Abstract
We have investigated the quorum sensing control in Aeromonas veronii MTCC 3249, originally isolated as A. culicicola from the midgut of Culex quinquefasciatus. Based on biosensor assays, the bacterium showed constant production of multiple acyl-homoserine lactones (AHLs) with increasing cell-density. The luxRI gene homologs, acuR (A. culicicola transcriptional Regulator) and acuI (A. culicicola autoInducer) were successfully amplified by inverse-PCR. Sequence analysis indicated acuRI were divergent from all known quorum sensing gene homologs in Aeromonas. Two localized regions in the C-terminal autoinducer binding domain of acuR showed indels suggesting variations in autoinducer specificity. Further, only a single copy of the quorum sensing genes was detected, suggesting a tight regulation of mechanisms under its control. Chromatography and further chemical analysis identified two AHLs in the culture supernatant: 6-carboxy-HHL (homoadipyl homoserine lactone), a novel AHL, and N-tetradecanoylhomoserine lactone. The existence of a potentially variant quorum sensing system might therefore, reflect in some way the ecological strategies adopted by this bacterium in the mosquito midgut.
Highlights
Aeromonas spp. are important disease-causing pathogens of fish and other cold-blooded species, as well as humans [1]
While A. veronii MTCC 3249 has already been shown to possess LuxRI gene homologs [3], the bioassay based detection reconfirmed the corresponding phenotype in this strain (Figure 2)
A curve with zero slope was observed when fold induction/OD540 was plotted (Figure 3(b)) indicating that the production of acyl-L-homoserine lactones (AHLs) was constant and proportional to CFU/mL of A. veronii MTCC 3249, and there was a linear correlation between AHL amounts and production of light by E. coli JM109 with pSB401
Summary
Aeromonas spp. are important disease-causing pathogens of fish and other cold-blooded species, as well as humans [1]. Given the close proximity of iciA homolog downstream of the autoinducer synthase gene in Aeromonas, the involvement of quorum sensing in increasing the cell density cannot be ruled out This tempted us to investigate the nature of this control. This stems from the fact that luxRI gene homologs in Aeromonas share high sequence similarity [3] and it is likely that if multiple quorum sensing systems are present in this strain, these might share high sequence similarity with the acuRI system This specific aspect has not been investigated in the genus Aeromonas, results from A. hydrophila and A. salmonicida [2,4] suggest the involvement of multiple AHLs and as-yet unidentified factors controlling different phenotypes. We present an analysis of the quorum sensing system in A. veronii MTCC 3249 that might in some way reflect on its ecological strategies in mosquito midgut
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