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    Molecular Fingerprinting to Understand Diazotrophic Microbe Distribution in Oligotrophic Oceans

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    Name:
    Roslinda Mohamed Dissertation.pdf
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    6.146Mb
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    PDF
    Description:
    Roslinda Mohamed Dissertation
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    Type
    Dissertation
    Authors
    MOHAMED, ROSLINDA cc
    Advisors
    Duarte, Carlos M. cc
    Committee members
    Jones, Burton cc
    Saikaly, Pascal cc
    Mohr, Wiebke
    Program
    Marine Science
    KAUST Department
    Biological and Environmental Science and Engineering (BESE) Division
    Date
    2018-07
    Embargo End Date
    2019-08-05
    Permanent link to this record
    http://hdl.handle.net/10754/628063
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2019-08-05.
    Abstract
    In oligotrophic systems, where primary production is low and nitrogen is in short supply, nitrogen fixation process is intense. Although a few diazotrophs (eg. Trichodesmium) have been widely-studied, the rest of the diazotrophic community is still poorly understood. Furthermore, the global distribution of diazotrophs are yet to be clearly resolved. This dissertation assessed the distribution of diazotrophs in oligotrophic systems, particularly in the tropical and subtropical oceans, using genomics tools including next-generation sequencing. We first tested out a pair of nifH-specific primer that previously performed well in silico, but found that its application on seawater samples was biased towards paralogous, non-functional nitrogenase nifH genes. Instead, we found that the use of a nested PCR method using different primers sets to be more effective in amplifying functional nifH genes. Trichodesmium sp., UCYN-A and Pseudomonas sp. forms the core of the diazotrophic communities in oligotrophic oceans. Temperature is the primary driver of the abundances and distributions of these organisms in the Pacific, Atlantic and Indian Oceans, as well as in the oligotrophic Red Sea. Trichodesmium tends to dominate warm, surface waters, while UCYN-A prefers cooler environments and dwell in sub-surface waters in the Red Sea. Due to the dominance of Pseudomonas in the large-sized fraction samples, they are believed to be part of the Trichodesmium-associated consortia, although this requires further investigations. We also found non-cyanobacterial species of diazotrophs to be dominant previously-described hotspots of nitrogen fixation, and found evidence for the widespread of alternative nitrogenases (Cluster II). Using the Red Sea as an exemplar for future warming ocean, we found patterns of niche partitioning in the Red Sea diazotrophs, based on their distribution along seasons, latitude and depth. Our one-year observation of Red Sea Trichodesmium population witnessed the collapse of the population at temperatures above 32°C. This dissertation not only improve our understanding of the effects of future rising temperature on the natural populations of diazotrophs, but it also helps to establish a baseline understanding of the structure, spatial and temporal dynamics of Red Sea diazotrophs, which has not been discussed elsewhere.
    Citation
    MOHAMED, R. O. S. L. I. N. D. A. (2018). Molecular Fingerprinting to Understand Diazotrophic Microbe Distribution in Oligotrophic Oceans. KAUST Research Repository. https://doi.org/10.25781/KAUST-RU589
    DOI
    10.25781/KAUST-RU589
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-RU589
    Scopus Count
    Collections
    Biological and Environmental Science and Engineering (BESE) Division; Marine Science Program; PhD Dissertations

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