Sakacin P non-producing Lactobacillus sakei strains contain homologues of the sakacin P gene cluster

Abstract

Some strains of Lactobacillus sakei are known to produce the bacteriocin sakacin P, encoded by the spp gene cluster. In strains unable to produce sakacin P, spp homologues were observed. The analysis of 15 strains not producing sakacin P revealed that all contained a region corresponding to a part of sppKR encoding the regulatory elements for sakacin P production. In some strains homologues of sppE and sppT, responsible for sakacin P transport, and the sakacin P structural gene sppA and its immunity gene spiA, were also present. The sequence of the chromosomal spp-related gene cluster was determined in two non-producing strains: L. sakei Lb790 and L. sakei 23K. The L. sakei Lb790 spp gene cluster encompasses genes homologous to sppK, sppR, sppT and sppE. In L. sakei 23K, only sppK and sppR homologues were present. The sppK homologues appeared non-functional as they contained mutations and/or an insertion element. In addition to the spp homologues, several small putative genes were found in the gene clusters of the two strains. Some were similar in both strains, and their organization suggests a mosaic structure resulting from successive rearrangements. Transcriptional analysis showed that the genes of the L. sakei Lb790 spp cluster were expressed when genes encoding an operative sakacin P regulatory system were introduced in this strain, thus complementing the inactive sppK gene. Expression experiments also suggested that some of the spp homologues maintained their function in non-producing strains.