Enhanced production of CoQ10 by constitutive overexpression of 3-demethyl ubiquinone-9 3-methyltransferase under tac promoter in Rhodobacter sphaeroides

Removal of pollutants and accumulation of high-value cell inclusions in a batch reactor containing Rhodopseudomonas for treating real heavy oil refinery wastewater

Treating wastewater using purple non-sulfur bacteria (PNSB) is an environmentally friendly technique that can simultaneously remove pollutants and lead to the accumulation of high-value cell inclusions. However, no PNSB system for treating heavy oil refinery wastewater (HORW) and recovering high-value cell inclusions has yet been developed. In this study, five batch PNSB systems dominated by Rhodopseudomonas were used to treat real HORW for 186 d. The effects of using different hydraulic retention times (HRT), sludge retention times (SRT), trace element solutions, phosphate loads, and influent loads were investigated, and the bacteriochlorophyll, carotenoid, and coenzyme Q10 concentrations were determined. The community structure and quantity of Rhodopseudomonas in the systems were determined using a high-sequencing technique and quantitative polymerase chain reaction technique. The long-term results indicated that phosphate was the limiting factor for treating HORW in the PNSB reactor. The soluble chemical oxygen demand (SCOD) removal rates were 67.03% and 85.26% without and with phosphate added, respectively, and the NH4+-N removal rates were 32.18% and 89.22%, respectively. The NO3--N concentration in the effluent was stable at 0-3 mg/L with or without phosphate added. Adding phosphate increased the Rhodopseudomonas relative abundance and number by 13.21% and 41.61%, respectively, to 57.35% and 8.52 × 106 gene copies/μL, respectively. The SRT was the limiting factor for SCOD removal, and the bacteria concentration was the limiting factor for nitrogen removal. Once the inflow load had been increased, the total nitrogen (TN) removal rate increased as the HRT increased. Maximum TN removal rates of 64.46%, 68.06%, 73.89%, 82.15%, and 89.73% were found at HRT of 7, 10, 13, 16, and 19 d, respectively. The highest bacteriochlorophyll, carotenoid, and coenzyme Q10 concentrations were 2.92, 4.99, and 4.53 mg/L, respectively. This study provided a simple and efficient method for treating HORW and reutilizing resources, providing theoretical support and parameter guidance for the application of Rhodopseudomonas in treating HORW.

Valorization of CO2 to β-farnesene in Rhodobacter sphaeroides

The valorization of CO₂ into valuable products is a sustainable strategy to help overcome the climate crisis. In particular, biological conversion is attractive as it can produce long-chain hydrocarbons such as terpenoids. This study reports the high yield of β-farnesene production from CO₂ by expressing heterologous β-farnesene synthase (FS) into Rhodobacter sphaeroides. To increase the expression of FS, a strong active promoter and a ribosome binding site (RBS) were engineered. Moreover, β-farnesene production was improved further through the supply of exogenous antioxidants and additional nutrients. Finally, β-farnesene was produced from CO₂ at a titer of 44.53 mg/L and yield of 234.08 mg/g, values that were correspondingly 23 times and 46 times higher than those from the initial production of β-farnesene. Altogether, the results here suggest that the autotrophic production of β-farnesene can provide a starting point for achieving a circular carbon economy.

Production of Coenzyme Q10 by microbes: an update

Coenzyme Q₁₀ (CoQ₁₀) is the main CoQ species in human and is used extensively in food, cosmetic and medicine industries because of its antioxidant properties and its benefit in prophylactic medicine and therapy for a variety of diseases. Among various approaches to increase the production of CoQ₁₀, microbial fermentation is the most effective. As knowledge of the biosynthetic enzymes and regulatory mechanisms modulating CoQ₁₀ production increases, opportunities arise for metabolic engineering of CoQ₁₀ in microbial hosts. In this review, we present various strategies used up to date to improve CoQ₁₀ production and focus on metabolic engineering of CoQ₁₀ overproduction in microbes. General strategies of metabolic engineering include providing sufficient precursors for CoQ₁₀, increasing metabolic fluxes, and expanding storage capacity for CoQ₁₀. Based on these strategies, CoQ₁₀ production has been significantly improved in natural CoQ₁₀ producers, as well as in heterologous hosts.

