Abstract

We have identified an ethanol-assimilating bacterial strain of Pseudomonas stutzeri that produces copious amounts of an exopolysaccharide when cultured in 5% ethanol under the alkaline condition of pH 10. The objective of this study was to evaluate the potential industrial applications of this exopolysaccharide designated BL58 by characterization of its chemical, rheological and physiological properties. The polymer was purified from the 72 h culture broth with periodic feeding of ethanol and the chemical structure of the polymer was determined by NMR spectroscopy, GC-mass spectrometry and alditol-acetate analysis of methylated hydrolyzates. The analytical data showed the presence of glucose, mannose and 3-O-carboxyethyl rhamnose and suggested that the main chain consists primarily of 1,4-linked glucose and mannose units with unique branching of 3-O-[(R)carboxyethyl] rhamnose at the 3 position of the glucose unit, a structure not previously reported. The polysaccharide has an average molecular weight of 1,800 kDa and the rheological behavior of the aqueous solution from high viscosity sol to viscoelastic gel depended on temperature and pH. Although no overt cytotoxicity was observed, the polymer displayed anti-proliferative activity when tested with leukemia, liver carcinoma and normal pulmonary cells, indicating potential pharmaceutical applications.

Keywords: Pseudomonas stutzeri; Exopolysaccharides; 3-O-carboxyethyl rhamnose; Rheological characterization; Acute toxicity; Anti- proliferating activity; Leukemia cells; Liver carcinoma cells