Novel Archaeal Histamine Oxidase from Natronobeatus ordinarius : Insights into Histamine Degradation for Enhancing Food Safety.

Histamine, found abundantly in salt-fermented foods, poses a risk of food poisoning. Natronobeatus ordinarius , a halophilic archaeon isolated from a salt lake, displayed a strong histamine degradation ability. Its histamine oxidase (HOD) gene was identified ( hod Nbs ). This is the first report of an archaeal HOD. The HOD Nbs protein was determined to be a tetramer with a molecular weight of 307 kDa. HOD Nbs displayed optimum activity at 60-65 °C, 1.5-2.0 M NaCl, and pH 6.5. Notably, within the broad NaCl range between 0.5 and 2.5 M, HOD Nbs retained above 50% of its maximum activity. HOD Nbs exhibited good thermal stability, pH stability, and salinity tolerance. HOD Nbs was able to degrade various biogenic amines. The V max of HOD Nbs for histamine was 0.29 μmol/min/mg, and the K m was 0.56 mM. HOD Nbs exhibited high efficiency in histamine removal from fish sauce, namely, 100 μg of HOD Nbs degraded 5.63 mg of histamine (37.9%) in 10 g of fish sauce within 24 h at 50 °C. This study showed that HOD Nbs with excellent enzymatic properties has promising application potentials to degrade histamine in high-salt foods.