qss

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C. violaceum is a gram-negative bacterium. This bacterium possess CviI/CviR type quorum sensing, and uses QS to regulate cell density dependent production of water insoluble violacein, a purple pigment. McClean et al. (1997) developed AHL-negative mutant, C. violaceum strain CV026, by mini –T5 mutagenesis in cviI. CV026 is unable to synthesize its own AHL. CV026 have been widely used as a biosensor to screen AHL producing bacteria using agar plate and thin layer chromatography- agarose overlay methods. CV026 detects a wide range of AHLs ranging from C4- to C8-AHL. Limitation with CV026 is that this does not detect any of 3-hydroxy-AHLs. QS system of CV026 is not induced by AHL molecules with acyl side chains ranging from C10 to C14. But these larger AHL molecules can indirectly be detected by QS inhibition assay. It has been reported that larger AHL molecules act as antagonist of smaller molecule. So, CV026 once fully induced in presence of the small AHL, when is treated with large AHLs shows reduction in level of induction (McClean et al., 1997). In one of the latest studies CV026 was used to detect small chain AHLs C6-AHL and C8-AHL using TLC in soil and air living bacterium Burkholderia sp. strain A9. Extracts of Burkholderia sp. strain A9, along with AHL standards were loaded and separated on C18-TLC plates, when CV026 was overlaid, two spots were developed. These spots were matching with Rfs of C6-AHL and C8-AHL. Spots were further reconfirmed by Triple Quadrupole LC/MS(Chen et al., 2013). Anbazhagan et al. (2012) screened large AHL molecules from the biofilm forming clinical isolates of Acinetobacter sp. by performing well diffusion based inhibition assay, and later characterization by mass spectrometry. Acinetobacter sp. a... ... middle of paper ... ...g screened for possible AHL production, different groups of biosensors sensing different types of AHLs should be used. Biosensors derived from C. violaceum and A. tumefaciens are preferably used for the screening of unknown AHL producer, as these sense a broad range of AHLs. Responses of several biosensors including V. harveyi BB170 are influenced by the composition of growth medium, and also by the genotype of the biosensor strain (Lindsay and Ahmer, 2005). So, these limitations should be considered during selection of biosensor, and during interpreting screening results. Though biosensors have some drawbacks, but their ease of use and versatility, make them a preferable choice for the screening of new AI producing strains. Once AI producers are screened, further characterization of AI can be done by using sophisticated techniques like Mass Spectrometry and HPLC.

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