Effect of hydrogen index and sodium chloride concentration on bacterioruberin biosynthesis

<jats:p>This study investigated the effect of sodium chloride (NaCl) concentration and medium pH on the ability of Arthrobacter agilis wb28 to synthesize bacterioruberin. This compound is a carotenoid in nature and plays a functional role in protecting the cell against environmental stress, including oxidative and osmotic stress; therefore, it has attracted considerable attention as a potent antioxidant, antimicrobial agent, and radioprotective compound, with broad applications in the cosmetic, pharmaceutical, and food industries. To date, several potential producers of bacterioruberin have been identified; however, all of them are haloarchaea characterized by prolonged cultivation periods. The aim of this work was to increase the yield of the target compound by varying the nutrient medium parameters for the producer A. agilis wb28, one of the few prokaryotes capable of bacterioruberin biosynthesis. Luria–Bertani (LB) medium was used as the basal medium and subjected to modification. To determine bacterioruberin concentration, the pigment was preliminarily extracted with methanol from harvested bacterial biomass, and the resulting extract was analyzed spectrophotometrically by measuring optical density at 495 nm. Microbial growth was assessed during cultivation in a shaker-incubator and in a 1 L bioreactor at +28 °C for 24 h. The parameter limits were established as follows: at 10% NaCl and pH values above 9.1, visible growth was absent and biosynthesis was inhibited. The optimal pH for bacterioruberin biosynthesis was determined to be 8.5, at which maximum pigment accumulation was observed while maintaining a high culture growth rate, whereas the most favorable NaCl concentration was 0%, providing the highest yield of the target product. No culture growth was observed at pH values below 5.0, which is likely attributable to the physiological characteristics of the strain and its adaptation to predominantly neutral and alkaline environmental conditions.</jats:p>