Effects of dissolved oxygen and shear stress on the synthesis and molecular weight of welan gum produced from Alcaligenes sp. CGMCC2428

The effects of dissolved oxygen (DO) and shear stress on the synthesis and molecular weight (MW) of welan gum were systematically investigated in the batch fermentation of Alcaligenes sp. CGMCC2428 in a 7.5 L bioreactor with working volume of 4.5 L. The results showed that a high shear stress (1000 rpm) enhanced cell growth, but decreased MW and welan gum concentration. The welan gum concentration reached a maximum of 22.8 ± 0.61 g/L at 800 rpm, and the highest MW was (9.01 ± 0.12) × 10⁵ Da at 600 rpm. Furthermore, a moderate DO concentration (20%) enhanced MW and welan gum concentration; the maximum values were (9.20 ± 0.11) × 10 ⁵ Da and 24.5 ± 0.53 g/L, respectively. To further investigate the effects of DO concentration on the synthesis and MW of welan gum, this study also compared the metabolic flux distribution of Alcaligenes sp. CGMCC2428 at various DO concentrations. The results demonstrated that glucose-6-phosphate and acetyl-coenzyme A nodes were flexible. The flux of glucose-1-phosphate to welan gum was enhanced at DO concentration of 20%. Increased flux might also be a reason for the increased MW and welan gum concentration observed.