Optimization of exopolysaccharide production from Pseudomonas stutzeri AS22 and examination of its metal-binding abilities

Abstract

Aims: To investigate the effect of culture conditions and medium components on exopolysaccharide (EPS) production by Pseudomonas stutzeri AS22 and to access the EPS performance as a metal-binding exopolysaccharide.

Methods and results: The EPS production conditions of Ps. stutzeri AS22 in submerged culture were optimized using two approaches for EPS quantification, and its metal-binding capacity was evaluated using both single and mixed metal ions systems. Maximum EPS level was achieved after 24 h of incubation at 30°C with an initial pH of 8.0, 250 rev min(-1) stirring level and 10% inoculum size. 50 g l(-1) starch, 5 g l(-1) yeast extract, 0.5 g l(-1) NaCl, 1.4 g l(-1) K2 HPO4, 0.4 g l(-1) MgSO4, 0.4 g l(-1) CaCl2 and 1 g l(-1) mannose were found to be the most suitable carbon, nitrogen, mineral and additional carbohydrate sources, respectively. From metal-binding experiments, the crude EPS showed interesting metal adsorption capacity adopting the order Pb >> Co > Fe > Cu >> Cd. Lead was preferentially biosorbed with a maximal uptake of 460 mg g(-1) crude EPS.

Conclusions: Under the optimal culture requirements, EPS level reached 10.2 g l(-1) after 24 h of fermentation, seven times more than the production under initial conditions. According to the metal-binding assay, the crude EPS has potential to be used as a novel biosorbent in the treatment of heavy metals-contaminated water.

Significance and impact of the study: Our results are interesting in terms of yield as well as efficiency for the potential use of the Ps. stutzeri exopolysaccharide as a metal-absorbent polymer in the bioremediation field.

Keywords: Pseudomonas stutzeri AS22; bioremediation; exopolysaccharide; heavy metal adsorption; optimization; submerged culture.