| The excessive use and abuse of antibiotics and other antimicrobial agents in the medical,animal husbandry,agriculture,and other industries have resulted in the continuous improvement of bacterial resistance and even the generation of multi-resistance,promoted the spread of antibiotic resistance genes(ARGs)among bacteria in the environment,and posed a threat to human and animal life,health and public safety.ARGs are mainly transmitted between bacteria or pathogens through horizontal gene transfer(HGT)such as conjugation,transformation,and transduction,and the most likely to occur and the most efficient transfer is plasmid-mediated conjugation transfer of antibiotic-resistant genes.Therefore,it is imperative to strengthen the research and development of new substances and new methods to inhibit the junction transfer of antibiotic-resistant genes and prevent and control the pollution of antibiotic-resistant genes.With the development of nanomaterials science,more and more nanomaterials have been applied in medicine,energy,environmental pollution control,industry and agriculture,and other fields.Molybdenum sulfide is a flaky semiconductor material similar to two-dimensional layered graphene.It has a wide range of sources,low toxicity,and stable properties,with excellent electrical and optical properties.It has an important application prospect in the fields of material science,environment,energy,semiconductor devices,and so on.α-Fe2O3,γ-Fe2O3,Fe3O4,and other iron oxides widely exist in nature and have large specific surface area.Among them,the magnetic nanoparticles Fe3O4 have unique electrical and magnetic properties and have been widely used in medicine and other fields.In this paper,based on the excellent properties of the above nanomaterials,two kinds of iron-molybdenum nanocomposites were prepared,which were Fe2O3@MoS2 and Fe3O4@MoS2.The prepared two kinds of Fe-Mo nanocomposites were systematically characterized by transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),and X-ray diffraction(XRD).The bacterial strain culture,plate counting method,and quantitative real-time PCR(qPCR)were used to investigate the effect of the above-mentioned iron-molybdenum nanocomposites on the efficiency of splice transfer of resistance gene.On this basis,the mechanism of inhibition of antibiotic-resistant genes conjugation transfer by Fe-Mo nanocomposites was analyzed.(1)Fe2O3@MoS2 nanocomposites were synthesized by a two-step hydrothermal method.It is proved by TEM,X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS)that the Fe2O3@MoS2 composite is successfully synthesized,and the Fe2O3 microspheres are embedded in the MoS2 nanosheets.The effects of material composition,system pH,conjugation temperature,conjugation time,material concentration,and bacterial solution concentration on the inhibition of conjugation transfer of antibiotic-resistant genes by composite are studied systematically and the optimal experimental conditions are determined.In addition,toxicological analysis of Fe2O3@MoS2 show that it is very low toxic to organisms and an environmentally friendly nanomaterial capable of inhibiting horizontal gene transfer.(2)To explore the mechanism of inhibition of HGT by Fe2O3@MoS2,the qPCR method was used to analyze the expression of relevant genes involved in conjugation transfer carried by bacterial chromosomes and plasmids.The results of qPCR show that Fe2O3@MoS2 inhibits the conjugation transfer of antibiotic-resistant genes by promoting the expression of the global regulatory gene trbA and inhibiting the genes traF and trbB involved in "junction bridge" formation as well as the DNA replication gene trfA.(3)Based on the synthesis of Fe3O4 by chemical precipitation,Fe3O4 was loaded on MoS2 nanosheets by a hydrothermal method.The synthesis of Fe3O4@MoS2 nanocomposites is proved to be successful by characterization means such as TEM,HAADF-STEM,and XPS.In order to determine the optimal experimental conditions for the inhibition of antibiotic-resistant genes conjugation transfer by Fe3O4@MoS2,the effects of different material compositions,system pH,conjugation temperature,conjugation time,material concentration,and bacterial solution concentration on the inhibition of gene conjugation transfer are studied.The toxicological analysis of Fe3O4@MoS2 show that it has low toxicity to bacteria,seeds,fish,and other organisms,and is a green and environmentally friendly nano-material that can effectively inhibit the conjugation and transfer of antibiotic-resistant genes.(4)The results of qPCR analysis of relevant gene expression involving in conjugation and transfer carried by bacterial chromosomes and plasmids show that Fe3O4@MoS2 inhibits the conjugation and transfer of antibiotic-resistant genes by promoting the expression of global regulatory gene trbA,inhibiting the genes traF and trbB involved in "junction bridge"formation,and inhibiting the expression of gene trfA copied from DNA.In addition,compared with Fe2O3@MoS2,Fe3O4@MoS2 also inhibits the expression of outer membrane pore channel protein genes ompA and ompC,affecting the formation of membrane pore channels,thereby further inhibiting the conjugation and transfer of antibiotic-resistant genes. |
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