Fundamental Food Microbiology, Third Edition - Fuad Fathir

STARTER CULTURES AND BACTERIOPHAGES 179
assembly of the proteins and phage DNA to produce mature phages, the bacterial
cell lyses, releasing the phages (as many as 200) in the environment (Figure 13.2).
They, in turn, attack other bacterial cells. These are lytic phages. Their growth
cycles (lytic cycle) take ca. 20 to 30 min. There are other phages (called temperate
phages) that are nonlytic and their DNA, following injection into the cytoplasm,
is integrated with bacterial DNA. The phage DNA (called prophage) is carried by
a bacterial cell DNA (lysogeny state), and as a bacterial cell multiplies, the
prophage also multiplies without showing the presence of the phage in the bacterial
strain (lysogenic strain). As long as the host cell carries the prophage, it is immune
to attack by the same phage. Recent genome studies have shown that the DNA of
a host strain can have five or more types of prophages. 6 However, a prophage can
be induced by a physical (such as UV) or a chemical (such as mitomycin C) agent,
causing the phage DNA to separate out of bacterial DNA and resume the lytic
cycle (Figure 13.2).
3. Host Specificity
Bacteriophages against many species of Lactococcus, Streptococcus, Leuconostoc,
and Lactobacillus, and Oenococcus oenos that are currently used in food fermentation
have been discovered. The phages are host specific, and there can be one specific
host (strain) for a specific phage to several related strains for a phage. A bacterial
strain can also be the host of many different types of phages. A bacterial strain can
have restriction enzymes that can hydrolyze and destroy the DNA of a phage. A
phage can be lytic or temperate. All phages require Ca 2+ for their adsorption on the
cell surface of lactic cultures.
Figure 13.2 Schematic presentation of the lytic cycle and lysogenic cycle of bacteriophages
in bacteria: (1) Adsorption of a phage on the bacterial cell wall. (2) Injected phage
DNA in bacterial cell. (3–5) Lytic cycle by lytic phage showing formation of phage
DNA (3) and mature phages (4) in the cell and release of phages following lysis
of cell (5). (6–8) Lysogenic cycle by a temperate phage showing integration of
phage DNA in bacterial cell DNA (6), division of phage DNA during bacterial cell
division (prophage; 7), release of phage DNA because of activation (*; 8), causing
lysis of cell (3 to 5).
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