Effects Of Sulfamethoxazole On Microbial Community Characteristics And Resistance Genes In Arsenic-contaminated Soil

Arsenic(As)is a common heavy metal pollutant in soil.With the continuous expansion of livestock and poultry farming,As-contaminated soil is facing antibiotic stress.Antibiotics affect soil health by altering soil microbial communities,amplifying antibiotic resistance genes(ARGs),and threatening human health through the food chain.Sulfamethoxazole(SMX)is difficult to be degraded in soil,and the residual amount is high.Howerver,the effect of SMX on the microecological effects of Ascontaminated soil is still unclear.In this study,soil cultivation experiments were conducted to explore the effect and mechanism of different contents of SMX treatment on extracellular enzyme activity,microbial community diversity,and abundance and diversity of resistance genes in As-contaminated soil,to accurately evaluate antibiotic stress in the context of heavy metal pollution.It provides a theoretical basis for soil ecotoxicity,which is of great significance for the realization of multiple goals such as soil health,food security,and the protection of human health.The result is as follows:(1)The activities of leucine aminopeptidase and N-acetyl-β-D-glucosidase(LAP+NAG)in As-contaminated soil decreased significantly by 10.8%,20.8% and26.9%,respectively,after the applications of low,medium and high contents of SMX;β-glucosidase(BG)activity was significantly increased by 49.6%,25.5% and 44.2%,respectively.However,the activity of acid phosphatase(ACP)was only significantly decreased by 11.6% and 15.1% in low and medium contents of SMX,respectively.Through the enzyme vector model,it was found that the vector length increased by25.0%,16.6% and 21.6%,and the vector angle decreased by 4.37%,6.79% and 11.4%,respectively,under the low,medium and high content of SMX,which indicated that SMX increased the As-contaminated soil microbial carbon(C)limits,but reduced microbial phosphorus(P)limitation.In addition,the microbial C,N,and P-acquiring enzyme activities were affected by soil As fraction and pH under low and medium content of SMX,and the microbial C,N,and P-acquiring enzyme activities were affected by soil available N and P under high-content SMX treatment.(2)Different contents of SMX treatment significantly changed the β-diversity of bacterial,fungal and archaeal communities in As-contaminated soil.At the phylum level,only the bacterial community composition changed significantly.Under the low,medium and high content of SMX,the relative abundance of Actinobacteria significantly decreased by 7.14%,13.2% and 23.9%,respectively;the relative abundance of Gemmatimonadetes increased by 0.82 times,1.17 times and 1.67 times respectively.To resist SMX interference,bacterial communities occupy more ecological niches by increasing the complexity of the network structure in Ascontaminated soils,resulting in simpler community structures of fung and archaea and increased competition for limited ecological resources.In addition,there was significant agreement between changes in bacterial and fungal communities and soil factors.Under the applications of SMX,the bacterial community was mainly related to the availability of nutrients(N,P)in the As-contaminated soil,and the fungal community was mainly related to the C utilization and As fraction transformation in the As-contaminated soil.SMX pollution affects soil nutrient utilization by altering microbial community structure and composition.(3)There were significant differences in the assembly of ARGs,heavy metal resistance genes(HMRGs)and mobile genetic elements(MGEs)in As-contaminated soil under different contents of SMX.Compared with CK treatment,low content SMX treatment did not significantly affect the abundance of resistance genes in Ascontaminated soil.Under the applications of medium and high content SMX,the absolute abundance of total ARGs in As-contaminated soil strengthened by 2.15 times and 5.64 times,respectively;the absolute abundance of total HMRGs increased by 1.43 times and 5.86 times respectively;and the absolute abundance of total MGEs enhanced by 3.06 times and 9.83 times,respectively.In addition,total ARGs was significantly positively correlated with total MGEs,and ARGs(fluoroquinolones,MLSB)were significantly positively correlated with HMRGs(czc A,cop A)in As-contaminated soil microbiome.The diffusion of ARGs promoted by MGEs and the cross-resistance mechanism of SMX and As under SMX treatments.In addition,ARGs,HMRGs and MGEs were associated with the microbial community as bacteria>fungal>archaea,and were significantly negatively correlated with Actinobacteria(copiotrophic bacteria),obligately adsorbed As,available N,readily available P and soluble P,and significantly positively correlated correlation with Gemmatimonadetes(oligotrophic bacteria).This indicated that the addition of SMX reduced soil available nutrients,and oligotrophic bacteria became important host microorganisms for ARGs,HMRGs and MGEs.