Improving CoQ₁₀ productivity by strengthening glucose transmembrane of Rhodobacter sphaeroides

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.

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.

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.