FIG. 2.

Individual growth curves for M. album (•, ○) and Methylocystis sp. (▪, □) in cocultures. Cells of the two isolates were enumerated separately by qPCR. Cocultures were grown in NMS (closed symbols) or AMS (open symbols) without N amendment (A), with the addition of 2.5 mM NaNO₂ (B), or with the addition of 50 mM NH₄Cl (C). Standard errors for replicated experiments (n = 6) are indicated by bars. R² values and PCR efficiency for standard curves with known cell numbers were 0.99 and 107% for M. album and 0.94 and 137% for Methylocystis sp.