Inhibition of pathogenic Vibrio harveyi using calamenene, derived from the Indian gorgonian Subergorgia reticulata, and its synthetic analog.

We report the synthesis and antimicrobial properties of a partially reduced dihydronathphthoquinone analogue of 2-methoxy, 5-acetoxy calamenene, extracted from Subergorgia reticulata. The growth of a pathogenic Vibrio harveyi strain was effectively controlled by the calamenene derivative 1 (Cala1) and its synthetic analog 2 (Cala2). Complete mortality of V. harveyi was observed with 2.5 and 0.5 µg mL-1 concentrations of Cala1 and Cala2, respectively. The metabolic assays demonstrated that Cala1 is a bacteriostatic agent while Cala2 showed bactericidal properties. It was confirmed that translocation of Cala2 into the cytoplasm does not induce any change to the integrity of the bacterial cell wall. The Cala2 induced damage to the genetic material of 70% of cells while genetic material of 91% of cells treated with Cala1 remained intact. The Cala2 is, therefore, proposed as a potential bactericidal compound against the aquaculture pathogen V. harveyi. The fact that the Cala2 exhibited minimal cytotoxicity to Artemia nauplii indicates its potential use as an antimicrobial agent for aquaculture operations. © King Abdulaziz City for Science and Technology 2020.