Optimization of culture conditions for production of antivibrio compounds from probiotic purple nonsulfur bacteria against acute hepatopancreatic necrosis disease-causing Vibrio parahaemolyticus and Vibrio spp.

Shrimp cultivation has been faced with pathogenic bacterial infections, such as luminous vibriosis and acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio harveyi and Vibrio parahaemolyticus, respectively. Biodegradable compounds that act to prevent both serious shrimp diseases are to be explored for producing safe shrimp. The probiotic purple nonsulfur bacteria (PNSB) are safe for use in producing antivibrio compounds against shrimp pathogenic vibrios. The probiotic PNSB, Rhodobacter sphaeroides (SS15, TKW17) and Afifella marina STW181, released antivibrio compounds inhibiting various shrimp pathogenic Vibrio spp. in the optimum conditions that were similar to the conditions of shrimp cultivation. The antivibrio compounds by these PNSB were stable over the wide pH range from 3 to 10, and at elevated temperatures up to 121 °C for 20 min; they were also quite sensitive to lipase, pronase and α-chymotrypsin. All the antivibrio compounds had bactericidal activity as evidenced by damaged cells with many holes, and they also showed bacteriolytic activity with the highest found for the strain STW181. One of the purified antivibrio compounds produced by the strain SS15, a low molecular weight (<3000 Da) cationic compound containing NH ₂ group(s), was the most effective in inhibiting AHPND-causing V. parahaemolyticus SR2. Regarding toxicity to brine shrimp, the extract from water layer in ethyl acetate extraction of strain SS15 (extract-SS15) containing antivibrio peptides had LC50 at 6.79 ± 0.63 mg mL ⁻¹ . In challenge tests the extract-SS15 at 2.68 mg mL ⁻¹ adversely affected water quality; however, it could significantly decrease the mortality of white shrimp infected with the virulent AHPND strain SR2. All the tested probiotic PNSB produced antivibrio compounds that are biodegradable with great potential to control serious shrimp pathogenic vibrios for sustainable shrimp cultivation.