Effect of acetate and nitrate availability on DNRA growth. G. lovleyi SZ growth (optical density at 600 nm, OD₆₀₀) and N species (nitrate, nitrite and ammonium) in cultures with 5 mM or 10 mM (open symbols) nitrate and acetate concentrations yielding molar C/NO₃⁻ ratios of 1 (A), 2 (B), or 3 (C). The N species were measured in supernatant fluids recovered from early stationary phase cultures and differences for each treatment were statistically identified with a combined ANOVA and post-hoc Tukey HSD test (a, b or c for P < .05).