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The Essential tacF Gene Is Responsible for the Choline-Dependent Growth Phenotype of Streptococcus pneumoniae

Marlen Damjanovic,^1,, Arun S. Kharat,^2,, Alice Eberhardt,³ Alexander Tomasz,² and Waldemar Vollmer^1,3*

Microbial Genetics, University of Tübingen, Tübingen, Germany,¹ Laboratory of Microbiology, The Rockefeller University, New York, New York,² Institute for Cell and Molecular Biosciences, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom³

Received 1 May 2007/ Accepted 12 July 2007

Streptococcus pneumoniae has an absolute nutritional requirement for choline, and the choline molecules are known to incorporate exclusively into the cell wall and membrane teichoic acids of the bacterium. We describe here the isolation of a mutant of strain R6 in which a single GT point mutation in the gene tacF (formerly designated spr1150) is responsible for generating a choline-independent phenotype. The choline-independent phenotype could be transferred to the laboratory strain R6 and to the encapsulated strain D39 by genetic transformation with a PCR product or with a plasmid carrying the mutated tacF gene. The tacF gene product belongs to the protein family of polysaccharide transmembrane transporters (flippases). A model is presented in which TacF is required for the transport of the teichoic acid subunits across the cytoplasmic membrane. According to this model, wild-type TacF has a strict specificity for choline-containing subunits, whereas the TacF present in the choline-independent mutant strain is able to transport both choline-containing and choline-free teichoic acid chains. The proposed transport specificity of parental-type TacF for choline-containing subunits would ensure the loading of the cell wall with teichoic acid chains decorated with choline residues, which appear to be essential for the virulence of this pathogen.

Published ahead of print on 27 July 2007.

These authors contributed equally to this work.

Present address: Departement für Innere Medizin, Universitätsspital Zürich, Zürich, Switzerland.

Present address: Department of Biotechnology, Babasaheb Ambedkar Marathwada University, Osmanabad, Maharashtra, India.

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