Isolation And Identification Of Bacteria From S.slasa And S.alterniflora Roots And Study On Their Resistance Risk

The plant microbiome plays an important role in mediating bacteria exchanges between the human gut microbiome and environmental microbiomes,and also serves as one of the main sources of infective pathogens,particular the antibiotic-resistant infective pathogens that can infect humans.The bacteria carrying antibiotic-resistance genes can enrich towards the rhizosphere and rhizoplane from the soil microbiome under the plant-derived attractive effects,these antibiotic-resistant bacteria can then enter the inside parts of plants,and be transmitted to humans via animals and other ways,which potentially threaten the public health.On the other hand,the root-associated niches,including the rhizosphere and rhizoplane,harbor abundant plant-derived easy-to-use nutrients for the microbes to directly utilize.In this nutrient-rich environment,while some microbes compete with others by producing antibiotics,certain microbes can antagonize against the antibiotic-producing microbes by recruiting the antibiotic-resistance genes,which results in the production and evolution of antibioticresistant bacteria.However,little is yet known on the prevalence of antibiotic-resistant bacteria in the root-associated niches.Furthermore,the rhizosphere and rhizoplane represent 2 distinct niches with different amount of nutrients and selective pressures,whether these differences affect the prevalence of antibiotic-resistant bacteria in the two niches also remains largely unknown.In the present study,a total of 181 bacterial strains were isolated from 12 rhizosphere and rhizoplane soil samples of S.slasa and S.alterniflora from inner side of a aquafarm dam located in Yancheng,Jiangsu.The taxonomic affiliation of these isolated strains was further determined by 16S rDNA sequencing analysis.Compared with the strains isolated from the rhizosphere,the proportion of strains belonging to Proteobacteria was significantly higher,and the proportion of strains belonging to Firmicutes in the rhizoplane bacterial populations was lower for both plant species.We further determined the susceptibility and resistance of the obtained strains to the 13 antibiotics of 8 classes that are commonly used in clinic.The results showed that 81 out of 117 strains(69.30%)isolated from the S.salsa root-associated samples were antibiotic-resistant strains,and 34 strains were multidrug-resistant,accounting for 29.06%of the total strains.Among the 64 strains isolated from the root-associated samples of S.alterniflora,44 strains were antibiotic resistant,accounting for 68.75%of the total strains,and 17 strains were multidrug resistant,accounting for 26.56%of the total strains.Among the antibiotic-resistant strains,β-lactam antibiotics-resistant strains ranked as the top prevalent class.Several known opportunistic pathogens,such as Stenotrophomonas,Pantoea,Chryseobacterium,and Microbacterium,were identified in the isolated strains and they were antibiotic resistant,with several strains being multi-drug resistant.These antibiotic-resistant strains,particular the pathogenic ones,could threaten the public health as well as the efficiency of clinical antibiotic treatments.We further determined the abundance of the isolated antibiotic-resistant strains and important pathogens in the rhizosphere and rhizoplane bacteriomes of S.slasa and S.alterniflora via full-length 16S rDNA high throughput sequencing analysis using Pacbio sequencing platform.The results showed that the proportion of the isolated strains in the rootassociated bacteriomes ranged from 1,42-14.47%(on average 3.9%),and 102 antibioticresistant strains(accounting for 81.6%of the total identified antibiotic-resistant strains)exhibited relatively high abundance with relative abundance ranging from 0.01%to 2.96%for each of these strains.Furthermore,several known important pathogens were also identified in the S.slasa and S.alterniflora root-associated bacteriomes.These antibiotic-resistant strains and pathogens can threaten the fish farming and human health seriously.Overall,our results demonstrated that the root-associated bacteriomes of S.slasa and S.alterniflora,the two representative plant species grown in the inner side of a aquafarm dam contained high abundant antibiotic-resistant and pathogenic bacterial species,which could spread to humans.Furthermore,the selective pressure and nutrient content differences between the rhizosphere and rhizoplane exhibited strong influences on the prevalence of antibiotic-resistant and pathogenic bacteria in the bacteriomes.This study provides novel insights into controlling of the detriments of plant-mediated transmission of antibioticresistant and pathogenic bacteria.