Influence of Legacy Mercury on Antibiotic Resistomes: Evidence from Agricultural Soils with Different Cropping Systems

Agricultural
soils are important reservoirs for antibiotic resistance
genes (ARGs), which have close linkage to human health via crop production.
Metal stress in environments may function as a selection pressure
for antibiotic resistomes. However, there is still a lack of field
studies focusing on the effect of historical mercury (Hg) contamination
on antibiotic resistomes in agricultural soils. Here, we explored
the ARG profile in soils with different cropping systems (paddy and
upland) and linked them to legacy Hg exposure. We found that ARG profiles
were significantly different between paddy and upland soils. However,
both paddy and upland soils with long-term field Hg contamination
harbored higher diversity and abundance of ARGs than non-polluted
soils. The co-occurrence network reveals significant associations
among Hg, Hg resistance genes, mobile genetic elements (MGEs), and
ARGs. Together with path analysis showing legacy Hg possibly affecting
soil resistomes through the shifts of soil microbiota, Hg resistance
genes, and MGEs, we suggest that legacy Hg-induced potential co-selection
might elevate the ARG level. Redundancy analysis further supports
that legacy Hg pollution had a significant association with ARG variations
in the paddy and upland soils (P < 0.01). Collectively,
our results highlight the underappreciated role of legacy Hg as a
potential persistent selecting agent in contributing to soil ARGs
in agroecosystems.