Bacterial transport experiments in fractured crystalline bedrock

Area of Science:

• Environmental Microbiology
• Hydrogeology
• Biogeochemistry

Background:

• Groundwater contaminant biodegradation relies on the transport of degrading bacteria.
• Limited data exist on bacterial transport in saturated bedrock at the field scale.

Purpose of the Study:

• To investigate the transport behavior of different bacterial strains in fractured crystalline bedrock.
• To compare bacterial transport with microsphere tracers under field conditions.

Main Methods:

• Conducted forced-gradient tracer experiments over 36 meters in fractured bedrock.
• Utilized differentially stained bacteria with varying physicochemical and physiological properties (shape, cell-wall type, motility).
• Compared bacterial transport to that of microsphere tracers.

Main Results:

• No two bacterial strains exhibited identical transport behavior.
• Microspheres showed distinct breakthrough curves compared to bacteria.
• Nonmotile bacteria showed better recovery than motile strains.
• Gram-negative rods had higher recovery than Gram-positive rods of similar size.
• Spherical bacteria generally transported better than rod-shaped bacteria.

Conclusions:

• Bacterial physical properties, such as motility and cell shape, significantly influence transport in saturated bedrock.
• Even minor differences in bacterial characteristics can lead to substantial variations in field-scale transport.
• Findings are specific to the studied bacterial strains and groundwater environment but suggest broader implications for microbial transport modeling.