Enhanced pollutants removal and high-value cell inclusions accumulation with Fe2+ in heavy oil refinery treatment system using Rhodopseudomonas and Pseudomonas

Metal ions has been widely used as a method of improving pollutant removal efficiency in wastewater biological treatment system. In order to enhance pollutants removal and high-value cell inclusions accumulation in heavy oil refinery wastewater treatment systems using PSB, different reactors were built feeding with different Fe²⁺ concentrations respectively, and run with enriching Rhodopseudomonas and Pseudomonas in the reactors. Solute chemical oxygen demand (SCOD), ammonia (NH₄⁺-N), nitrate nitrogen (NO₃^--N), nitrous nitrogen (NO₂^--N), Fe²⁺, and related cell inclusions were all detected, moreover, microbial community structure and the quantity of Rhodopseudomonas and Pseudomonas were also detected. The results showed that at the optimal dosage of Fe²⁺ with 20 mg/L, the corresponding removal ratios of solute chemical oxygen demand and ammonia were 73.51% and 92.26%, respectively. The yields of carotenoid, bacteriochlorophyll, and coenzyme Q₁₀ were 11.18, 6.75, and 9.84 mg/g-DCW respectively. Furthermore, with 20 mg/L Fe²⁺ dosage, the relative abundance and gene number of Rhodopseudomonas were the highest in the system, which were 91.57% and 1.843 × 10⁶ gene copies/μL, while Fe²⁺ had no obvious effect on the growth of Pseudomonas. The results showed that adding Fe²⁺ has improved the removal of pollutants and accumulation of high-value cells inclusions, also provided theoretical guidance for the treatment of heavy oil refinery wastewater using PSB.

Regulation of Reactive Oxygen Species Promotes Growth and Carotenoid Production Under Autotrophic Conditions in Rhodobacter sphaeroides

Industrial demand for capture and utilization using microorganisms to reduce CO₂, a major cause of global warming, is significantly increasing. Rhodobacter sphaeroides is a suitable strain for the process of converting CO₂ into high-value materials because it can accept CO₂ and has various metabolic pathways. However, it has been mainly studied for heterotrophic growth that uses sugars and organic acids as carbon sources, not autotrophic growth. Here, we report that the regulation of reactive oxygen species is critical for growth when using CO₂ as a sole carbon source in R. sphaeroides. In general, the growth rate is much slower under autotrophic conditions compared to heterotrophic conditions. To improve this, we performed random mutagenesis using N-methyl-N’-nitro-N-nitrosoguanidine (NTG). As a result, we selected the YR-1 strain with a maximum specific growth rate (μ) 1.44 day^–1 in the early growth phase, which has a 110% faster growth rate compared to the wild-type. Based on the transcriptome analysis, it was confirmed that the growth was more sensitive to reactive oxygen species under autotrophic conditions. In the YR-1 mutant, the endogenous contents of H₂O₂ levels and oxidative damage were reduced by 33.3 and 42.7% in the cells, respectively. Furthermore, we measured that concentrations of carotenoids, which are important antioxidants. The total carotenoid is produced 9.63 g/L in the YR-1 mutant, suggesting that the production is 1.7-fold higher than wild-type. Taken together, our observations indicate that controlling ROS promotes cell growth and carotenoid production under autotrophic conditions.

Enhanced CoQ10 production by genome modification of Rhodobacter sphaeroides via Tn7 transposition

As a native CoQ10 producer, Rhodobacter sphaeroides has been extensively engineered to enhance CoQ10 production. However, the genetic manipulations using plasmids suffer from risk of plasmid loss during propagation process, biomass impairment due to cellular burden and bio-safety concerns. In this paper, genomic manipulations via Tn7 transposition was conducted to boost the CoQ10 biosynthesis in R. sphaeroides. The titer production and content of CoQ10 were improved by 18.44% and 18.87% respectively compared to the wild type, when an additional copy of dxs and dxr were integrated into the genome. Further overexpression of idi and ispD by genomic integration created strain RSPCDDII with CoQ10 production and content of 81.23 mg/L and 5.93 mg/g, which were 54.28% and 55.97% higher than those of the wild type. The gene segments were successfully inserted into the attTn7 site of the R. sphaeroides genome. Meanwhile, the biomass was not affected. Compared to overexpression of genes on plasmids, this strategy could enhance protein expression to a proper level without affecting cell growth, and in a more stable manner.

