Light calcium carbonate improves pullulan biosynthesis by Aureobasidium pullulans under high concentration of sugar

The effects of light calcium carbonate (CaCO₃) on pullulan biosynthesis by Aureobasidium pullulans NCPS2016 were investigated. Light CaCO₃ enhanced pullulan production by 12.4 % when added to the low concentration of fructose broth compared with K₂HPO₄. Pullulan production was further improved when increasing both the concentrations of light CaCO₃ and fructose. Compared to K₂HPO₄, light CaCO₃ improved the activities of UDP-glucose pyrophosphorylase, α-phosphoglucose mutase, UDP-glucosyltransferase, and glucosyltransferase relevant to pullulan biosynthesis, and the gene transcriptional levels of UDP-glucose pyrophosphorylase, α-phosphoglucose mutase, UDP-glucosyltransferase, and glucose kinase were enhanced. During 30-liter fermentation, 144.3 g/L of purified pullulan was produced from 200 g/L of fructose and 15 g/L of light CaCO₃ within 168 h, with the yield and productivity of 0.72 g/g and 0.86 g/L/h respectively. This is the first report that light CaCO₃ improves pullulan production significantly.