Fig. 4.

Growth and transcription of V-ATPase genes in strain Nitrosocosmicus oleophilus MY3 at different pH. a Strain MY3 was grown in artificial fresh water medium (AFM) containing 500 μM NH₄Cl at pH 5.2, 5.5, and 7.5, respectively. Growth was monitored via nitrite accumulation. The initial cell density after inoculation was ~1.0 × 10⁵ cells ml⁻¹. b Transcript abundance of 16S rRNA, amoA, 4-hydroxybutyryl-CoA dehydratase, methylmalonyl-CoA mutase large subunit, and ATPase subunit A were determined by quantitative PCR (qPCR) after reverse transcription of total RNA extracted from MY3 at mid-exponential phase (marked with arrows) at pH 5.5 and 7.5, respectively. All qPCR results were normalized to 1 ng of RNA for comparison between pH 5.5 and 7.5. Error bars represent the standard errors of triplicate incubations. For each gene, significance difference in measured cDNA copy numbers between pH 5.5 and 7.5 was detected using a t test (**P < 0.01)