Biology subjects

Brazelton, W.

Publications and source records attributed to Brazelton, W..

4 recordsLinked to original sources

bioRxiv2019

Microbial residents of the Atlantis Massif's shallow serpentinite subsurface

The Atlantis Massif rises 4,000 m above the seafloor near the Mid-Atlantic Ridge and consists of rocks uplifted from Earths upper mantle. Exposure of the mantle rocks to seawater leads to their alteration into serpentinites. These aqueous geochemical reactions, collectively known as the process of serpentinization, are exothermic and are associated with the release of hydrogen gas (H2), methane (CH4), and small organic molecules. The biological consequences of this flux of energy and organic compounds from the Atlantis Massif were explored by International Ocean Discovery Program (IODP) Expedition 357, which used seabed drills to collect continuous sequences of shallow (<16 meters below seafloor) marine serpentinites and mafic assemblages. Here, we report the first census of microbial diversity in samples of the drill cores, as measured by environmental 16S rRNA gene amplicon sequencing. The problem of contamination of subsurface samples was a primary concern during all stages of this project, starting from the initial study design, continuing to the collection of samples from the seafloor, handling the samples shipboard and in the lab, preparing the samples for DNA extraction, and analyzing the DNA sequence data. To distinguish endemic microbial taxa of serpentinite subsurface rocks from seawater residents and other potential contaminants, the distributions of individual 16S rRNA gene sequences among all samples were evaluated, taking into consideration both presence/absence as well as relative abundances. Our results highlight a few candidate residents of the shallow serpentinite subsurface, including uncultured representatives of the Thermoplasmata, Acidobacteria, Acidimicrobiia, and Chloroflexi. ImportanceInternational Ocean Discovery Program Expedition 357: "Serpentinization and Life" utilized seabed drills for the first time to collect rocks from the oceanic crust. The recovered rock cores represent the shallow serpentinite subsurface of the Atlantis Massif, where reactions between uplifted mantle rocks and water, collectively known as serpentinization, produce environmental conditions that can stimulate biological activity and are thought to be analogous to environments that were prevalent on the early Earth and perhaps other planets. The methodology and results of this project have implications for life detection experiments, including sample return missions, and provide the first window into the diversity of microbial communities inhabiting subseafloor serpentinites.

microbiology↗

bioRxiv2019

Genomic Evidence for Formate Metabolism by Chloroflexi as the Key to Unlocking Deep Carbon in Lost City Microbial Ecosystems

The Lost City hydrothermal field on the Mid-Atlantic Ridge supports dense microbial life on the lofty calcium carbonate chimney structures. The vent field is fueled by chemical reactions between the ultramafic rock under the chimneys and ambient seawater. These serpentinization reactions provide reducing power (as hydrogen gas) and organic compounds that can serve as microbial food; the most abundant of these are methane and formate. Previous studies have characterized the interior of the chimneys as a single-species biofilm inhabited by the Lost City Methanosarcinales, but also indicated that this methanogen is unable to metabolize formate. The new metagenomic results presented here indicate that carbon cycling in these Lost City chimney biofilms could depend on the metabolism of formate by low-abundance Chloroflexi species. Additionally, we present evidence that metabolically diverse, formate-utilizing Sulfurovum species are living in the transition zone between the interior and exterior of the chimneys.\n\nIMPORTANCEPrimitive forms of life may have originated around hydrothermal vents at the bottom of the ancient ocean. The Lost City hydrothermal vent field, fueled by just rock and water, provides an analog for not only primitive ecosystems but also extraterrestrial ecosystems that might support life. The microscopic life covering towering chimney structures at the Lost City has been well characterized, yet little is known about the carbon cycling in this ecosystem. These results provide a better understanding of how carbon from the deep subsurface can fuel rich microbial ecosystems on the seafloor.

microbiology↗

bioRxiv2019

Carbon Assimilation Strategies in Ultrabasic Groundwater: Clues from the Integrated Study of a Serpentinization-Influenced Aquifer

