New two-stage pH combined with dissolved oxygen control strategy for cyclic β-1,2 glucans synthesis

On the basis of a novel two-stage pH combined with dissolved oxygen (DO) control strategy in fed-batch fermentation, this research addresses the influence of pH on cyclic beta-1,2-glucans (C beta Gs) biosynthesis and melanin accumulation during the production of C beta Gs by Rhizobium radiobacter ATCC 13,333. Under these optimal fermentation conditions, the maximum cell concentration and C beta Gs concentration in a 7-L stirred-tank fermenter were 7.94 g L-1 and 3.12 g L-1, which were the maximum production reported for R. radiobacter. The melanin concentration of the fermentation broth was maintained at a low level, which was beneficial to the subsequent separation and purification of the C beta Gs. In addition, a neutral extracellular oligosaccharide (COGs-1) purified by the two-stage pH combined with DO control strategy fermentation medium was structurally characterized. Structural analyses indicated that COGs-1 was a family of unbranched cyclic oligosaccharides composed of only beta-1,2-linked D-glucopyranose residues with degree of polymerization between 17 and 23, namely C beta Gs. This research provides a reliable source of C beta Gs and structural basis for further studies of biological activity and function.

Automated summary

This research investigates the influence of pH on the biosynthesis of cyclic beta-1,2-glucans (CβGs) and melanin accumulation during the production of CβGs by Rhizobium radiobacter ATCC 13,333. Under optimal fermentation conditions, the maximum cell concentration and CβGs concentration achieved were 7.94 g L-1 and 3.12 g L-1, respectively, which are the highest reported production levels for R. radiobacter. The low melanin concentration in the fermentation broth benefits the subsequent separation and purification of CβGs. Additionally, a neutral extracellular oligosaccharide (COGs-1) was characterized and identified as CβGs. This research provides a reliable source of CβGs and establishes a structural basis for further studies on their biological activity and function.