Biological production and utilization of volatile fatty acids and alcohols in hydrothermally altered sediments of the Guaymas Basin
Abstract
Seafloor hydrothermal systems provide unique habitats for a diverse array of microorganisms that live and thrive under extreme conditions. The Guaymas Basin in the Gulf of California is a deep-sea hydrothermal system characterized by active seafloor spreading coincident with an area of massive sediment accumulation. Advection of hydrothermally-altered fluids through the organic-rich sediments generates significant amounts of low molecular weight products such as methane, hydrogen, short chain alkanes and fatty acids, providing important substrates that fuel microbial activity and promote microbial diversity. Volatile fatty acids (VFAs) and alcohols are key intermediates of anaerobic carbon metabolism and they can serve as important energy sources to support microbial growth in marine sediments, yet their biogeochemical cycling remains poorly constrained in hydrothermal systems. We investigated the abundance, stable carbon isotopic composition and metabolic cycling of VFAs and alcohols to elucidate their generation and utilization pathways in hydrothermally influenced sediments (4 °C~90 °C) from the Guaymas Basin. Abundant acetate (up to 229 μM) and methanol (up to 37 μM) were detected in the porewaters, indicating their high potential as carbon substrates and energy sources for microbes at different temperatures. The δ13C values of acetate varied between -35.6‰ and -18.1‰. Carbon isotopic signatures, thermodynamic predictions, and experimental incubations suggested that biological sources such as fermentation and acetogenesis provide acetate. Acetate and methanol were predominantly consumed by non-methanogenic processes (e.g., sulfate reduction), as reflected in high oxidation rates versus low methanogenesis rates, and further evidenced through inhibition experiments with molybdate. These results reveal an important role for VFAs and alcohols as energy sources for diverse chemoheterotrophs in organic-rich hydrothermally influenced sediments and provide new insight into the carbon metabolism and cycling in seafloor hydrothermal systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11K2206Z
- Keywords:
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- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 0456 Life in extreme environments;
- BIOGEOSCIENCES;
- 0463 Microbe/mineral interactions;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES