A plasmid-encoded nicotinamidase (PncA) is essential for infectivity of Borrelia burgdorferi in a mammalian host

Authors

  • Joye E. Purser,

    1. Graduate School of Biomedical Sciences and Department of Pathology and Laboratory Medicine, and
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  • Matthew B. Lawrenz,

    1. Graduate School of Biomedical Sciences and Department of Pathology and Laboratory Medicine, and
    2. Department of Microbiology and Molecular Genetics, Medical School, University of Texas Health Science Center at Houston, MSB 2.278, 6431 Fannin St., Houston, TX 77225, USA.
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  • Melissa J. Caimano,

    1. Center for Microbial Pathogenesis,
    2. Department of Pathology and
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  • Jerrilyn K. Howell,

    1. Graduate School of Biomedical Sciences and Department of Pathology and Laboratory Medicine, and
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  • Justin D. Radolf,

    1. Center for Microbial Pathogenesis,
    2. Department of Medicine and Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
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  • Steven J. Norris

    Corresponding author
    1. Graduate School of Biomedical Sciences and Department of Pathology and Laboratory Medicine, and
    2. Department of Microbiology and Molecular Genetics, Medical School, University of Texas Health Science Center at Houston, MSB 2.278, 6431 Fannin St., Houston, TX 77225, USA.
    • For correspondence at the Department of Pathology and Laboratory Medicine. E-mail Steven.J.Norris@uth.tmc.edu; Tel. (+1) 713 500 5338; Fax (+1) 713 500 0738.

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Summary

Borrelia burgdorferi, a spirochaete that causes Lyme borreliosis, contains 21 linear and circular plasmids thought to be important for survival in mammals or ticks. Our results demonstrate that the gene BBE22 encoding a nicotinamidase is capable of replacing the requirement for the 25 kb linear plasmid lp25 during mammalian infection. Transformation of B. burgdorferi lacking lp25 with a shuttle vector containing the lp25 gene BBE22 (pBBE22) restored infectivity in mice to a level comparable to that of wild-type Borrelia. This complementation also restored the growth and host adaptation of lp25B. burgdorferi in dialysis membrane chambers (DMCs) implanted in rats. A single Cys to Ala conversion at the putative active site of BBE22 abrogated the ability of pBBE22 to re-establish infectivity or growth in DMCs. Additional Salmonella typhimurium complementation studies and enzymatic analysis demonstrated that the BBE22 gene product has nicotinamidase activity and is most probably required for the biosynthesis of NAD. These results indicate that some plasmid-encoded products fulfil physiological functions required in the enzootic cycle of pathogenic Borrelia.

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