Studies on regulation of the plantaricin 423 gene

[摘要] ENGLISH ABSTRACT:Lactic acid bacteria play an essential role in the majority of fermented foods by producingorganoleptic compounds and increasing the shelf life. The best-studied antimicrobial compoundsare bacteriocins, i.e. ribosomally synthesized peptides. Most of these peptides have a narrowspectrum of activity and are usually only active against bacteria from the same ecological niche.The fact that all bacteriocins are degraded by proteolytic enzymes enlarges their potential use asnatural food preservatives. The ideal would be to replace or reduce chemical preservatives suchas sulfur dioxide, nitrates and nitrites.Bacteriocins are classified into four groups according to their structural and functionalcharacteristics. Plantaricin 423, produced by Lactobacillus plantarum 423, is heat stable,plasmid encoded, relatively small (3.5 kDa) and is classified as a class Iia bacteriocin. Thepeptide is active from pH 1.0 to 10.0 and inhibits Gram-positive bacteria, including Lactobacillusspp., Leuconostoc spp., Oenococcus oeni, Pediococcus spp., Enterococcus spp.,Propionibacterium spp. and pathogens such as Bacillus cereus, Clostridium spp. and Listeriamonocytogenes.Production of bacteriocins may occur constitutively or may be regulated by a cell-densitydependent system called quorum sensing. Plantaricin 423 is produced throughout logarithmicgrowth, with no apparent change in production levels when the producer strain is cultured in thepresence of plantaricin 423 or Listeria innocua and Lactobacillus sakei. This led us to believethat plantaricin 423 may be produced constitutively.A reporter system was constructed which consisted of the plantaricin 423 promoter, P423,fused to the luxAB genes and cloned into a shuttle vector, pTRKH2. The newly constructedplasmid, pTAB4, was transformed to a bacteriocin-negative mutant of L. plantarum (423 B}Despite several repeats, no luciferase activity was recorded and no RNA homologous to theluxAB genes was detected.The region necessary for expression of plantaricin 423 may be located stream-up of the -80region homologous to the -80 and -40 conserved repeats of regulated class II bacteriocins.Inclusion of the latter region in the reporter construct may result in the successful expression ofluxAB.

[发布机构] Stellenbosch University