Abstract
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 DH5α. The AHLs were extracted from the culture supernatants of the B1 strain and E. coli DH5α 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.
Highlights
Activated sludge systems are used for the treatment of wastewater produced by various industries [1] and are complicated mixtures of many types of microorganisms
The results showed that Runella was the predominant genus in the activated sludge sample (72.6%; Table 1), followed by Methylibium, Acidovorax, and Alicycliphilus (8.4%, 5.3%, and 3.2%, respectively)
We demonstrated for the first time the structure of the acylhomoserine lactone (AHL) produced by an Alicycliphilus sp. strain isolated from an activated sludge sample at an electronic component
Summary
Activated sludge systems are used for the treatment of wastewater produced by various industries [1] and are complicated mixtures of many types of microorganisms. For stable operation of these systems, it is necessary to understand the bacterial interactions in activated sludge. Quorum sensing is a cell density-dependent cell-to-cell communication system that regulates gene expression [2]. In gram-negative bacteria, N-acylhomoserine lactones (AHLs) are used as the quorum-sensing signaling molecules [3]. Various AHL-producing bacteria have been isolated from activated sludge [5]. These bacteria regulate the expression of exoenzymes, which are involved in wastewater treatment, through AHL-mediated quorum-sensing
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