Fundamental Food Microbiology, Third Edition - Fuad Fathir

GENETICS OF SOME BENEFICIAL TRAITS 167
ticals, 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 to 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.
A. Lactic Acid Bacteria
As of 2002, complete genome sequences of five lactic acid bacteria have been
completed and of 25 other important strains (of which 23 are lactic acid bacteria,
including Bifidobacteria) are in progress. 16 These results have provided much important
information, such as the size of each genome; number of ORFs a genome carries;
and the frequency of prophages, IS-elements, and rRNA operons in a genome (Table
12.1). 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 ca. 2.4 Mb and has 2310 ORFs with 138 potential regulators, 5 prophages, 6
different types of IS elements, and 6 rRNA operons. The genome encodes nucleotide
sequences for de novo biosynthetic pathways of 24 amino acids, folate, riboflavin,
Table 12.1 Some Features of Sequenced Genome of Lactic Acid Bacteria a
Species/
Strains
Lac. lactis
IL 1403
Lab.
plantarum
WCFS 1
Lab. johnsonii
NCC 533
Lab.
acidophilus
ATCC 700396
Bif. longum
NCC 2705
\
Genome
IS
Size %
Element rRNA
(Mb) GC ORFs Prophages Types Operons
2.4 35.4 2310 5 6 6
3.3 44.5 3050 2 2 5
2.0 34.6 1857 0 6 6
2.0 34.7 1979 3 3 6
2.2 60.1 1730 Some 5 4
a Genome sequences of other lactic acid bacteria now being determined are Lac. lactis ssp.
cremoris (3 strains); Str. thermophilus (3 strains); Leu. mesenteroides (1 strain); Oen. oeni
(2 strains); Ped. pentosaceus (1 strain); Bif. breve (1 strain) and longum (1 strain); Lab.
delbrueckii ssp. bulgaricus (3 strains); Lab. casei (2 strains), helveticus(2 strains), rhamnosus
(1 strain), brevis (1 strain), sake (1 strain), and gasseri (1 strain); Pro. freudenreichii (1 strain);
and Bre. linen (1 strain).
Source: Adapted from Klaenhammer, T. et al., Ant. van Leeuwen., 82, 29, 2002.