Adaptation mechanisms of ANAMMOX bacteria to extreme environments.

Anaerobic ammonium oxidation (ANAMMOX) bacteria (AnAOB) play a vital role in the global nitrogen cycle and have emerged as a promising alternative for sustainable nitrogen removal in wastewater treatment. They directly convert ammonium and nitrite into dinitrogen gas under anaerobic conditions, without the need for high energy and external carbon associated with conventional nitrification-denitrification. With increasing global demands to mitigate nutrient pollution and improve water quality, a deeper understanding of AnAOB has become both scientifically significant and practically necessary. Despite the successful application of anammox technology across a diverse wastewater treatment streams, the mechanisms underlying their translation into predictive, scalable process control remain poorly understood. So, it's imperative to develop an understanding of their enzymatic systems, metabolic pathways, cellular structure, and adaptive responses, which provides deeper insights into optimizing ANAMMOX-based biotechnologies for wastewater treatment for commercial viability. Therefore, this review reports strategies to reframe AnAOB resilience developed by analysing physiological, molecular, and ecological adaptation mechanisms that enable AnAOB to survive and function under extreme environmental conditions. A conceptual framework has been developed using three key strategies: (i) membrane remodeling through changes in membrane fluidity, transporter activity, and ladderane lipid composition; secondly, (ii) metabolic flux redistribution involving regulation of stress response proteins, metabolic flexibility, and energy conservation; and (iii) biofilm formation and interactions within microbial consortia which is providing insights regarding quorum sensing and community cross feeding. Furthermore, detailed insights into their substrate preferences, growth rates, stress responses, and microbial interactions can advance reactor designs, operational stability, and industrial scalability. Final, this review highlights the major knowledge gaps and challenges that limit its broader implementation and discusses future research directions required to advance predictive process control and next-generation ANAMMOX-based wastewater treatment systems.