Characterization of a bioflocculant produced by the marine myxobacterium Nannocystis sp. NU-2

Abstract.

The marine myxobacterium strain NU-2, which can grow on high concentrations (up to 7%) of NaCl, was isolated from a salt soil sample collected from the coast of the Huanghai Sea, China. Morphological properties and 16S rDNA sequence analysis indicated that the isolate is a novel species related to the genus Nannocystis. Nannocystis sp. NU-2 produced a new kind of flocculating substance in a starch medium with a yield of 14.8 g l^–1. The NU-2 flocculant was composed of 40.3% proteins and 56.5% polysaccharides, of which glucose, mannose and glucuronic acid were the principal constituents in the relative proportions of 5:4:1. The flocculation activity of the NU-2 flocculant depends strongly on cations such as Fe³⁺ and Al³⁺. When a 30 mg l^–1 FeCl₃ solution is present in kaolin clay suspension, 30 mg l^–1of the flocculant produced a high flocculating activity value of 90%, which remained unchanged over an extensive pH range (pH 2.0–13.0). The flocculant was tested for its ability to bleach dyeing liquors, and the bleaching activities were 98.2% for acid red in 100 mg l^–1of the flocculant and 99.0% for direct emerald blue in 50 mg l^–1of the flocculant under test conditions. Use of the flocculant to bleach basic pink and cation emerald blue liquors was not effective.