Serpentinization is a low-temperature metamorphic process by which ultramafic rock chemically reacts with water. These reactions provide energy and materials that may be harnessed by chemosynthetic microbial communities at hydrothermal springs and in the subsurface. However, the biogeochemistry of microbial populations that inhabit these environments are understudied and are complicated by overlapping biotic and abiotic processes. We applied metagenomics, metatranscriptomics, and untargeted metabolomics techniques to environmental samples taken from the Coast Range Ophiolite Microbial Observatory (CROMO), a subsurface observatory consisting of twelve wells drilled into the ultramafic and serpentinite melange of the Coast Range Ophiolite in California. Using a combination of DNA and RNA sequence data and mass spectrometry data, we determined that several carbon assimilation strategies, including the Calvin-Benson-Bassham cycle, the reverse tricarboxylic acid cycle, the reductive acetyl-CoA pathway, and methylotrophy are used by the microbial communities inhabiting the serpentinite-hosted aquifer. Our data also suggests that the microbial inhabitants of CROMO use products of the serpentinization process, including methane and formate, as carbon sources in a hyperalkaline environment where dissolved inorganic carbon is unavailable.\n\nImportanceThis study describes the metabolic pathways by which microbial communities in a serpentinite-influenced aquifer may produce biomass from the products of serpentinization. Serpentinization is a widespread geochemical process, taking place over large regions of the seafloor, particularly in slow-spreading mid ocean ridge and subduction zone environments. The serpentinization process is implicated in the origin of life on Earth and as a possible environment for the discovery of life on other worlds in our solar system. Because of the difficulty in delineating abiotic and biotic processes in these environments, major questions remain related to microbial contributions to the carbon cycle and physiological adaptation to serpentinite habitats. This research explores multiple mechanisms of carbon assimilation in serpentinite-hosted microbial communities.

microbiology↗

bioRxiv2019

Robust archaeal and bacterial communities inhabit shallow subsurface sediments of the Bonneville Salt Flats

We report the first census of natural microbial communities of the Bonneville Salt Flats (BSF), a perennial salt pan at the Utah-Nevada border. Environmental DNA sequencing of archaeal and bacterial 16S rRNA genes was conducted on samples from multiple evaporite sediment layers of the surface salt crust. Our results show that at the time of sampling (September 2016), BSF hosted a robust microbial community dominated by diverse Halobacteriaceae and Salinibacter species. Desulfuromonadales from GR-WP33-58 are also abundant in all samples. We identified taxonomic groups enriched in each layer of the salt crust sediment and revealed that the upper gypsum sediment layer found immediately under the uppermost surface halite contains a robust microbial community. We found an increased presence of Thermoplasmatales, Nanohaloarchaeota, Woesearchaeota, Acetothermia, Halanaerobium, Parcubacteria, Planctomycetes, Clostridia, Gemmatimonadetes, Marinilabiaceae and other Bacteroidetes in this upper gypsum layer. This study provides insight into the diversity, spatial heterogeneity, and geologic context of a surprisingly complex microbial ecosystem within this macroscopically-sterile landscape. IMPORTANCEOver the last [~]13,000 years the Pleistocene Lake Bonneville, which covered a large portion of Utah, drained and desiccated leaving behind the Bonneville Salt Flats (BSF). Today BSF is famous for its use as a speedway, which has hosted many land-speed records and a community that greatly values this salty landscape. Additionally, the salts that saturate BSF basin are extracted and sold as an additive for agricultural fertilizers. The salt crust is a well-known recreational and economic commodity, but the roles of microbes in the formation and maintenance of the salt crust are generally unknown. This study is the first geospatial analysis of microbial diversity at this site using cultivation-independent environmental DNA sequencing methods. Identification of the microbes present within this unique, dynamic, and valued sedimentary evaporite environment is an important step toward understanding the potential consequences of perturbations to the microbial ecology on the surrounding landscape and ecosystem.

microbiology↗