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Journal of Bacteriology, August 2001, p. 4599-4608, Vol. 183, No. 15
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.15.4599-4608.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Competence Repression under Oxygen Limitation through the Two-Component MicAB Signal-Transducing System in Streptococcus pneumoniae and Involvement of the PAS Domain of MicB

José R. Echeniquedagger and Marie-Claude Trombe*

Laboratoire de Genétique et Physiologie Bactérienne, E.A. 3036, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse Cedex, France

Received 21 February 2001/Accepted 14 May 2001

In Streptococcus pneumoniae, a fermentative aerotolerant and catalase-deficient human pathogen, oxidases with molecular oxygen as substrate are important for virulence and for competence. The signal-transducing two-component systems CiaRH and ComDE mediate the response to oxygen, culminating in competence. In this work we show that the two-component MicAB system, whose MicB kinase carries a PAS domain, is also involved in competence repression under oxygen limitation. Autophosphorylation of recombinant MicB and phosphotransfer to recombinant MicA have been demonstrated. Mutational analysis and in vitro assays showed that the C-terminal part of the protein and residue L100 in the N-terminal cap of its PAS domain are both crucial for autokinase activity in vitro. Although no insertion mutation in micA was obtained, expression of the mutated allele micA59DA did not change bacterial growth and overcame competence repression under microaerobiosis. This was related to a strong instability of MicA59DA-PO4 in vitro. Thus, mutations which either reduced the stability of MicA-PO4 or abolished kinase activity in MicB were related to competence derepression under microaerobiosis, suggesting that MicA-PO4 is involved in competence repression when oxygen becomes limiting. The micAB genes are flanked by mutY and orfC. MutY is an adenine glycosylase involved in the repair of oxidized pyrimidines. OrfC shows the features of a metal binding protein. We did not obtain insertion mutation in orfC, suggesting its requirement for growth. It is proposed that MicAB, with its PAS motif, may belong to a set of functions important in the protection of the cell against oxidative stress, including the control of competence.


* Corresponding author. Mailing address: Laboratoire de Genétique et Physiologie Bacterienne, E.A. 3036, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse Cedex, France. Phone: (33)61-322974. Fax: (33)61-322620. E-mail: trombe{at}cict.fr.

dagger Present address: Departmento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Pabellón Argentina, Ciudad Universitaria, CP 5000 Córdoba, Argentina.


Journal of Bacteriology, August 2001, p. 4599-4608, Vol. 183, No. 15
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.15.4599-4608.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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Copyright © 2001 by the American Society for Microbiology. All rights reserved.