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Updated: Jan 28, 2026
09:21
Sediment Core Sectioning and Extraction of Pore Waters under Anoxic Conditions
Published on: March 7, 2016
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Bacterial fermentation and respiration processes are uncoupled in anoxic permeable sediments
Adam J Kessler1,2, Ya-Jou Chen3, David W Waite4,5
1Water Studies Centre, School of Chemistry, Monash University, Melbourne, Victoria, Australia.
Nature Microbiology
|March 13, 2019
Summary
Molecular hydrogen (H₂) builds up in sandy ocean sediments when oxygen levels change. This H₂ is produced by bacterial fermentation and consumed by aerobic respiration, fueling carbon cycling in these dynamic environments.
Area of Science:
- Marine microbial ecology
- Biogeochemistry
- Sedimentary processes
Background:
- Permeable sandy sediments cover vast areas of continental margins and significantly influence oceanic carbon cycling.
- Microbial communities in these dynamic sediments experience frequent shifts between oxygen-rich (oxic) and oxygen-depleted (anoxic) conditions.
- Understanding how these microbial communities sustain metabolism during oxic-anoxic transitions is crucial.
Purpose of the Study:
- To investigate the role of molecular hydrogen (H₂) in microbial metabolism within permeable sandy sediments during oxic-anoxic transitions.
- To identify the microbial players and metabolic pathways involved in H₂ production and consumption in these environments.
Main Methods:
- In situ measurements of H₂ supersaturation and isotopic composition in sediment porewater and overlying water.
- Genome-resolved shotgun metagenomic profiling to assess microbial community structure and functional gene abundance (e.g., [NiFe]-hydrogenase genes).
- Flow-through reactor and slurry experiments to simulate anoxic and reaeration conditions and track H₂ dynamics.
Main Results:
- Significant accumulation of molecular hydrogen (H₂) was observed in silicate sand sediments, with H₂ being 250-fold supersaturated in the overlying water column.
- Metagenomic analysis revealed a high abundance of [NiFe]-hydrogenase genes, suggesting a significant role for H₂ metabolism.
- Experimental data confirmed rapid H₂ production via fermentation under anoxia and immediate consumption by aerobic respiration upon reaeration, with sulfate reduction occurring only during prolonged anoxia.
Conclusions:
- Fermentation is the dominant process for anoxic carbon mineralization in permeable sediments, largely uncoupled from anaerobic respiration.
- The dynamic oxygen availability in these sediments selects for metabolically flexible bacteria capable of utilizing H₂, such as facultative fermenters and aerobic respirers.
- This H₂ cycling mechanism is a key feature of microbial life in permeable marine sediments, distinct from that in cohesive sediments.
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