Screening and engineering of high-activity promoter elements through transcriptomics and red fluorescent protein visualization in Rhodobacter sphaeroides

The versatile photosynthetic α-proteobacterium Rhodobacter sphaeroides, has recently been extensively engineered as a novel microbial cell factory (MCF) to produce pharmaceuticals, nutraceuticals, commodity chemicals and even hydrogen. However, there are no well-characterized high-activity promoters to modulate gene transcription during the engineering of R. sphaeroides. In this study, several native promoters from R. sphaeroides JDW-710 (JDW-710), an industrial strain producing high levels of co-enzyme Q₁₀ (Q₁₀) were selected on the basis of transcriptomic analysis. These candidate promoters were then characterized by using gusA as a reporter gene. Two native promoters, P_{rsp_7571} and P_{rsp_6124}, showed 620% and 800% higher activity, respectively, than the tac promoter, which has previously been used for gene overexpression in R. sphaeroides. In addition, a P_{rsp_7571}-derived synthetic promoter library with strengths ranging from 54% to 3200% of that of the tac promoter, was created on the basis of visualization of red fluorescent protein (RFP) expression in R. sphaeroides. Finally, as a demonstration, the synthetic pathway of Q₁₀ was modulated by the selected promoter T334* in JDW-710; the Q₁₀ yield in shake-flasks increased 28% and the production reached 226 mg/L. These well-characterized promoters should be highly useful in current synthetic biology platforms for refactoring the biosynthetic pathway in R. sphaeroides-derived MCFs.

Co-production of polyhydroxybutyrate (PHB) and coenzyme Q10 (CoQ10) via no-sugar fermentation—a case by Methylobacterium sp. XJLW

Purpose

To explore a competitive PHB-producing fermentation process, this study evaluated the potential for Methylobacterium sp. XJLW to produce simultaneously PHB and coenzyme Q10 (CoQ10) using methanol as sole carbon and energy source.

Methods

The metabolic pathways of PHB and CoQ10 biosynthesis in Methylobacterium sp. XJLW were first mined based on the genomic and comparative transcriptomics information. Then, real-time fluorescence quantitative PCR (RT-qPCR) was employed for comparing the expression level of important genes involved in PHB and CoQ10 synthesis pathways’ response to methanol and glucose. Transmission electron microscope (TEM), gas chromatography/mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), Fourier transformation infrared spectrum (FT-IR), and liquid chromatography/mass spectrometry (LC-MS) methods were used to elucidate the yield and structure of PHB and CoQ10, respectively. PHB and CoQ10 productivity of Methylobacterium sp. XJLW were evaluated in Erlenmeyer flask for medium optimization, and in a 5-L bioreactor for methanol fed-batch strategy according to dissolved oxygen (DO) and pH control.

Results

Comparative genomics analysis showed that the PHB and CoQ10 biosynthesis pathways co-exist in Methylobacterium sp. XJLW. Transcriptomics analysis showed that the transcription level of key genes in both pathways responding to methanol was significantly higher than that responding to glucose. Correspondingly, strain Methylobacterium sp. XJLW can produce PHB and CoQ10 simultaneously with higher yield using cheap and abundant methanol than using glucose as sole carbon and energy source. The isolated products showed the structure characteristics same to that of standard PHB and CoQ10. The optimal medium and cultural conditions for PHB and CoQ10 co-production by Methylobacterium sp. XJLW was in M3 medium containing 7.918 g L-1 methanol, 0.5 g L-1 of ammonium sulfate, 0.1% (v/v) of Tween 80, and 1.0 g L-1 of sodium chloride, under 30 °C and pH 7.0. In a 5-L bioreactor coupled with methanol fed-batch process, a maximum DCW value (46.31 g L-1) with the highest yields of PHB and CoQ10, reaching 6.94 g L-1 and 22.28 mg L-1, respectively.

Conclusion

Methylobacterium sp. XJLW is potential for efficiently co-producing PHB and CoQ10 employing methanol as sole carbon and energy source. However, it is still necessary to further optimize fermentation process, and genetically modify strain pathway, for enhanced production of PHB and CoQ10 simultaneously by Methylobacterium sp. XJLW. It also suggests a potential strategy to develop efficiently co-producing other high-value metabolites using methanol-based bioprocess.

