ISL2, A NEW MOBILE GENETIC ELEMENT IN LACTOBACILLUS-HELVETICUS

Spontaneous, phenotypically stable mutations at the beta-galactosidase locus (lacL-lacM) in Lactobacillus helveticus were identified and ana lyzed. We found that a significant number of mutations were caused by integration of a new IS element, ISL2, into these lac genes. ISL2 is 8 58 bp long, flanked by 16-bp perfect inverted repeats and generates 3- bp target duplications upon insertion. It contains one open reading fr ame, which shows significant homology (40.1% identity) to the putative transposase of IS702 from Cyanobacterium calothrix. ISL2 is present i n 4-21 copies in the L. helveticus genome, but it is not found in othe r lactic acid bacteria. Its divergence in copy number and genomic loca tions in different L. helveticus strains makes it useful as a tool for strain identification by genetic fingerprinting.