Chemoorganotrophic Bacteria From Lake Fryxell, Antarctica, Including Pseudomonas Strain LFY10, a Cold-Adapted, Halotolerant Bacterium Useful in Teaching Labs

Lake Fryxell, situated in the McMurdo Dry Valleys of Antarctica, is an intriguing aquatic ecosystem because of its perennial ice cover, highly stratified water column, and extreme physicochemical conditions, which collectively restrict lake biodiversity to solely microbial forms. To expand our current understanding of the cultivable biodiversity of Lake Fryxell, water samples were collected from depths of 10 and 17 m, and pure cultures of eight diverse strains of aerobic, chemoorganotrophic bacteria were obtained. Despite having high 16S rRNA gene sequence similarity to mesophilic bacteria inhabiting various temperate environments, all Lake Fryxell isolates were psychrotolerant, with growth occurring at 0°C and optimal growth from 18–24°C for all isolates. Phylogenetic analyses showed the isolates to be members of six taxonomic groups, including the genera Brevundimonas, Arthrobacter, Sphingobium, Leifsonia, and Pseudomonas, as well as the family Microbacteriaceae (one strain could not reliably be assigned to a specific genus based on our analysis). Pseudomonas strain LFY10 stood out as a useful tool for teaching laboratory activities because of its substantial cold adaptation (visible growth is evident in 1–2 days at 4°C), beta-hemolytic activity, and halotolerance to 8.5% (w/v) NaCl. These cold-adapted bacteria likely play a role in carbon mineralization and other nutrient cycling in Lake Fryxell, and their characterization broadens our understanding of microbial biodiversity in aquatic polar ecosystems

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

Design, Construction, and Application of an Inexpensive, High-Resolution Water Sampler

The cost of high-resolution water sampling devices for ecological studies and water quality analyses can be prohibitive. Moreover, the potential for operator error in the use of complicated sampling equipment can lead to inaccuracies. Here we describe the construction and operation of an inexpensive and easy-to-use water sampler that achieves a water column sampling resolution of approximately 1 cm. The device is driven by a peristaltic pump and is constructed entirely of non-corrosive and non-reactive materials. The sampler has no moving parts and was completely reliable in fieldwork on temperate and Antarctic lakes. The device is especially suited for the collection of water samples from calm or stagnant surface waters, such as lakes, ponds, reservoirs, and deep swamps or other wetlands. In addition, because its components are unaffected by corrosive salts and sulfides, the device is suitable for sampling calm inlet waters, including shallow bays and estuaries. Because of its low cost, simple construction, compact design, and precision performance, this water sampler is an excellent option for studying and monitoring shallow to moderately deep (<50 m) natural waters

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

Biodiversity of Methanogenic and Other Archaea in the Permanently Frozen Lake Fryxell, Antarctica

Archaea were detected in molecular diversity studies of the permanently frozen Lake Fryxell, Antarctica. Two clusters of methanogens were detected in the sediments, and another cluster of possibly methanotrophic Euryarchaeota was detected in the anoxic water column just above the sediments. One crenarchaeote was detected in water just below the oxycline. The Archaea present in Lake Fryxell are likely involved in the major biogeochemical cycles that occur there

A Green Sulfur Bacterium From Epsomitic Hot Lake, Washington, USA

Hot Lake is a small heliothermal and hypersaline lake in far north-central Washington State (USA) and is limnologically unusual because MgSO4 rather than NaCl is the dominant salt. In late summer, the Hot Lake metalimnion becomes distinctly green from blooms of planktonic phototrophs. In a study undertaken over 60 years ago, these blooms were predicted to include green sulfur bacteria but no cultures were obtained. We sampled Hot Lake and established enrichment cultures for phototrophic sulfur bacteria in MgSO4-rich sulfidic media. Most enrichments turned green or red within two weeks, and from green-colored enrichments, pure cultures of a lobed green sulfur bacterium (Phylum Chlorobi) were isolated. Phylogenetic analyses showed the organism to be a species of the prosthecate green sulfur bacterium Prosthecochloris. Cultures of this Hot Lake phototroph were halophilic and tolerated high levels of sulfide and MgSO4. In addition, unlike all recognized species of Prosthecochloris, the Hot Lake isolates grew at temperatures up to 45C, indicating an adaptation to the warm summer temperatures of the lake. Photoautotrophy by Hot Lake green sulfur bacteria may contribute dissolved organic matter to anoxic zones of the lake, and their diazotrophic capacity may provide a key source of bioavailable nitrogen, as well.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Cold-Active, Heterotrophic Bacteria from the Highly Oligotrophic Waters of Lake Vanda, Antarctica

The permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica are distinctive ecosystems that consist strictly of microbial communities. In this study, water samples were collected from Lake Vanda, a stratified Dry Valley lake whose upper waters (from just below the ice cover to nearly 60 m) are highly oligotrophic, and used to establish enrichment cultures. Six strains of psychrotolerant, heterotrophic bacteria were isolated from lake water samples from a depth of 50 or 55 m. Phylogenetic analyses showed the Lake Vanda strains to be species of Nocardiaceae, Caulobacteraceae, Sphingomonadaceae, and Bradyrhizobiaceae. All Lake Vanda strains grew at temperatures near or below 0 °C, but optimal growth occurred from 18 to 24 °C. Some strains showed significant halotolerance, but no strains required NaCl for growth. The isolates described herein include cold-active species not previously reported from Dry Valley lakes, and their physiological and phylogenetic characterization broadens our understanding of these limnologically unique lakes

Genomic Features of the Bundle-Forming Heliobacterium Heliophilum fasciatum

Eight species of heliobacteria have had their genomes sequenced. However, only two of these genomes have been analyzed in detail, those from the thermophilic Heliomicrobium (Hmi.) modesticaldum and the alkaliphilic Heliorestis (Hrs.) convoluta. Here we present analyses of the draft genome sequence of a species of heliobacterium that grows optimally at a moderate temperature and neutral pH. The organism, Heliophilum (Hph.) fasciatum, is phylogenetically unique among cultured heliobacteria and was isolated from rice soil, a common habitat for heliobacteria. The Hph. fasciatum genome contains 3.14 Mbp—similar to that of other reported heliobacteria—but has a G+C base ratio that lies between that of Hmi. modesticaldum and Hrs. convoluta. Many of the genomic features of Hmi. modesticaldum and Hrs. convoluta, such as the absence of genes encoding autotrophic pathways, the presence of a superoperonal cluster of photosynthesis-related genes, and genes encoding endospore-specific proteins, are also characteristic of the Hph. fasciatum genome. However, despite the fact that Hph. fasciatum is diazotrophic, classical nif genes encoding the alpha and beta subunits of dinitrogenase (nifDK) present in other heliobacteria could not be identified. Instead, genes encoding several highly divergent NifDK homologs were present, at least one of which likely encodes a functional dinitrogenase and another a methylthio-alkane reductase (MarDK) for sulfur assimilation. A classical NifH (dinitrogenase reductase) homolog was also absent in Hph. fasciatum, but a related protein was identified that likely carries out this function as well as electron delivery to MarDK. The N2-fixing system of Hph. fasciatum is therefore distinct from that of other heliobacteria and may have unusual properties

Genome Sequence of Rhodoferax antarcticus ANT.BRT; A Psychrophilic Purple Nonsulfur Bacterium from an Antarctic Microbial Mat

Rhodoferax antarcticus is an Antarctic purple nonsulfur bacterium and the only characterized anoxygenic phototroph that grows best below 20 °C. We present here a high-quality draft genome of Rfx. antarcticus strain ANT.BRT, isolated from an Antarctic microbial mat. The circular chromosome (3.8 Mbp) of Rfx. antarcticus has a 59.1% guanine + cytosine (GC) content and contains 4036 open reading frames. In addition, the bacterium contains a sizable plasmid (198.6 kbp, 48.4% GC with 226 open reading frames) that comprises about 5% of the total genetic content. Surprisingly, genes encoding light-harvesting complexes 1 and 3 (LH1 and LH3), but not light-harvesting complex 2 (LH2), were identified in the photosynthesis gene cluster of the Rfx. antarcticus genome, a feature that is unique among purple phototrophs. Consistent with physiological studies that showed a strong capacity for nitrogen fixation in Rfx. antarcticus, a nitrogen fixation gene cluster encoding a molybdenum-type nitrogenase was present, but no alternative nitrogenases were identified despite the cold-active phenotype of this phototroph. Genes encoding two forms of ribulose 1,5-bisphosphate carboxylase/oxygenase were present in the Rfx. antarcticus genome, a feature that likely provides autotrophic flexibility under varying environmental conditions. Lastly, genes for assembly of both type IV pili and flagella are present, with the latter showing an unusual degree of clustering. This report represents the first genomic analysis of a psychrophilic anoxygenic phototroph and provides a glimpse of the genetic basis for maintaining a phototrophic lifestyle in a permanently cold, yet highly variable, environment