Co-selection Mechanism Of Heavy Metals And Antibiotic Resistance In The Treatment Of Chromium-containing Wastewater By Microbial Process

The treatment of chromium-containing wastewater is one of the research focuses of water body remediation.In recent years,microbial methods have attracted much attention due to their simplicity,effectiveness,low cost,and greenness.Studies have shown that heavy metals in polluted environments will up-regulate the expression of heavy metal resistance genes(MRGs)and co-select antibiotic resistance genes(ARGs)in microorganisms,making microorganisms both heavy metal resistance and antibiotic resistance.In the process of microbial treatment of chromium-containing wastewater,bacteria will be actively added and exposed under chromium for Cr(VI)reduction,ARGs could be potentially up-regulated.Antibiotic resistance function can be spread among environmental microorganisms through the horizontal transfer of ARGs,posing a serious threat to the ecological environment.Thus,it is urgent to study the relationship among heavy metals,heavy metal resistance and antibiotic resistance in the process of microbial treatment of chromium-containing wastewater.The problem of "new ARGs pollution" caused by cooperative selection expression provides basic data support.This paper takes the self-screening bacteria Acinetobacter sp.SL-1 as the research object,and mainly completes the following research work:(1)Under different environmental factors,the Cr(Ⅵ)in the process of SL-1 treatment of chromium-containing wastewater was studied.Based on the reduction efficiency and the growth of the strain,the optimal conditions for the process were determined to be anaerobic environment,30 °C,5 g/L waste molasses,100 mg/L Cr(Ⅵ),p H=7,and the reaction was 168 h.The removal rate of Cr(Ⅵ)was 99.10%.Meanwhile,waste molasses synergized with SL-1 can effectively reduce Cr(Ⅵ)in the p H range of 3～10,which has great potential for industrial application.(2)The maximum tolerated concentration of SL-1 to Cr(Ⅵ)was 300 mg/L.After Cr(Ⅵ)stress,SL-1 was resistant to tetracycline(TET),gentamicin(GEN)and clarithromycin.(CLA)and ofloxacin(OFX)changed from intermediate drug susceptibility(I)to drug resistance(R),and showed Cr(Ⅵ)and antibiotics after stress higher than 50 mg/L Cr(Ⅵ)of cross resistance.Metagenome sequencing analysis showed that SL-1 contains an ABC transporter that regulates efflux pumps;3D-EEM,SEM-EDS,and FTIR analysis showed that the surface secretions of the strains increased and contained more organic substances after Cr(Ⅵ)stress.The enrichment of functional groups and Cr revealed that the mechanism of SL-1 producing Cr(Ⅵ)and antibiotic cross-resistance was efflux pump and biofilm mechanism.(3)The relative expression abundance of MRGs and ARGs in SL-1under Cr(Ⅵ)stress was measured,and the correlation analysis and environmental risk assessment of environmental factors,ARGs and MRGs were carried out.Under the condition of 30℃,p H=9,50 mg/L Cr(Ⅵ),waste molasses combined with SL-1 for treat chromiumcontaining wastewater is not only effectively removed Cr(Ⅵ),but also minimized the pollution risk of ARGs in the environment.The results of this study provide theoretical support for reducing the generation of drugresistant microorganisms and the risk of ARGs transmission in the process of microbial remediation of chromium-containing wastewater,and provide an important basis for improving the prevention and control strategy of ARGs pollution in the process of microbial treatment of chromium-containing wastewater.