Carotenoid Nostoxanthin Production by Sphingomonas sp. SG73 Isolated from Deep Sea Sediment

Abstract

Carotenoids are used commercially for dietary supplements, cosmetics, and pharmaceuticals because of their antioxidant activity. In this study, colored microorganisms were isolated from deep sea sediment that had been collected from Suruga Bay, Shizuoka, Japan. One strain was found to be a pure yellow carotenoid producer, and the strain was identified as Sphingomonas sp. (Proteobacteria) by 16S rRNA gene sequence analysis; members of this genus are commonly isolated from air, the human body, and marine environments. The carotenoid was identified as nostoxanthin ((2,3,2',3')-β,β-carotene-2,3,2',3'-tetrol) by mass spectrometry (MS), MS/MS, and ultraviolet-visible absorption spectroscopy (UV-Vis). Nostoxanthin is a poly-hydroxy yellow carotenoid isolated from some photosynthetic bacteria, including some species of Cyanobacteria. The strain Sphingomonas sp. SG73 produced highly pure nostoxanthin of approximately 97% (area%) of the total carotenoid production, and the strain was halophilic and tolerant to 1.5-fold higher salt concentration as compared with seawater. When grown in 1.8% artificial sea salt, nostoxanthin production increased by 2.5-fold as compared with production without artificial sea salt. These results indicate that Sphingomonas sp. SG73 is an efficient producer of nostoxanthin, and the strain is ideal for carotenoid production using marine water because of its compatibility with sea salt.

Keywords: Sphingomonas; carotenoid; deep sea microorganism; nostoxanthin.

Figure 1

The structure of nostoxanthin.

Figure 2

Chromatograph of carotenoids. (A) Carotenoids extracted from strain SG73; (B) authentic standards: astaxanthin, α-carotene, and β-carotene; (C) yellow wet colonies of strain SG73. The colonies were grown on YM agar medium at 22 °C for 3 days. The separation was performed at 35 °C, with methanol/tetrahydrofuran = 8/2 (v/v) as the mobile phase at a flow rate of 1.0 mL/min, and the detection was performed at 470 nm with an SPD-20AV detector.

Figure 3

Phylogenetic tree of strain SG73 and related microorganisms created with the neighbor-joining method. Numbers indicate bootstrap values. ^T indicates type strain of a species.

Figure 4

Spectra of mass spectroscopy (MS) (A), MS/MS (B), and ultraviolet visible absorption spectroscopy (UV-Vis) (C) of the main carotenoid from Sphingomonas sp. SG73. * Main product ions derived from carotenoids.

Figure 4

Spectra of mass spectroscopy (MS) (A), MS/MS (B), and ultraviolet visible absorption spectroscopy (UV-Vis) (C) of the main carotenoid from Sphingomonas sp. SG73. * Main product ions derived from carotenoids.

Figure 5

Presumed pathway of nostoxanthin biosynthesis in Sphingomonas sp. SG73.

Figure 6

Effect of sea salt on growth and nostoxanthin production by Sphingomonas sp. SG73. (A) Cell density (OD₆₆₀) of Sphingomonas sp. SG73 cultured with sea salt; (B) Relative production of nostoxanthin by Sphingomonas sp. SG73. Black bars indicate the relative production level, and gray bars indicate the relative value of production per cell density. All values are means and standard deviations for triplicate experiments. ** p < 0.01.