Metagenomic analysis of bacteria from human tongue scrapings reveals novel bacterial communities that contribute nitrite and nitric oxide to the host

Abstract

Human nitrate reduction requires the presence of nitrate reducing bacteria since mammals cannot reduce this anion. Understanding this pathway will provide a more effective system for recycling endogenously produced nitrate and to enhance nitrite and NO formation from dietary sources of nitrate. The purpose of our study was to analyze and identify the nitrate reducing capacity of tongue scrapings from three subsets of human volunteers that had a high, moderate and low nitrate reductase activity over a period of four days in vitro and to perform a parallel metagenomic analysis of the bacterial community structure over the same time period to identify bacteria that may be reducing nitrate. Through 16S rRNA pyrosequencing and analysis using the CloVR 16S analysis pipeline and the Genboree Machine Learning Toolkit, we were able to identify notable changes in community structure and identify taxa that contribute to nitrate reduction. Biochemically and genetically we found significant community diversity between high, moderate and low nitrate reducing tongue scrapings and have identified specific bacteria that are unique to each level of nitrate reduction. Further characterization of these species and their nitrate reducing activity will enable exploitation of the oral microbiota and/or the development of specific pre/probiotic treatments that may be useful for treating any condition related to NO insufficiency. Therapeutically, our data suggests that the best way to promote NO production and overcome conditions of NO insufficiency may not be targeted at eNOS, but rather on targeting specific oral bacterial communities and a diet rich in nitrate.