Microbial community structure in autotrophic nitrifying granules characterized by experimental and simulation...

Area of Science:

• Environmental microbiology
• Biotechnology
• Wastewater treatment

Background:

• Nitrifying granules are crucial for efficient ammonia removal in wastewater treatment.
• Understanding the microbial community structure and spatial organization within these granules is essential for optimizing their performance.
• Previous studies often relied on single techniques, potentially limiting a holistic view of granule ecology.

Purpose of the Study:

• To elucidate the community structure and spatial distribution of bacteria in aerobic nitrifying granules.
• To investigate the interactions between ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and heterotrophic bacteria within the granules.
• To validate experimental findings with mathematical modeling for a comprehensive understanding.

Main Methods:

• Multivalent approach combining Fluorescence In Situ Hybridization (FISH) and 16S rRNA clone library analysis for bacterial identification and localization.
• Microelectrode measurements to determine microprofiles of key substrates and products (ammonium, nitrite, nitrate, oxygen).
• One- and two-dimensional numerical biofilm models to simulate granule development and bacterial interactions.

Main Results:

• Ammonia-oxidizing bacteria were found in the outer layer (0-200 µm), nitrite-oxidizing bacteria in a deeper layer (200-300 µm), and heterotrophic bacteria in the core.
• Measured microprofiles of NH(4)(+), NO(2)(-), NO(3)(-), and O(2) correlated well with the observed bacterial distribution.
• Numerical models accurately predicted bacterial distribution and substrate/product profiles, supporting the proposed interactions.

Conclusions:

• The combination of molecular techniques, microelectrode measurements, and mathematical modeling provides a powerful tool for understanding nitrifying granule structure and function.
• The spatial segregation of bacterial groups is driven by substrate availability and microbial interactions within the granule.
• This integrated approach offers deeper insights into nitrifying granules than individual methods alone, crucial for optimizing wastewater treatment processes.