Estimation of spatial distribution of quorum sensing signaling in sequencing batch biofilm reactor (SBBR) biofilms

Highlights: • Biofilms has been divided into three different fractions by centrifugal forces; • SEPS and LB EPS concentration in different fractions of biofilms displayed significant positive relationship with the distribution of C12-HSL; • Biofilm adhesion and compliance was the strongest in the tightly-bound biofilm, the weakest in the supernatant/surface biofilm; • QS and QQ bacteria have been recognized in the wastewater treatment biofilms. Quorum sensing (QS) signaling, plays a significant role in regulating formation of biofilms in the nature; however, little information about the occurrence and distribution of quorum sensing molecular in the biofilm of carriers has been reported. In this study, distribution of QS signaling molecules (the acylated homoserine lactones-AHLs, and AI-2), extracellular polymeric substances (EPS) and the mechanical properties in sequencing batch biofilm reactor (SBBR) biofilms have been investigated. Using increased centrifugal force, the biofilms were detached into different fractions. The AHLs ranged from 5.2 ng/g to 98.3 ng/g in different fractions of biofilms, and N-decanoyl-dl-homoserine lactone (C10-HSL) and N-dodecanoyl-dl-homoserine lactone (C12-HSL) in the biofilms obtained at various centrifugal forces displayed significant differences (p < 0.01). Interspecies communication signal autoinducer-2(AI-2) in the biofilms ranged from 79.2 ng/g to 98.3 ng/g. Soluble EPS and loosely bound EPS content in the different fractions of biofilms displayed significant positive relationship with the distribution of C12-HSL (r = 0.86, p < 0.05). Furthermore, 49.62% of bacteria in the biofilms were positively related with AHLs with 22.76% was significantly positively (p < 0.05) related with AHLs. Biofilm adhesion and compliance was the strongest in the tightly-bound biofilm, the weakest in the supernatant/surface biofilm, which was in accordance with the distribution of C12 HSL(r = 0.77, p < 0.05) and C10-HSL(r = 0.75, p < 0.05), respectively. This study addressed on better understanding of possible methods for the improvement of wastewater bio-treatment through biofilm application.