Table 4. The fraction of the population with Nar (F_Na) and NirS (F_Ni) estimated based on the optimal specific-probability of nar and nirS transcriptional initiation (r_Na and r_Ni), respectively.

Batch	C-source	O2 (vol.%), ${\mathrm{NO}}_3^{-}$ (mM)	Functional FNa * (unitless)	Theoretical FNa * (unitless)	FNi (unitless)
1	Butyrate	~0, 2	0.433	0.813	0.221
2	Butyrate	7, 2	0.343	0.656	0.088
3	Succinate	~0, 2	0.357	0.803	0.206
4	Succinate	7, 2	0.230	0.564	0.077

*Functional F_Na is the fraction of cells expressing Nar while ${\text{NO}}_3^{-}$ is still present, while Theoretical F_Na is the fraction expressing Nar when including the theoretical recruitment after ${\text{NO}}_3^{-}$ depletion (supported by energy from N₂O reduction).