Ferrate(VI) oxidation drives adaptation toward a putative VBNC-like state in Escherichia coli associated with oxidative stress, metabolic repression, and membrane remodeling.

Ferrate(VI) is emerging as a promising eco-friendly oxidant for advanced water treatment, yet its interactions with bacterial dormancy states and subsequent water-safety implications remain poorly understood. This study investigated the formation and implications of the viable but non-culturable (VBNC) state in Escherichia coli under ferrate(VI) stress in both saline and surface water matrices. While ferrate(VI) effectively induced a rapid loss of culturability in E. coli, it generated a non-culturable but membrane-intact population associated with physiological adaptation mechanisms, including oxidative stress response, metabolic repression, and membrane remodeling. This adaptive strategy not only supported cellular persistence but also conferred significant cross-resistance to environmental stressors and antibiotics. Crucially, upon resuscitation, the bacteria partially recovered epithelial-cell interaction-associated phenotypes, including adhesion, invasion, and cytotoxicity-related responses in Caco-2 intestinal epithelial cells. These findings demonstrate that ferrate(VI) oxidation may inadvertently select for resilient bacterial populations that evade conventional detection while retaining resuscitation-associated host-cell interaction capacity. This discrepancy between non-detectability and residual physiological activity poses a critical challenge to current culture-dependent water quality standards and engineering dosing strategies. Consequently, this study highlights the necessity of integrating molecular viability assessments into water safety monitoring to manage the hidden risks associated with resuscitable non-culturable bacterial populations in full-scale facilities.