Abstract
Abuse of heavy metals and antibiotics results in the dissemination of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). Ditch wetlands are important sinks for heavy metals and antibiotics. The relationships between bacterial communities and MRG/ARG dissemination under dual stresses of heavy metals and antibiotics remain unclear. The responses of MRGs and ARGs to the co-selective pressure of cadmium (Cd) and doxycycline (DC) in ditch wetlands were investigated after 7-day and 84-day exposures. In ecological ditches, residual rates of Cd and DC varied from 0.4 to –5.73% and 0 to –0.61%, respectively. The greatest total relative abundance of ARGs was observed in the Cd 5 mg L–1 + DC 50 mg L–1 group. A significant level of DC (50 mg L–1) significantly reduced the total relative abundances of MRGs at a concentration of 5 mg L–1 Cd stress. Redundancy analysis indicated that Cd and DC had strong positive effects on most ARGs and MRGs after a 7-day exposure. Meanwhile, the class 1 integron gene (intI1) exhibited strong positive correlations with most ARGs and cadmium resistance genes (czcA) after an 84-day exposure. Network analysis showed that Acinetobacter and Pseudomonas were the potential dominant host genera for ARGs and MRGs, and tetracycline resistance genes (tetA), czcA, and intI1 shared the same potential host bacteria Trichococcus after an 84-day exposure.
Highlights
Doxycycline (DC), a low-cost broad-spectrum antibiotic, is widely used as a medicine for disease prevention and treatment and as a feed additive for growth promotion in animal husbandry (Zhang et al, 2015)
These mechanisms were associated with a class of coding genes named antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs) (Yang et al, 2019; Wang et al, 2020)
The coexistence of heavy metals and antibiotics would enhance their co-selection effects, especially when ARGs and MRGs are situated in the same mobile genetic elements (MGEs), such as the class 1 integron-integrase (IntI1) (Di Cesare et al, 2016)
Summary
Doxycycline (DC), a low-cost broad-spectrum antibiotic, is widely used as a medicine for disease prevention and treatment and as a feed additive for growth promotion in animal husbandry (Zhang et al, 2015). The overuse of chemical fertilizers is an important cause of global heavy-metal environmental pollution, especially in China. This largescale usage results in heavy metals, especially cadmium (Cd), being released from soils, thereby. Previous studies reported that some bacteria formed defense mechanisms against heavy metals and antibiotic contaminants These mechanisms were associated with a class of coding genes named antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs) (Yang et al, 2019; Wang et al, 2020). The coexistence of heavy metals and antibiotics might exacerbate the dissemination of MRGs and ARGs in a water body, which will in turn lead to harmful effects on human health
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