BACKGROUND: Agmatine is a valuable pharmaceutical intermediate biosynthesised fromL-arginine by arginine decarboxylase (EC 4.1.1.19). It has various potential therapeutic functions in neurotransmitter systems, nitric oxide synthesis, and polyamine metabolism. To establish a green and efficient process for agmatine production, a novel arginine decarboxylase (SpA9) from Shewanella putrefaciens was identified, overexpressed, and functionally characterised in this study. RESULTS: The SpA9 gene from S. putrefaciens was overexpressed in Escherichia coli BL21(DE3), and the recombinant SpA9 was purified 7.7-fold. The recombinant SpA9 exhibited a higher K-cat/K-m value (4.8 s(-)1 mM(-1)). Furthermore, SpA9 showed the highest activity at pH 8.5 and 37 degrees C towards L-arginine. The highest enzyme activity of 1281 U mL(-1) was achieved by optimising the nutrient, culture, and induction conditions. Under optimum transformation conditions, the maximum conversion yield of agmatine was 92.6%, with a space-time yield of 276.88 g L-1 . day(-1) at a 1 L scale. CONCLUSIONS: To our best knowledge, this bioprocess produced the highest yield and conversion rate of any biocatalyst method reported yet. It is also a greener and more cost-effective method for agmatine production compared with other available methods in the pharmaceutical industry. (C) 2017 Society of Chemical Industry