Fig. 3.

Copy numbers of bacterial amoA genes in total DNA isolated from biofilm enrichments (A and B) and presumably labeled DNA after isopycnic centrifugation (C and D) of total DNA extracts. “Labeled” (NaH¹³CO₃) and “Control” refer to the respective treatment of stream biofilms for a 6-week incubation. The ¹³C-associated bacterial amoA copy numbers in C and D are the sum of those in the heavy DNA—fractions 5, 6, and 7—of the labeled treatments incubated for 3 and 6 weeks in the experiment whose results are shown in Fig. 1.