**2.3 Starvation process**

Studies have shown that nitrite accumulation occurs when nitrification system is restarted after being idle for a period of time. The attenuation rate of AOB is smaller than that of NOB in the starvation process [14, 15]. Jia et al. [16] found that AOB has a unique hunger response strategy, and its cells are in a state of readiness at any time. Once the substrate appears, it can produce substrate invertase (gene transcription speed is fast), so that AOB can quickly recover its activity from starvation. However, NOB does not have this ability, so AOB has a stronger ability to adapt to environmental changes than NOB.
