**4. Opportunities and Challenges**

The vast and mysterious ocean breeds diverse marine lives and provides unexhausted foodstuffs, nutriment, and drugs for humans. Diverse carotenoids are found from marine species and show broad utilities as colorant fragrance cosmetics and pharmaceuticals. The synthetic pathway of several carotenoids has been illuminated from marine species, which could benefit engineering processes in several host organisms for the production of carotenoids such as Ά-carotene, astaxanthin, and lutein. On the other hand, carotenoids such as Ά-carotene often undergo a series of modifications in the miraculous marine ecosphere. And indeed, several novel carotenoids have been isolated during the exploration of the marine ecosphere, while their pharmaceutical potentials remain to be examined due to the limited amount of extracts. Metabolic engineering and synthetic biology allow the assembly of such a chimeric pathway in a tractable organism for the mass production of rare carotenoids and also exhibit the potential to extend the catalogs of carotenoids to non-natural carotenoids, which could accelerate the exploration of novel carotenoids. It is noted that decoded carotenoid pathways and enzymes are still limited to a few marine organisms, although the J. Craig Venter Institute with worldwide collaboration had sequenced and annotated the genomes of 177 marine microbes up until 2010. However, we believe that the developed and developing technologies will allow us to search for novel marine carotenoid pathways in the future. 

## **Acknowledgments**

This work was supported by a grant (NRF-2013R1A1A2008289) from the National Research Foundation, the Intelligent Synthetic Biology Center of Global Frontier Project funded by the MSIP (2011-0031964), and a grant from the Next-Generation BioGreen 21 Program (SSAC, grant#: PJ00952003), Rural Development Administration (RDA), Korea. J.K. is supported by scholarships from the BK21 Plus Program, Ministry of Education, Science & Technology (MEST), Korea. 
