Cold-Active Chemoorganotrophic Bacteria from Permanently Ice-Covered Lake Hoare, McMurdo Dry Valleys, Antarctica

Eight strains of chemoorganotrophic bacteria were isolated from the water column of Lake Hoare, McMurdo Dry Valleys, Antarctica, using cold enrichment temperatures. The isolates were Alpha-, Beta-, and Gammaproteobacteria and Actinobacteria spp. All isolates grew at 0°C, and all but one grew at subzero temperatures characteristic of the water column of Lake Hoare. Growth temperature optima varied among isolates, but the majority showed optima near 15°C, indicative of cold-active phenotypes. One isolate was truly psychrophilic, growing optimally around 10°C and not above 20°C. Half of the isolates grew at 2% salt while the other half did not, and all but one isolate grew at 2 atm of O₂. Our isolates are the first prokaryotes from the water column of Lake Hoare to be characterized phylogenetically and physiologically and show that cold-active species of at least two major phyla of Bacteria inhabit Lake Hoare.     

Cold-active chemoorganotrophic bacteria from permanently ice-covered Lake Hoare, McMurdo Dry Valleys, Antarctica

Eight strains of chemoorganotrophic bacteria were isolated from the water column of Lake Hoare, McMurdo Dry Valleys, Antarctica, using cold enrichment temperatures. The isolates were Alpha-, Beta-, and Gammaproteobacteria and Actinobacteria spp. All isolates grew at 0 degrees C, and all but one grew at subzero temperatures characteristic of the water column of Lake Hoare. Growth temperature optima varied among isolates, but the majority showed optima near 15 degrees C, indicative of cold-active phenotypes. One isolate was truly psychrophilic, growing optimally around 10 degrees C and not above 20 degrees C. Half of the isolates grew at 2% salt while the other half did not, and all but one isolate grew at 2 atm of O(2). Our isolates are the first prokaryotes from the water column of Lake Hoare to be characterized phylogenetically and physiologically and show that cold-active species of at least two major phyla of Bacteria inhabit Lake Hoare.     

Stromatolite records of environmental change in perennially ice-covered Lake Joyce,McMurdo Dry Valleys,Antarctica

Calcite-rich columnar stromatolites grew in perennially ice-covered Lake Joyce in the McMurdo Dry Valleys, Antarctica, during a period of environmental change associated with rising lake level. Stromatolite calcite contains carbon and oxygen isotope records of changes to microbial activity in response to variable light environments and water chemistry through time. The stromatolites grew synchronously with correlative calcite zones. The innermost (oldest) calcite zone has a wide range of δ¹³C_calcite values consistent with variable photosynthetic effects on local DIC ¹³C/¹²C. Subsequent calcite zones preserve a progressive enrichment in δ¹³C_calcite values of approximately + 2.6‰ through time, with δ¹³C_calcite values becoming less variable. This enrichment likely records the removal of ¹²C by photosynthesis from the DIC reservoir over decades, with photosynthetic effects decreasing as light levels became lower and more consistent through time. Mean δ¹⁸O_calcite values of the innermost calcified zone were at least 1‰ lower than those of the other calcified zones (t test p-level < 0.001). The significant difference in δ¹⁸O_calcite values between the innermost and other calcified zones could be a product of mixing source waters with different isotopic values associated with the initiation of lake stratification associated with rising lake level. Overall, Lake Joyce stromatolites record significant lateral variability in relative photosynthetic rate and long-lived lake water stratification with microbial modification of the DIC pool. Such processes provide criteria for interpreting microbial activity within polar paleolake deposits and may shed light on variability in lake environments associated with changing climate in the McMurdo Dry Valleys.     

Bacterial and Archaeal Diversity in Sediments of West Lake Bonney,McMurdo Dry Valleys,Antarctica

Bacterial and archaeal diversity was examined in a sediment core from Lake Bonney, Antarctica. Members of the Archaea showed both low abundance and diversity, whereas bacterial diversity was moderately high and some phyla were fairly abundant, even in geologically old samples. Microbial diversity correlated with sample texture and differed in silty and coarse samples.     

