Improved production of an acidic exopolysaccharide, the efficient flocculant, by Lipomyces starkeyi U9 overexpressing UDP-glucose dehydrogenase gene

Abstract

In order to increase content of glucuronic acid in the exopolysaccharide (EPS) and its flocculating activity, an UDP-glucose dehydrogenase gene was overexpressed in Lipomyces starkeyi V19. The obtained U9 strain could produce 62.1 ± 1.2 g/l EPS while the V19 strain only produced 53.5 ± 1.3 g/l EPS. The compositions of monosaccharides (mannose, glucuronic acid and galactose) in the purified EPS (U9-EPS) from the U9 strain contained 3.79:1:5.52 while those in the purified EPS (V19-EPS) were 3.94:1:6.29. The flocculation rate of the U9-EPS on kaolin clay reached 87.9%, which was significantly higher than that (74.7%) of the V19-EPS while the decolorization rate of Congo Red (CR) by the U9-EPS reached 94.3%, which was significantly higher than that of CR by the V19-EPS (86.23%). The results showed that the purified bioflocculant U9-EPS had effective flocculation of kaolin clay. The U9-EPS also had high ability to flocculate the polluted river water and decolorize Congo red.