Exobiopolymer from polyhydroxyalkanoate-producing transgenic yeast

Abstract

Recently, the wild type yeast Kloeckera sp. strain KY1 was equipped in their cytoplasm with the phaABC operon containing genes phbA, phbB and phbC of the PHA biosynthetic pathway of Ralstonia eutropha. Unpredicted, resulted transgenic yeast strain KY1/PHA was able to synthesize another exopolymer beside the production of PHA. Subsequently, produced exopolymer was subject for further identification, characterization and analysis. Partial purification of exopolymer was performed and characterized as glycoprotein. HPLC analysis of the polymer revealed the presence of a fructose chain. The functional group analysis by FT-IR spectroscopy showed the presence of carboxyl, hydroxyl and amid groups. The exopolymer was soluble in water and insoluble in any tested organic solvents and could flocculate kaolin suspension (5 g/l) over a wide range of pH (pH 3 to 9) and temperature (5 to 50°C) tested in the presence of CaCl₂. The highest flocculation activity of 99% for kaolin suspension was achieved at a dosage of 13 mg/l. Thus, it is possible that this glycoprotein could be substituted for a commercial polymer with respect to flocculation.

Key word: Transgenic yeast, bioflocculant, exopolymer, glycoprotein,  spectroscopic analysis.