Wind dispersal of soil invertebrates in the McMurdo Dry Valleys, Antarctica

Dispersal of soil organisms is crucial for their spatial distribution and adaptation to the prevailing conditions of the Antarctic Dry Valleys. This study investigated the possibility of wind dispersal of soil invertebrates within the dry valleys. Soil invertebrates were evaluated in (1) pockets of transported sediments to lake ice and glacier surfaces, (2) wind-transported dust particles in collection pans (Bundt pans) 100 cm above the soil surface, and (3) sediments transported closer to the surface (<50 cm) and collected in open top chambers (OTCs). Invertebrates were extracted and identified. Nematodes were identified to species and classified according to life stage and sex. Three species of nematodes were recovered and Scottnema lindsayae was the most dominant. There were more juveniles (∼71%) in the transported sediments than adults (29%). Tardigrades and rotifers were more abundant in sediments on lake and glacier surfaces while nematodes were more abundant in the dry sediment collections of Bundt pans and OTCs. The abundance of immobile (dead) nematodes in the Bundt pans and OTCs was three times greater than active (live) nematodes. Anhydrobiosis constitutes a survival mechanism that allows wind dispersal of nematodes in the McMurdo Dry Valleys. Our results show that soil invertebrates are dispersed by wind in the Dry Valleys and are viable in ice communities on lake surfaces and glaciers.     

Microbial diversity of cryptoendolithic communities from the McMurdo Dry Valleys,Antarctica

In the McMurdo Dry Valleys of Antarctica, microorganisms colonize the pore spaces of exposed rocks and are thereby protected from the desiccating environmental conditions on the surface. These cryptoendolithic communities have received attention in microscopy and culture-based studies but have not been examined by molecular approaches. We surveyed the microbial biodiversity of selected cryptoendolithic communities by analyzing clone libraries of rRNA genes amplified from environmental DNA. Over 1,100 individual clones from two types of cryptoendolithic communities, cyanobacterium dominated and lichen dominated, were analyzed. Clones fell into 51 relatedness groups (phylotypes) with > or =98% rRNA sequence identity (46 bacterial and 5 eucaryal). No representatives of Archaea were detected. No phylotypes were shared between the two classes of endolithic communities studied. Clone libraries based on both types of communities were dominated by a relatively small number of phylotypes that, because of their relative abundance, presumably represent the main primary producers in these communities. In the lichen-dominated community, three rRNA sequences, from a fungus, a green alga, and a chloroplast, of the types known to be associated with lichens, accounted for over 70% of the clones. This high abundance confirms the dominance of lichens in this community. In contrast, analysis of the supposedly cyanobacterium-dominated community indicated, in addition to cyanobacteria, at least two unsuspected organisms that, because of their abundance, may play important roles in the community. These included a member of the alpha subdivision of the Proteobacteria that potentially is capable of aerobic anoxygenic photosynthesis and a distant relative of Deinococcus that defines, along with other Deinococcus-related sequences from Antarctica, a new clade within the Thermus-Deinococcus bacterial phylogenetic division.     

Diversity and distribution of sulfate-reducing bacteria in permanently frozen Lake Fryxell, McMurdo Dry Valleys, Antarctica

