Research On The Regularity Of Emergence And Transfer Of Enrofloxacin-induced Resistance Genes In Crayfish Culture System

A global health issue has been sparked by the emergence and transfer of antibiotic resistance genes(ARGs).The over-used antibiotic in aquaculture provides a wider environmental exposure pathway for ARGs.However,the origin,chronical changes,and mobility of ARGs under antibiotic exposure in aquaculture systems are largely unclear.In this study,we used crayfish model to analyze the composition and temporal changes of microbial community,changes of various ARGs and MGEs after enrofloxacin exposure,the mechanisms underlying ARG mobility between bacteria in crayfish gut and sediment.Specific results were revealed as follows:1.Proteobacteria,Bacteroidetes,Tenericutes,Firmicutes,and Rsa HF231 constituted the predominant phyla in the crayfish gut.During the crayfish development,the diversity of gut microbiota showed decreased.In the larva and preadult stages,the most dominant bacterial community transformation in the gut.In the adult and berried stage,the gut microbial structure basically tends to be stable.2.The diversity of the microbial community in both guts and sediments were reduced exposed to antibiotic.The composition of the microorganism was with a intensity and longer-term effect in gut than sediment samples.The family of Enterococcaceae showed the highest sensitivity to enrofloxacin application.While the relative abundance of Enterobacteriaceae family and Citrobacter genus exhibited the little change trend in the guts.3.Enrofloxacin application not only increased the relative abundance of quinolone resistance gene but also promoted emergence of other antibiotics resistance genes,mainly including multidrug and beta-lactam resistance genes.The common resistance genes of gut and sediment accounted for 26.9% and 45.1% of the total resistance genes,respectively.These genes had greater mobility.At the same time,the influence of ARGs in abundance and species in gut was more intense than that in sediment,and the recovery time was more delayed.4.The relative abundance of MGEs was increasement exposed to enrofloxacin in gut and sediments and these MGEs had significant positive correlation with most of the core ARGs.MGEs highly frequently occurred neighboring ARGs.The prime driver of horizontal gene transfer of ARGs was the recombination mediated by transposase in the press of enrofloxacin.Additionally,it revealed that sul2,tet A and tet R showed intracellular and intercellular horizontal transfer in the samples.5.Enterobacteriaceae may constitutes a mobile ARG pool in nature,collecting ARGs with different origins.Citrobacter genes was significantly correlated with multiple ARGs.The relatively abundance of MAGs of Citrobacter braakii which carried 5 core ARGs accounted for 16%.The pollution of these bacteria should be concerned.6.Metagenomic assembly genome(MAGs)carrying multiple ARGs were all identified belong to Enterobacteriaceae family,and they are all zoonotic drug-resistant pathogens.Some of them exhibited low average nucleotide identity with other type of strains belonging to the same genus.Hence,these ARGs were present in the unknown bacteria.In summary,this study revealed the changes of microbe,the selective increment and mobility of ARGs exposed to antibiotic,reconstructed some novel multiple ARGs carrying bacterial genomes.It emphasizes the threats of ARG dissemination in aquaculture environment induced by antibiotic application,provides reference for optimizing antibiotic prescription,minimize antibiotic consumption and resistance spread.