Nitrite Production from Nitrate and Its Link with Lactate Metabolism in Oral Veillonella spp.

Veillonella species are among the major anaerobes in the oral cavity and are frequently detected in both caries lesions and healthy oral microbiomes. They possess the ability to utilize lactate and convert nitrate (NO₃ ^-) into nitrite (NO₂ ^- ). Recently, interest in NO₂ ^- has increased rapidly because of its beneficial ef-fects on oral and general health; i.e., it inhibits the growth and metabolism of oral pathogenic bacteria, such as Streptococcus mutans, and lowers systemic blood pres-sure. However, there is only limited information about the biochemical characteris-tics of NO₂ ^- production by Veillonella species. We found that NO₃ ^- did not inhibit the growth of Veillonella atypica or Veillonella parvula, and it inhibited the growth of Streptococcus mutans only at a high concentration (100 mM). However, NO₂ ^- inhib-ited the growth of Streptococcus mutans at a low concentration (0.5 mM), while a higher concentration of NO₂ ^- (20 mM) was needed to inhibit the growth of Veillo-nella species. NO₂ ^- production by Veillonella species was increased by environmental factors (lactate, acidic pH, and anaerobic conditions) and growth conditions (the presence of NO₃ ^- or NO₂ ^-) and was linked to anaerobic lactate metabolism. A stoi-chiometric evaluation revealed that NO₃ ^- is reduced to NO₂ ^- by accepting reducing power derived from the oxidization of lactate. These findings suggest that the bio-chemical characteristics of NO₂ ^- production from NO₃ ^- and its linkage with lactate metabolism in oral Veillonella species may play a key role in maintaining good oral and general health.