Lab-scale membrane bioreactors (MBRs) were investigated at 12, 18, and 25 degrees C to identify the correlation between quorum sensing (QS) and biofouling at different temperatures. The lower the reactor temperature, the more severe the membrane biofouling measured in terms of the transmembrane pressure (TMP) during filtration. More extracellular polymeric substances (EPSs) that cause biofouling were produced at 18 degrees C than at 25 degrees C, particularly polysaccharides, closely associated with QS via the production of N-acyl homoserine lactone (AHL). However, at 12 degrees C, AHL production decreased, but the release of EPSs due to deflocculation increased the soluble EPS concentration. To confirm the temperature effect related to QS, bacteria producing AHL were isolated from MBR sludge and identified as Aeromonas sp., Leclercia sp., and Enterobacter sp. through a 16S rDNA sequencing analysis. Batch assays at 18 and 25 degrees C showed that there was a positive correlation between QS through AHL and biofilm formation in that temperature range.