Screening Method and Antibacterial Activity of 1,3,4-Oxadiazole Sulfone Compounds against Citrus Huanglongbing

Abstract

Citrus Huanglongbing (HLB) is one of the most destructive diseases in the citrus industry. At present, Candidatus Liberibacter asiaticus (CLas) cannot be cultured in vitro, and there is a lack of rapid methods to test antibacterial activity, which greatly hinders the discovery of new antibacterial agents against HLB. To establish a rapid screening method for antibacterial agents against HLB with simple operation, a short cycle, and a large number of tests, the CLas contents in leaves from different citrus branches, different leaves from the same citrus branch, and two halves of the same citrus leaf were detected. Compared with the leaves on different branches and different leaves on the same branch, the difference in CLas content of the left and right halves of the same leaf was small; the difference was basically between 0.7 and 1.3. A rapid and efficient method for primary screening agents against HLB termed the "half-leaf method" was established through our long-term optimization and improvement. To verify the stability and reliability of the activity data measured using this method, 6-chloropurine riboside, which is highly soluble in water, was used as the test agent, and its antibacterial activity against HLB was tested 45 times. The results of the antibacterial activity test showed little difference in the mean values of each data group, indicating that this method could be used as a rapid method for screening agents against HLB. We used this method to test the antibacterial activity of compounds synthesized by our research group against HLB and found that some of the compounds showed good activity.

Keywords: Citrus Huanglongbing; antibacterial activity; antibacterial agent; rapid screening method.

Figure 1

The PCR products of citrus leaves were electrophoretically amplified with OI1/OI2C primers. M, 2000 maker; 1–5, samples at different locations.

Figure 2

Comparison of CLas content in leaves. The red line indicates the same CLas content, and the green and blue horizontal lines indicate a deviation of 0.7–1.3 times. The purple dots represent the CLas content of each leaf. (A) CLas content in leaves from different branches; (B) CLas content in different leaves from the same branch (9 branches were taken, and the black dots represent the reference leaves of each branch); (C) CLas content in two halves of the same leaf.

Figure 3

Half-leaf method for rapid screening of anti-HLB agents.

Figure 4

Chemical structures of sulfonamide compounds containing 1,3,4-oxadiazole sulfone moiety.

Figure 5

Chemical structures of amide compounds containing 1,3,4-oxadiazole sulfone moiety.