Lee and coworkers found that whole-cell extracts of several photobacteria could convert GlcNAc to ManNAc [13] . Among them, Anabaena sp. CH1 exhibited the highest GlcNAc 2-epimerase activity; consequently, they cloned and characterized a gene encoding GlcNAc 2-epimerase from Anabaena sp. CH1 (E.C. 5.1.3.8), which was used in the present study as a Hypocrea codon-optimized gene. For the second step (the condensation of ManNAc to NeuNAc), the currently used enzyme-catalyzed processes use a lyase, which requires an excess of pyruvate. Use of this incurs high downstream processing costs. Therefore, we used the NeuNAc synthase (EC 2.5.1.56) from Campylobacter jejuni [23] in the Hyprocrea process. This enzymatic step entails the use of PEP instead of pyruvate, which in the intended in vivo process is supplied by the fungus, thereby leading to an irreversible and more efficient reaction towards NeuNAc [24] . Moreover, the need for an excess of pyruvate becomes obsolete, and the resulting downstream process is significantly simplified. Similar to the GlcNAc 2-epimerase, the coding sequence for the NeuNAc synthase was codon-optimized for the usage in Hypocrea. The synthetic pathway is presented in Figure 1 . The complete nucleotide sequences for both genes encoding the recombinant enzymes, tbage and tneub, are shown in additional file 1.