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<b><span style="font-size:16.0pt;font-family:"Times New Roman",serif;color:black">Oceanography Seminar</span></b><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-size:16.0pt;font-family:"Times New Roman",serif;color:black">Lauren Gillies Campbell</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black">Ph.D. Biological Oceanography Candidate<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><u><span style="font-family:"Times New Roman",serif;color:black">Title:</span></u><span style="font-family:"Times New Roman",serif;color:black"> Analysis of microbial abundance,
transcriptional activity and metabolic potential in the Gulf of Mexico “dead zone” reveals an ammonia-oxidizing hotspot</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<u><span style="font-family:"Times New Roman",serif;color:black">Major Professor:</span></u><span style="font-family:"Times New Roman",serif;color:black"> Dr. Olivia U. Mason</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<u><span style="font-family:"Times New Roman",serif;color:black">Defense Date:</span></u><span style="font-family:"Times New Roman",serif;color:black"> April 2, 2019</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<u><span style="font-family:"Times New Roman",serif;color:black">Time:</span></u><span style="font-family:"Times New Roman",serif;color:black"> 10:00 AM</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<u><span style="font-family:"Times New Roman",serif;color:black">Location:</span></u><span style="font-family:"Times New Roman",serif;color:black"> Chemistry 1005 (CSL1005)</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><u><span style="font-family:"Times New Roman",serif;color:black">Abstract:</span></u><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-family:"Times New Roman",serif;color:black">Ocean deooxygenation is accelerating as a result of greenhouse gas-driven atmospheric warming and subsequent increase in global ocean temperature. One of the world’s largest coastal hypoxic zones
occurs annually in the northern Gulf of Mexico (nGOM). These hypoxic zones are also known as “dead zones” because dissolved oxygen (DO) concentrations of ˜ 2 mg L</span><sup><span style="font-size:9.0pt;font-family:"Times New Roman",serif;color:black">-1</span></sup><sup><span style="font-family:"Times New Roman",serif;color:black">
</span></sup><span style="font-family:"Times New Roman",serif;color:black">are inhospitable to economically valuable fisheries. However, microorganisms flourish in “dead zones” because of their ability to utilize diverse metabolic pathways. Decades worth of
geochemical data has provided fine-scale resolution on nutrient and oxygen dynamics the nGOM, however little is known about microbial community structure and activity despite the implication that microbial respiration is responsible for forming low DO conditions.
To begin to fill this knowledge gap, samples collected across the nGOM shelf for two consecutive hypoxic seasons in July 2013 (Y13) and 2014 (Y14) were analyzed using<span style="background:white">
</span>16S rRNA gene iTag sequencing, quantification of bacterial and <span style="background:white">
thaumarchaeal 16S rRNA</span> genes and archaeal ammonia-monooxygenase (<i>amoA</i>)<i>
</i>genes using quantitative polymerase chain reaction (qPCR) assays, as well as <span style="background:white">
shotgun </span>metagenomic and metatranscriptomic sequencing. </span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-family:"Times New Roman",serif;color:black">Analysis of the microbial community16S rRNA gene sequence data (iTag) showed that ammonia-oxidizing Thaumarchaeota (100% similar to
<i>Nitrosopumilus maritimus</i>) were significantly enriched in hypoxic samples and inversely correlated with DO concentrations. In agreement with the iTag data, subsequent analyses of the absolute abundance (qPCR) of
<span style="background:white">Thaumarchaeota</span> 16S rRNA and <i>amoA</i> gene copy numbers revealed these data to be significantly more abundant in hypoxic samples and inversely correlated with DO concentrations. These results of significantly higher Thaumarchaeota
abundances and <i>amoA</i> gene copy numbers in hypoxic samples were confirmed with analyses of Y14 data.</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-family:"Times New Roman",serif;color:black">To better understand the ecological significance of the high thaumarchaeal abundances in the hypoxic zone, shotgun metagenomic and metatranscriptomic sequencing was carried out. Annotation of unassembled
metatranscriptomic reads revealed that functional genes involved in nitrification and ammonia assimilation were some of the most abundant transcripts in both hypoxic and oxic samples, with urease enzymes being significantly more abundant in hypoxic samples.
Next, the physiological and metabolic potential of two novel Thaumarchaeota metagenome assembled genomes (MAGs) was described. Bioinformatic analyses of these MAGs revealed that one contained transcripts coding for urea utilization, consistent with the analysis
of unassembled metatranscriptomic sequences. Both MAGs recruited more metatranscriptomic reads derived from hypoxic samples compared to oxic samples, suggesting that archaeal ammonia oxidation (AOA) may be influenced by local changes in DO concentrations.</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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<span style="font-family:"Times New Roman",serif;color:black">Collectively, analyses of the datasets in this dissertation that include data from iTag sequencing, qPCR assays, and meta-omics sequencing, found that seasonal hypoxic conditions influenced Thaumarchaeota
abundance, activity and diversity, with the annual nGOM “dead zone” emerging as a niche for low DO-adapted, cosmopolitan AOA. Overall, the findings in this dissertation provided significant new insights into the ecology and biogeochemical contributions of
marine Archaea, particularly in regards to the nitrogen cycle during a eutrophic-driven hypoxic event.</span><span style="font-size:14.0pt;font-family:"Times New Roman",serif;color:black"><o:p></o:p></span></p>
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