Comparison of enumeration methods for ammonia-oxidizing bacteria.

Area of Science:

• Environmental microbiology
• Molecular biology techniques

Background:

• Accurate enumeration of ammonia-oxidizing bacteria is crucial for understanding nitrogen cycling in aquatic systems.
• Various molecular and culture-based methods exist, each with limitations.

Purpose of the Study:

• To compare the efficacy of Most Probable Number (MPN), antibody-based methods, fluorescent in situ hybridization (FISH), and dot blot hybridization for enumerating ammonia-oxidizing bacteria.
• To evaluate the suitability of these methods for different environmental samples, including wastewater treatment plant (WWTP) influents and effluents.

Main Methods:

• Application of MPN, antibody, FISH, and dot blot hybridization to diverse suspended system samples.
• Reoptimization of the Nso 190 oligonucleotide probe for FISH.
• Comparative analysis of method performance, including detection limits and reliability.

Main Results:

• MPN underestimated bacterial counts.
• Dot blot hybridization demonstrated a lower detection limit and higher reliability, suitable for mixed liquors, effluents, and enrichment cultures.
• FISH performed well in high-ammonium systems but struggled with weak signals and non-specific binding in low-ammonium environments like WWTP effluents and river water.

Conclusions:

• Dot blot hybridization is a reliable method for enumerating ammonia-oxidizing bacteria across various sample types.
• FISH requires careful optimization and may not be ideal for low-ammonium environments due to signal and specificity issues.
• Method selection depends on the specific application and sample characteristics.