Recent advances in isolation and physiological characterization of planktonic anaerobic ammonia-oxidizing bacteria

Anaerobic ammonia oxidation (anammox) is widely regarded as an efficient biological nitrogen removal technology and is increasingly applied in wastewater treatment processes. However, the long doubling time and sensitivity to environmental pressures of anaerobic ammonia-oxidizing bacteria (AnAOB) often lead to unstable nitrogen removal performance. Various combined processes are being explored to overcome these limitations, providing insights into the ecological, physiological, and biochemical characteristics of AnAOB. Nevertheless, due to the lack of AnAOB pure cultures, the mechanisms of nitrogen metabolism, growth regulation, and cell communication remain unclear. This review highlights the unique physiological structures of AnAOB, current techniques for isolating and enriching planktonic AnAOB, and the associated challenges. A deeper understanding of these aspects offers guidance for improving planktonic AnAOB enrichment and incubation.