Enhancement of carotenoid production in the new carotenoid-producing photosynthetic bacterium Rhodopseudomonas faecalis PA2

Use of photosynthetic bacteria to produce carotenoids has increased considerably in recent decades; however, few studies have been conducted to identify additional carotenoid producers. In this study, Rhodopseudomonas faecalis PA2 was shown to be capable of carotenoid production, and factors influencing this production were identified. The maximum carotenoid content was observed at an initial pH of 7 in the presence of 0.8% malic acid, 0.4% yeast extract, and 0.05% Fe3+ under light at 4,000 lux. Fe3+ significantly enhanced carotenogenesis, resulting in a production rate of 2.5 mg/g/day and a reduction in time to maximum production from 12 to 8 days. The carotenoid content and carotenoid yield under modified conditions were 413 mg/L and 13 mg/g (mg total carotenoids per gram of dry cells), respectively, representing an increase of 117% relative to the original condition. The biomass and carotenoid productivity reached 4 g/L/day and 51.6 mg/L/day, respectively. To the best of our knowledge, this is the first study of carotenoid production by Rps. faecalis PA2. The results indicated that the productivity of this organism under the aforementioned conditions was comparable to that of previously described purple photosynthetic bacterial species.