Coenzyme Q10 Biosynthesis Established in the Non-Ubiquinone Containing Corynebacterium glutamicum by Metabolic Engineering

Coenzyme Q₁₀ (CoQ10) serves as an electron carrier in aerobic respiration and has become an interesting target for biotechnological production due to its antioxidative effect and benefits in supplementation to patients with various diseases. For the microbial production, so far only bacteria have been used that naturally synthesize CoQ10 or a related CoQ species. Since the whole pathway involves many enzymatic steps and has not been fully elucidated yet, the set of genes required for transfer of CoQ10 synthesis to a bacterium not naturally synthesizing CoQ species remained unknown. Here, we established CoQ10 biosynthesis in the non-ubiquinone-containing Gram-positive Corynebacterium glutamicum by metabolic engineering. CoQ10 biosynthesis involves prenylation and, thus, requires farnesyl diphosphate as precursor. A carotenoid-deficient strain was engineered to synthesize an increased supply of the precursor molecule farnesyl diphosphate. Increased farnesyl diphosphate supply was demonstrated indirectly by increased conversion to amorpha-4,11-diene. To provide the first CoQ10 precursor decaprenyl diphosphate (DPP) from farnesyl diphosphate, DPP synthase gene ddsA from Paracoccus denitrificans was expressed. Improved supply of the second CoQ10 precursor, para-hydroxybenzoate (pHBA), resulted from metabolic engineering of the shikimate pathway. Prenylation of pHBA with DPP and subsequent decarboxylation, hydroxylation, and methylation reactions to yield CoQ10 was achieved by expression of ubi genes from Escherichia coli. CoQ10 biosynthesis was demonstrated in shake-flask cultivation and verified by liquid chromatography mass spectrometry analysis. To the best of our knowledge, this is the first report of CoQ10 production in a non-ubiquinone-containing bacterium.

The transition of Rhodobacter sphaeroides into a microbial cell factory

Microbial cell factories are the workhorses of industrial biotechnology and improving their performances can significantly optimize industrial bioprocesses. Microbial strain engineering is often employed for increasing the competitiveness of bio‐based product synthesis over more classical petroleum‐based synthesis. Recently, efforts for strain optimization have been standardized within the iterative concept of “design‐build‐test‐learn” (DBTL). This approach has been successfully employed for the improvement of traditional cell factories like Escherichia coli and Saccharomyces cerevisiae. Within the past decade, several new‐to‐industry microorganisms have been investigated as novel cell factories, including the versatile α‐proteobacterium Rhodobacter sphaeroides. Despite its history as a laboratory strain for fundamental studies, there is a growing interest in this bacterium for its ability to synthesize relevant compounds for the bioeconomy, such as isoprenoids, poly‐β‐hydroxybutyrate, and hydrogen. In this study, we reflect on the reasons for establishing R. sphaeroides as a cell factory from the perspective of the DBTL concept. Moreover, we discuss current and future opportunities for extending the use of this microorganism for the bio‐based economy. We believe that applying the DBTL pipeline for R. sphaeroides will further strengthen its relevance as a microbial cell factory. Moreover, the proposed use of strain engineering via the DBTL approach may be extended to other microorganisms that have not been critically investigated yet for industrial applications.

Purple phototrophic bacteria for resource recovery: Challenges and opportunities

Sustainable development is driving a rapid focus shift in the wastewater and organic waste treatment sectors, from a "removal and disposal" approach towards the recovery and reuse of water, energy and materials (e.g. carbon or nutrients). Purple phototrophic bacteria (PPB) are receiving increasing attention due to their capability of growing photoheterotrophically under anaerobic conditions. Using light as energy source, PPB can simultaneously assimilate carbon and nutrients at high efficiencies (with biomass yields close to unity (1 g COD_biomass·g COD_removed^-1)), facilitating the maximum recovery of these resources as different value-added products. The effective use of infrared light enables selective PPB enrichment in non-sterile conditions, without competition with other phototrophs such as microalgae if ultraviolet-visible wavelengths are filtered. This review reunites results systematically gathered from over 177 scientific articles, aiming at producing generalized conclusions. The most critical aspects of PPB-based production and valorisation processes are addressed, including: (i) the identification of the main challenges and potentials of different growth strategies, (ii) a critical analysis of the production of value-added compounds, (iii) a comparison of the different value-added products, (iv) insights into the general challenges and opportunities and (v) recommendations for future research and development towards practical implementation. To date, most of the work has not been executed under real-life conditions, relevant for full-scale application. With the savings in wastewater discharge due to removal of organics, nitrogen and phosphorus as an important economic driver, priorities must go to using PPB-enriched cultures and real waste matrices. The costs associated with artificial illumination, followed by centrifugal harvesting/dewatering and drying, are estimated to be 1.9_, 0.3-2.2 and 0.1-0.3 $·kg_{dry biomass}^-1. At present, these costs are likely to exceed revenues. Future research efforts must be carried out outdoors, using sunlight as energy source. The growth of bulk biomass on relatively clean wastewater streams (e.g. from food processing) and its utilization as a protein-rich feed (e.g. to replace fishmeal, 1.5-2.0 $·kg^-1) appears as a promising valorisation route.

