Microorganisms oxidize glucose through distinct pathways in permeable and cohesive sediments

Area of Science:

• Marine microbiology
• Biogeochemical cycles
• Environmental science

Background:

• Microbial degradation of organic matter in marine sediments typically involves fermentation followed by oxidation.
• Fermentation uncoupled from external electron acceptors is hypothesized for environments with variable oxygen.

Purpose of the Study:

• To provide direct evidence of uncoupled fermentation in marine sediments.
• To quantify the relative contributions of respiration and fermentation under different conditions.

Main Methods:

• Development and application of a novel differentially labeled glucose isotopologue assay.
• Analysis of permeable (sandy) and cohesive (muddy) sediments.
• Incubation of four bacterial isolates.

Main Results:

• Microbial communities in permeable sediments exhibited uncoupled fermentation via the Embden-Meyerhof-Parnas pathway under anoxia, lasting up to 160 hours.
• Communities in muddy sediments primarily performed complete oxidation of glucose to CO2 under anoxia.
• Fermentation was unexpectedly observed under oxic conditions in permeable sediments.

Conclusions:

• Microbial communities in variable oxygen environments utilize uncoupled fermentation for metabolizing organic matter during transient anoxia.
• Sediment type and oxygen variability significantly influence microbial metabolic pathways.