Fig. 3

Plasmid maps of the constructed plasmids. a The cytosine methyltransferase-containing plasmid and psy-containing plasmid are shown. The psy-containing plasmid was constructed in a proof-of-concept metabolic engineering process to increase the metabolic flux towards carotenoid, and the cytosine methyltransferase-containing plasmid was used to methylate the psy-containing plasmid. The psy gene was under the control of the mxaF promoter, encoding subunit of methanol dehydrogenase [32], which was predicted using Promoter Hunter [37]. b The overall strategy of plasmid methylation in E. coli (JM110) and transformation into Methylomonas sp. DH-1. The first step was to methylate the target plasmid using cytosine methyltransferase, and the second step was to transform it into Methylomonas sp. DH-1 after separation from the methylase-containing plasmid