Fig. 2: Relative abundances of 16S rRNA genes across CsCl gradient fractions during the incubation periods at days 7, 14, and 28.

A–F Quantitative distribution of 16S rRNA genes across CsCl gradient fractions from the ¹²CH₃Hg⁺ and ¹³CH₃Hg⁺ treatments in the paddy soil from high Hg contaminated site (High-P) and upland soil from low Hg contaminated site (Low-U). G, H Venn diagrams showing the shared and exclusive bacterial OTUs in the fraction of the highest 16S rRNA gene copies from ¹³CH₃Hg⁺ treatment and the corresponding fraction in ¹²CH₃Hg⁺ treatment at day 28 in the High-P and Low-U soils. I, J The proportion of different bacterial phylum/class incorporating ¹³C in the labeled microcosms from High-P and Low-U soils at 28 d. Eighteen fractions from each CsCl gradient were analyzed, and the abundance of the 16S rRNA genes in each fraction was converted to the proportion of total 16S rRNA gene abundance throughout the gradient fractions. Vertical bars in (A–F) represent standard deviations of the relative abundance (three biological replicates, n = 3) in the ¹²CH₃Hg⁺ (control) and ¹³CH₃Hg⁺ treatments, and horizontal error bars in (A–F) represent the standard deviations of the buoyant density of the same order fractions (three biological replicates, n = 3) in the ¹²CH₃Hg⁺ (control) and ¹³CH₃Hg⁺ treatments. The data in (A–F) are presented as mean values ± standard deviation. The shadings in (A–F) indicated the fraction of the highest 16S rRNA gene copies from ¹²CH₃Hg⁺ and ¹³CH₃Hg⁺ treatments. Source data are provided as a Source Data file.