Submitted to: Biotechnology Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/19/2007
Publication Date: 10/12/2007
Citation: Somkuti, G.A., Steinberg, D.H. 2007. Molecular organization of plasmid per13 in streptococcus thermophilus st113. Biotechnology Letters. 29:1991-1999. Interpretive Summary: The lactic fermentation bacterium Streptococcus thermophilus is used extensively as a starter culture in the industrial production of fermented dairy foods (cheeses, yogurt). Since it is an edible, food-grade organism, it is ideally suited for testing genetic engineering methods to improve its performance needed to enhance the functionality of foods. Culture ST113 was found to contain a small circular DNA molecule (plasmid) that can be used to transport new genes into food fermentation microbes. Analysis of this plasmid revealed several unusual structural elements, including a special gene that is apparently involved in the mobilization and transfer of the plasmid between food fermentation bacteria. This feature will be used in the construction of efficient gene transport molecules to introduce beneficial genes in starter cultures to improve their metabolic performance in dairy fermentations and to enhance the quality of foods.
Technical Abstract: Molecular features of the 4139-bp plasmid pER13 found in the dairy fermentation bacterium Streptococcus thermophilus ST113 include five open reading frames (ORFs). ORF1, ORF2 and ORF3 encode proteins for transcriptional repression (CopG), replication (RepB) and mobilization (Mob) that share a high level of homology with corresponding proteins of the pMV158 plasmid family. In pER13 ORF4 and ORF5 are both located on the complementary DNA strand and encode 157-amino acid and 92-amino acid proteins with unspecified functions but only ORF5 shares homology with a similar domain found on plasmid pSSU1 of S. suis. Sequence homologies shared with plasmids found in group B and group D streptococci imply the possibility for genetic exchange between the food-grade S. thermophilus and pathogenic streptococci. The structural characteristics of pER13 in S. thermophilus also may be of value in designing strategies for facilitating gene transfer in dairy fermentation bacteria.