Deciphering energy trade-offs and dormancy mechanisms in a PCB-degrading bacterium Rhodococcus biphenylivorans TG9 under acid stress

Adverse conditions in water treatment system can induce bacteria into a viable but non-culturable (VBNC) state. This enables pathogens to evade detection during disinfection, and affect functional bacteria crucial for pollutants removal. However, the mechanisms underlying VBNC induction remain poorly understood. Here, we investigated Rhodococcus biphenylivorans TG9, a polychlorinated biphenyl (PCB)-degrading bacterium, under prolonged acid stress (pH 4). After 40 days, TG9 entered the VBNC state, resulting in a sharp decline in pollutants degradation efficiency due to reduced substrate transport capacity and enzymes activity. Under continuous acid stress, TG9 prioritized energy for maintaining intracellular pH homeostasis, at the expense of catabolic and anabolic functions. Such an energy trade-off facilitated VBNC as a surviving strategy, enabling the preservation of viable cells for potential resuscitation. However, prolonged acid stress depleted intracellular energy below a critical threshold, leading to an irreversible transition to a non-resuscitable state. These findings demonstrate the vital role of energy metabolism in bacterial stress responses, and suggest that manipulating energy availability may help prevent bacterial dormancy or reactivate dormant cells in engineered water systems.