Spectroscopic analysis of tylosin adsorption on extracellular DNA reveals its interaction mechanism

Extracellular DNA (eDNA), which is commonly detected in aquatic and terrestrial environments, may be involved in gene transfer, increases in genetic diversity, and evolution. However, it has been reported that some small organic molecules or heavy metal ions can influence the transformation of DNA and even destroy its structure. We previously found that tylosin (TYL, a kind of antibiotic) is adsorbed onto salmon sperm DNA in a mixed solution. However, it is not clear whether this antibiotic affects the structure of DNA, and the mechanism of their interaction needs to be clarified. Therefore, we investigated the adsorption of TYL on different concentrations of salmon sperm DNA using agarose gel electrophoresis, ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, and surface enhanced Raman spectroscopy (SERS) to elucidate the interaction mechanism between TYL and DNA. The results showed that the adsorption of TYL decreased with increased concentrations of DNA. The electrophoresis band of pristine DNA was at 5000 bps. The brightness of the DNA band decreased with the TYL concentration and their incubation time. As the concentration of TYL increased, the fluorescence absorption intensity of DNA decreased significantly. Redshift and hyperchromicity were observed in the UV-vis adsorption spectrum with the presence of TYL in DNA solution, and they weakened as the DNA concentration increased. The Raman spectrum intensities of characteristic peaks in the mixed solution were weaker than that of pure TYL solution, and the peak intensity increased with increasing DNA concentration. Even a part of TYL characteristic peaks disappeared in the mixed solution. These results indicated that the pyran and macrolide of TYL might intercalate into the base pair plane of DNA. In addition, electrostatic attraction between TYL and DNA and interactions among TYL molecules may also play a role in the interaction mechanism. However, the double helix structure of DNA was not subject to the interaction of TYL.