Microbial selenate reduction in membrane biofilm reactors using ethane and propane as electron donors

Area of Science:

• Environmental Microbiology
• Bioremediation
• Geochemistry

Background:

• Selenate (Se(VI)) in groundwater poses significant human health risks, especially near shale gas sites.
• Microbial reduction of selenate linked to methane oxidation is known, but ethane and butane roles are unexplored.
• Ethane (C2H6) and butane (C3H8) are key shale gas components with potential for bioremediation.

Purpose of the Study:

• To investigate the potential of ethane (C2H6) and butane (C3H8) to drive microbial selenate (Se(VI)) bio-reduction.
• To identify microbial communities and metabolic pathways involved in Se(VI) reduction using these alkanes.
• To assess the feasibility of using shale gas components for groundwater remediation.

Main Methods:

• Incubation of microbial biofilms with Se(VI) and either C2H6 or C3H8 as electron donors.
• Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) for product analysis.
• 16S rRNA gene sequencing and PICRUSt analysis for microbial community and functional gene profiling.

Main Results:

• Successful bio-reduction of Se(VI) to elemental selenium (Se(0)) using C2H6 and C3H8.
• Formation of polyhydroxyalkanoates (PHAs) as internal electron storage within biofilms.
• Dominance of alkane-oxidizing bacteria (Mycobacterium, Rhodococcus) and detection of potential Se(VI) reducers (Variovorax).
• Enrichment of genes related to alkane oxidation, denitrification, and PHA cycling.

Conclusions:

• Ethane (C2H6) and butane (C3H8) effectively support microbial selenate (Se(VI)) reduction, producing elemental selenium (Se(0)).
• Biofilms utilize polyhydroxyalkanoates (PHAs) for sustained Se(VI) reduction, indicating robust metabolic strategies.
• This research provides a basis for developing bioremediation strategies using shale gas for contaminated groundwater near extraction sites.