Culture optimization to enhance carotenoid production of a selected purple nonsulfur bacterium and its activity against acute hepatopancreatic necrosis disease‐causing Vibrio parahaemolyticus.

Purple nonsulfur bacteria (PNSB) were investigated for their carotenoid production and anti‐vibrio activity against acute hepatopancreatic necrosis disease (AHPND)‐causing Vibrio parahaemolyticus. To test carotenoid production, selected strains were cultivated in basic isolation medium (BIM), glutamate acetate medium, G5 medium and artificial acetic acid wastewater (AAW) medium. From 144 PNSB, Rhodopseudomonas palustris KTSSG46 was selected to produce carotenoids under microaerobic light conditions in BIM. When the culture medium was optimized, strain KTSSG46 grown in BIM modified with l‐glutamate at 1 g/L more effectively inhibited AHPND‐causing V. parahaemolyticus strains than standard BIM with 1 g/L (NH4)2SO4. BIM was further modified with 1.23 g/L MgSO4·7H2O and carotenoid production increased 40.22%. Carotenoid production at day 2 by strain KTSSG46 grown in BIM modified with l‐glutamate at 1 and 1.23 g/L MgSO4·7H2O was the same as production in BIM modified with monosodium glutamate (MSG). Culture supernatants from all BIM formulations showed similar activity against the resistant AHPND strain SR2. Based on high‐performance liquid chromatography, carotenoids of strain KTSSG46 might be canthaxanthin. Grown in BIM modified with MSG, strain KTSSG46 could produce inexpensive carotenoids and release anti‐vibrio compounds that, applied as shrimp feed additive, would prevent AHPND strains. [ABSTRACT FROM AUTHOR]