title: Metagenomic analysis of nitrate-reducing bacteria in the oral cavity: implications for nitric oxide homeostasis.
abstract: The microbiota of the human lower intestinal tract helps maintain healthy host physiology, for example through nutrient acquisition and bile acid recycling, but specific positive contributions of the oral microbiota to host health are not well established. Nitric oxide (NO) homeostasis is crucial to mammalian physiology. The recently described entero-salivary nitrate-nitrite-nitric oxide pathway has been shown to provide bioactive NO from dietary nitrate sources. Interestingly, this pathway is dependent upon oral nitrate-reducing bacteria, since humans lack this enzyme activity. This pathway appears to represent a newly recognized symbiosis between oral nitrate-reducing bacteria and their human hosts in which the bacteria provide nitrite and nitric oxide from nitrate reduction. Here we measure the nitrate-reducing capacity of tongue-scraping samples from six healthy human volunteers, and analyze metagenomes of the bacterial communities to identify bacteria contributing to nitrate reduction. We identified 14 candidate species, seven of which were not previously believed to contribute to nitrate reduction. We cultivated isolates of four candidate species in single- and mixed-species biofilms, revealing that they have substantial nitrate- and nitrite-reduction capabilities. Colonization by specific oral bacteria may thus contribute to host NO homeostasis by providing nitrite and nitric oxide. Conversely, the lack of specific nitrate-reducing communities may disrupt the nitrate-nitrite-nitric oxide pathway and lead to a state of NO insufficiency. These findings may also provide mechanistic evidence for the oral systemic link. Our results provide a possible new therapeutic target and paradigm for NO restoration in humans by specific oral bacteria.
authors.affiliation: Integrative Molecular and Biomedical Sciences Graduate Program, Baylor College of Medicine, Houston, Texas, United States of America; Alkek Center for Metagenomics and Microbiome Research, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Embriette R
authors.initials: ER
authors.lastname: Hyde
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical School, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Fernando
authors.initials: F
authors.lastname: Andrade
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical School, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Zalman
authors.initials: Z
authors.lastname: Vaksman
authors.affiliation: Department of Periodontics, School of Dentistry, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Parthasarathy
authors.affiliation: Texas Therapeutics Institute, Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Hong
authors.initials: H
authors.lastname: Jiang
authors.affiliation: Texas Therapeutics Institute, Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Deepa K
authors.initials: DK
authors.lastname: Parthasarathy
authors.affiliation: Texas Therapeutics Institute, Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Ashley C
authors.initials: AC
authors.lastname: Torregrossa
authors.affiliation: Department of Periodontics, School of Dentistry, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Gena
authors.initials: G
authors.lastname: Tribble
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical School, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Heidi B
authors.initials: HB
authors.lastname: Kaplan
authors.affiliation: Alkek Center for Metagenomics and Microbiome Research, Baylor College of Medicine, Houston, Texas, United States of America; Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Petrosino
authors.affiliation: Texas Therapeutics Institute, Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center Houston, Houston, Texas, United States of America.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Bryan
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000145:classification / Q000235:genetics*; D044822:Biodiversity; D018441:Biofilms / Q000254:growth & development; D006706:Homeostasis; D006801:Humans; D053858:Metabolic Networks and Pathways / Q000235:genetics; D056186:Metagenomics / Q000379:methods*; D059013:Microbial Consortia; D064307:Microbiota / Q000235:genetics; D009055:Mouth / Q000382:microbiology*; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010084:Oxidation-Reduction; D025341:Principal Component Analysis; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013997:Time Factors
chemical_list: D009566:Nitrates; D009573:Nitrites; D009569:Nitric Oxide