Marine Microbial-Derived Resource Exploration: Uncovering the Hidden Potential of Marine Carotenoids  
[PERSON]  
1 Institut Teknologi Bandung, School of Life Sciences and Technology, Bandung 40132, Indonesia; [PERSON]@students.itb.ac.icd (R.S.); [PERSON]@students.itb.ac.icd (Z.H.); [EMAIL_ADDRESS] (Y.N.)  
[PERSON]  
1 Institut Teknologi Bandung, School of Life Sciences and Technology, Bandung 40132, Indonesia; [PERSON]@students.itb.ac.icd (R.S.); [EMAIL_ADDRESS] (Z.H.); [EMAIL_ADDRESS] (Y.N.)  
[PERSON]  
1 Institut Teknologi Bandung, School of Life Sciences and Technology, Bandung 40132, Indonesia; [PERSON]@students.itb.ac.icd (R.S.); [PERSON]@students.itb.ac.icd (Z.H.); [EMAIL_ADDRESS] (Y.N.)  
[PERSON]  
1 Institut Teknologi Bandung, School of Life Sciences and Technology, Bandung 40132, Indonesia; [PERSON]@students.itb.ac.icd (R.S.); zzalfahumaira@students.itb.ac.icd (Z.H.); [EMAIL_ADDRESS] (Y.N.)  
[PERSON]  
2 Department of Life Sciences, Imperial College London, South Kensington Campus, London SW72 AZ, UK; [PERSON]@l6 imperial.ac.uk  
[PERSON]  
3 CNSSCREATE Ltd, 1 Create Way, 608-01 Create Tower, Singapore 138602, Singapore; arid:[EMAIL_ADDRESS].  
of macro- and microorganisms. The mucus layer of corals is rich in polysaccharides and is used as a growth medium by a variety of bacterial communities, including those that produce bioactive compounds [6; 7]. Meanwhile, the deep sea is located in the aphotic zone with a depth of >200 m, which has extreme and unique ecological properties. The lack of sunlight, low temperature, high hydrostatic pressure, and oligotrophic environment all contribute to the deep sea being a habitat for adaptive microorganisms with distinctive metabolic characteristics from those found in the photic zone [8]. The abundance of literature discussing secondary metabolite exploration from coastal areas to the deep sea demonstrates tremendous and significant potential for the discovery of this resource (reviewed in ref. [9]).  
Secondary metabolites are low-molecular-weight compounds that are not directly involved in an organism's primary metabolic processes. They are, however, necessary for the long-term survival of these species [10]. At the end of 2016, approximately 28,500 secondary metabolites were discovered in marine organisms, including marine microorganisms (bacteria and fungi), porifera, cnidaria, marine algae, and marine phytoplankton (such as dinoflagellates and cyanobacteria) [11; 12]. Numerous publications reported the discovery of new secondary metabolites, including 1490 compounds in 2017 [13], 1554 compounds in 2018 [14], and 1490 compounds in 2019 [15]. In general, these secondary metabolites can be grouped into polykeptides (PKS), nonribosomal peptides (NRPs), hybrid PKS and NRPs (PKS/NRPs), terpenoids/isoprenoids, ribosomally synthesized and post-translationally modified peptides (RiPs), and bisindoles [16]. Carotenoids are a class of secondary metabolites belonging to the terpenoids/isoprenoids [17]. Certain caroten-producing bacteria live with coral symbionts [18] (Figure 1) such as the Red Gorgonian (_Leptogorgia_ sp.) and Softcorals (_Sinularia_ sp.) [19].  
Due to the important role of carotenoids in the industry, this review emphasizes the current knowledge and technologies on marine carotenoids types, function, screening methods, and its utilization in health and pharmaceutical industries. First, this review discusses the characteristics, biological function, and biosynthetic gene cluster of marine carotenoids. Second, this review discusses the various in vitro and in silico screening methods for marine carotenoid. Lastly, this review discusses the economic potential of marine carotenoids and its usage in the health and pharmaceutical industry.  
Figure 1: Corals with their carotenoid-producing bacteria. (**a**) _Leptogorgia_ sp. with red-colored morphology and red-colored colony reflects red-colored carotenoid. (**b**) _Sinularia_ sp. with yellow-colored morphology and yellow-colored colony reflects yellow-colored carotenoid.