Affiliation:
1. Laboratoire de Génétique Microbienne, Institut National de Recherches Agronomiques, 78352 Jouy-en-Josas Cedex, France
Abstract
ABSTRACT
Streptococcus thermophilus
is perceived as a recently emerged food bacterium that evolved from a commensal ancestor by loss and gain of functions. Here, we provide data allowing a better understanding of this evolutionary scheme. A multilocus sequence typing approach that we developed showed that
S. thermophilus
diverges significantly from its potential ancestors of the salivarius group and displays a low level of allelic variability, confirming its likely recent emergence. An analysis of the origin and dissemination of the
prtS
gene was carried out within this evolutionary scheme. This gene encodes a protease that allows better growth in milk by facilitating casein breakdown to supply amino acids. The
S. thermophilus
protease exhibits 95% identity to the animal
Streptococcus suis
protein PrtS. Genomic analysis showed that
prtS
is part of an island flanked by two tandem insertion sequence elements and containing three other genes which present the best identities and synteny with the
S. suis
genome. These data indicate a potential origin for this “ecological” island in a species closely related to
S. suis
. The analysis of the distribution of the
prtS
gene in
S. thermophilus
showed that the gene is infrequent in historical collections but frequent in recent industrial ones. Moreover, this “ecological” island conferring an important metabolic trait for milk adaptation appears to have disseminated by lateral transfer in the
S. thermophilus
population. Taken together, these data support an evolutionary scheme of
S. thermophilus
where gene acquisition and selection by food producers are determining factors. The source and impact of genes acquired by horizontal gene transfer on the physiology and safety of strains should be addressed.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
89 articles.
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