Abstract
Veillonella, a strict anaerobe, which is one of the constituents of the habitual oral microflora, is known to have the strongest nitrate reduction ability of the oral microorganisms.
The author isolated some Veillonella from human saliva and identified them as two species, V. alcalescens and V. parvula. Each Veillonella was inoculated and cultured in a medium containing nitrate. The concentration of nitrite produced by the action of nitrate reduction and the turbidity in the growth medium were measured. The processes of nitrate reduction was compared in the two Veillonella species in regard to the nitrite production, the bacterial growth, nitrate reduction ability, and nitrite reduction ability in the medium.
The difference of nitrate reduction between V. alcalescens and V. parvula was not obvious in the logarithmic growth phase, but it was clearly demonstrated in the stationary phase, where the nitrite reduction was observed only in V. alcalescens. However, it was also found that V. parvula acquired nitrite reduction ability when it was cultured under aerobic conditions. This change in V. parvula seemed to be related to catalase action.
Nitrate reductase activities of Veillonella were present mainly in the membrane-bound fraction at both the logarithmic and the stationary phases. But cytoplasmic nitrate reductase activities increased exceptionally at the stationary phase in V. alcalescens.
From these results, it seemed that V. parvula showed the respiratory type of nitrate reduction, whereas V. alcalescens showed both the respiratory and the assimilative types; the respiratory type appeared at the logarithmic phase and the assimilative one mainly at the stationary phase.
