STUDY OF REGULATION MECHANISMS CONTROLLING
COMPETENCE IN STREPTOCOCCUS THERMOPHILUS
CÉLINE BOUTRY1*, LAETITIA FONTAINE1, BRIGITTE DELPLACE1, ELVIS
BERNARD1, ERIC GUÉDON2, AND PASCAL HOLS1
Unité de Génétique, Institut des Sciences de la Vie, Université catholique de Louvain, Place Croix
du Sud 5, B-1348 Louvain-la-Neuve, Belgium1 and Institut National de la Recherche Agronomique
(INRA), Unité de Génétique Microbienne, Jouy en Josas, France2
*Celine.Boutry@uclouvain.be
Competence for natural transformation is a frequent property among pathogenic
streptococci and is considered a general mechanism for genome plasticity. In S. pneumoniae,
competence is a transient event relying on an alarmone, ComC, that activates the ComDE twocomponent system. This results in the induction of comX, encoding an alternative sigma factor
(σX). ComX is the central regulator of competence that activates all essential late genes required
for DNA transformation. Recently, functional natural transformation was also shown in S.
thermophilus LMG18311, a non-pathogenic streptococcus used in the dairy industry. However,
this was achieved through the artificial expression of comX under control of a non-native
promoter. Indeed, no functional homolog of the ComC/D/E system was found in S. thermophilus,
and the mechanisms and natural growth conditions regulating comX expression and/or ComX
stability still remain unknown. The aim of this study was to elucidate the regulation pathway
underlying competence development in S. thermophilus.
A targeted mutagenesis strategy was followed to identify genes involved in the early steps
of competence development. Targets were selected according to their implication in comX
induction (stkP, pppL, micAB, codY, hdiR) or ComX degradation/stabilization (spxB, stu0161,
mecA) in S. pneumoniae and B. subtilis. The effect of gene deletion on competence was studied at
the functional and transcriptional level. For this latter purpose, disruption of target genes was
performed in strains containing either a PcomX-luxAB or a PcomGA-luxAB fusion. Preliminary results
suggest a post-translational regulation mechanism of competence development acting at the level
of ComX. A random mutagenesis strategy is currently under progress to identify new specific
regulators controlling comX expression in S. thermophilus.