02Characterization of a__ bioflocculant produced by the marine myxobacterium Nannocystis sp.__ NU-2..pdf
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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 prop-
erties 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 floccula-
ting 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 constitu-
ents 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 FeCl
3
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.
Introduction
The interest in biotechnological methods for production
of bioflocculant lies in the possibility of using different
microorganisms to synthesize extracellular matter that
has found application in treating various industrial and
domestic sewages (Nakata and Kurane 1999; Toeda and
Kurane 1991). Bioflocculants are important in environ-
mental protection because of their biodegradability and
safety for ecosystems (Crescenzi 1995).
Extracellular substances, which are composed of
polysaccharides and proteins, are thought to mediate
cell-cell interactions or the adherence of cells to surfaces
(Roberts 1996). Their functions in flocculation and
adhesion are similar to some amphoteric polymer
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