The β-galactosidase of DSM 20017 is encoded by two genes located on its chromosome. These genes designated and were cloned in NM 554 on an 8.65 kbp fragment inserted in vector pRB473. Deletion analysis of the originally cloned fragment revealed that both genes are required for the formation of a functional β-galactosidase. and are transcribed as a single transcript of approximately 2.9 kbp starting 34 bp upstream of the translational start codon. The proteins derived from and share only 18-59% homology with other β-galactosidases. The genes encoding the β-galactosidase are scattered with multiple direct and inverted repeats of 9-12 bp. However, comparison with the plasmid-encoded β-galactosidase revealed equal distribution of conserved amino acid residues and suggests that the genes have a common origin. Specific deletions or insertions resulting from the presence of the repeats were not observed. The β-galactosidase was phenotypically expressed in NM 554 and LTH 1432. Its two genes can be used to replace antibiotic reporter genes to develop food-grade vectors and á-complementation systems for self-cloning in meat lactobacilli.


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