Production and characterisation of alginate fromAzotobacter vinelandii

Abstract

The alginate produced from glucose by Azotobacter vinelandii DSM 576 in the shaken-flask (SF) scale was characterised in terms of chemical composition and average molecular mass (Mn). Its chemical composition was practically independent of the fermentation time with an average content in uronic acids of 0.66±0.09 g/g, a high proportion of mannuronic acid (M =0.75±0.04) and a mean acetylation degree of 18.5±7.9%. On the contrary, Mn reached a maximum value of ca. 220 kDa after 40–42 h fermentation and then decreased to 60 kDa in the following 20–22 hours. The fermentation process was scaled-up in a laboratory fermenter (LF) and the kinetics of alginate production was classified of the mixed-growth -associated product formation type with a contribution of non-growth associated production of the order of 70 or 80% depending on the LF or SF scale used. However, the rate of Mn increase was found to be strictly growth-associated, since alginate depolymerisation was observed as soon as the exponential cell growth rate stopped and this coincided with ammoniac nitrogen levels smaller than 10–15 g m −3. © 1999 Society of Chemical Industry