The permanently frozen freshwater Lake Fryxell, located in the Dry Valleys of Antarctica, exhibits an ideal geochemistry for microbial sulfate reduction. To investigate the population of sulfate-reducing bacteria in Lake Fryxell, both 16S rRNA gene and metabolic primer sets targeting the dsrA gene for the dissimilatory sulfite reductase alpha subunit were employed to analyze environmental DNA obtained from the water column and sediments of Lake Fryxell. In addition, enrichment cultures of sulfate-reducing bacteria established at 4 degrees C from Lake Fryxell water were also screened using the dsrA primer set. The sequence information obtained showed that a diverse group of sulfate-reducing prokaryotes of the domain Bacteria inhabit Lake Fryxell. With one exception, the enrichment culture sequences were not represented within the environmental sequences. Sequence data were compared with the geochemical profile of Lake Fryxell to identify possible connections between the diversity of sulfate-reducing bacteria and limnological conditions. Several clone groups were highly localized with respect to lake depth and, therefore, experienced specific physiochemical conditions. However, all sulfate-reducing bacteria inhabiting Lake Fryxell must function under the constantly cold conditions characteristic of this extreme environment.     

Diversity and Distribution of Sulfate-Reducing Bacteria in Permanently Frozen Lake Fryxell, McMurdo Dry Valleys, Antarctica

The permanently frozen freshwater Lake Fryxell, located in the Dry Valleys of Antarctica, exhibits an ideal geochemistry for microbial sulfate reduction. To investigate the population of sulfate-reducing bacteria in Lake Fryxell, both 16S rRNA gene and metabolic primer sets targeting the dsrA gene for the dissimilatory sulfite reductase alpha subunit were employed to analyze environmental DNA obtained from the water column and sediments of Lake Fryxell. In addition, enrichment cultures of sulfate-reducing bacteria established at 4°C from Lake Fryxell water were also screened using the dsrA primer set. The sequence information obtained showed that a diverse group of sulfate-reducing prokaryotes of the domain Bacteria inhabit Lake Fryxell. With one exception, the enrichment culture sequences were not represented within the environmental sequences. Sequence data were compared with the geochemical profile of Lake Fryxell to identify possible connections between the diversity of sulfate-reducing bacteria and limnological conditions. Several clone groups were highly localized with respect to lake depth and, therefore, experienced specific physiochemical conditions. However, all sulfate-reducing bacteria inhabiting Lake Fryxell must function under the constantly cold conditions characteristic of this extreme environment.     

Airborne Bacterial Populations Above Desert Soils of the McMurdo Dry Valleys,Antarctica

Bacteria are assumed to disperse widely via aerosolized transport due to their small size and resilience. The question of microbial endemicity in isolated populations is directly related to the level of airborne exogenous inputs, yet this has proven hard to identify. The ice-free terrestrial ecosystem of Antarctica, a geographically and climatically isolated continent, was used to interrogate microbial bio-aerosols in relation to the surrounding ecology and climate. High-throughput sequencing of bacterial ribosomal RNA (rRNA) genes was combined with analyses of climate patterns during an austral summer. In general terms, the aerosols were dominated by Firmicutes, whereas surrounding soils supported Actinobacteria-dominated communities. The most abundant taxa were also common to aerosols from other continents, suggesting that a distinct bio-aerosol community is widely dispersed. No evidence for significant marine input to bio-aerosols was found at this maritime valley site, instead local influence was largely from nearby volcanic sources. Back trajectory analysis revealed transport of incoming regional air masses across the Antarctic Plateau, and this is envisaged as a strong selective force. It is postulated that local soil microbial dispersal occurs largely via stochastic mobilization of mineral soil particulates.     

Characterization of Chasmoendolithic Community in Miers Valley,McMurdo Dry Valleys,Antarctica

