Production of long-chain free fatty acids from metabolically engineered Rhodobacter sphaeroides heterologously producing periplasmic phospholipase A2 in dodecane-overlaid two-phase culture

Sustainability of in vitro light-dependent NADPH generation by the thylakoid membrane of Synechocystis sp. PCC6803

BACKGROUND

NADPH is used as a reductant in various biosynthetic reactions. Cell-free bio-systems have gained considerable attention owing to their high energy utilization and time efficiency. Efforts have been made to continuously supply reducing power to the reaction mixture in a cyclical manner. The thylakoid membrane (TM) is a promising molecular energy generator, producing NADPH under light. Thus, TM sustainability is of major relevance for its in vitro utilization.

RESULTS

Over 70% of TMs prepared from Synechocystis sp. PCC6803 existed in a sealed vesicular structure, with the F1 complex of ATP synthase facing outward (right-side-out), producing NADPH and ATP under light. The NADPH generation activity of TM increased approximately two-fold with the addition of carbonyl cyanide-p-(trifluoromethoxy) phenylhydrazone (FCCP) or removal of the F1 complex using EDTA. Thus, the uncoupling of proton translocation from the electron transport chain or proton leakage through the Fo complex resulted in greater NADPH generation. Biosilicified TM retained more than 80% of its NADPH generation activity after a week at 30°C in the dark. However, activity declined sharply to below 30% after two days in light. The introduction of engineered water-forming NADPH oxidase (Noxm) to keep the electron transport chain of TM working resulted in the improved sustainability of NADPH generation activity in a ratio (Noxm to TM)-dependent manner, which correlated with the decrease of singlet oxygen generation. Removal of reactive oxygen species (ROS) by catalase further highlighted the sustainable NADPH generation activity of up to 80% in two days under light.

CONCLUSION

Reducing power generated by light energy has to be consumed for TM sustainability. Otherwise, TM can generate singlet oxygen, causing oxidative damage. Thus, TMs should be kept in the dark when not in use. Although NADPH generation activity by TM can be extended via silica encapsulation, further removal of hydrogen peroxide results in an improvement of TM sustainability. Therefore, as long as ROS formation by TM in light is properly handled, it can be used as a promising source of reducing power for in vitro biochemical reactions.

Improving CoQ10 productivity by strengthening glucose transmembrane of Rhodobacter sphaeroides

Background

Several Rhodobacter sphaeroides have been widely applied in commercial CoQ₁₀ production, but they have poor glucose use. Strategies for enhancing glucose use have been widely exploited in R. sphaeroides. Nevertheless, little research has focused on the role of glucose transmembrane in the improvement of production.

Results

There are two potential glucose transmembrane pathways in R. sphaeroides ATCC 17023: the fructose specific-phosphotransferase system (PTS^Fru, fruAB) and non-PTS that relied on glucokinase (glk). fruAB mutation revealed two effects on bacterial growth: inhibition at the early cultivation phase (12–24 h) and promotion since 36 h. Glucose metabolism showed a corresponding change in characteristic vs. the growth. For ΔfruAΔfruB, maximum biomass (Bio_max) was increased by 44.39% and the CoQ₁₀ content was 27.08% more than that of the WT. glk mutation caused a significant decrease in growth and glucose metabolism. Over-expressing a galactose:H⁺ symporter (galP) in the ΔfruAΔfruB relieved the inhibition and enhanced the growth further. Finally, a mutant with rapid growth and high CoQ₁₀ titer was constructed (ΔfruAΔfruB/tac::galP_OP) using several glucose metabolism modifications and was verified by fermentation in 1 L fermenters.

Conclusions

The PTS^Fru mutation revealed two effects on bacterial growth: inhibition at the early cultivation phase and promotion later. Additionally, biomass yield to glucose (Y_b/glc) and CoQ₁₀ synthesis can be promoted using fruAB mutation, and glk plays a key role in glucose metabolism. Strengthening glucose transmembrane via non-PTS improves the productivity of CoQ₁₀ fermentation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01695-z.

Efficient application of a baculovirus-silkworm larvae expression system for obtaining porcine circovirus type 2 virus-like particles for a vaccine

Porcine circovirus type 2 (PCV2) is a major pathogen associated with swine diseases. It is the smallest single-stranded DNA virus, and its genome contains four major open reading frames (ORFs). ORF2 encodes the major structural protein Cap, which can self-assemble into virus-like particles (VLPs) in vitro and contains the primary antigenic determinants. In this study, we developed a high-efficiency method for obtaining VLPs and optimized the purification conditions. In this method, we expressed the protein Cap with a 6× His tag using baculovirus-infected silkworm larvae as well as the E. coli BL21(DE3) prokaryotic expression system. The PCV2 Cap proteins produced by the silkworm larvae and E. coli BL21(DE3) were purified. Cap proteins purified from silkworm larvae self-assembled into VLPs in vitro, while the Cap proteins purified from bacteria were unable to self-assemble. Transmission electron microscopy confirmed the self-assembly of VLPs. The immunogenicity of the VLPs produced using the baculovirus system was demonstrated using an enzyme-linked immunosorbent assay (ELISA). Furthermore, the purification process was optimized. The results demonstrated that the expression system using baculovirus-infected silkworm larvae is a good choice for obtaining VLPs of PCV2 and has potential for the development of a low-cost and efficient vaccine.