Exopolysaccharide biosynthesis by a newly-isolated Cryptococcus laurentii SD7 in sugar cane molasses and inorganic nitrogen sources

Microbial polysaccharides are of great biotechnological and industrial importance due to their functional properties and wide range of applications in the food, cosmetic and pharmaceutical industries. For the microbial synthesis of polysaccharides, f by-products or agro-industrial residues has been widely used as alternative substrates to reduce production costs. In this study, we evaluated several sources of carbon (sucrose, lactose, glucose, glycerol and sugarcane molasses at 5%) and nitrogen (organic and inorganic at 1%) as substrates for the biosynthesis of exopolysaccharides (EPS) by Cryptococcus laurentii SD7. The best substrates were sugarcane molasses and the combination of (NH4)2SO4 and NaNO3 salts. To study the effect of combining these substrates and optimize EPS production, the Central Composite Design (CCD) 23 methodology was used, resulting in 17 trials, where the concentration of sugarcane molasses varied from 1% to 9% and nitrogen sources varied from 0.2% to 0.8%. The factorial design showed that NaNO3 did not affect EPS production, but sugarcane molasses and (NH4)2SO4 were effective at concentrations of 9% and 0.2%, respectively, reaching EPS production of 11.0 g L-1. The results were very promising, showing that C. laurentii SD7 has high potential for EPS production on low-cost substrates.