A novel strategy for the isolation of luxl homologues: evidence for the widespread distribution of a LuxR:Luxl superfamily in enteric bacteria

Abstract

The pheromone N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) regulates expression of bioluminescence in the marine bacterium Vibrio fischeri, the production of carbapenem antibiotic in Erwinia carotovora and exoenzymes in both E. carotovora and Pseudomonas aeruginosa. A characteristic feature of this regulatory mechanism in V. fischeri is that it is cell density-dependent, reflecting the need to accumulate sufficient pheromone to trigger the induction of gene expression. Using a lux plasmid-based bioluminescent sensor for OHHL, pheromone production by E. carotovora, Enterobacter agglomerans, Hafnia alvei, Rahnella aquatilis and Serratia marcescens has been demonstrated and shown also to be cell density-dependent. Production of OHHL implies the presence in these bacteria of a gene equivalent to luxI. Chromosomal banks from all five enteric bacteria have yielded clones capable of eliciting OHHL production when expressed in Escherichia coli. The luxI homologue from both E. carotovora (carI) and E. agglomerans (eagI) were characterized at the DNA sequence level and the deduced protein sequences have only 25% identity with the V. fischeri LuxI. Despite this, carI, eagI and luxI are shown to be biologically equivalent. An insertion mutant of eagI demonstrates that this gene is essential for OHHL production in E. agglomerans.

A novel regulatory system required for pathogenicity of Xanthomonas campestris is mediated by a small diffusible signal molecule

“…Liu et al (1990); this work pSB315 Bioluminescence reporter for N-acyl homoserine lactones Swift et al (1993) …”

The Rap and Hor proteins of Erwinia, Serratia and Yersinia: a novel subgroup in a growing superfamily of proteins regulating diverse physiological processes in bacterial pathogens

“…In an attempt to determine the level at which the hor Er ::kan mutation affected the production of carbapenem, Hor ¹ mutants were constructed, which had lacZ transcriptional fusions to the carbapenem regulatory genes, carI and carR (Swift et al, 1993;McGowan et al, 1995), and to the carbapenem biosynthetic gene, carA (McGowan et al, 1996). A ⌽KP lysate grown on Ecc strain ATM101 (hor Er ::kan) was used to transduce Ecc strains, MR1 (carI ::lacZ ), GB3 (carR ::lacZ ) and GB7 (carA::lacZ ), as described previously by Toth et al (1993), to kanamycin resistance.…”

“…Genetic investigations of Ecc have shown that the production of carbapenem by this bacterium is regulated by the CarI and CarR proteins in a system analogous to that controlling bioluminescence in the marine bacterium Vibrio fischeri, i.e. by quorum sensing (Bainton et al, 1992a;Swift et al, 1993;McGowan et al, 1995).…”

Quorum Sensing and the Lifestyle ofYersinia

“…When introduced into E. coli, this lux-based AHL reporter (termed pSB401) is dark but responds to the presence of exogenous AHLs by emitting light. The advantage of this AHL reporter compared with earlier versions employing luxAB alone (Bainton et al, 1992;Swift et al, 1993) is that it does not require the addition of a long chain fatty aldehyde (which is required by the luciferase) since the inclusion of the luxCDE genes provides for in situ synthesis of the aldehyde.…”

“…Since AHL synthesis depends on the presence of an AHL synthase, a plasmid-based in trans complementation strategy in which a Y. enterocolitica chromosomal gene library was transformed into E. coli [pSB401] was devised (Swift et al, 1993;Throup et al, 1995). This approach yielded a highly bioluminescent clone indicative of an insert carrying a gene whose product was capable of inducing the AHL reporter fusion.…”