[Effect of gene deletion on heme synthesis in ].

Heme, which exists widely in living organisms, is a porphyrin compound with a variety of physiological functions. is an important industrial strain with the characteristics of easy cultivation and strong ability for expression and secretion of proteins. In order to screen the optimal starting strain for heme synthesis, the laboratory preserved strains were screened with and without addition of 5-aminolevulinic acid (ALA). There was no significant difference in the heme production of strains BA, BAΔ6 and BAΔ6Δ. However, upon addition of ALA, the heme titer and specific heme production of strain BAΔ6Δ were the highest, reaching 200.77 μmol/L and 615.70 μmol/(L·g DCW), respectively. Subsequently, the gene (encoding the cytochrome assembly protein HemX) of strain BAΔ6Δ was knocked out to explore its role in heme synthesis. It was found that the fermentation broth of the knockout strain turned red, while the growth was not significantly affected. The highest ALA concentration in flask fermentation reached 82.13 mg/L at 12 h, which was slightly higher than that of the control 75.11 mg/L. When ALA was not added, the heme titer and specific heme production were 1.99 times and 1.45 times that of the control, respectively. After adding ALA, the heme titer and specific heme production were 2.08 times and 1.72 times higher than that of the control, respectively. Real-time quantitative fluorescent PCR showed that the expressions of , , , , , and genes at transcription level were up-regulated. We demonstrated that deletion of gene can improve the production of heme, which may facilitate future development of heme-producing strain.