ABSTRACT
Since the 1930s, it has been recognized that many important characteristics (traits or phenotypes) in dairy starter-culture bacteria are unstable. For example, a Lactococcus lactis strain, while growing in milk, once able to ferment lactose and coagulate the milk, was found to no longer ferment lactose and became useless commercially. Similar losses of other commercially important traits of starter cultures used in dairy and nondairy fermentations, such as the ability to hydrolyze proteins (necessary for some cheese production), the ability to utilize citrate (for diacetyl production), resistance to bacteriophages, and hydrolysis of sucrose, were observed. However, the specific mechanisms involved in the instability of these important phenotypes were not understood. In the 1960s, the genetic basis of instability of different microbial phenotypes started unfolding. Similar studies, when extended to dairy starter-culture bacteria, revealed the genetic basis of the instability of the important traits. In those days, only a few laboratories were conducting research on the genetics of lactic acid bacteria (notably, Dr. Larry McKay’s laboratory at the University of Minnesota). Since the late 1970s, many other laboratories have started working in this area, and, at present, genetic research of starter-culture bacteria has generated a major interest in many laboratories worldwide. The genetic basis of some of the commercially important phenotypes in some lactic acid bacteria; methods of transfer of desirable traits from one bacterial strain to another to develop a better strain for use in food fermentation; and current advances in genetic studies, such as metabolic engineering and genome sequencing in lactic acid bacteria, are discussed briefly in this chapter.
