Bioreactor function under perturbation scenarios is affected by interactions between bacteria and protozoa

Area of Science:

• Environmental microbiology
• Biotechnology
• Wastewater treatment

Background:

• Activated sludge systems are crucial for wastewater treatment.
• Microbial community structure and function are vital for bioreactor performance.
• Understanding responses to toxicant perturbations is essential for system stability.

Purpose of the Study:

• To investigate the impact of transient cadmium perturbations on activated sludge microbial communities.
• To examine effects on bioreactor performance, bacterial activity, community structure, and microbial interactions.
• To elucidate the mechanisms behind process recovery after cadmium exposure.

Main Methods:

• Laboratory- and pilot-scale activated sludge bioreactors were subjected to pulse cadmium perturbations.
• Bacterial community structure and abundance were analyzed.
• Bioreactor performance and bacterial activity were monitored.
• Bacteria-protozoa interactions, specifically protozoal grazing, were assessed through independent experiments.

Main Results:

• A short-term inhibition of the bacterial community was observed following cadmium perturbation.
• Process recovery was characterized by increased bacterial abundance and high biomass activity.
• Bacterial community structure changes did not fully explain the increased biomass activity.
• Reduced protozoal grazing, due to higher ciliate protozoa inhibition compared to bacteria, drove the bacterial abundance increase.

Conclusions:

• Protozoal grazing significantly influences microbial community dynamics and bioreactor recovery after toxicant perturbation.
• The role of protozoa in bioengineered systems, especially under stress, warrants further investigation.
• Expanding ecological studies to include predator-prey dynamics is crucial for understanding system resilience.