Production and characterisation of alginate from Azotobacter vinelandii

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 (M-n). Its chemical composition was practically independent of the fermentation time with an average content in uronic aci ds 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, M-n 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 o f 70 or 80% depending on the LF or SF scale used. However, the rate of M, i ncrease was found to be strictly growth-associated, since alginate depolyme risation was observed as soon as the exponential cell growth rate stopped a nd this coincided with ammoniac nitrogen levels smaller than 10-15 g m(-3) (C) 1999 Society of Chemical Industry.