Enrichment strategies for comammox Nitrospira: Ecological insights and technological innovations

Comammox Nitrospira, microorganisms capable of converting ammonia to nitrate independently, are ubiquitous in diverse ecosystems and play pivotal roles in global nitrogen cycling and sustainable wastewater treatment. However, their cultivation and purification remain challenging due to their slow growth rates. This review systematically summarized enrichment strategies from ecophysiology and niche differentiation perspectives. We first depict their distribution across natural and engineered systems, revealing their dominance in oligotrophic habitats and even some mesotrophic habitats. By analyzing the niche differentiation among ammonia-oxidizing microorganisms, we highlight how substrate affinity, oxygen tolerance, and metabolic versatility determine the competitiveness of comammox Nitrospira, aiming to guide selective enrichment designs. Enrichment strategies including prolonged sludge retention time, biofilm-enhanced systems, and low-dissolved oxygen/ammonium, are evaluated alongside mechanistic insights into physiological adaptations. We underscore the necessity of isolating comammox Nitrospira clade B, developing standardized quantification methods and specific inhibitors. This review highlights the viability of energy-efficient wastewater treatment technologies that prioritize comammox Nitrospira and underscores their underestimated contributions in mesotrophic environments. Future studies would integrate ecophysiological insights with bioreactor engineering innovations to fully exploit their biotechnological potential.