Studies on the Fermentation Strategies for Production of the High-Viscosity Scleroglucan Polysaccharide (poster)

J.I. FARIÑA; C.F. GONZÁLEZ; N.I. PEROTTI; O.E. MOLINA; L.I.C. FIGUEROA

Los Angeles

Congreso; 100th GENERAL MEETING OF THE AMERICAN SOCIETY FOR MICROBIOLOGY; 2000

ASM

Scleroglucan is a homopolymer of glucose with a beta-1,3-linked backbone and side groups attached via beta-1,6-bonds at every third residue in the main chain. This exopolysaccharide (EPS) was first studied for chemically enhanced oil recovery but recently, more interest is being focused on its use as immunostimulant or antitumor agent. This biopolymer is produced in submerged cultures by fungi of the genus Sclerotium. Although typical batch cultures last for around 100 h or longer, in our case EPS production by Sclerotium rolfsii ATCC 201126 could be shortened to 48 h after culture medium optimization. Despite we reached very high yields (> 25 g/l EPS), two unexpected facts were observed, a reduced consumption of the carbon source and low levels of nitrogen assimilation. On the other hand, growing in batch mode to obtain high EPS yields usually involves extremely high viscosities to be achieved, condition which determines tedious, and frequently, inefficient downstream processing. The aim of our work was to study the possible effects on EPS production of different operational strategies, in particular changes or temporal gradients of the carbon source. Attempting to improve biopolymer yield with respect to the consumed carbon source and/or to lower biomass concentration to facilitate EPS recovery, two different strategies for fed-batch fermentation were performed. This involved single shot addition and continous feeding of the supplementary carbon source. In order to make some assessment of the impact of these processes, the optimization parameters; yield of scleroglucan on sucrose, productivity (g/l h) and specific productivity (g of EPS /g biomass h) were compared.