The present disclosure relates to a method for the incorporation of formaldehyde into biomass comprising the following enzymatically catalyzed steps: (1) condensation of pyruvate with formaldehyde into 4-hydroxy-2-oxobutanoic acid (HOB); (2) amination of the thus produced 4-hydroxy-2-oxobutanoic acid (HOB) to produce homoserine; (3) conversion of thus produced homoserine to threonine; (4) conversion of the thus produced threonine into glycine and acetaldehyde or acetyl-CoA; (5) condensation of the thus produced glycine with formaldehyde to produce serine; and (6) conversion of the thus produced serine to produce pyruvate, wherein said pyruvate can then be used as a substrate in step (1). The disclosure also relates to enzymes for catalyzing the corresponding enzymatic reactions and recombinant microorganisms which express the enzymes for catalyzing the corresponding enzymatic reactions.