Synthesis of multiple N-acylhomoserine lactones is wide-spread among the members of the Burkholderia cepacia complex

Seventy strains of the Burkholderia cepacia complex, which currently compri ses six genomic species, were tested for their ability to produce N-acylhom oserine lactone (AHL) signal molecules. Using thin layer chromatography in conjunction with a range of AHL biosensors, we show that most strains prima rily produce two AHLs, namely N-octanoylhomoserine lactone (C8-HSL) and N-h exanoylhomoserine lactone (C6-HSL). Furthermore, some strains belonging to B. vietamiensis (genomovar V) produce additional long chain AHL molecules w ith acyl chains ranging from C10 to C14. For B. vietnamiensis R-921 the str ucture of the most abundant long chain AHL was confirmed as N-decanoylhomos erine lactone (C10-HSL) by liquid chromatography mass spectrometry (LC-MS) in combination with total chemical synthesis. Interestingly a number of str ains, most notably all representatives of B. multivorans (genomovar II), di d not produce AHLs at least under the growth conditions used in this study. All strains were also screened for the production of extracellular lipase, chitinase, protease, and siderophores. How ever, no correlation between th e AHL production and the synthesis of these exoproducts was apparent. South ern blot analysis showed that all the B. cepacia complex strains investigat ed, including the AHL-negative strains, possess genes homologous to the C8- HSL synthase cepI and to cepR, which encodes the cognate receptor protein. The nucleotide sequence of the cepI and cepR genes from one representative strain from each of the six genomovars was determined. Furthermore, the cep I genes from the different genomovars were expressed in Escherichia coli an d it is demonstrated that all genes encode functional proteins that direct the synthesis of C8-HSL and C6-HSL. Given that cepI from the B. mtiltivoran s strain encodes a functional AHL synthase, yet detectable levels of AHLs w ere not produced by the wild-type, this suggests that additional regulatory functions may be present in members of this genomovar that negatively affe ct expression of cepI.