Characterization of a bioflocculant produced by Citrobacter sp TKF04 from acetic and propionic acids

A bacterial strain, TKF04, capable of producing a bioflocculant from acetic and/or propionic acids was isolated from a biofilm formed in inside a kitc hen drain. It was identified as a Citrobacter based on its morphological an d physiological characteristics and the partial sequences of its 16S rRNA, TKF04 produced the bioflocculant during the logarithmic phase of growth, an d the optimum temperature and pH for the bioflocculant production were 30 d egrees C and 7.2-10.0, respectively. It could utilize some organic acids an d sugars for its growth as the sole carbon sources when yeast extract was s upplemented; however, only acetate and propionate were found to be good sub strates for the bioflocculant production. The crude bioflocculant could be recovered from the supernatant of the culture broth by ethanol precipitatio n and dialysis against deionized water. It was found to be effective for fl occulation of a kaolin suspension, when added at a final concentration of 1 -10 mg/l, over a wide range of pHs (2-8) and temperatures (approximately 3- 95 degrees C), while the co presence of cations (Na+, K+, Ca2+, Mg2+, Fe2+, Al3+ Or Fe3+) did not enhance the flocculating activity. It could efficien tly flocculate a variety of inorganic and organic suspended particles, incl uding kaolin, diatomite, bentonite, activated carbon, soil and activated sl udge. It contained glucosamine as the major component, and the molecular we ight was estimated to be between 232 and 440 kDa by gel filtration. The obs ervation that the flocculating activity was completely lost following chiti nase treatment and its analysis with a Fourier transform infrared spectrome ter suggested that the bioflocculant is a biopolymer structurally-similar t o chitin or chitosan.