The Antarctic Dry Valleys are unable to support higher plant and animal life and so microbial communities dominate biotic ecosystem processes. Soil communities are well characterized, but rocky surfaces have also emerged as a significant microbial habitat. Here, we identify extensive colonization of weathered granite on a landscape scale by chasmoendolithic microbial communities. A transect across north-facing and south-facing slopes plus valley floor moraines revealed 30–100 % of available substrate was colonized up to an altitude of 800 m. Communities were assessed at a multidomain level and were clearly distinct from those in surrounding soils and other rock-inhabiting cryptoendolithic and hypolithic communities. All colonized rocks were dominated by the cyanobacterial genus Leptolyngbya (Oscillatoriales), with heterotrophic bacteria, archaea, algae, and fungi also identified. Striking patterns in community distribution were evident with regard to microclimate as determined by aspect. Notably, a shift in cyanobacterial assemblages from Chroococcidiopsis-like phylotypes (Pleurocapsales) on colder–drier slopes, to Synechococcus-like phylotypes (Chroococcales) on warmer–wetter slopes. Greater relative abundance of known desiccation-tolerant bacterial taxa occurred on colder–drier slopes. Archaeal phylotypes indicated halotolerant taxa and also taxa possibly derived from nearby volcanic sources. Among the eukaryotes, the lichen photobiont Trebouxia (Chlorophyta) was ubiquitous, but known lichen-forming fungi were not recovered. Instead, fungal assemblages were dominated by ascomycetous yeasts. We conclude that chasmoendoliths likely constitute a significant geobiological phenomenon at lower elevations in granite-dominated Antarctic Dry Valley systems.     

Cultivable bacteria from ancient algal mats from the McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys in Antarctica are a favorable location for preservation of dormant microbes due to their persistent cold and dry climate. In this study, we examined cultivable bacteria in a series of algal mat samples ranging from 8 to 26539 years old. Cultivable bacteria were found in all samples except one (12303 years old), but abundance and diversity of cultivable bacteria decreased with increasing sample age. Only members of the Actinobacteria, Bacteroidetes, and Firmicutes were found in the ancient samples, whereas bacteria in the 8-year-old sample also included Cyanobacteria, Proteobacteria, and Deinococcus-Thermus. Isolates of the Gram-positive spore-forming bacterium Sporosarcina were found in 5 of 8 samples. The growth of these isolates at different temperatures was related to the phylogenetic distance among genotypes measured by BOX-PCR. These findings suggest that adaptation to growth at different temperatures had occurred among Sporosarcina genotypes in the Dry Valleys, causing the existence of physiologically distinct but closely related genotypes. Additionally, fully psychrophilic isolates (that grew at 15°C, but not 25°C) were found in ancient samples, but not in the modern sample. The preservation of viable bacteria in the Dry Valleys could potentially represent a legacy of bacteria that impacts on current microbial communities of this environment.     

Distribution and diversity of soil protozoa in the McMurdo Dry Valleys of Antarctica

The polar desert soils of the McMurdo Dry Valley region support a limited water film community dominated by flagellates, amoebae, and nematodes. This study describes the protozoa and compares their distribution to nematodes. In 50 samples collected from 12 locations, rotifers and tardigrades were infrequent, and ciliates and testacea were rare. Soil protozoa occurred at all sites but the dominant nematode, Scottnema lindsayae (Timm 1971), did not, indicating soil habitat factors limiting nematode distribution are not limiting to protozoa. In contrast to the nematode species, which are all endemic to Antarctica, there were no endemic protozoan morphospecies found in our samples. The protozoan abundance was several orders of magnitude greater than that of the nematodes, and the species diversity was much greater. Most of the protozoa grew better at lower incubation temperatures. The ubiquitous distribution of protozoa suggests their importance in soil food webs and nutrient cycling in the dry valleys.     

