Microbial biosynthesis biocatalysts

As in vitro regeneration of SAM 1 is currently not feasible, MT reactions were often performed with live whole-cell biocatalysts to avoid the need of cofactor supply (i.e., microbial hosts expressing recombinant MTs, see next section). However, a drawback of this strategy is the relatively low intracellular concentration of endogenous SAM 1, which limits methylation capacity and, thus, leads to low product yield. Even in the biosynthesis of natural products in microorganisms, such as methylated antibiotics [69] and triterpenoids [70] or fatty acid methyl esters [71], or in the biotransformation of phenolic compounds by plant cell cultures, for example, of protocatechuic aldehyde to vanillin 28 [72], availability of SAM 1 is rate-limiting. 

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