## 4 Discussion  
_Sphingomonas morindae_ sp. NBD5 had two genomes, which were relatively rare in _Sphingomonas_. Two genomes and two plasmids may have special significance in the biosynthesis and regulation of macular pigment of this strain. Both plasmids were stable in the strain, indicating that they have different replicons. Two genomes have been reported in eukaryotes, and this heterokaryosis plays a role in the adaptation of arbuscular mycorrhizal fungi to different plant hosts [24]. _Sphingomonas morindae_ sp. NBD5 strain is an endophyte from Noni fruit, and the two genomes may play a key role in its adaptation in the host. Recent studies prove that genome-wide phylogeny can improve the phylogenetic accuracy and preferably delimit the species borderlines [25]. As of 7 May 2022, 127 strains of _Sphingomonas_ have published genome data in the National Center for Biotechnology Information (NCBI) database. _Sphingomonas morindae_ sp. NBD5 whole-genome sequencing enriches the whole genome data of MP-producing bacterium. Lutein and zexansthin biosynthesis can be divided into three stages: basic components formation, components condensation, and skeleton structure assembly (Figure 4). Synthease genes related to lutein and zexansthin are discovered in the glycolysis/gluconeogenesis pathway, terpenoid skeleton biosynthesis pathway and carotenoid biosynthesis pathway (Figures S3-S5). In the first stage, glyceraldehyde 3-phosphate (G3P) and pyruvate are  
Figure 5: (**a**) The streak plate colonies of _Sphingomonas morindae_ sp. NBD5 grown on solid medium at five day; (**b**) the streak plate colonies of _Sphingopyxis_ sp. USTB-05 grown on solid medium at five day. synthesized via the glycolysis pathway (Figure S3). In the glycolysis pathway, the glucose was transferred into the bacteria through the receptors on the surface of the bacteria in two strains. All enzymes involved in the conversion of \(\alpha\)-D-glucose 1-phosphate to pyruvate were found in two strains. PGM, iPGAM, PCKA are three unique enzymes in the genome of _Sphingomonas moridae_ sp. NBD5. PCKG is a unique enzyme in the genome of _Sphingopyxis_ sp. USTB-05. PGM is \(\alpha\)-D-glucose-1,6-bisphosphate dependent phosphoglucomutases. iPGAM is 2,3-diphosphoglycerate independent phosphoglycerate mutase. In particularly, iPGAM shows the greatest activity in the absence of 2,3-diphosphoglycerate in Gram-positive bacteria and is rarely reported in Gram-negative bacteria [26]. In the second stage, the 2-C-methyl-D-erythnitol 4-phosphate (MEP) pathway, also known as the 1-deoxy-D-xylulose 5-phosphate (DXP) or non-mevalonate pathway [27]. DXS, DXR, ISPD, ISPE, ISPE, GcpE, ISPH, and FDPS are annotated in the genome of _Sphingomonas moridae_ sp. NBD5 and _Sphingopyxis_ sp. USTB-05 (Figure S4). DXS catalyzes the condensation of pyruvate and glyceraldehyde 3-phosphate to form 1-deoxy-D-xylulose 5-phosphate. DXS is an open reading frame-encoding enzyme on the chromosomal map of _E. coli_. Cloning of _dxs_ was overexpressed and purified to produce a specific activity of enzyme protein of 0.85 units per mg, and DXS may be widespread in bacteria and plant chloroplasts [28]. The _dxs_ gene was cloned from _Streptomyces_ sp. CL190 and _E. coli_, respectively. The overexpressed and purified experiments show that they have the same enzymatic properties although they have different origins [29]. DXR catalyses transform 1-deoxy-D-xylulose 5-phosphate into 2-C-methyl-D-erythnitol 4-phosphate. DXR is an NADPH-dependent enzyme that also requires metal ions (Mn\({}^{2+}\), Co\({}^{2+}\) or Mg\({}^{2+}\)) with Mn\({}^{2+}\) being the most efficient. The reaction mechanism of this enzyme is shown to be a retro-aldol/aldol reaction [30]. Earlier experiments, overexpressing the recombinant gene _yueM_ corresponding to DXR in _E. coli_ is found that the enzyme can convert 1-deoxy-D-xylulose 5-phosphate to 2-C-methyl-D-erythnitol 4-phosphate through one-step intramolecular rearrangement and reduction. This result suggests that DXR is responsible for terpenoid biosynthesis in _E. coli_[31].