Figure 1.

(A) Representative 16S rRNA gene counts vs. DNA density for SIP experiments using GraylingRiver1 sediment, illustrating the shifts in relative 16S rRNA gene copies associated with different incubations. The incubations using only ¹³CO as the sole carbon and energy source showed the greatest increase in the relative number of 16S rRNA gene copies in heavy fractions at densities of approximately 1.730 g ml⁻¹. DNA from these heavy fractions was used for 16S rRNA gene pyrosequencing. (B) Relative 16S rRNA gene copies from PB1 sediment showing no density shift with ¹³CO incubations despite active CO oxidation. Circles indicate ¹³CO incubation fractions used for 16S rRNA gene pyrosequencing analyses. “Control” represents the un-incubated (no CO or CO₂ added) environmental sample.