The generally accepted opinion is that the natural niche for lactococci are plants. Several genes reminiscent of the environmental adaptation of these bacteria to the plant habitat were found as a result of our work on the pullulanase coding region in the Lactococcus lactis IBB500 strain. All genes were located within an 11-kb DNA fragment of a 35-kb plasmid. Analysis of the nucleotide sequence of the 11-kb DNA fragment showed three regions: (i) a middle region - encoding the potential pullulanase operon (ii); a pullulanase upstream region - encoding two cold shock proteins; and (iii) a pullulanase downstream region - encoding two cadmium resistance proteins. Analysis of the phylogenetic relationships of these regions through inspection of their G+C content and codon preference, as well as homology of their protein products and constructions of phylogenetic trees strongly supported the hypothesis of their acquisition through a horizontal gene transfer. Focusing further research on the middle region we have found that the pullulanase gene, belonging to the putative pul operon, was preceded by a long, non-translated region in which five putative promoter sequences were identified. Moreover, a DNA sequence similar to the highly conserved cre box involved in glucose repression was found in front of one of them. The hypothesis of glucose repression was further tested using transcriptional fusion between the pul and luxAB-reporter genes, located on the parental plasmid in the L. lactis IBB500 strain. Lactococcus lactis / adaptation / gene-cassette / horizontal gene transfer / pullulanase