Fig. 1

Hemoglobin genes from different sources and codon optimization. A Schematic diagram of gene selection, codon optimization, and characterization of hemoglobin expression in C. glutamicum. B Homology analysis of hemoglobin sequences from different sources. C Expression of hemoglobin genes from different sources after codon optimization. The hemoglobin expression levels were characterized by measuring the fluorescence intensities of hemoglobin–GFP fusion. Cg and Ec represent codon optimization according to the codon usage bias of C. glutamicum and E. coli, respectively. Values and error bars represent means and standard deviations (n = 3). D Relative codon adaptiveness of optimized genes with the codon usage frequency of C. glutamicum genome as a reference. For the codons encoding an amino acid, the relative codon adaptiveness of the codon with the highest usage frequency was set as 1. The relative codon adaptiveness of other codons for this amino acid was calculated based on their usage frequencies. For example, ATC, ATT, and ATA encode isoleucine and have usage frequencies of 34.2, 21.8, and 1.8 per thousand codons according to the Codon Usage Database (www.kazusa.or.jp/codon). The relative codon adaptiveness of ATC is set as 1, and those of ATT and ATA are calculated as 0.64 and 0.05, respectively