Anammox endogenous metabolism during long-term starvation: Impacts of intermittent and persistent modes and phosphates

Starvation of anaerobic ammonium oxidation (anammox) bacteria can occur in underloaded bioreactors or during the storage of sludge. In this study, the impacts of intermittent and persistent resting modes and phosphates on the endogenous metabolism of anammox bacteria during long-term starvation were investigated. Batch experiments were performed to evaluate the response of anammox granules to different modes of starvation (persistent-resting and intermittent-resting cells) in the presence and absence of phosphates. The endogenous decay coefficient of anammox granules (based on the decreased biomass) over a 30-d persistent starvation period was 0.0062 d−1, while the intermittent starvation by means of providing substrates every 10 days accelerated the biomass decay approximately twice (0.0110 d−1). Moreover, the intermittent-resting cells displayed exacerbated decreases in specific anammox activity relative to the persistent-resting cells, whereas no significant difference was observed in the heme c contents. Regardless of the physiological status of the cells, the presence of low levels of phosphates may be beneficial; however, a high level of phosphates is not recommended. Although different metabolic strategies were adopted depending on the starvation mode, anammox bacteria possessed a better survival strategy via a relatively low maintenance energy requirement to ensure their survival in nutrient-limited systems. In addition, the variations in extracellular protein-like components were indicative of different intracellular metabolic regulation mechanisms. These results provide a better understanding of the endogenous metabolism of anammox bacteria.