INVESTIGADORES
CAPRA Maria Lujan
capítulos de libros
Título:
Lysogeny in probiotic lactobacilli
Autor/es:
MARÍA LUJÁN CAPRA; DIEGO JAVIER MERCANTI
Libro:
Bacteriophages in Dairy Processing
Editorial:
Nova Science Publishers, Inc.
Referencias:
Lugar: New York; Año: 2012; p. 123 - 147
Resumen:
Bacteriophages show several life cycles: lytic (as a virulent phage), lysogenic (as a
temperate phage or prophage) and persistent infections (pseudolysogeny, phage-carrier
state). The lysogenic decision of a temperate phage to either follow a lytic cycle or
insert its genome into host chromosome and continue to replicate in a dormant stage
(prophage) is made just after infection, and depends upon host density and environmental
factors. Bacterial and phage genomes are not completely independent entities; they
underwent a co-evolution which favored both. During evolution, bacteria tend to
eliminate unessential prophage DNA giving place to the following sequence: inducible
prophages - defective prophages (with deletions, insertions and/or rearrangements) -
prophage remnants (with massive loss of the original phage genome) - isolated prophage
genes. The latter, called lysogenic conversion genes (LCG) confer a competitive
advantage to the host cell. Hence, lysogeny greatly contributed to the generation of
diversity, being responsible for almost all genetic differences found among strains of the
same species. Lysogeny is more the rule than the exception and many bacteria harbour
more than one prophage (poly-lysogeny). Prophages and LCG were first described on
pathogenic bacteria, where they are known to encode for diverse virulence factors, but
later they were postulated to help in the adaptation of any bacterial strain to their
ecological niche. This obviously applies to gut commensal bacteria, which are constantly
under selection pressure and include probiotic strains. Among lactic acid bacteria, most
lactococcal strains are lysogenic and poly-lysogenic, but lysogeny was also found to be
highly widespread in lactobacilli, which encompasses most probiotic strains currently
used by dairy industries. In particular, phage infections in probiotic lactobacilli are
especially important due to singular and unique characteristics ascribed to each strain. In
addition, lysogeny could potentially affect strain functionality, either by improving or counteracting its probioticity. Finally, it is known that lactobacilli play an active role in
the maintaining of mucosal health. Several studies have correlated the alteration of this
equilibrium with the presence of virulent phages or furthermore, with prophages that are
induced under certain circumstances, causing lactobacilli depletion.