Bioengineering and physicochemical optimization of ergothioneine production by Aspergillus oryzae

Ergothioneine (EGT) is a bioactive, rare variant of histidine with many applications in the medical, pharmaceutical, and food fields. Therefore, we aimed to investigate in this study the impact of genomic and physicochemical factors on EGT production by the industrial filamentous fungus Aspergillus oryzae. Firstly, to facilitate efficient EGT production, we analyzed the subcellular localization of the three EGT biosynthetic enzymes present in A. oryzae. During screening for the most potent producer of EGT among bioengineered constructed transformants, the strain EgtACO overexpressing both AoegtA and AoegtC showed promising EGT production in DPY medium. Five days of incubation was the optimum period, and CZYP medium was the optimum medium for EGT production. Co-cultivation with the nisin Z-producing Lactococcus lactis JCM 7638 yielded EGT production equivalent to that of the EgtACO strain alone. Having broad-spectrum antimicrobial activity without suppressing growth of the EgtACO strain suggested that bacteriocin may help reduce the risk of contamination during long-term cultivation. Moreover, supplementing the production medium with L-methionine or zinc sulfate improved EGT production (1468.5 or 1565mg/L, respectively). Furthermore, repeated inoculation of the producer strain EgtACO and incubation in blue light were the optimum conditions for EGT production (1895 mg/L). Finally, we achieved cost-effective EGT production using A. oryzae strain EgtACO under the optimal culture conditions using agricultural wastes: potato peel and sweet potato peel (293 and 308mg/L, respectively).