| The antibiotic resistance genes(ARGs), a new type of environmental pollutants, mainly present in microorganisms or exposed outside. The ARGs are not only persistent remain in the environment, but also transport in different environmental media via the horizontal gene transfer(HGT), potentially endangers the ecosystem health. Based on the growing cross-contamination of heavy metals and antibiotics in soil, the response characteristics of antibiotic resistant bacteria, resistance genes and mobile genetic elements(MGEs) to heavy metal zinc were explored.We sprayed different concentrations of ZnSO4 to the soil samples, which collected in the Zhenjiang mulberry germplasm nursery. The results of high-throughput sequencing technology showed that soil microbial diversity and abundance would be reduced via adding high concentrations of zinc to soil for a long time, but to a certain extent, the growth and reproduction of predominant resistant bacteria could be promoted. The results indicated that no significant difference in the level of phylum, and Proteobacteria was the largest phylum in all samples. Otherwise the large species difference existed in different samples in the genus level, and Flavisolibacter, Gemmatimonas, Gp4 and Gp6 were the common predominant genus. The results of cluster analysis revealed that there was a high similarity of microbial community structure between the samples with similar concentration of zinc, but there were exceptions, for example the similarity between samples 2(100) and 2(1000) for 2 months treatment was more than 0.6. Comprehensive analysis shows that the effect of concentration of zinc on microbial community structure is greater than treatment time of heavy metal zinc.Seven different antibiotic-resistant bacteria were isolated from the soil samples by antibiotic selective screening medium, designated strains C1, STZ2, S3, N2, G1, G2 and G5. The morphology observation and 16 S rDNA identification revealed that the strains C1 and G2 belongs to Pseudomonas sp. Strain N2 and G1 belongs to Bacillus sp. Strain S3, STZ2, and G5 belongs to Brevundimonas sp. Castellaniella sp. and Arthrobactor sp. respectively. The results of antibiotic susceptibility test showed that all the seven strains had multiple antibiotic resistance and cross-resistance between antibiotics and heavy metal zinc. The cross-effects between antibiotics and heavy metals related to concentration of zinc, antibiotics and bacterial species. When gentamicin and neomycin coexisted with 50~150 mg/kg heavy metal zinc, the bacterial growth curves of STZ2 and C1 was mainly for the lag phase of strains extended, logarithmic phase delayed, and growth decreased in stationary phase.The abundances of ARGs, transposase genes and the class 1 integron integrase gene intI1, were quantified using real-time PCR. The results revealed the heavy metal zinc in a high levels of 800 and 1000mg/kg resulted in up-regulation of aminoglycoside resistance gene aacA/aphD, aac(6')-Iy, aac(6')-II and spcN, transposase gene tnpA, and integrase gene intI1 being enriched 1851-fold(maximum) compared with control. Furthermore, the high concentrations of heavy metals zinc play a primary role in up-regulation of aminoglycoside resistance gene, transposons and integrons. Maybe the heavy metals zinc driven co-selection of horizontal transfer of ARGs in soil. We expect to provide an important theoretical basis for suppressing the horizontal dissemination of aminoglycoside resistance genes. |
PDF Full Text Request