Siderophores of Bacillus pumilus promote 2-keto-L-gulonic acid production in a vitamin C microbial fermentation system.

The precursor of vitamin C, 2-keto-l-gulonic acid (2-KLG), is bio-converted from l-sorbose by a microbial consortium of Ketogulonicigenium vulgare and a helper strain (Bacillus spp.). Most helper strains produce siderophores. To understand the effects of siderophores on promoting 2-KLG yield, the siderophores of Bacillus pumilus SY-A9 were purified and added to a monoculture fermentation system of K. vulgare 25B-1. The results revealed that the titer of 2-KLG reached 7.18 g/L within 60 h and increased by 71.45% when the added concentration of siderophores was 500 µg/L. Moreover, the increased production of 2-KLG was accompanied by the overexpressed iron uptake system-related genes, electron transfer chain-related genes, ATP synthesis enzyme-related genes, antioxidant enzyme-related genes, and 2-KLG producing enzyme-related genes, which reduced oxidative stress and ensured the normal energy metabolism of K. vulgare 25B-1. This study demonstrated that siderophores of the helper strain play a key role in the enhancement of 2-KLG biosynthesis.