Cloning and characterization of short‐chain N ‐acyl homoserine lactone‐producing Enterobacter asburiae strain L1 from lettuce leaves

In gram‐negative bacteria, bacterial communication or quorum sensing ( QS ) is achieved using common signaling molecules known as N ‐acyl homoserine lactones ( AHL ). We have previously reported the genome of AHL ‐producing bacterium, Enterobacter asburiae strain L1. In silico analysis of the strain L1 genome revealed the presence of a pair of luxI/R genes responsible for AHL ‐type QS , designated as eas IR . In this work, the 639 bp luxI homolog, encoding 212 amino acids, have been cloned and overexpressed in Escherichia coli BL 21 ( DE 3) pL ysS. The purified protein (~25  kD a) shares high similarity to several members of the LuxI family among different E   asburiae strains. Our findings showed that the heterologously expressed EasI protein has activated violacein production by AHL biosensor Chromobacterium violaceum CV 026 as the wild‐type E .  asburiae . The mass spectrometry analysis showed the production of N ‐butanoyl homoserine lactone and N –hexanoyl homoserine lactone from induced E .  coli harboring the recombinant EasI, suggesting that EasI is a functional AHL synthase. E .  asburiae strain L1 was also shown to possess biofilm‐forming characteristic activity using crystal violet binding assay. This is the first report on cloning and characterization of the luxI homolog from E .  asburiae .