Date of Award


Degree Name

Master of Science


Geological Sciences


Jie Xu


Microbial communities have been commonly found to survive and thrive in arid to hyper-arid gypsic environments that are considered hostile to most other forms of life. The mechanisms through which microbes have conquered these harsh environments remain poorly understood. Here I hypothesize that the microbial communities in water-restricted gypsic settings could benefit in terms of energy and water sources via their interactions with the abundant hydrous sulfate minerals [i.e., gypsum (CaSO4·2H2O)] that build up these niches. Gypsum is of high bio-relevance because its sulfate component may be used as electron acceptor by sulfate-reducing bacteria and the crystallization water may be released as untapped water source along with the bacterial scavenging of sulfate. The focus of this study is to investigate if sulfate-reducing bacteria are significant within the existing bacterial communities in water-limited gypsic environment and if the bacterial interaction with gypsum provides essential support for the overall bacterial communities. I based this study at the White Sands National Monument, which contains the largest field of gypsum sand dunes in the world, in association with deflation plains and evaporite flats and obtained samples at various locations and depths. By analyzing the various biogeochemical components of the collected samples, including indigenous bacterial nucleic acids, associated mineral compositions and morphology and field geochemical conditions, I aim to constrain the relationship between the abundance and composition of bacterial communities and the modification of hydrous sulfate minerals reflected in their compositional and morphological variations. The major tools I used include real-time PCR (qPCR), 16S amplicon sequencing, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The sediments at various depths from the investigated five distinct sites are primarily composed of gypsum with considerable amounts of glauberite present in most samples. Basanite and anhydrite as well as calcite and dolomite were also identified in certain samples. Bacterial communities exist at readily recoverable levels in all collected sediments but higher overall abundances (up to 5 orders of magnitude higher) are associated with top layers of the sediments where there is the presence of water. Preliminary results also showed that significant sulfate-reducing communities exist in the samples form Alkali Flat and inter-dune puddles only, where the highest amounts of 16S genes were recovered. The SEM analysis revealed higher heterogeneity in terms of the minerals' sizes and morphology in the crust samples compared to those at depth, indicative of higher extent of modification, either biologically or abiotically. Slimy aggregates that are comparable to biofilm structures were directly observed in some of the sediment crusts. The agreement between qPCR data of 16S and dsrA genes and coincidence of higher levels of those data with increased heterogeneity in sediment mineralogy lend credence to the hypothesis that the SRB may play a critical role mediating the habitability of water-restricted gypsic environments.




Received from ProQuest

File Size

64 pages

File Format


Rights Holder

Brandon Nicholas LaJoie

Included in

Geology Commons