Role of GlnR in Acid-Mediated Repression of Genes Encoding Proteins Involved in Glutamine and Glutamate Metabolism in Streptococcus mutans

Author:

Chen Pei-Min1,Chen Yi-Ywan M.23,Yu Sung-Liang4,Sher Singh5,Lai Chern-Hsiung6,Chia Jean-San1

Affiliation:

1. Department of Microbiology and Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan

2. Department of Microbiology and Immunology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan

3. Research Center for Pathogenic Bacteria, Chang Gung University, Tao-Yuan, Taiwan

4. Department of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan

5. Department of Life Sciences, National Taiwan Normal University, Taipei, Taiwan

6. Research Center for Anaerobic and Oral Microbiology, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan

Abstract

ABSTRACT The acid tolerance response (ATR) is one of the major virulence traits of Streptococcus mutans . In this study, the role of GlnR in acid-mediated gene repression that affects the adaptive ATR in S. mutans was investigated. Using a whole-genome microarray and in silico analyses, we demonstrated that GlnR and the GlnR box (ATGTNAN 7 TNACAT) were involved in the transcriptional repression of clusters of genes encoding proteins involved in glutamine and glutamate metabolism under acidic challenge. Reverse transcription-PCR (RT-PCR) analysis revealed that the coordinated regulation of the GlnR regulon occurred 5 min after acid treatment and that prolonged acid exposure (30 min) resulted in further reduction in expression. A lower level but consistent reduction in response to acidic pH was also observed in chemostat-grown cells, confirming the negative regulation of GlnR. The repression by GlnR through the GlnR box in response to acidic pH was further confirmed in the citBZC operon, containing genes encoding the first three enzymes in the glutamine/glutamate biosynthesis pathway. The survival rate of the GlnR-deficient mutant at pH 2.8 was more than 10-fold lower than that in the wild-type strain 45 min after acid treatment, suggesting that the GlnR regulon participates in S. mutans ATR. It is hypothesized that downregulation of the synthesis of the amino acid precursors in response to acid challenge would promote citrate metabolism to pyruvate, with the consumption of H + and potential ATP synthesis. Such regulation will ensure an optimal acid adaption in S. mutans .

Publisher

American Society for Microbiology

Subject

Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology

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