Microbial hydrogen oxidation potential in seasonally hypoxic Baltic Sea sediments

Area of Science:

• Marine microbial ecology
• Biogeochemical cycles
• Sedimentary processes

Background:

• Organic matter degradation on the seafloor is vital for nutrient cycling.
• Microbial sulfate reduction and fermentation dominate organic matter decomposition in oxygen-depleted coastal sediments.
• Hydrogen (H2) accumulation can limit organic matter mineralization, highlighting the importance of H2-scavenging microorganisms.

Purpose of the Study:

• Investigate the role and constraints of hydrogen (H2) oxidizers in coastal marine sediments.
• Assess the seasonal influence on H2 oxidation potential and microbial communities.
• Determine the contribution of different microbial groups to H2 consumption.

Main Methods:

• Incubation of coastal sediment slurries spiked with H2 under oxygen-free conditions.
• Measurement of H2 consumption potential and methane production over 4 weeks.
• Analysis of bacterial and archaeal community composition using 16S rRNA gene amplicon sequencing (from RNA).

Main Results:

• Sediments from deeper, anoxic layers exhibited higher H2 oxidation potential, especially during periods of low oxygen.
• Hydrogenotrophic sulfate reducers were the primary H2 consumers.
• Significant enrichment of ANME (Anaerobic Methanotrophic Archaea) was observed in specific horizons, suggesting their involvement in H2 cycling.

Conclusions:

• Seasonal variations and redox conditions significantly impact H2 oxidation potential in coastal sediments.
• Hydrogenotrophic sulfate reducers play a key role in H2 scavenging.
• Further studies are needed to fully elucidate the microbial interconnections and dynamics of H2 cycling in these environments.