold Desert Mineral Soils

A bacterial phylogenetic survey of three environmentally distinct Antarctic Dry Valley soil biotopes showed a high proportion of so-called “uncultured” phylotypes, with a relatively low diversity of identifiable phylotypes. Cyanobacterial phylotypic signals were restricted to the high-altitude sample, whereas many of the identifiable phylotypes, such as the members of the Actinobacteria, were found at all sample sites. Although the presence of Cyanobacteria and Actinobacteria is consistent with previous culture-dependent studies of microbial diversity in Antarctic Dry Valley mineral soils, many phylotypes identified by 16S rDNA analysis were of groups that have not hitherto been cultured from Antarctic soils. The general belief that such “extreme” environments harbor a relatively low species diversity was supported by the calculation of diversity indices. The detection of a substantial number of uncultured bacterial phylotypes showing low BLAST identities (<95%) suggests that Antarctic Dry Valley mineral soils harbor a pool of novel psychrotrophic taxa.     

Comparing temperature sensitivity of bacterial growth in Antarctic marine water and soil

The western Antarctic Peninsula is an extreme low temperature environment that is warming rapidly due to global change. Little is known, however, on the temperature sensitivity of growth of microbial communities in Antarctic soils and in the surrounding oceanic waters. This is the first study that directly compares temperature adaptation of adjacent marine and terrestrial bacteria in a polar environment. The bacterial communities in the ocean were adapted to lower temperatures than those from nearby soil, with cardinal temperatures for growth in the ocean being the lowest so far reported for microbial communities. This was reflected in lower minimum (T_min) and optimum temperatures (T_opt) for growth in water (?17 and +20°C, respectively) than in soil (?11 and +27°C), with lower sensitivity to changes in temperature (Q₁₀; 0–10°C interval) in Antarctic water (2.7) than in soil (3.9). This is likely due to the more stable low temperature conditions of Antarctic waters than soils, and the fact that maximum in situ temperatures in water are lower than in soils, at least in summer. Importantly, the thermally stable environment of Antarctic marine water makes it feasible to create a single temperature response curve for bacterial communities. This would thus allow for calculations of temperature‐corrected growth rates, and thereby quantifying the influence of factors other than temperature on observed growth rates, as well as predicting the effects of future temperature increases on Antarctic marine bacteria.     

Effects of nutritional input and diesel contamination on soil enzyme activities and microbial communities in antarctic soils

Pollution of Antarctic soils may be attributable to increased nutritional input and diesel contamination via anthropogenic activities. To investigate the effect of these environmental changes on the Antarctic terrestrial ecosystem, soil enzyme activities and microbial communities in 3 types of Antarctic soils were evaluated. The activities of alkaline phosphomonoesterase and dehydrogenase were dramatically increased, whereas the activities of β-glucosidase, urease, arylsulfatase, and fluorescein diacetate hydrolysis were negligible. Alkaline phosphomonoesterase and dehydrogenase activities in the 3 types of soils increased 3- to 10-fold in response to nutritional input, but did not increase in the presence of diesel contamination. Consistent with the enzymatic activity data, increased copy numbers of the phoA gene, encoding an alkaline phosphomonoesterase, and the 16S rRNA gene were verified using quantitative real-time polymerase chain reaction. Interestingly, dehydrogenase activity and 16S rRNA gene copy number increased slightly after 30 days, even under diesel contamination, probably because of adaptation of the bacterial population. Intact Antarctic soils showed a predominance of Actinobacteria phylum (mostly Pseudonorcarida species) and other phyla such as Proteobacteria, Chloroflexi, Planctomycetes, Firmicutes, and Verrucomicrobia were present in successively lower proportions. Nutrient addition might act as a selective pressure on the bacterial community, resulting in the prevalence of Actinobacteria phylum (mostly Arthrobacter species). Soils contaminated by diesel showed a predominance of Proteobacteria phylum (mostly Phyllobacterium species), and other phyla such as Actinobacteria, Bacteroidetes, Planctomycetes, and Gemmatimonadetes were present in successively lower proportions. Our data reveal that nutritional input has a dramatic impact on bacterial communities in Antarctic soils and that diesel contamination is likely toxic to enzymes in this population.     

The environmental physiology of Antarctic terrestrial nematodes: a review

The environmental physiology of terrestrial Antarctic nematodes is reviewed with an emphasis on their cold-tolerance strategies. These nematodes are living in one of the most extreme environments on Earth and face a variety of stresses, including low temperatures and desiccation. Their diversity is low and declines with latitude. They show resistance adaptation, surviving freezing and desiccation in a dormant state but reproducing when conditions are favourable. At high freezing rates in the surrounding medium the Antarctic nematode Panagrolaimus davidi freezes by inoculative freezing but can survive intracellular freezing. At slow freezing rates this nematode does not freeze but undergoes cryoprotective dehydration. Cold tolerance may be aided by rapid freezing, the production of trehalose and by an ice-active protein that inhibits recrystallisation. P. davidi relies on slow rates of water loss from its habitat, and can survive in a state of anhydrobiosis, perhaps aided by the ability to synthesise trehalose. Teratocephalus tilbrooki and Ditylenchus parcevivens are fast-dehydration strategists. Little is known of the osmoregulatory mechanisms of Antarctic nematodes. Freezing rates are likely to vary with water content in Antarctic soils. Saturated soils may produce slow freezing rates and favour cryoprotective dehydration. As the soil dries freezing rates may become faster, favouring freezing tolerance. When the soil dries completely the nematodes survive anhydrobiotically. Terrestrial Antarctic nematodes thus have a variety of strategies that ensure their survival in a harsh and variable environment. We need to more fully understand the conditions to which they are exposed in Antarctic soils and to apply more natural rates of freezing and desiccation to our studies.Communicated by: I.D. Hume     

Problems of Pollen Zone Correlation in Southeastern Canada

A brief account is given documenting the development of aerobiological research in the Antarctic. The results of the British Antarctic Survey's contribution to an international programme on long-distance dispersal of aeroplankton over the Southern Ocean are presented. This was achieved by collecting airspora deposited in Tauber traps and in surface snow at sites on South Georgia (sub-Antarctic) and Signy Island (maritime Antarctic). Although only a small number of the samples were analysed, the results provided ample evidence of a continuous immigration of exotic sporomorpha of southern South American provenance. The cause of this rain of biological material is attributed to the not infrequent easterly tracking storm events generated over the south-east Pacific Ocean. As they gain momentum over southern South America they become seeded with pollen and spores, and possibly by larger organelles such as invertebrates and seeds. These high winds may be deflected southwards by a blocking anticyclone over the South Atlantic Ocean, allowing a proportion of the sporomorpha to be deposited over land far to the south. The occurrence of such exotic sporomorpha in these remote and environmentally hostile regions is used here as evidence to support the hypothesis that there is a continuous input into the Antarctic biome of viable propagules from more northerly landmasses. While no exotic bryophyte or lichen spores have yet been detected in trapping experiments, the extremely rare occurrence of certain bryophytes associated only with geothermal sites in the Antarctic and in laboratory-cultured soils from barren ice-free terrain indicates that a pool of viable but dormant propagules is probably widespread in Antarctic soils and ice. However, germination and development in situ are possible only under exceptional environmental circumstances. An international programme is being planned to detect the main trajectories of long-distance transport of propagules into the Antarctic and to test their viability.     

Hexose metabolism in pancreatic islets: preferential utilization of mitochondrial ATP for glucose phosphorylation

The respective contribution of exogenous and intramitochondrially formed ATP to D-glucose phosphorylation by mitochondria-bound hexokinase was examined in both rat liver and pancreatic islet mitochondria by comparing the generation of D-glucose 6-[32P]phosphate from exogenous [gamma-32P]ATP to the total rate of D-[U-14C]glucose phosphorylation. In liver mitochondria, the fractional contribution of exogenous ATP to D-glucose phosphorylation ranged from 4 to 74%, depending on the availability of endogenous ATP formed by either oxidative phosphorylation or in the reaction catalyzed by adenylate kinase. Likewise, in islet mitochondria exposed to exogenous ATP but deprived of exogenous nutrient, about 60% of D-glucose phosphorylation was supported by mitochondrial ATP. Such a fractional contribution was further increased in the presence of ADP and succinate, and suppressed by mitochondrial poisons. It is concluded that, in islet like in liver mitochondria, mitochondrial ATP is used preferentially to exogenous ATP as a substrate for D-glucose phosphorylation by mitochondria-bound hexokinase. This may favour the maintenance of a high cytosolic ATP concentration in glucose-stimulated islet cells.     

