Ferrous-driven microbial synergy enhances reductive dechlorination under sulfide stress

Area of Science:

• Environmental Microbiology
• Bioremediation
• Geochemistry

Background:

• Chlorinated ethenes (CEs) like trichloroethene (TCE) contaminate groundwater, often with high sulfate levels.
• Sulfate-reducing bacteria produce sulfide, which severely inhibits Dehalococcoides mccartyi (Dhc), crucial for TCE breakdown.
• Sulfide toxicity to Dhc is significant, nearly eliminating TCE dechlorination above 5 mM concentrations.

Purpose of the Study:

• To develop a strategy to overcome sulfide inhibition of TCE dechlorination in co-contaminated aquifers.
• To investigate the effectiveness of a synergistic system involving Dhc and sulfate-reducing bacteria with ferrous chloride supplementation.

Main Methods:

• Co-cultivation of Dhc strain CWV2 and Nitratidesulfovibrio liaohensis strain KPS.
• Supplementation with ferrous chloride (Fe(II)) to precipitate sulfide as ferrous sulfide (FeS).
• Transcriptomic analysis to assess gene expression changes in Dhc and KPS.
• Microbial community analysis to evaluate changes in bacterial populations and functional partners.

Main Results:

• Fe(II) supplementation effectively detoxified sulfide by forming FeS, restoring Dhc-mediated TCE dechlorination.
• Optimal Fe/S molar ratios were identified to maximize sulfide removal without adverse pH or mineral formation.
• FeS treatment reactivated Dhc's dehalogenase and hydrogenase genes and enhanced KPS sulfur metabolism.
• Microbial communities shifted, increasing Dhc abundance and enriching hydrogen-producing fermentative bacteria.

Conclusions:

• Fe(II)-mediated sulfide precipitation is a viable strategy for in situ remediation of TCE-sulfate co-contaminated groundwater.
• This approach stabilizes microbial interactions, sustaining essential reductive dechlorination processes.
• The synergistic system offers a practical solution for complex groundwater contamination challenges.