Phosphate limitation increases coenzyme Q10 production in industrial Rhodobacter sphaeroides HY01

Coenzyme Q₁₀ (CoQ₁₀) is an important component of the respiratory chain in humans and some bacteria. As a high-value-added nutraceutical antioxidant, CoQ₁₀ has excellent capacity to prevent cardiovascular disease. The content of CoQ₁₀ in the industrial Rhodobacter sphaeroides HY01 is hundreds of folds higher than normal physiological levels. In this study, we found that overexpression or optimization of the synthetic pathway failed CoQ₁₀ overproduction in the HY01 strain. Moreover, under phosphate- limited conditions (decreased phosphate or in the absence of inorganic phosphate addition), CoQ₁₀ production increased significantly by 12% to220 mg/L, biomass decreased by 12%, and the CoQ₁₀ productivity of unit cells increased by 27%. In subsequent fed-batch fermentation, CoQ₁₀ production reached 272 mg/L in the shake-flask fermentation and 1.95 g/L in a 100-L bioreactor under phosphate limitation. Furthermore, to understand the mechanism associated with CoQ₁₀ overproduction under phosphate- limited conditions, the comparatve transcriptome analysis was performed. These results indicated that phosphate limitation combined with glucose fed-batch fermentation represented an effective strategy for CoQ₁₀ production in the HY01. Phosphate limitation induced a pleiotropic effect on cell metabolism, and that improved CoQ₁₀ biosynthesis efficiency was possibly related to the disturbance of energy metabolism and redox potential.

Elevated β-Carotene Synthesis by the Engineered Rhodobacter sphaeroides with Enhanced CrtY Expression

β-Carotene is a precursor of vitamin A and a dietary supplement for its antioxidant property. Producing β-carotene by microbial fermentation has attracted much attention owing to consumers' preference for the natural product. In this study, an engineered photosynthetic Rhodobacter sphaeroides producing β-carotene was constructed by the following strategies: (1) five promoters of different strengths were used to investigate the effect of the expression level of crtY on β-carotene content. It was found that P_rrnB increased the β-carotene content by 109%. (2) blocking of the branched pentose phosphate pathway by zwf deletion, and (3) overexpressing dxs could restore the transcriptional levels of crtE and crtB. Finally, the engineered RS-C3 has the highest β-carotene content of 14.93 mg/g dry cell weight (DCW) among all of the reported photosynthetic bacteria and the β-carotene content reached 3.34 mg/g DCW under light conditions. Our results will be available for industrial use to supply a large quantity of natural β-carotene.

Chromosome engineering of Escherichia coli for constitutive production of salvianic acid A

Background

Salvianic acid A (SAA), a valuable natural product from herbal plant Salvia miltiorrhiza, exhibits excellent antioxidant activities on food industries and efficacious therapeutic potential on cardiovascular diseases. Recently, production of SAA in engineered Escherichia coli was established via the artificial biosynthetic pathway of SAA on the multiple plasmids in our previous work. However, the plasmid-mediated system required to supplement expensive inducers and antibiotics during the fermentation process, restricting scale-up production of SAA. Microbial cell factory would be an attractive approach for constitutive production of SAA by chromosome engineering.

Results

The limited enzymatic reactions in SAA biosynthetic pathway from glucose were grouped into three modules, which were sequentially integrated into chromosome of engineered E. coli by λ Red homologous recombination method. With starting strain E. coli BAK5, in which the ptsG, pykF, pykA, pheA and tyrR genes were previously deleted, chassis strain BAK11 was constructed for constitutive production of precursor l-tyrosine by replacing the 17.7-kb mao-paa cluster with module 1 (P_lacUV5-aroG^fbr-tyrA^fbr-aroE) and the lacI gene with module 2 (P_trc-glk-tktA-ppsA). The synthetic 5tacs promoter demonstrated the optimal strength to drive the expression of hpaBC-d-ldh^Y52A in module 3, which then was inserted at the position between nupG and speC on the chromosome of strain BAK11. The final strain BKD13 produced 5.6 g/L of SAA by fed-batch fermentation in 60 h from glucose without any antibiotics and inducers supplemented.

