Carotenoids provide the major antioxidant defence in the globally significant N2-fixing marine cyanobacterium Trichodesmium
Article first published online: 9 APR 2009
© 2009 The Authors. Journal compilation © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd
Volume 11, Issue 7, pages 1897–1908, July 2009
How to Cite
Kelman, D., Ben-Amotz, A. and Berman-Frank, I. (2009), Carotenoids provide the major antioxidant defence in the globally significant N2-fixing marine cyanobacterium Trichodesmium. Environmental Microbiology, 11: 1897–1908. doi: 10.1111/j.1462-2920.2009.01913.x
- Issue published online: 1 JUL 2009
- Article first published online: 9 APR 2009
- Received 15 October, 2008; accepted 22 February, 2009.
Photosynthetic oxygen-evolving microorganisms contend with continuous self-production of molecular oxygen and reactive oxygen species. The deleterious effects of reactive oxygen species are exacerbated for cyanobacterial nitrogen-fixers (diazotrophs) due to the innate sensitivity of nitrogenase to oxygen. This renders incompatible the processes of oxygen-evolving photosynthesis and N-fixation. We examined total antioxidative potential of various diazotrophic and non-diazotrophic cyanobacteria. We focused on Trichodesmium spp., a bloom-forming marine diazotroph that contributes significantly to global nitrogen fixation. Among the species tested, Trichodesmium possessed the highest antioxidant activity. Moreover, while proteins constituted the dominant antioxidative component of all other cyanobacteria tested, Trichodesmium was unique in that small-molecule natural products provided the majority of antioxidant activity, while proteins constituted only 13% of total antioxidant activity. Bioassay-guided fractionation followed by high-performance liquid chromatography profiling of antioxidant purified fractions identified the highly potent antioxidant all-trans-β-carotene, and small amounts of 9-cis-β-carotene and retinyl palmitate. Search of the Trichodesmium genome identified protein sequences homologous to key enzymes in the β-carotene to retinyl palmitate biosynthetic pathway, including 33–37% identity to lecithin retinol acyltransferase. The present study demonstrates the importance of carotenoids in Trichodesmium's arsenal of defensive compounds against oxidative damage and protection of nitrogenase from oxygen and its radicals.