Doctoral Theses

Permanent link for this collection

https://hdl.handle.net/10292/4
The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.

For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.

Browse

Browsing Doctoral Theses by Subject "16S"

Now showing 1 - 2 of 2
  • Item
    Functional Diversity of Microbial Communities in the McMurdo Dry Valleys, Antarctica
    (Auckland University of Technology, 2016) Wei, Ting-Shyang (Sean)
    In dryland ecosystems species richness for all domains decreases with increasing aridity. Several environmental stressors (desiccation, thermal and radiation stress) in hyper-arid drylands limit the complex life forms, thus microorganisms comprise most of the standing biomass and diversity in this particular ecosystem. Interestingly, these microorganisms colonize cryptic habitats that provide shelter from harsh environmental conditions. They form unique hypolithic, cryptoendolithic and chasmoendolithic communities beneath and within rocks and soil. The microbial diversity and community structure in refugia of the McMurdo Dry Valleys, the coldest and driest dryland on Earth, has been extensively studied using 16S rRNA gene surveys. These have revealed photoautotrophic cyanobacteria dominate hypoliths and endoliths whereas Actinobacteria dominate soil communities. Despite this, very little is known about the functionality of these communities and how they respond to environmental stress. In the first part of this study, the GeoChip DNA microarray was used to interrogate carbon and nitrogen transformation pathways of asmoendoliths, hypoliths and soil communities in a maritime-influenced location, Miers Valley. The chasmoendoliths, and hypoliths were identified as the potential primary production sites since cyanobacterial rubisco signatures were not commonly recovered from soils. Other forms of rubisco originated from Proteobacteria and archaea were identified, suggesting that chemoautotrophic pathways also contributed to carbon fixation. All communities supported diverse carbohydrate transformation pathways. However, soil communities supported significantly greater aromatic carbon utilization genes than hypoliths and chasmoendoliths, and this was related to the recalcitrant ‘legacy’ carbon stored in Antarctic soils. For nitrogen fixation, all communities displayed the full suite of genes involved in nitrogen transformations. Soil communities generally supported slightly higher abundance of proteobacterial nitrogenase than chasmoendoliths and hypoliths, and so soil may be more important than rock as a site for microbial nitrogen fixation. Stress response pathways were also identified, and soil communities displayed higher diversity and abundance of environmental stress response pathways compared to more cryptic rock communities. The high throughput 16S rRNA gene sequencing showed Cyanobacteria (46%), Actinobacteria (31%), Proteobacteria (25%) and were relatively dominant in hypolithic and soil communities, and these phyla also displayed the greatest functional diversity. This suggests that the metabolic plasticity for these taxa may be an important factor in their role as keystone species in these communities. In addition, GeoChip analyses also identified possible sources of community regulation in the Dry Valleys where grazing and predation are minimal or non-existent. Widespread occurrence of antibiotic resistance genes indicated that inter-specific competition may be important among these diverse communities, and phage signatures indicated a potential bottom-up control via phage lysis of microbial cells. In a metagenomic study, protein sequences involved in extracellular polymer substances (EPS) synthesis (Wzy-dependent pathway) of dryland cyanobacteria were identified by de novo sequencing on the Miseq platform, since EPS played important roles in bio-weathering, nutrient repositories and stress response. Together with other cyanobacterial EPS synthesis protein sequences, phylogenetic analyses showed that these proteins derived different environments were not correlated to their habitats, indicating these genes were highly conserved and that EPS production might be induced and regulated under specific conditions and mechanisms.
  • Item
    Spatiotemporal Variability of Bioaerosols
    (Auckland University of Technology, 2021) Miaow, Katie
    The aim of this thesis was to understand variation in microbial aerosol (or bioaerosol) communities at differing spatial and temporal scales. Bioaerosols in urban parks were shown to vary as a result of location, sampled air-mass source and, for fungi in particular, time. Modelling was able to explain 38% of the fungal variation and 19% of the bacterial variation. Urban sampling over two years confirmed that bioaerosol communities varied over time in a non-linear fashion, exhibiting marked seasonality, which was especially pronounced for fungi. Non-linear diel variation was detected for Antarctic fungi. Bacteria in common between Antarctica and New Zealand increased markedly when New Zealand air was coming from Antarctica, suggesting intercontinental transport for bacteria at notable rates. Fungi appeared to undergo much less long-range atmospheric transport. This thesis research contributes innovative, validated data collection and processing pipelines for sparse microbial community data to our body of information. Novel patterns in bioaerosol spatiotemporal variation have been revealed that lead to new questions about bioaerosol community structure and ecosystem connectivity via bioaerosols. As understanding of the drivers of bioaerosol variation improves, predictions can be made regarding future ecosystem changes and spread of infectious microorganisms. This will be crucial for managing the impacts of these increasingly likely events in the face of climate change.
Theses are protected by the Copyright Act 1994 (New Zealand). The thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use:
  • Any use you make of these documents or images must be for research or private study purposes only, and you may not make them available to any other person.
  • Authors control the copyright of their thesis. You will recognise the author’s right to be identified as the author of the thesis, and due acknowledgement will be made to the author where appropriate.
  • You will obtain the author’s permission before publishing any material from the thesis.