DOES GENE HORIZONTAL TRANSFER OCCUR IN LACTIC-ACID BACTERIA COCULTURES

Four types of insertion sequences, IS1191, IS981, ISS1 and IS1194, wer e identified in Streptococcus thermophilus CNRZ368. The ISS1 elements can be divided into three subgroups, alpha, beta and gamma sharing 75- 85% nucleotide sequence identity. Mosaic elements resulting from recom bination between ISS1 belonging to different subgroups were also ident ified. The IS1191, IS981, alpha and beta ISS1 nucleotide sequences fro m S. thermophilus CNRZ368 were found to be almost identical to inserti on sequences from Lactococcus lactis, suggesting that horizontal trans fers have recently occurred between these distantly related lactic aci d bacteria. IS distribution indicates that horizontal transfers have p robably occurred from S. thermophilus to L. lactis and from L. lactis to S. thermophilus during cocultures used for cheese manufacture. Furt hermore, IS1194 distribution also suggests that some strains of S. the rmophilus and L. lactis have acquired this IS by horizontal transfer(s ) from an unidentified bacterium. The three ISS1 copies, two of the fo ur IS981 copies and the unique IS1194 copy of S. thermophilus CNRZ368 are clustered in the same 12 kb chromosomal region which could have be en acquired from L. lactis. Furthermore, other sequence comparisons sh owed that horizontal transfers of IS and other genes like citP encodin g citrate permease occurred between various species belonging to five genera of lactic acid bacteria, Lactococcus, S. treptococcus, Lactobac illus, Leuconostoc and Enterococcus. (C) Inra/Elsevier, Paris.