<p>Soil communities are regarded as among the most complex and diverse assemblages of microorganisms with estimated bacterial numbers in the order of 10â?¹ cells.gâ?»&sup1 / . Studies on extreme soils however, have reported lower cell densities, supporting the perception that the so-called extreme environments exhibit low species diversity. To assess the extent of microbial diversity within an extreme environment, the mineral soils of the Dry Valleys, Ross Dependency, Eastern Antarctica were investigated using 16S rDNA analysis.</p>

Antarctica provides some of the most extreme environments on earth. Low temperatures, low water availability and nutrient deficiency are contributing factors to the limited colonisation of Antarctic biotopes, particularly in the continental Dry Valleys. The survival of microorganisms in this harsh continent provides the basis for the significance of this study. This study aimed to explore microbial phylotypic diversity across a 500 m altitudinal transect in the Miers Dry Valley, Ross Desert, East Antarctica. The study also attempted to infer from phylogenetic data, the possible presence of indicative phenotypes which might contribute to a functional microbial community.

Antarctica provides some of the most extreme environments on earth. Low temperatures, low water availability and nutrient deficiency are contributing factors to the limited colonisation of Antarctic biotopes, particularly in the continental Dry Valleys. The survival of microorganisms in this harsh continent provides the basis for the significance of this study. This study aimed to explore microbial phylotypic diversity across a 500 m altitudinal transect in the Miers Dry Valley, Ross Desert, East Antarctica. The study also attempted to infer from phylogenetic data, the possible presence of indicative phenotypes which might contribute to a functional microbial community.

<p>Soil communities are regarded as among the most complex and diverse assemblages of microorganisms with estimated bacterial numbers in the order of 10â?¹ cells.gâ?»&sup1 / . Studies on extreme soils however, have reported lower cell densities, supporting the perception that the so-called extreme environments exhibit low species diversity. To assess the extent of microbial diversity within an extreme environment, the mineral soils of the Dry Valleys, Ross Dependency, Eastern Antarctica were investigated using 16S rDNA analysis.</p>

Thesis (Ph. D.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: John C. Priscu. Includes bibliographical references (leaves 181-201).

Philosophiae Doctor - PhD / Soil communities are regarded as among the most complex and diverse assemblages of microorganisms with estimated bacterial numbers in the order of 109-1 cells.g. Studies on extreme soils however, have reported lower cell densities, supporting the perception that the so-called extreme environments exhibit low species diversity. To assess the extent of microbial diversity within an extreme environment, the mineral soils of the Dry Valleys, Ross Dependency, Eastern Antarctica were investigated using 16S rDNA analysis. Three mineral soils designated MVG, PENP and BIS were analysed, each differing with respect to altitude, protein, lipid, water and DNA content. The mid-altitude sample, MVG, yielded the highest levels of DNA and the low altitude BIS soil contained the highest levels of protein, lipid and water. 16S clone libraries were constructed and 60 unique clones were identified and sequenced. BLASTn analysis revealed eight phylogenetic groups with Cyanobacteria, Actinobacteria and Acidobacteria representing the majority. The Cyanobacterial phylotypes were unique to the desiccated high-altitude soils of the PENP sample, suggesting a soil-borne Cyanobacterial population. 21% of the phylotypes identified were assigned as ‘uncultured’. DNA isolated from the Antarctic mineral soils was also used to construct a metagenomic clone library consisting of 90700 clones with an average insert size of 3.5 kb, representing an estimated 3.4% of the available metagenome. Activity-based screening of the library for genes conferring lipolytic activity yielded no positive clones. It is suggested that the failure to produce positive clones might be a result of insufficient nucleotide coverage of the metagenomic DNA. The metagenomic DNA extracted from the Dry Valley mineral soils was further analyzed using PCR. Two sets of degenerate primers based on conserved regions within lipolytic genes were used to target lipase and esterase genes. One set of primers was selected from a previous study. A second primer set was designed manually from amino acid alignments of true lipase genes from family I, sub-families I-VI. PCR analysis resulted in nine partial gene fragments varying between 240 bp and 300 bp. Bioinformatic analysis revealed that all nine partial gene fragments harboured α/β-hydrolase motifs, putatively identifying two esterases and three lipases from both bacterial and fungal origin. / South Africa

The McMurdo Dry Valleys comprise some 4,800km2 of ice-free terrain in east Antarctica and this constitutes the coldest and most arid desert on Earth. The ecosystem of the Dry Valleys is characterized by microbial processes since environmental extremes severely limit higher plant and animal life. A major international collaborative research effort co-ordinated by the International Center for Terrestrial Antarctic Research (ICTAR), identified long-term study sites representative of maritime and inland Dry Valleys environments. The maritime site, Miers Valley, has been the subject of intensive multi-disciplinary study in recent years, of which the work in this thesis is a part. Previous studies have identified soil microbial communities and their putative functional roles, but lithic communities have not been previously appreciated. This thesis reports aspects on the biodiversity and ecology of lithic microbial communities in Miers Valley. A survey of terrain revealed extensive weathered granite, but no porous sandstone or limestone rocks more commonly associated with cryptoendolithic communities (those colonizing pore spaces within rock substrates). Granite was extensively colonized (30-100% of available substrate) by chasmoendolithic microorganisms (colonizing cracks and fissures in weathered rock). Visual examination of colonized rocks revealed a distinct zone of biomass 2-5mm below the rock surface, and this was overlain by a weathered and friable matrix of rock. Microscopy revealed a community dominated by diverse cyanobacterial morphotypes, plus other unidentifiable microbes of varied morphology. A quantitative approach to broad-scale community fingerprinting was adopted, utilizing terminal restriction fragment length polymorphism (TRFLP) and sequence based identifications of restriction fragments. The multi-domain approach encompassed Archaea, Bacteria and Eukarya. The results revealed relatively low species richness (0.6-1.8) for each domain with community richness estimates also relatively low (<3). Nonetheless very clear and statistically supported patterns in the occurrence of phylotypes within chasmolithic communities were related to aspect (which strongly affects temperature and moisture availability in Dry Valleys locations). The bacterial assemblages formed two groups (cold-dry south facing slopes and valley floor moraine). The eukaryal assemblages also formed two groups although here the moraine samples grouped with the warmer wetter north facing slope and the cold-dry south facing slope assemblages formed a separate group. The archaeal assemblages displayed no difference within different valley terrain. Extensive sequence based interrogation of community structure using clone libraries revealed a community dominated by cyanobacteria, Actinobacteria, Deinococci and putative lichens. These phyla are all known for their extreme tolerance to desiccation and occurrence in arid landscapes. Phylogenetic analysis revealed that these abundant taxa shared close affiliation with those from other Antarctic refuge niches such as hypoliths and cryptoendoliths. The cyanobacteria were mainly Oscillatoriales, but other genera such as Chroococcidiopsis and Nostoc commonly recovered in hot desert lithic communities were generally absent. The eukaryal community was dominated by chlorophyte algae, whilst the archaeal phylotypes were a diverse collection spanning both euryachaeal and crenarchaeal lineages. Overall the data revealed the chasmoendolithic community in Miers Valley was widespread and with relatively restricted diversity. The selection pressures related to topology of the valley have resulted in different community structure within the valley. / published_or_final_version / Biological Sciences / Master / Master of Philosophy