The presence and role of bacterial quorum sensing in activated sludge.
Bottom Line: N-acylated-l-homoserine lactone and exoenzyme production were frequently observed among the isolates.N-acylated-l-homoserine lactones produced by this strain were identified and genes ahyI/R and chiA, encoding AHL production and response and chitinase activity respectively, were sequenced.These experiments provide insight into the relationship between AHL-mediated gene expression and exoenzyme activity in activated sludge and may ultimately create opportunities to improve sludge performance.
Affiliation: Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.Show MeSH
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Mentions: The isolation of AHL‐producing bacteria from activated sludge raises the question of whether AHLs are produced in activated sludge at biologically relevant concentrations. Ethyl acetate extracts of activated sludge were analysed by LC‐ESI‐MS revealing the presence of a molecule with peaks at 214.14261 (M+H)+ and 236.12418 (M+Na)+ and a retention time corresponding to synthetic N‐heptanoyl‐l‐homoserine lactone applied as a standard (Fig. 1A). LC‐ESI‐MS analysis also identified a compound with a retention time slightly longer than synthetic N‐dodecanoyl‐l‐homoserine lactone (36 versus 32 min) and peaks with m/z ratios of 284.13983 (M+H)+ and 306.12140 (M+Na)+, similar but not identical to the N‐dodecanoyl‐l‐homoserine lactone standard (Fig. 1B). The extract was also subjected to thin‐layer chromatography and assessed for AHL‐like compounds using CviR and TraR‐based overlays. While the CviR overlay assay did not detect any compounds with AHL‐like activity, the TraR‐based assay revealed a compound with stimulatory activity migrating between N‐decanoyl‐l‐homoserine lactone and N‐dodecanoyl‐l‐homoserine lactone (Fig. 2). It is tentatively suggested that this unknown compound observed by both MS and TLC is N‐3‐oxo‐undecanoyl‐l‐homoserine lactone, although a standard was not available to verify this. While these analyses confirm the presence of AHLs in activated sludge amid a complex background of solvent extractable organic matter, they do not address questions of biological relevance. Hence, an alternative strategy was devised to assess AHL production in activated sludge based on a fluorescent AHL biosensor strain.
Affiliation: Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.