Hypolithic microbial communities of quartz rocks from Miers Valley, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys region of eastern Antarctica is a cold desert that presents extreme challenges to life. Hypolithic microbial colonisation of the subsoil surfaces of translucent quartz rocks represent a significant source of terrestrial biomass and productivity in this region. Previous studies have described hypoliths as dominated by cyanobacteria. However, hypoliths that occur in the lower Dry Valleys such as the Miers, Garwood and Marshall Valleys are unusual as they are not necessarily cyanobacteria-dominated. These hypoliths support significant eukaryal colonisation by fungi and mosses in addition to cyanobacteria-dominated bacterial assemblages and so have considerable ecological value in this barren landscape. Here, we characterise these novel hypoliths by analysis of environmental rRNA gene sequences. The hypolithic community was demonstrated to be distinct from the surrounding soil and non-translucent rocks. Hypoliths supported cyanobacterial signatures from the Oscillatoriales and Nostocales. Other heterotrophic bacterial signatures were also recovered, and these were phylogenetically diverse and spanned 8 other bacterial phyla. Archaeal phylotypes recovered were phylogenetically affiliated with the large group of unclassified, uncultured Crenarcheota. Eukaryal phylotypes indicated that free-living ascomycetous fungi, chlorophytes and mosses (Bryum sp.) were all supported by these hypoliths, and these are thought to be responsible for the extensive eukaryotic biomass that develops around quartz rocks.     

Isolation, Characterization, and Ecology of Cold-Active, Chemolithotrophic, Sulfur-Oxidizing Bacteria from Perennially Ice-Covered Lake Fryxell, Antarctica

Novel strains of obligately chemolithoautotrophic, sulfur-oxidizing bacteria have been isolated from various depths of Lake Fryxell, Antarctica. Physiological, morphological, and phylogenetic analyses showed these strains to be related to mesophilic Thiobacillus species, such as T. thioparus. However, the psychrotolerant Antarctic isolates showed an adaptation to cold temperatures and thus should be active in the nearly freezing waters of the lake. Enumeration by most-probable-number analysis in an oxic, thiosulfate-containing medium revealed that the sulfur-oxidizing chemolithotroph population peaks precisely at the oxycline (9.5 m), although viable cells exist well into the anoxic, sulfidic waters of the lake. The sulfur-oxidizing bacteria described here likely play a key role in the biogeochemical cycling of carbon and sulfur in Lake Fryxell.     

Distribution of organic carbon and nitrogen in surface soils in the McMurdo Dry Valleys, Antarctica

The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding several lakes in the McMurdo Dry Valleys were measured in a relatively high-density sampling grid, in order to better understand the present-day distribution of organic matter in the ecosystem that is most readily transportable via aeolean processes. Carbon and nitrogen contents of the bulk sediments and size-differentiated sediments decreased in a series according to lake basins oriented along the Taylor Valley's main axis (Lake Fryxell > Hoare ≥ west lobe Bonney ≥ east lobe Bonney). Samples were also obtained around Lake Vida and showed this basin to contain less organic matter than those in the Taylor Valley. This regional spatial analysis supports the emerging view that each basin provides distinct environments for in situ microbial activity, lithogenic weathering, aeolian deposition and sorting that can be detected through synoptic sampling. Accepted: 2 August 1999     

16S rDNA diversity of cultured and uncultured prokaryotes of a mat sample from Lake Fryxell, McMurdo Dry Valleys, Antarctica

The prokaryotic diversity of aerobic and anaerobic bacterial isolates and of bacterial and archaeal 16S rDNA clones was determined for a microbial mat sample from the moated region of Lake Fryxell, McMurdo Dry Valleys, Antarctica. Among the anaerobic bacteria, members of Clostridium estertheticum and some other psychrotolerant strains dominated whereas methanogens and other Archaea were lacking. Isolates highly related to Flavobacterium hibernum, Janthiniobacterium lividum, and Arthrobacter flavus were among the aerobic bacteria most frequently isolated. Assessment of more than 350 partial 16S rDNA clone sequences of libraries generated by Bacteria- and Archaea-specific PCR primers revealed a rich spectrum of bacterial diversity but only two different archaeal clone sequences. Among the Bacteria, representative sequences belonged to the class Proteobacteria, order Verrucomicrobiales, class Actinobacteria, Clostridium/Bacillus subphylum of Gram-positives, and the Cytophaga-Flavobacterium-Bacteroides phylum. The clones formed about 70 higher taxonomy groups (<98% sequence similarity) and 133 potential species, i.e., groups of clones sharing greater than 98% similarity. Only rarely were clone sequences found to be highly related to Lake Fryxell isolates and to strains of described species. Subsequent analysis of ten sequencing batches of 36 individual clones indicated that the diversity might be still higher than had been assessed.     