Soil properties of an Antarctic inland site: implications for ecosystem development

Inland Antarctic nunataks typically have simple physically weathered soils and limited ecosystem complexity. In this paper we present quantitative measurements of soil physical and chemical properties at one Antarctic nunatak. We measured pH, grain size, field capacity, soil organic carbon, phosphate, nitrate, ammonium and the cations magnesium, calcium and potassium along two transects. The data obtained indicated that very low levels of nutrients were present/available to biota, and that liquid water was absent, at least from the surface depths of soil, except during periods of active snow melt. Consequently, biological activity is severely limited. We conclude that, due to the climatic and microclimatic conditions at this location, the development of biological communities and soils is maintained in an extremely simple but still apparently stable ‘quasi climax’ state. Increased soil development and biological complexity can be expected if the contemporary rapid regional warming in the Antarctic Peninsula region continues.     

Exogenous ATP induces electrical membrane responses in fibroblasts

Mouse fibroblastic L cells responded to exogenous ATP (0.2 mM) with a transient hyperpolarization due to increased membrane permeability to K⁺. By contrast, intracellular injection of ATP (up to about 3 mM) produced no noticeable effects on the membrane potential. The effects of a non-hydrolysable analogue of ATP (AMP-PNP) were similar to those of ATP. After successive applications of ATP, the cell membrane became virtually unresponsive (desensitized). Extracellular ADP was also effective, but AMP or adenosine was not. Antazoline suppressed the ATP response. Thus, exogenous ATP and ADP appear to stimulate P₂-purinoceptors. Similar responses to ATP (or ADP) were also observed in human normal diploid fibroblasts (Flow 1000 line).     

Free-Living Heterotrophic Nitrogen-Fixing Bacteria Isolated from Fuel-Contaminated Antarctic Soils

Five bacterial isolates enriched from fuel-contaminated Antarctic soils fixed nitrogen in the dark heterotrophically and nonsymbiotically. Two isolates utilized jet fuel vapors and volatile hydrocarbons for growth but not in N-deficient medium. Bacteria such as these may contribute to in situ biodegradation of hydrocarbons in Antarctic soils.     

Free-living heterotrophic nitrogen-fixing bacteria isolated from fuel-contaminated antarctic soils

Five bacterial isolates enriched from fuel-contaminated Antarctic soils fixed nitrogen in the dark heterotrophically and nonsymbiotically. Two isolates utilized jet fuel vapors and volatile hydrocarbons for growth but not in N-deficient medium. Bacteria such as these may contribute to in situ biodegradation of hydrocarbons in Antarctic soils.     

Molecular Analysis of Geographic Patterns of Eukaryotic Diversity in Antarctic Soils

We describe the application of molecular biological techniques to estimate eukaryotic diversity (primarily fungi, algae, and protists) in Antarctic soils across a latitudinal and environmental gradient between approximately 60 and 87°S. The data were used to (i) test the hypothesis that diversity would decrease with increasing southerly latitude and environmental severity, as is generally claimed for “higher” faunal and plant groups, and (ii) investigate the level of endemicity displayed in different taxonomic groups. Only limited support was obtained for a systematic decrease in diversity with latitude, and then only at the level of a gross comparison between maritime (Antarctic Peninsula/Scotia Arc) and continental Antarctic sites. While the most southerly continental Antarctic site was three to four times less diverse than all maritime sites, there was no evidence for a trend of decreasing diversity across the entire range of the maritime Antarctic (60 to 72°S). Rather, we found the reverse pattern, with highest diversity at sites on Alexander Island (ca. 72°S), at the southern limit of the maritime Antarctic. The very limited overlap found between the eukaryotic biota of the different study sites, combined with their generally low relatedness to existing sequence databases, indicates a high level of Antarctic site isolation and possibly endemicity, a pattern not consistent with similar studies on other continents.     

