The dyeing effect of acridine orange for multiple plasmid systems is sensitive to temperature

The Goldview dyeing of the natural multiplasmid system of Lactobacillus plantarum PC518 was affected by temperature. The article want to identify the specific molecules that cause temperature sensitivity, then experiment on the universality of temperature sensitivity, and finally preliminarily analyze the influencing factors. At 5°C and 25°C, single pDNA, multiplasmid system, and linear DNA samples were electrophoretic on agarose gel prestained by Goldview 1, 2, 3, and acridine orange (AO), respectively. Eighteen vectors of Escherichia coli and two vectors shortened by cloning were mixed into multiplasmid systems with different member numbers, and then electrophoresis with AO staining was performed within the range of 5°C-45°C, with a linearized multiplasmid system as the control. The lane profiles (peaks) were captured with Image Lab 5.1 software. After electrophoresis, the nine-plasmid-2 system was dyed with AO solutions of different ionic strengths to detect the effect of ionic strength on temperature sensitivity. It was measured that the UV-visible absorption spectra of the nine-plasmid-2 system dissolved in AO solutions with different ionic strengths and pH. Further, a response surface model was constructed using Design-Expert.V8.0.6 software. The electrophoresis result showed that the multiplasmid system from L. plantarum PC518 stained by AO staining showed a weak band at 5°C and five bands at 25°C, which was similar to the result of staining with Goldview 1, 2, and 3. The synthetic nine-plasmid-1 system and nine-plasmid-2 system displayed different band numbers on the electrophoresis gel in the electrophoresis temperature range of 5°C-45°C, namely 3, 4, 6, 4, and 2 bands, as well as 2, 6, 7, 8, and 5 bands. Using the 1× Tris-acetate-EDTA (TAE)-AO solution, the poststaining results of the nine-plasmid-2 system in the temperature range of 5°C-45°C were 4, 6, 9, 9, and 7 bands, respectively. Further, using 5×, 10×, or 25× TAE buffer, the AO poststaining results at 5°C were 4, 2, and 1 bands, respectively. The ultraviolet spectral results from 5°C to 25°C showed that there was a significant difference (3.5 times) in the fluctuation amplitude at the absorption peak of 261.2 nm between 0× and 1-10× TAE-AO solution containing the nine-plasmid-2 system. Specifically, the fluctuation amplitudes of 0×, 1×, 5×, and 10× samples were 0.032, 0.109, 0.112, and 0.110, respectively. At the same time, using 1× and 10× TAE buffer, the AO-stained linear nine-plasmid-2 system remained stable and did not display temperature sensitivity. The response surface models of the AO-stained nine-plasmid-2 system intuitively displayed that the absorbance of the 1× TAE samples increased significantly with increasing temperature compared to the 0× TAE samples, regardless of the pH value. The findings confirmed a temperature-dependent effect in AO staining of natural or synthetic multiplasmid systems, with the optimum staining result occurring at 25°C. Ion strength was a necessary condition for the temperature sensitivity mechanism. This study layed the groundwork for further investigation into the reasons or underlying mechanisms of temperature sensitivity in AO staining of multiplasmid systems.