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Postgraduate Thesis: Molecular microbial ecology of Mars-like environments on earth, for application in astrobiology
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TitleMolecular microbial ecology of Mars-like environments on earth, for application in astrobiology
 
AuthorsChan, Wai, Olivia.
陳卉.
 
Issue Date2012
 
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
AbstractAstrobiology 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.
 
AdvisorsPointing, SB
Aitchison, JC
 
DegreeDoctor of Philosophy
 
SubjectExtreme environments - Microbiology.
Exobiology.
 
Dept/ProgramBiological Sciences
 
DC FieldValue
dc.contributor.advisorPointing, SB
 
dc.contributor.advisorAitchison, JC
 
dc.contributor.authorChan, Wai, Olivia.
 
dc.contributor.author陳卉.
 
dc.date.hkucongregation2012
 
dc.date.issued2012
 
dc.description.abstractAstrobiology 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.
 
dc.description.naturepublished_or_final_version
 
dc.description.thesisdisciplineBiological Sciences
 
dc.description.thesisleveldoctoral
 
dc.description.thesisnameDoctor of Philosophy
 
dc.identifier.hkulb4832999
 
dc.languageeng
 
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
dc.relation.ispartofHKU Theses Online (HKUTO)
 
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.
 
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License
 
dc.source.urihttp://hub.hku.hk/bib/B4832999X
 
dc.subject.lcshExtreme environments - Microbiology.
 
dc.subject.lcshExobiology.
 
dc.titleMolecular microbial ecology of Mars-like environments on earth, for application in astrobiology
 
dc.typePG_Thesis
 
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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.</description.abstract>
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