Quorum Sensing in Burkholderia cepacia : Identification of the LuxRI Homologs CepRI

Abstract

Burkholderia cepacia has emerged as an important pathogen in patients with cystic fibrosis. Many gram-negative pathogens regulate the production of extracellular virulence factors by a cell density-dependent mechanism termed quorum sensing, which involves production of diffusible N-acylated homoserine lactone signal molecules, called autoinducers. Transposon insertion mutants of B. cepacia K56-2 which hyperproduced siderophores on chrome azurol S agar were identified. One mutant, K56-R2, contained an insertion in a luxR homolog that was designated cepR. The flanking DNA region was used to clone the wild-type copy of cepR. Sequence analysis revealed the presence of cepI, a luxI homolog, located 727 bp upstream and divergently transcribed from cepR. Alux box-like sequence was identified upstream ofcepI. CepR was 36% identical to Pseudomonas aeruginosa RhlR and 67% identical to SolR of Ralstonia solanacearum. CepI was 38% identical to RhlI and 64% identical to SolI. K56-R2 demonstrated a 67% increase in the production of the siderophore ornibactin, was protease negative on dialyzed brain heart infusion milk agar, and produced 45% less lipase activity in comparison to the parental strain. Complementation of acepR mutation restored parental levels of ornibactin and protease but not lipase. An N-acylhomoserine lactone was purified from culture fluids and identified asN-octanoylhomoserine lactone. K56-I2, a cepImutant, was created and shown not to produceN-octanoylhomoserine lactone. K56-I2 hyperproduced ornibactin and did not produce protease. These data suggest both a positive and negative role for cepIR in the regulation of extracellular virulence factor production by B. cepacia.

Production of N-acyl-?-homoserine lactones by P. aeruginosa isolates from chronic lung infections associated with cystic fibrosis

“…We also analyzed the AHL pro¢les of the two cocolonizing B. cepacia strains. In agreement with the results of Lewenza et al [19] it was found that the B. cepacia strain isolated from patient P1 produced an AHL molecule that, based on TLC analyses, most likely represents OHL. In addition, signi¢cant amounts of a second AHL molecule, the mobility of which was found to be similar to that of HHL, were detected (data not shown).…”

“…cepacia syndrome', a fulminant, fatal pneumonia [2]. Recently, B. cepacia has been demonstrated to utilize a N-octanoyl-L-homoserine lactone (OHL)-dependent quorum sensing system to control expression of virulence factors [19]. Moreover, it has been shown that spent culture supernatants of P. aeruginosa enhance AHL-regulated virulence factor production in B. cepacia [20].…”

Quorum-sensing and siderophore biosynthesis in Pseudomonas aeruginosa: lasRllasI mutants exhibit reduced pyoverdine biosynthesis

“…although in that instance inactivation of a hsR homolog, cepR. actually increased siderophore production [23].…”

Characterization of N-acyl homoserine lactone overproducing mutants of Burkholderia multivorans ATCC 17616

“…Expression of bacterial functions important for hostcolonization and pathogenicity is commonly cell-densitydependent and related to the accumulation of N-acyl homoserine lactones (AHLs) [10,11]. Typically such`quorum sensing' systems involve luxI and luxR homologs specifying an AHL synthase and AHL-binding transcriptional activator [10^12].…”