152 ◾ Fundamental Food Microbiology
the bacteriocin lactococcin A in a Lac. lactis strain. The structural gene was cloned in the same Lac.
lactis strain, which produced propediocin with a different leader peptide but produced matured
pediocin by using the lactococcin A-transport system. However, the level of production was very
low, suggesting the important roles of leader peptides and specific transporters in high-level production of pediocin (Chapter 17). 13
Bioengineered Bacteriocins
By random as well as site-directed PCR, mutagenesis of nucleotides is used to improve bacteriocin
activity. 14 This strategy was used in the mature pediocin segment; many variant molecules have
been isolated that have one or two different amino acids among the 44 amino acids. The variants
have different levels of activity: Some do not have detectable activity, many have reduced activity,
and one has greater activity. These results indicate the importance of specific amino acid sequences
of a bacteriocin for its normal level of activity. 13 Amino acid substitution in the bioengineered
bacteriocins also helped improve solubility or made bacteriocins resistant to intestinal proteolytic
enzymes, ensuring their activity in the gastrointestinal tract. 14
Genome Mapping and Sequencing
Because of the importance of many lactic acid bacteria in the production of bioprocessed foods,
food preservatives and different food additives, enzymes and nutraceuticals; maintenance of intestinal health; and as agents for drug-delivery systems, considerable research with many species of
lactic acid bacteria has been conducted in the last 20–30 years. To understand the characteristics
at the molecular level, for the last several years, there have been efforts to sequence the complete
genome (chromosome) of some strains of important lactic acid bacteria. Availability of new techniques and necessary facilities (equipment, computerized programs, and others) has greatly helped
generate information in a relatively short time. These techniques have also helped sequence the
genomes of many phages and prophages of lactic acid bacteria. The available information is briefly
summarized here.
Lactic Acid Bacteria
As of 2011, complete genome sequences of 35 lactic acid bacteria have been completed, and 100
more are in progress. 9,15,16 These results have provided much important information, such as the
size of each genome; the number of ORFs a genome carries; and the frequency of prophages,
IS-elements, and rRNA operons in a genome (Table 13.1). In addition, other genetic information, such as biosynthetic pathways of amino acids, vitamins, nucleotides, and polysaccharides,
synthesis of bacteriocins, and sugar transport and metabolism systems, is now available for these
strains. The Lac. lactis IL 1403 genome is the first to be completely sequenced. 17 The genome size
is approximately 2.4 Mb and has 2310 ORFs with 138 potential regulators, five prophages, six
different types of IS elements, and six rRNA operons. The genome encodes nucleotide sequences
for de novo biosynthetic pathways of 24 amino acids, folate, riboflavin, purines and pyrimidines, complete PTS-sugar transport systems, and partial components of aerobic respiration. The
genome appears to have a fluid structure and is able to undergo changes through point mutation,
DNA rearrangements, and horizontal gene transfer. The genome organization has resulted from
the evolutionary pressure to enable the species to grow optimally in a nutritionally rich medium.
the bacteriocin lactococcin A in a Lac. lactis strain. The structural gene was cloned in the same Lac.
lactis strain, which produced propediocin with a different leader peptide but produced matured
pediocin by using the lactococcin A-transport system. However, the level of production was very
low, suggesting the important roles of leader peptides and specific transporters in high-level production of pediocin (Chapter 17). 13
Bioengineered Bacteriocins
By random as well as site-directed PCR, mutagenesis of nucleotides is used to improve bacteriocin
activity. 14 This strategy was used in the mature pediocin segment; many variant molecules have
been isolated that have one or two different amino acids among the 44 amino acids. The variants
have different levels of activity: Some do not have detectable activity, many have reduced activity,
and one has greater activity. These results indicate the importance of specific amino acid sequences
of a bacteriocin for its normal level of activity. 13 Amino acid substitution in the bioengineered
bacteriocins also helped improve solubility or made bacteriocins resistant to intestinal proteolytic
enzymes, ensuring their activity in the gastrointestinal tract. 14
Genome Mapping and Sequencing
Because of the importance of many lactic acid bacteria in the production of bioprocessed foods,
food preservatives and different food additives, enzymes and nutraceuticals; maintenance of intestinal health; and as agents for drug-delivery systems, considerable research with many species of
lactic acid bacteria has been conducted in the last 20–30 years. To understand the characteristics
at the molecular level, for the last several years, there have been efforts to sequence the complete
genome (chromosome) of some strains of important lactic acid bacteria. Availability of new techniques and necessary facilities (equipment, computerized programs, and others) has greatly helped
generate information in a relatively short time. These techniques have also helped sequence the
genomes of many phages and prophages of lactic acid bacteria. The available information is briefly
summarized here.
Lactic Acid Bacteria
As of 2011, complete genome sequences of 35 lactic acid bacteria have been completed, and 100
more are in progress. 9,15,16 These results have provided much important information, such as the
size of each genome; the number of ORFs a genome carries; and the frequency of prophages,
IS-elements, and rRNA operons in a genome (Table 13.1). In addition, other genetic information, such as biosynthetic pathways of amino acids, vitamins, nucleotides, and polysaccharides,
synthesis of bacteriocins, and sugar transport and metabolism systems, is now available for these
strains. The Lac. lactis IL 1403 genome is the first to be completely sequenced. 17 The genome size
is approximately 2.4 Mb and has 2310 ORFs with 138 potential regulators, five prophages, six
different types of IS elements, and six rRNA operons. The genome encodes nucleotide sequences
for de novo biosynthetic pathways of 24 amino acids, folate, riboflavin, purines and pyrimidines, complete PTS-sugar transport systems, and partial components of aerobic respiration. The
genome appears to have a fluid structure and is able to undergo changes through point mutation,
DNA rearrangements, and horizontal gene transfer. The genome organization has resulted from
the evolutionary pressure to enable the species to grow optimally in a nutritionally rich medium.