Veillonella species are one of 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 effects 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 pressure. However, there is only limited information about the biochemical characteristics of NO2- production by Veillonella species. We found that NO3- did not inhibit the growth of Veillonella atypica or Veillonella parvula, and it only inhibited the growth of Streptococcus mutans at a high concentration (100 mM). However, NO2- inhibited 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 Veillonella species. The NO2- production of Veillonella species was increased by environmental factors (lactate, acidic pH, and anaerobic conditions) and growth conditions (the presence of NO3-/NO2-), and was linked to anaerobic lactate metabolism. A stoichiometric evaluation revealed that NO3- is reduced to NO2- by accepting reducing power derived from the oxidization of lactate. These findings suggest that the biochemical 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. IMPORTANCE The prevalence of dental caries is still high around the world. Dental caries is initiated when the teeth are exposed to acid, such as lactic acid, produced via carbohydrate metabolism by acidogenic microorganisms. Veillonella species, one of the major oral microorganisms, are considered to be beneficial bacteria due to their ability to convert lactic acid to weaker acids and to produce NO2- from NO3-, which is thought to be good for both oral and general health. Therefore, it is clear that there is a need to elucidate the biochemical characteristics of NO2- production in Veillonella species. The significance of our research is that we have found that lactate metabolism is linked to NO2- production in Veillonella species in the environment found in the oral cavity. This study suggests that Veillonella species are potential candidates for maintaining oral and general health.

The dependence of magnetic properties and microstructure on the composition of CrMox (x=0–40 at. %) underlayer and CoCr-based nonmagnetic interlayer has been examined for CoCr18Pt20B4 longitudinal media. In the media using a single CrMo (10 nm) underlayer, the highest coercivity that can be obtained is only 1.9 kOe. The coercivity is drastically increased up to 5.0 and 6.4 kOe by using substrate/Cr (5 nm)/CrMo (5 nm) dual underlayer and substrate/CrMo (10 nm)/CoCr38Mo2 (1.3 nm), respectively. It is clarified that the improvement of the coercivity is mainly due to the enhancement of the quality of the crystal growth of the magnetic layer, which results in the improvement of magnetocrystalline anisotropy field and in-plane crystallographic orientation.

To realize CoB15/Pd multilayer perpendicular media with weak intergranular exchange coupling, we utilize PdSi18 (at. %) alloy, which contains elements that have large difference of affinity for oxygen, as the underlayer. It is clarified that introducing oxygen into Ar atmosphere during deposition of the underlayer substantially reduces the intergranular exchange coupling of the multilayer. Microstructural analysis reveals that the introduction of oxygen has separated the PdSi18 underlayer into two phases and enhances the formation of grain boundaries of the multilayer. It is suggested that the two-phase-separated Pd–SiO underlayer becomes a template for the growth of the multilayer and promotes the formation of grain boundaries in the multilayer, which reduces the exchange coupling through isolation of grains of the multilayer. In addition, independent of the oxygen pressure, coercivity and anisotropy energy maintain values of around 3.5 kOe and 2.3×106 erg/cm3, respectively. It is concluded that the two-phase-separated Pd–SiO underlayer, fabricated by introducing oxygen during sputtering of PdSi18 underlayer, is effective for reducing the magnetic exchange coupling without degrading the magnetic properties.

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In order to develop a magnetic material for high-density magnetic recording media which overcomes the thermal agitation effect, the magnetic properties, such as saturation magnetization and magnetic anisotropy, were evaluated for Co–M (M=Pt, Pd, Ru, Rh, Os, Cr, Ge, Mo, Mn, Re, and Si) binary alloys. Ge addition was found to be effective in maintaining the value of the magnetic anisotropy field of Co. Furthermore, a ternary magnetic alloy of Co–Ge–Cr (85 at. % Co, 10 at. % Ge, 5 at. % Cr) was found to have the following magnetic properties: Kugrain⩾3×106 erg/cm3, Hkgrain≈10 kOe, and 4πMs/Hkgrain<1.0. This magnetic material is a very promising candidate for use in high-density magnetic recording media.