1,721,073 research outputs found
Phylogenetic diversity and cultivation of cyanobacteria from geothermal springs in Asia
No full textpublished_or_final_versionabstractEcology and BiodiversityDoctoralDoctor of Philosoph
Biodiversity and ecology of geothermal springs in the Philippines
No full textpublished_or_final_versionabstractEcology and BiodiversityDoctoralDoctor of Philosoph
Environmental genomic analysis of refuge habitats in hyper-arid deserts
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Molecular ecology of chasmoendolithic environments in Miers Valley, McMurdo Dry Valleys, Antarctica
No full textThe 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_versionBiological SciencesMasterMaster of Philosoph
Revision of Pleosporales : morpho-molecular phylogeny and typification
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Biodiversity, systematics and ecology of nematode-trapping fungi from Hong Kong
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Molecular ecology of lithic microbial communities
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Molecular microbial ecology of Mars-like environments on earth, for application in astrobiology
No full textAstrobiology is a multidisciplinary topic that addresses the origin, distribution and evolution of life in the universe. One of the key questions relates to whether life could have evolved on other planetary bodies, and Mars has been the major focus. Biologists contribute to this question by studying the ecology of extreme environments on Earth that share closest analogy to Mars’ past or present environment. In this thesis, molecular-level interrogations were used to address some aspects of microbial biodiversity, ecology and stress tolerance in two such extreme environments. The high-altitude cold and intense UV irradiance of central Tibet was selected as an analogue for Mars surface today, whilst cold alkaline high-carbonate freshwater lakes were chosen as an analogue for Mars’ previous late wet phase.
Biological soil crusts from central Tibet supported a diverse microflora and these were variously bacteria or eukarya dominated. The relatively well-developed eukarya-dominated crusts were characterized and showed they comprised of Stichococcus bacillaris, plus alphaproteobacteria, betaproteobacteria, bacteroidetes and gemmatimonadetes. In order to evaluate the diversity of radiation-tolerant taxa in these soils, samples were exposed to ionizing radiation and viability, physiology and phylogenetic identity determined. The most radio-tolerant taxa isolated and characterized were from the radiation tolerant phylum Deinococci (15kGy), whilst a relatively diverse range of Actinobacteria, Bacilli, Cyanobacteria and Proteobacteria were also recovered after exposure to doses up to 10kGy. This implies the high-radiation environment has selected for tolerance among diverse phyla, with tolerances that far exceed environmental exposure. It is not known at this stage if they all employ similar protective strategies.
Microbial reefs that have developed in cold alkaline lakes in British Columbia were studied as analogues for a late-wet Mars environment. Molecular ecological analysis revealed that communities consisted largely of of Proteobacteria (alpha), Cyanobacteria (Leptolyngbya) and Acidobacteria, with similarities in community assembly to marine stromatolites. Microbial diversity varied spatially and temporally within microbialites, and indicated that geographically proximal structures can develop with different communities. Significant changes also occur between summer and winter when the lake surface is frozen. Investigation of other nearby lakes with similar geochemistry but not supporting microbialites revealed extensive microbial mats. These developed in the presence of relatively high concentrations of methane or sulfate, and their biodiversity reflected this with several putative methanotrophic and sulphate utilizing taxa identified. No obvious cues that inhibit or promote microbialite formation were observed in this study.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Ecological risk analysis of polycyclic aromatic hydrocarbons, black carbon and heavy metals on soils and plants from coal factories inJiyuan City, China
No full textpublished_or_final_versionEarth SciencesMasterMaster of Philosoph
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