Conclusions

The plasmid-free and inducer-free strain for SAA production was developed by targeted integration of the constitutive expression of SAA biosynthetic genes into E. coli chromosome. Our work provides the industrial potential for constitutive production of SAA by the indel microbial cell factory and also sets an example of further producing other valuable natural and unnatural products.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0700-2) contains supplementary material, which is available to authorized users.

Synergic regulation of redox potential and oxygen uptake to enhance production of coenzyme Q10 in Rhodobacter sphaeroides

The physiological role of Coenzyme Q₁₀ (CoQ₁₀) as an electron carrier suggests its association with redox potential. Overexpression of glyceraldehyde-3-phosphate dehydrogenase type I (gapA-1) in Rhodobacter sphaeroides elevated the NADH/NAD⁺ ratio and meanwhile enhanced the CoQ₁₀ content by 58%, but at the sacrifice of biomass. On the other hand, Vitreoscilla hemoglobin was heterologously expressed to enhance the oxygen uptake ability of the cells, leading to 127% improvement of biomass. Subsequent coexpression of gapA-1 and vgb resulted in a CoQ₁₀ titer of 83.24mg/L, representing 71% improvement as compared to the control strain RspMCS. When gapA-1 and vgb genes were co-expressed in a previously created strain RspMQd [1], 163.5mg/L of CoQ₁₀ was produced. Finally, 600mg/L of CoQ₁₀ production was achieved in fed-batch fermentation. These results demonstrated the synergic effect of redox potential regulation and oxygen uptake improvement on enhancing CoQ₁₀ production in R. sphaeroides.

Cellular factories for coenzyme Q10 production

Coenzyme Q₁₀ (CoQ₁₀), a benzoquinone present in most organisms, plays an important role in the electron-transport chain, and its deficiency is associated with various neuropathies and muscular disorders. CoQ₁₀ is the only lipid-soluble antioxidant found in humans, and for this, it is gaining popularity in the cosmetic and healthcare industries. To meet the growing demand for CoQ₁₀, there has been considerable interest in ways to enhance its production, the most effective of which remains microbial fermentation. Previous attempts to increase CoQ₁₀ production to an industrial scale have thus far conformed to the strategies used in typical metabolic engineering endeavors. However, the emergence of new tools in the expanding field of synthetic biology has provided a suite of possibilities that extend beyond the traditional modes of metabolic engineering. In this review, we cover the various strategies currently undertaken to upscale CoQ₁₀ production, and discuss some of the potential novel areas for future research.

Integration of heterologous 4-hydroxybenzoic acid transport proteins in Rhodobacter sphaeroides for enhancement of coenzyme Q10production

This work provides a novel genetic engineering strategy that improves uptake of extracellular 4-hydroxybenzoic acid by heterologously expressing the membrane transport protein PcaK inR. sphaeroidesfor enhancement of CoQ₁₀production.

Enhanced production of coenzyme Q10 by self-regulating the engineered MEP pathway in Rhodobacter sphaeroides

Fine-tuning the expression level of an engineered pathway is crucial for the metabolic engineering of a host toward a desired phenotype. However, most engineered hosts suffer from nonfunctional protein expression, metabolic imbalance, cellular burden or toxicity from intermediates when an engineered pathway is first introduced, which can decrease production of the desired product. To circumvent these obstacles, we developed a self-regulation system utilizing the trc/tac promoter, LacI(q) protein and ribosomal binding sites (RBS). With the purpose of improving coenzyme Q10 (CoQ10 ) production by increasing the decaprenyl diphosphate supplement, enzymes DXS, DXR, IDI, and IspD were constitutively overexpressed under the control of the trc promoter in Rhodobacter sphaeroides. Then, a self-regulation system combining a set of RBSs for adjusting the expression of the LacI(q) protein was applied to tune the expression of the four genes, resulting in improved CoQ10 production. Finally, another copy of the tac promoter with the UbiG gene (involved in the ubiquinone pathway of CoQ10 biosynthesis) was introduced into the engineered pathway. By optimizing the expression level of both the upstream and downstream pathway, CoQ10 production in the mutants was improved up to 93.34 mg/L (7.16 mg/g DCW), about twofold of the wild-type (48.25 mg/L, 3.24 mg/g DCW).