Why does formaldehyde impair methanol assimilation in engineered E. coli strains?

Formaldehyde is a central intermediate in methylotrophic pathways but is also a highly reactive and toxic compound that damages DNA and proteins. Understanding how formaldehyde impedes methanol assimilation is essential for engineering more efficient methylotrophic strains.

Formaldehyde impairs methanol assimilation in engineered E. coli strains by causing DNA-protein cross-links (DPCs), DNA strand breaks, and protein crosslinking. These damages inhibit cellular processes such as DNA replication and protein folding, thereby reducing cell growth and methanol utilization efficiency. The accumulation of intracellular formaldehyde, not methanol itself, was shown to be the major toxic factor limiting methanol assimilation. Experimental data indicated that 1.25 mM formaldehyde is lethal to E. coli, whereas the cells can tolerate methanol concentrations up to 2,400 mM, highlighting the critical need to alleviate formaldehyde toxicity for improved methanol assimilation.