Characterization of an N-acylhomoserine lactonase from Serratia sp. and its biofouling mitigation in a membrane bioreactor

Abstract

Membrane biofouling is a process that can impede the development of membrane bioreactor (MBR), which constitutes an important system of the wastewater treatment process. Membrane biofouling is governed by quorum sensing (QS), a communication system heavily dependent on the activities of signal molecules. Certain bacteria, known as quorum quenching (QQ) bacteria, can quench the QS process by destroying the signal molecules. These QQ bacteria are considered a sustainable and feasible way of mitigating membrane biofouling in MBR. In this study, a QQ enzyme (designated as AisZ) from a Serratia sp. was first identified and characterized. Escherichia coli BL21 expressing AisZ was able to degrade different QS signal molecules. Furthermore, these cells could also mitigate membrane biofouling in MBR during a 29-day operation by reducing the transmembrane pressure from 31 to 21 kPa. The metal ions Co2+ and Ni2+ were relatively important to AisZ in that they could significantly enhance the activity of AisZ and restore the EDTA-inactivated AisZ. Expression of the aisA gene was not influenced by Co2+, Ni2+ and QS signal molecules. AisZ might, therefore, extend the diversity of potential candidates for the mitigation of biofouling associated with membrane filtration technologies.