Antibiotic Resistance Gene Transformation and Ultrastructural Alterations of Lettuce (Lactuca sativa L.) Resulting from Sulfadiazine Accumulation in Culture Solution

Liang Mei,Yan Wang,Min-Yao Zhou,Jia-Hua Chen,Chao Wang,Zhi-Jin Zhang,Ying-Xin Chen,Jin-Tao Feng

doi:10.3390/pr9081451

Abstract

The research herein explored the possible mechanism of toxicity of the antibiotic sulfadiazine (SD) and the related antibiotic resistance gene transformation in lettuce by systematically investigating its growth responses, ultrastructural changes, and antibiotic resistance gene transformation via solution culture experiments. The results showed that SD mainly accumulated in the roots of lettuce at concentrations ranging from 6.48 to 120.87 μg/kg, which were significantly higher than those in leaves (3.90 to 16.74 μg/kg). Lower concentrations of SD (0.5 and 2.0 mg/L) in the culture nutrient solution exerted little effect on lettuce growth, while at SD concentrations higher than 10 mg/L, the growth of lettuce was significantly inhibited, manifesting as shorter root length and lower dry matter yield of whole lettuce plants. Compared with that for the control group, the absolute abundance of bacteria in the root endophyte, rhizosphere, and phyllosphere communities under different concentrations of SD treatment decreased significantly. sul1 and sul2 mainly accumulated in the root endophyte community, at levels significantly higher than those in the leaf endophyte community. Studies of electrolyte leakage and ultrastructural characteristics of root and leaf cells indicated that lettuce grown in culture solutions with high SD concentrations suffered severe damage and disintegration of the cell walls of organs, especially chloroplasts, in leaves. Furthermore, the possible mechanism of SD toxicity in lettuce was confirmed to start with the roots, followed by a free flow of SD into the leaves to destroy the chloroplasts in the leaf cells, which ultimately reduced photosynthesis and decreased plant growth. Studies have shown that antibiotic residues have negative effects on the growth of lettuce and highlight a potential risk of the development and spread of antibiotic resistance in vegetable endophyte systems.

Highlights

Introduction published maps and institutional affilIntensive animal farming is often associated with the use of considerable amounts of drugs, including antibiotics for disease prevention and animal growth [1,2]
Effect of SD Accumulation on Lettuce Growth which indicated that this vegetable can grow under high SD concentrations, even up to 50 mg/L, in culture solutions
The results indicate that an SD concentration of 10 mg/L is the threshold for SD toxicity in Electrolyte Leakage no significant differences compared with the control

Summary

Introduction

Intensive animal farming is often associated with the use of considerable amounts of drugs, including antibiotics for disease prevention and animal growth [1,2]. Attributed to its high efficacy and affordable price, SD has been long and widely used in intensive livestock production. The amounts of antibiotics excreted from animals vary with the type and dosage level of antibiotics, as well as the species and age of the animals [3], the overall majority (25–75%) of the administered drugs are excreted via feces and urine [4]. Due to its high nutrient content, animal manure is often applied as an organic fertilizer to arable lands for crop production, which has resulted in the large-scale introduction of antibiotics into the terrestrial environment.

Methods

Results

Discussion

Conclusion