Postdoctoral Scientist in Huber Lab
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Microbiological characterization of a post-eruption “snowblower” event at the Axial Seamount, Juan de Fuca Ridge.
Microbial processes within the subseafloor can be examined during the ephemeral and uncommonly observed phenomenon known as a “snowblower” during which large quantities of flocculent material are expelled from the seafloor following an eruption at a mid-ocean ridge. During eruption events, an increase in the available geochemical fuels in hydrothermal fluids allows subseafloor microbial populations to bloom. The first snowblower event was observed following an eruption on the East Pacific Rise in 1991. Microscopic analysis of white flocculent material from that event revealed a single filamentous cell type. In contrast, orange flocculent material coating the seafloor following the 1994 eruption of the CoAxial Segment of the Juan de Fuca ridge contained a diverse assemblage of cell types. Enzyme activity assays from the orange floc demonstrated the presence of microbes capable of both carbon fixation and sulfide oxidation. Here we build upon these studies using both white and orange flocculent material collected shortly after the April 2011 eruption at Axial Seamount, an active deep-sea volcano on the Juan de Fuca Ridge.
Using a suction sampler on the ROV ROPOS, we obtained white flocculent material from a snowblower venting site and orange flocculent material coating the surrounding seafloor. Under scanning electron microscopy, both sample types were characterized by diverse mineral and diatomaceous debris as well as several cell types. The white floc also contained large clumps of filaments. Cell counts indicated that the white floc contained roughly 9 x 108 cells per gram of flocculent material and the orange floc had 3 x 107 cells per gram. Community DNA was extracted from both, with higher yields from the white floc.
Sequencing of bacterial 16S rRNA genes revealed distinct community composition between white and orange floc. The white floc was dominated by Epsilonproteobacteria, especially Arcobacter, Sulfurimonas, and an unclassified group of Campylobacterales. While 81% of bacterial community in the white floc was made up of Epsilonproteobacteria, only 20% of the orange floc was classified as such. The orange floc was instead dominated by the Gammaproteobacterial genus, Thiothrix. Isolated members of Arcobacter, Sulfurimonas, and Thiothrix have all been characterized as sulfur-oxidizing bacteria, supporting the original theory that snowblower vents are blooms of sulfur oxidizers. Amplification of the sulfur oxidation gene soxB using primers specific to Epsilonproteobacteria confirmed the presence of sulfur-oxidizers in both types of flocculent material from snowblower vents. The soxB genes were most closely related to Sulfurovum in the white floc and to Sulfurimonas and Nitratiruptor in the orange floc. These observations from ephemeral snowblower events demonstrate that subseafloor microbial communities are active and capable of responding quickly to favorable changes in environmental conditions.
Fig. 1. Suction sampling of white flocculent material from a “snowblower” vent in August 2011. An eruption occurred at this site 3 months earlier, during which molten lava flowed onto the seafloor and quickly cooled and hardened into hollow pillow lava, with sea water trapped inside. The pillow lava later partially collapsed, releasing a cloud of white floc. Orange floc can also be seen coating the cooled lava outside of the snowblower orifice. For scale, the tubing at the center of the photo is the size of an average vacuum cleaner hose. Photo courtesy of NSF and the Ocean Observatories Initiative.
Fig. 2. Fixed samples of white floc viewed by SEM showing a large clump of filamentous cells as well as inorganic debris.
Fig. 3 Fixed sample of orange floc viewed by SEM showing clumps of inorganic and organic debris.