Protistan predation affects trichloroethene biodegradation in a bedrock aquifer

Area of Science:

• Environmental microbiology
• Bioremediation
• Aquatic ecology

Background:

• Trichloroethene (TCE) contamination is a persistent environmental issue.
• Slow biodegradation rates and stalling at intermediate compounds like cis-dichloroethene (cDCE) limit bioremediation success.
• Resource availability (bottom-up forces) is well-studied, but top-down ecological pressures are less understood.

Purpose of the Study:

• To investigate the impact of protistan predation (a top-down force) on TCE biodegradation.
• To determine if protists affect the efficiency of reductive dechlorination in contaminated aquifers.
• To evaluate the role of protists in the context of resource availability and bioaugmentation.

Main Methods:

• Laboratory microcosms were established using indigenous bacteria from TCE-contaminated aquifers.
• Experiments involved varying conditions: presence/absence of protists, organic carbon amendments, and addition of commercial bacterial cultures.
• Bacterial morphology and reductive dechlorination activity were monitored.

Main Results:

• Indigenous protists completely inhibited reductive dechlorination when present with indigenous bacteria.
• Protists caused bacterial elongation but still inhibited dechlorination under organic carbon-amended conditions.
• In the presence of protists, bioaugmentation with a commercial culture also stalled dechlorination at cDCE.
• Removal of protists allowed for significant TCE degradation to ethene and/or CO2 under amended conditions.

Conclusions:

• Indigenous protists significantly suppress TCE-degrading bacteria through predation.
• Protistan grazing can prevent successful bioremediation and bioaugmentation by reducing microbial populations.
• Inhibiting protistan predation may be a necessary strategy to enhance TCE mineralization in contaminated sites.