Antibacterial Activity and Possibly Made of Action of Isoquinoline-3-Carboxylic Acid

Due to the urgent need to develop innovative, environmentally sustainable bactericides, we use the natural product isoquinoline as a lead compound to discover highly active bactericides from isoquinoline derivatives. In this paper, the antibacterial activity of 49 isoquinoline derivatives was evaluated against three plant bacteria in vitro. Among all the derivatives, isoquinoline-3-carboxylic acid (IQ3CA) demonstrated significant antibacterial activity against Ralstonia solanacearum ( Rs), Acidovorax citrulli ( Ac), X. oryzae pv. oryzicola ( Xoc), X. campestris pv. campestris ( Xcc), P. carotovorum subsp. carotovorum ( Pcc), and X. fragariae ( Xf), with EC50 values ranging from 8.38 to 17.35 μg/mL. Furthermore, IQ3CA exhibited a potent protective effect against Ac, with an efficacy of 68.56% at 200 μg/mL, which was not significantly different from that of the positive control kasugamycin (72.48%) and was superior to that of the positive control thiosen copper (64.62%). The scanning electron microscopy observations revealed that treatment of Ac cells with IQ3CA at a concentration of 25 μg/mL resulted in a curved and sunken cell morphology, along with destroyed cell membrane integrity. Additionally, the motility and exopolysaccharides production of Ac were inhibited, and biofilm formation was prevented. These results suggest that IQ3CA holds promise as a lead compound with antibacterial properties against plant diseases.