The essential roles of Adenosine Triphosphate (ATP) and ATP-associated cellular communication in aerobic granulation

Abstract

Aerobic granulation is a process to form dense and spherical aggregates through cell-to-cell self-immobilization without addition of biocarriers. Recently, intensive research efforts have been dedicated to the development of aerobic granules and their applications for wastewater treatment. However, the microbiological origin of this phenomenon is still largely unknown and very little information is currently available regarding the mechanisms of aerobic granulation at levels of energy metabolism and cellular communication. This study, therefore, attempts to address a basic question: Are adenosine triphosphate (ATP) and cellular communication required in the formation and maintenance of aerobic granules? In the first phase of this study, the possible roles of ATP and cellular communication in the formation of aerobic granules were investigated. For this purpose, three sequencing batch reactors (SBRs) inoculated with synthetic wastewater-acclimated activated sludge were operated in the absence and presence of a chemical uncoupler, 3,3’,4’,5-tetrachlorosalicylanilide (TCS), which has the ability to dissipate the Proton Motive Force (PMF) and subsequently inhibit ATP synthesis. Results showed that aerobic granules were successfully cultivated in the control reactor free of TCS, while aerobic granulation was completely inhibited with the addition of 2 and 4 mg L-1 TCS. It was found that cellular ATP content in the control reactor increased along granulation process, meanwhile, the increase in the production of signaling molecules, i.e., autoinducer-2 (AI-2) and N-acylhomoserine lactones (AHLs), as well as, extracellular polymeric substances (EPS) was also observed. However, in the presence of TCS, the production of AI-2, AHLs and EPS was significantly inhibited due to the suppressed ATP synthesis, which ultimately resulted in the failure of aerobic granulation. It was, therefore, demonstrated that ATP and cellular communication played important roles in the development of aerobic granules.