17A-11 |
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L. TU, Food Science, University of Missouri - Columbia, 256 William Stringer Wing, Eckles Hall, University of Missouri, Columbia, MO 65211, F. Du, Genome Sequencing Center, Washington University School of Medicine, 4444 Forest Park Boulevard, St Louis, MO 63108, and A. Mustapha, Department of Food Science, University of Missouri, 256 Eckles Hall - Stringer Wing, Columbia, MO 65211. Lipases of starter cultures hydrolyze milk fat and generate free volatile fatty acids which play an important role in the flavor characteristics of cheese. Microbial lipases may also accelerate the maturation of cheeses. Moreover, previous studies have shown that adding lipase to milk may increase the antimutagenicity activity of dairy products. Since bifidobacteria are added to certain dairy products and have been used as potential cheese starter cultures, increased lipase activity of this organism will not only enhance flavor, but also, most importantly, may promote health benefits. Therefore, cloning and sequencing the lipase gene of bifidobacteria will eventually lead to the potential development of commercial strains with improved starter characteristics. Our objectives were to clone and sequence the lipase gene from Bifidobacterium infantis. A genomic DNA library of B. infantis 15702 was constructed in l phage and 5 positive clones were further analyzed. Sequencing was performed by primer walking from both directions of the cloned DNA. Sequence results revealed the presence of one open reading frame on the 3280-bp cloned DNA fragment. The deduced amino acid sequence consists of 273 residues with the highest identity to the lipases of Deinococcus radiodurans (strain R1) and Clostridium acetobutylicum (34.2% and 32.9%, respectively). Comparison with numerous lipase amino acid sequences obtained from different sources has shown weak homology except for a highly conserved Gly-Xaa-Ser-Xaa-Gly motif. This consensus domain represents the only feature shared by all determined lipases. The conserved pentapeptide is thought to be characteristic of the catalytic site of lipase enzymes. For B. infantis, this sequence was found at positions 114-118 of the lipase gene. Knowledge of the structure of the bifidobacterial lipase gene will contribute substantially to our understanding and ability to manipulate and improve this bacterium for future commercial application purposes.
Session 17A, Dairy Foods: Cheese and microbiology
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