Enhancing pigment production by a chromogenic bacterium (Exiguobacterium aurantiacum) using tomato waste extract: A Statistical approach

Abstract

There is high demand for microbial pigments as promising alternative for synthetic pigments basically for safety and economic reasons. This study aimed at the optimization of yellowish-orange pigment production by Exiguobacterium aurantiacum using agro-waste extract as growth substrate. Air samples were collected using depositional method. Pure cultures of pigment producing bacteria were isolated by subsequent culturing on fresh nutrient agar medium and the potent isolate was identified using MALDI-TOF technique. Culture conditions were screened using Plackett-Burman design and the most three significant variables were optimized by response surface methodology. Fermentation was conducted in 150 mL agro-waste decoctions from which tomato waste extract was selected because of higher optical density of the culture compared to other agro-waste extracts. Pigment was extracted by solvent extraction method and the best solvent was selected based on its ability to dissolve the culture suspension. The pigment was characterized using spectroscopic and chromatographic techniques. Culture agitation rate, initial medium pH and concentration of yeast extract were identified as the most significant (p< 0.0001) variables affecting pigment production. At optimized conditions, 0.96 g/L of pigment was extracted from 4.73 g/L of culture biomass and the extracted pigment under optimized conditions was 1.6 times higher than the pigment extracted under un-optimized conditions. The spectroscopic and chromatographic analyses demonstrated the presence of different functional groups and carotenoids were identified as parts of the molecule responsible for the yellowish-orange pigmentation of the extract. This study demonstrated the potential for optimization of pigment production by bacteria using agro-waste extract as substrate. Hence, the current findings strongly encourage for further study at a large-scale level for industrial production.