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French scientists sequence the genome of a bacterium vital for cheese production
By Bijal P. Trivedi

The French, who are known for their Camembert, Roquefort and Brie, have now sequenced the genome of a rod-shaped bacterium that is critical for manufacturing dairy products like buttermilk, yogurt and, of course, cheese.

The bacterium, Lactococcus lactis ssp. lactis, is also used to prepare pickled vegetables, beer, wine, some breads and sausages, and other fermented foods. Researchers anticipate that understanding the physiology and genetic make-up of this bacterium will prove invaluable for food manufacturers as well as the pharmaceutical industry, which is exploring the capacity of L. lactis ssp. lactis to serve as a vehicle for delivering drugs.

When L. lactis ssp. lactis is added to milk, the bacterium uses enzymes to produce energy molecules, called ATP, from lactose (milk sugar). The byproduct of ATP energy production is lactic acid. The lactic acid produced by the bacterium curdles the milk that then separates to form curds, which are used to produce cheese and whey. But curdling the milk is not the bacterium's only role in cheese production.

The genome sequence reveals 12 enzymes called aminotransferases, some of which are used to break down complex, branched, ring-shaped, and sulfur-containing amino acids. The molecules produced when the amino acids are degraded are very important for cheese flavor. Understanding which amino acids are broken down by which enzymes could give cheese makers greater control over flavor and fragrance of their fromage.

The sequence also led to the identification of 29 genes that are required to build the mesh-like component of the bacterium's cell wall. Inducing some of these enzymes can accelerate the slow, expensive process of cheese ripening, during which the cheese ages and develops its characteristic flavor. Learning how to selectively activate some of these enzymes could revolutionize the cheese manufacturing process.

The L. lactis ssp. lactis genome has 2,365,589 units of DNA, which contain 2,310 predicted genes. About 64 percent of the genes have assigned roles in the cell, while 20 percent match other hypothetical genes with unknown function. Almost 16 percent of the genes bear no resemblance to genes from other species and are considered to be unique to this bacterium.

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Bolotin, A. et al. The complete genome sequence of the lactic acid bacterium Lactococcus lactis ssp. lactis IL1403. Genome Res 11 (published online April 11, 2001).

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