Quorum sensing in Burkholderia cepacia: Identification of the LuxRI homologs CepRI

Burkholderia cepacia has emerged as an important pathogen in patients with cystic fibrosis. Many gramnegative pathogens regulate the production of ext racellular virulence factors by a cell density-dependent mechanism termed q uorum sensing, which involves production of diffusible N-acylated homoserin e lactone signal molecules, called autoinducers. Transposon insertion mutan ts 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 Banking 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. A lux box-like sequence was identified upstream of cepI. CepR was 36% identical to Pseudomonas aeruginosa RhlR and 67% identical to SolR of Rals tonia solanacearum. CepI was 38% identical to RhlI and 64% identical to Sol I. K56-R2 demonstrated a 67% increase in the production of the siderophore ornibactin, was protease negative on dialyzed brain heart infusion milk aga r, and produced 45% less lipase activity In comparison to the parental stra in. Complementation of a cepR mutation restored parental levels of ornibact in and protease but not lipase, An N-acylhomoserine lactone was purified fr om culture fluids and identified as N-octanoylhomoserine lactone. K56-12, a cep1 mutant, was created and shown not to produce N-octanoylhomoserine lac tone. K56-I2 hyperproduced ornibactin and did not produce protease. These d ata suggest both a positive and negative role for cepIR in the regulation o f extracellular,virulence factor production by B. cepacia.