Effect of interspecies quorum sensing on the formation of aerobic granular sludge

Quorum sensing (QS) is a form of microbial communication that relies on small signal molecules to regulate group behaviors such as biofilm formation in response to population density. In this study, we attempted to apply the paradigm of bacterial QS to aerobic granular sludge (AGS) formation for wastewater treatment. An essential element of interspecies QS signals, boron, was added to a sequencing batch reactor (SBR) to stimulate AGS growth. Bioassays elaborated the activity of autoinducer-2 (AI-2). We found that boron accelerated AGS growth, resulting in improved settlement performance and increased biomass in the SBR. During continuous SBR operation, the AGS showed an obvious increase in AI-2 activity, which implies that interspecies QS was closely associated with AGS formation. Analysis of EPS showed that boron stimulated tryptophan production, and increased the hydrophobia of AGS. From these results, it was speculated that the addition of boron may have promoted the formation of boron complexed to (R)-4, 5-dihydroxy-2,3-pentanedione (DPD) as the precursor of AI-2, which resulted in accelerated interspecies QS. The results also suggested QS as a novel regulation target for the biogranulation process, such as AGS formation.