Effects of Carbon Nanotubes on Microbial Growth and Horizontal Gene Transfer
Carbon nanotubes (CNTs) have widely studied in various fields since its discovery. The wide research and application of CNTs may result in the occurrence of CNTs in natural environment and their nanotoxicity has been widely recognized. Moreover, a less frequently studied effect of CNTs is the promotion of spread of antibiotic resistance. CNTs may function as a reservoir of antibiotic resistance genes (ARGs) and pose additional health risks associated with the spread of ARGs in natural environment, but no previous studies have been reported on the effects of CNTs on horizontal gene transfer. The objective of this study was to study the effects of CNTs on microbial growth and horizontal gene transfer. Two species of indigenous bacteria (erythromycin-resistant Escherichia coli (E. coli) and erythromycin-sensitive Bacillus cereus (B. cereus)) were isolated from Wabash River in West Lafayette, IN and the effects of CNTs and antibiotics on these bacteria were further evaluated. No effects were observed on growth of E. coli under the exposure of 500 mg/L CNTs, while growth of B. cereus was delayed with 500 mg/L CNTs. The minimum inhibition concentration (MIC) of B. cereus to erythromycin was identified as 0.4 mg/L. When B. cereus was cultivated under 0.4 mg/L (1MIC) erythromycin for 24 hours, its resistance to erythromycin increased to 2 mg/L. When B. cereus was cultivated under 0.4 mg/L erythromycin and 500 mg/L CNTs for 24 hours, its resistance to erythromycin increased to 10 mg/L. Finally, erythromycin-resistant E. coli—which harbors erythromycin resistance methylase (erm) gene erm80—and erythromycin-sensitive B. cereus—which does not harbor gene erm80—were co-cultivated with CNTs and erythromycin. The results showed that horizontal gene transfer efficiency was highest under 0.4 mg/L erythromycin and 500 mg/L CNTs. The results suggest that CNTs may create additional selective pressure for the spread of antibiotic resistance genes and their effects of horizontal gene transfer should be further investigated.
Zhou, Purdue University.
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