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Chapter 13
Genetics of Some
Beneficial traits
introduction
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.
Plasmids and Plasmid-Linked traits in Starter-Culture Bacteria
Starter-culture bacteria, like other bacteria, carry genetic information (a genetic code) in the
circular chromosomal DNA, circular plasmids, and transposons. Chromosomal DNA carries
Chapter 13
Genetics of Some
Beneficial traits
introduction
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.
Plasmids and Plasmid-Linked traits in Starter-Culture Bacteria
Starter-culture bacteria, like other bacteria, carry genetic information (a genetic code) in the
circular chromosomal DNA, circular plasmids, and transposons. Chromosomal DNA carries