Fundamental Food Microbiology, Third Edition - Fuad Fathir

152 FUNDAMENTAL FOOD MICROBIOLOGY
6. Production of Folic Acid and Riboflavin ..................................164
7. Enhancing Proteolysis by Cell Lysis .........................................164
C. Protein Targeting ..............................................................................164
1. Expression of Interleukin ...........................................................165
2. Drug-Delivery System ...............................................................165
3. Production of Pediocin in Heterologous Hosts .........................165
D. Protein Engineering .........................................................................166
1. Production of Hybrid Prepediocin .............................................166
2. Amino Acid Variants of Pediocin ..............................................166
V. Genome Mapping and Sequencing ..........................................................166
A. Lactic Acid Bacteria ........................................................................167
B. Bacteriophages .................................................................................168
C. The lac and las Genes .....................................................................168
VI. Conclusion ................................................................................................170
References ............................................................................................................170
Questions ..............................................................................................................171
I. 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 ability to
hydrolyze proteins (necessary for some cheese production), 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 in the genetics of lactic acid bacteria
(notably, Dr. Larry McKay's laboratory at the University of Minnesota). Since
the late 1970s, many other laboratories 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.