Antioxidant properties of carotenoid pigments from Rhodovulum viride strain JA814

Pigment producing bacteria commonly occur in nature and have intense colour. Bacterial secondary metabolites-pigments are secreted during unfavorable conditions. The exponential growth of bacterial pigments augmented several times as they are more beneficial over synthetic pigments. Biologically originated carotenoid pigments are significant for their wide distribution, structural diversity, varied functions and their actions. It is very crucial to try because bacterial pigments contain certain restorative characteristics including cytotoxicity, antibacterial activity, anticancer activity and exceptional antioxidant activity. Hence, it is important to study a pigment producing photoheterotrophic purple non- sulfur bacterial species. The present study reports on the general characteristics of a photosynthetic bacterium, Rhodovulum viride strain JA814, extraction of carotenoid pigments and evaluation for antioxidant properties. Strain JA814 was identified through 16S rRNA gene sequencing analysis showing high sequence similarity value (100%) with closely related species, Rhodovulum viride JA756. Since all other species of the genus Rhodovulum are brown to red in colour, except R. viride JA756 and the strain JA814 is green in pigmentation. UV-visible spectrophotometric analysis indicated the presence of carotenoids. Carotenoid composition is determined through HPLC and revealed the presence of neurosporene contributing as a major carotenoid (19.44%) and minor components of dihydroxy neurosporene (13%), 1,2 dihydroneurosporene (14.02), hydroxyl dimethyl spheroidenone (9.4%) and dimethylspheroidene (10.45%). The crude extract of carotenoids having potential/radical scavenging activity was evaluated by in vitro assay methods such as total antioxidant capacity and DPPH assay. The crude pigment extracts in methanolic solutions showed maximum antioxidant activity at moderate/minimum concentrations. The sample extracts significantly inhibited the DPPH free radical by a proportion of 92 per cent at 800 mu g/ml. The standard reference L-ascorbic acid showed inhibition of DPPH radical 85%. In the phosphomolybdenum assay of total antioxidant capacity, the efficiency of antioxidant potential is 0.25 mg/g ascorbic acid equivalents at a concentration of 100 mu g/ml. The standard reference value of L-ascorbic acid is 1.07 mg/g equivalents. These findings suggest that the carotenoid pigments proved as promising bioactive compounds and can be exploited in therapeutics.