Sustainable Exopolysaccharide Production by Rhizobium viscosum CECT908 Using Corn Steep Liquor and Sugarcane Molasses as Sole Substrates

Microbial exopolysaccharides (EPS) are promising alternatives to synthetic polymers in a variety of applications. Their high production costs, however, limit their use despite their outstanding properties. The use of low-cost substrates such as agro-industrial wastes in their production, can help to boost their market competitiveness. In this work, an alternative low-cost culture medium (CSLM) was developed for EPS production by Rhizobium viscosum CECT908, containing sugarcane molasses (60 g/L) and corn steep liquor (10 mL/L) as sole ingredients. This medium allowed the production of 6.1 ± 0.2 g EPS/L, twice the amount produced in the standard medium (Syn), whose main ingredients were glucose and yeast extract. This is the first report of EPS production by R. viscosum using agro-industrial residues as sole substrates. EPS(CSLM) and EPS(Syn) exhibited a similar carbohydrate composition, mainly 4-linked galactose, glucose and mannuronic acid. Although both EPS showed a good fit to the Herschel–Bulkley model, EPS(CSLM) displayed a higher yield stress and flow consistency index when compared with EPS(Syn), due to its higher apparent viscosity. EPS(CSLM) demonstrated its potential use in Microbial Enhanced Oil Recovery by enabling the recovery of nearly 50% of the trapped oil in sand-pack column experiments using a heavy crude oil.