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

Abstract

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 easIR. In this work, the 639 bp luxI homolog, encoding 212 amino acids, have been cloned and overexpressed in Escherichia coli BL21 (DE3)pLysS. The purified protein (~25 kDa) 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 CV026 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.

Functional characterization of quorum sensing LuxR-type transcriptional regulator, EasR in Enterobacter asburiae strain L1

“…On top of that, β-galactosidase activities of cells harboring TOP10-pMULTI-pLNBAD- easR with the addition of C4-HSL was present in a higher amount than C6-HSL. This was in agreement with the previous hypothesis that the former AHL may possess a more important role in executing the physiological functions of the cells or expression of virulence factors ( Lau et al, 2018 ). Surprisingly, a combination of C4-HSL and C6-HSL were not able to elicit higher activity than C4-HSL alone.…”

“…Furthermore, in previous study, E. asburiae strain L1 was found to produce C4-HSL as the major AHL and C6-HSL as the minor AHL ( Lau et al, 2018 ). Therefore, in the current study, it was predicted that C4-HSL will elicit higher β-galactosidase activities than C6-HSL alone.…”

“…Although efforts have been made to unravel the complex mechanisms that contribute to the pathogenicity of different Enterobacter spp., there is very little information associated with AHL-type QS mechanisms in Enterobacter spp. ( Lau et al, 2018 ).…”