Dilution-to-Extinction Culturing of Psychrotolerant Planktonic Bacteria from Permanently Ice-covered Lakes in the McMurdo Dry Valleys,Antarctica

Lakes in the McMurdo Dry Valleys of Antarctica are characterized by a permanent ice cover and little or no anthropogenic influence. Although bacterial cultures have been obtained from these habitats, recent culture-independent studies indicate that the most abundant microbes in these systems are not yet cultivated. By using dilution-to-extinction cultivation methods with sterilized and nutrient-amended lake water as media, we isolated 148 chemotrophic psychrotolerant bacterial cultures from fresh surface water of Lake Fryxell and the east lobe of Lake Bonney and the hypersaline, suboxic bottom water from the west lobes of Lake Bonney. Screening of the 16S ribosomal ribonucleic acid (rRNA) genes of the cultures by restriction fragment length polymorphism (RFLP) yielded 57 putatively pure psychrotolerant, slow growing cultures grouped into 18 clusters. The sequencing of 16S rRNA genes of randomly selected representatives of each RFLP cluster revealed that the corresponding isolates belong to the Alphaproteobacteria (six RFLP patterns), Betaproteobacteria (six RFLP patterns), Bacteroidetes (four RFLP patterns), and Actinobacteria (two RFLP patterns). Phylogenetic analysis of the sequences showed that the vast majority of the isolates were not closely related to previously described species. Thirteen of 18 RFLP patterns shared a 16S ribosomal deoxyribonucleic acid sequence similarity of 97% or less with the closest described species, and four isolates had a sequence similarity of 93% or less with the nearest described species. Phylogenetic analysis showed that these sequences were representatives of deeply branching organisms in the respective phylum. A comparison of the isolates with 16S rRNA clone libraries prepared from the same environments showed substantial overlap, indicating that dilution-to-extinction culturing in natural lake water media can help isolate some of the most abundant organisms in these perennially ice-covered lakes.     

The Occurrence of Lysogenic Bacteria and Microbial Aggregates in the Lakes of the McMurdo Dry Valleys,Antarctica

The McMurdo Dry Valleys of Antarctica form the coldest and driest ecosystem on Earth. Within this region there are a number of perennially ice-covered (3–6 m thick) lakes that support active microbial assemblages and have a paucity of metazoans. These lakes receive limited allochthonous input of carbon and nutrients, and primary productivity is limited to only 6 months per year owing to an absence of sunlight during the austral winters. In an effort to establish the role that bacteria and their associated viruses play in carbon and nutrient cycling in these lakes, indigenous bacteria, free bacteriophage, and lysogen abundances were determined. Total bacterial abundances (TDC) ranged from 3.80 × 10⁴ to 2.58 × 10⁷ cells mL^–1 and virus-like particle (VLP) abundances ranged from 2.26 × 10⁵ to 5.56 × 10⁷ VLP mL^–1. VLP abundances were significantly correlated (P < 0.05) with TDC, bacterial productivity (TdR), chlorophyll a (Chl a), and soluble reactive phosphorus (SRP). Lysogenic bacteria, determined by induction with mitomycin C, made up between 2.0% and 62.5% of the total population of bacteria when using significant decreases and increases in TDC and VLP abundances, respectively, and 89.5% when using increases in VLP abundances as the sole criterion for a successful induction event. The contribution of viruses released from induced lysogens contributed <0.015% to the total viral production rate. Carbohydrate and protein based organic aggregates were abundant within the water column of the lakes and were heavily colonized by bacteria and VLPs. Alkaline phosphatase activity was detected within the matrix of the aggregates, implying phosphorus deficiency and consortial nutrient exchanges among microorganisms.