FIG. 4.

Growth of strain TR2 and of P. denitrificans under various conditions. P. denitrificans (A, C, and E) (123 mg cells [dry weight]) and strain TR2 (B, D, and F) (166 mg cells) were cultured first aerobically, with shaking at 150 rpm (phase I; DO = 5.0 mg liter⁻¹), and then microaerobically, with a rotation speed of 75 rpm (phases II and III; DO = 0 mg liter⁻¹). At 4 h, 10 mM NaNO₃ or NaNO₂ was added (phase III). Throughout the culture, time-dependent changes in the indicated items were monitored. (A and B) Closed circles, OD₆₆₀ (cell growth) of the culture to which NO₃⁻ was added at phase III (upon NO₃⁻ addition); closed triangles, OD₆₆₀ upon NO₂⁻ addition; open circles, pH upon NO₃⁻ addition; open triangles, pH upon NO₂⁻ addition. (C and D) Open circles, NO₃⁻ upon NO₃⁻ addition; closed circles, NO₂⁻ upon NO₃⁻ addition (not indicated in panel D, because all plots were at zero level); closed triangles, NO₂⁻ upon NO₂⁻ addition. NO₃⁻ was not detected upon nitrite addition (data not shown). (E and F) Gene expression upon NO₃⁻ addition. Closed circles, nosZ; open circles, nirS. Similar results were obtained with NO₂⁻ addition (data not shown).