Phenanthrene Biodegradation in Soils Using an Antarctic Bacterial Consortium

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in Antarctic soils is limited by low temperatures, lack of adequate levels of nutrients, low number of PAH-tolerant members in the autochthonous microbiota and low bioavailability of contaminants. In the present work, microcosms systems (performed in 1-L glass flasks containing Antarctic soil supplemented with 1744 ppm of phenanthrene) were used to study (i) the effect of biostimulation with a complex organic source of nutrients (fish meal) combined with a surfactant (Brij 700); (ii) the effect of bioaugmentation with a psychrotolerant PAH-degrading bacterial consortium (M10); (iii) the effect of the combination of both strategies. The authors found that combination of biostimulation and bioaugmentation caused a significant removal (46.6%) of phenanthrene after 56 days under Antarctic environmental conditions. When bioaugmentation or biostimulation were applied separately, nonsignificant reduction in phenanthrene concentration was observed. Microtox test showed a low increase in toxicity only in the most efficient system. Results proved that “in situ” bioremediation process of phenanthrene-contaminated soils is possible in Antarctic stations. In addition, inoculation with a psychrotolerant PAH-degrading bacterial consortium in association with a mix of fish meal and a high-molecular-weight surfactant improved phenanthrene removal and should be the selected strategy when the number of hydrocarbons degrading bacteria in the target soil is low.     

ATP potently modulates anion channel-mediated excitatory amino acid release from cultured astrocytes

Volume-dependent ATP release andsubsequent activation of purinergic P2Y receptors have been implicatedas an autocrine mechanism triggering activation of volume-regulatedanion channels (VRACs) in hepatoma cells. In the brain ATP is releasedby both neurons and astrocytes and participates in intercellularcommunication. We explored whether ATP triggers or modulates therelease of excitatory amino acid (EAAs) via VRACs in astrocytes inprimary culture. Under basal conditions exogenous ATP (10 µM)activated a small EAA release in 70-80% of the cultures tested.In both moderately (5% reduction of medium osmolarity) andsubstantially (35% reduction of medium osmolarity) swollen astrocytes,exogenous ATP greatly potentiated EAA release. The effects of ATP weremimicked by P2Y agonists and eliminated by P2Y antagonists or the ATPscavenger apyrase. In contrast, the same pharmacological maneuvers didnot inhibit volume-dependent EAA release in the absence of exogenous ATP, ruling out a requirement of autocrine ATP release for VRAC activation. The ATP effect in nonswollen and moderately swollen cellswas eliminated by a 5-10% increase in medium osmolarity or byanion channel blockers but was insensitive to tetanus toxin pretreatment, further supporting VRAC involvement. Our data suggest that in astrocytes ATP does not trigger EAA release itself but actssynergistically with cell swelling. Moderate cell swelling and ATP mayserve as two cooperative signals in bidirectional neuron-astrocytecommunication in vivo.

     

Radioprotective properties of ATP and modification of acid phosphatase response after a lethal dose of whole body p(66MeV)/Be neutron radiation to BALB/c mice.

The intraperitoneal administration of exogenous ATP prior to a lethal dose (7 Gy) of whole body neutron irradiation increased the radioresistance of BALB/c mice. This radiation used the beam from a neutron therapy facility produced by the reaction p(66 MeV)/Be. Survival of the mice, determined 7 days post-irradiation as the endpoint, was increased from 26% to 86% by the action of the exogenous ATP. Furthermore, the response of acid phosphatase activity as an indicator of the acute radiation effects showed a marked augmentation in both tissues studied, testes and small intestine. The activity of the enzyme after neutron irradiation with prior administration of ATP showed smaller increases when compared with the increases observed after neutron irradiation alone. This implies that exogenous ATP reduces the effect of the lytic enzyme and, hence, damage. Finally, changes were observed in the activity of acid phosphatase in the testes and intestine with different concentrations of exogenous ATP. In both tissues there was a monotonic decrease in the activity of the enzyme with increase of the concentration of exogenous ATP administrated before radiation. These results reflect the protective ability of exogenous ATP as an adaptive defence mechanism to reduce radiation damage in normal tissues after a lethal dose of neutron radiation.     

