The role of AHL-mediated quorum sensing system in Chitinase production of Aeromonas sp. strains isolated from a municipal wastewater treatment plant

摘要

This thesis explores the role of AHL-mediated quorum sensing system in chitinase production of Aeromonas sp. strains isolated from a municipal wastewater treatment (WWT) plant. AHL production and chitinase activity was assessed in twelve different Aeromonas strains, isolated previously. LuxR and TraR based cross-streaking assays, colloidal chitin plates and colorimetric chitinase activity assays were performed. Six out of twelve isolates were exhibited both AHL and chitinase activity. AHL-mediated chitinase activity was explored by supplementing different AHLs into growing cultures of six selected isolates. Results showed that addition of butanoyl-homoserine lactone (BHL) and 3-oxo-hexanoyl-homoserine lactone (OHHL) induced the expression of chitinase in two of the Aeromonas sp. isolates early in the logarithmic growth phase.Aeromonas sp. strain GC1 was found to produce BHL, hexanoyl-homoserine lactone (HHL), octanoyl-homoserine lactone (OHL) and dodecanoyl-homoserine lactone (dDHL) by Thin Layer Chromatograhy (TLC) overlay plate assay and Mass Spectrometric analysis. PCR amplification and sequencing confirmed the presence of Aeromonas sp. LuxR/I homologues, AhyR/I, and chitinase genes in Aeromonas sp. strain GC1. These experiments are consistent with the hypothesis that AHL mediated quorum sensing plays a role in regulating chitinase activity in Aeromonas sp. and add to our understanding of AHL mediated gene expression in activated sludge.