Identification of Quorum-Sensing Signal Molecules and a Biosynthetic Gene in Alicycliphilus sp Isolated from Activated Sludge

Activated sludge is a complicated mixture of various microorganisms that is used to treat sewage and industrial wastewater. Many bacteria produce N-acylhomoserine lactone (AHL) as a quorum-sensing signal molecule to regulate the expression of the exoenzymes used for wastewater treatment. Here, we isolated an AHL-producing bacteria from an activated sludge sample collected from an electronic component factory, which we named Alicycliphilus sp. B1. Clone library analysis revealed that Alicycliphilus was a subdominant genus in this sample. When we screened the activated sludge sample for AHL-producing strains, 12 of 14 the AHL-producing isolates were assigned to the genus Alicycliphilus. A putative AHL-synthase gene, ALISP 0667, was cloned from the genome of B1 and transformed into Escherichia coli DH5 alpha. The AHLs were extracted from the culture supernatants of the B1 strain and E. coli DH5 alpha cells harboring the ALISP 0667 gene and were identified by liquid chromatography-mass spectrometry as N-(3-hydroxydecanoyl)-L-homoserine lactone and N-(3-hydroxydodecanoyl)-L-homoserine lactone. The results of comparative genomic analysis suggested that the quorum-sensing genes in the B1 strain might have been acquired by horizontal gene transfer within activated sludge.