Photosynthesis‐based microbial communities on two churches in northern Germany: Weathering of granite and glazed brick

Microbial communities on two churches in Schleswig‐Holstein (northern Germany) were characterized using cultural methods as well as light and scanning electron microscopy. Dilution‐plate counts of fungi [10⁶/g dry weight (gdw) stone] and heterotrophic bacteria (10⁵/gdw) were as high as those reported for soils. Counts of algae (10⁶/gdw) were somewhat higher than those for soils. Biomass expressed as phospholipid phosphate concentration (PLP; 115–137 nmol PLP/gdw) was nearly 10 times that of Antarctic sandstone, at least twice that in an architectural red sandstone, and approached that found in soils. Amounts of chlorophyll a were higher than those for the Antarctic sandstone (known to contain algae and cyanobacteria) and were at the lower end of the range reported for soils. The high biomass is supported by photosynthetic carbon input, and hypotheses are presented that describe the role of these epi‐ and endolithic communities in the weathering of their substrata.     

Effect of glucose on ATP dephosphorylation in rat spermatids

Round spermatids were isolated from rat testes and the effects of different energy-yielding substrates on the cellular ATP content were estimated. The ATP content was constant and high (6-8 nmol/10(6) cells) during metabolism of exogenous lactate. During incubation for 30 min in the absence of exogenous lactate, there was a remarkably slow decline of the ATP content, indicating ATP production from other substrates. It was shown that this could reflect beta-oxidation of fatty acids, but not the mobilization of an endogenous pool of acetylcarnitine. Glucose metabolism in the absence of exogenous lactate resulted in a rapid decline of the ATP content. This effect of glucose was correlated with a high fructose 1,6-biphosphate content (6-7 nmol/10(6) cells) and could be prevented by the addition of lactate. It is suggested that metabolism of glucose (and also mannose and fructose, but not galactose) in the absence of exogenous lactate can result in ATP dephosphorylation.     

A high-activity ATP translocator in mesophyll chloroplasts of Digitaria sanguinalis, a plant having the C-4 dicarboxylic acid pathway of photosynthesis

The effect of exogenous adenine nucleotides on CO₂ fixation and oxygen evolution was studied with mesophyll protoplast extracts of the C₄ plant Digitaria sanguinalis. Exogenous ATP was found to stimulate the rate of pyruvate and pyruvate + oxalacetate induced CO₂ fixation, as well as reverse the inhibition of CO₂ fixation by carbonyl cyanide m-chlorophenyl hydrazone and several electron transport inhibitors. The ATP-dependent stimulation of CO₂ fixation varied from 40 to 70 μmol CO₂ fixed/mg chlorophyll per h, suggesting that ATP was crossing the chloroplast membranes at rates of 80–140 μmol/mg chlorophyll per h, since 2 ATP are required for each CO₂ fixed. Fixation of CO₂ could also be induced in the dark by exogenous ATP, in which case ADP accumulated outside the chloroplasts. This suggests that external ATP is exchanging for internal ADP. In contrast, ADP and AMP were found not to traverse chloroplast membranes, on the basis that neither nucleotide inhibited CO₂ fixation or stimulated oxygen evolution that was limited by available ADP for phosphorylation. Further evidence that ATP can enter the chloroplasts was obtained by direct measurements of the increase in ATP in the chloroplasts due to addition of exogenous ATP in the dark. These studies yielded minimal rates of ATP uptake on the order of 30–40 μmol/mg chlorophyll per h. It is suggested that a membrane translocator exists that specifically transports ATP into the chloroplasts in exchange for ADP. The significance of these findings are considered with respect to the C₄ pathway of photosynthesis.