Production And Flocculanting Properties Of Poly γ-glutamic Acid From A Screening Bacillus Sp.

Poly γ-glutamic acid (γ-PGA) is a water-soluble, biodegradable, elible and non-toxic toward humans and the environment. Theirefore, potential applications of y-PGA and its derivatives have been of interest in the past few years in a broad range of industrial fields such as food, cosmetics, medicine and water treatment. y-PGA and its derivatives offer a wide range of unique applications including being used as biopolymer flocculants, thickener, humectant, sustained-release material, drug carrier, highly water absorbable hydrogels, heavy metal absorber.A bacterium with high γ-PGA productivity was isolated from the cantaloupe juice,This bacterium could be classified as Bacillus sp. B-53.The production of y-PGA was greatly influenced by the composition of medium and culture condition. A number of experiments were done to evaluate the culture conditions, such as carbon, nitrogen, mineral salts, medium pH, temperature, time, inoculation amount, seed age and aeration. The results shew the optimum culture conditions were as follows (g/L) : Acetic acid 12, Glycerol 80, L-Glutamate 20, (NH4)2SO4 7, K2HPO4 0.7, MgSO4-7H2O 0.5, MnSO4-H2O 0.3, CaCl2 0.25, FeCl3.6H2O 0.02, initial pH 6.5, temperature 37℃, seed age 48h, inoculation amount 4%, culture time 96h.γ-PGA was purified by ethanol precipitation, acetone precipitation and dialysis. The purified material showed a absorption peak at 212nm, and was only composed of Glu. The Mw could be detected through SDS-PAGE, and its Mw was about a molecular mass between 440kDa with 669kDa. Study on the isolated y-PGA 's property shew that the y-PGA had good stability under 90 癈 and was rapidly hydrolyzed by heating at 100℃,and the hydrolysis of γ-PGA in the aqueous solution by heating was a random chain scission. Maximum viscosity was observed under conditions of neutral pH.This bioflocculant y-PGA efficiently flocculated various organic and inorganic suspensions. It flocculated a suspended kaolin suspension without cations, although its flocculating activity was synergistically stimulated by the addition of ca2+ (0.2%) and rose from 67.31% to above 90%.The sunergistic effect of ca2+ was most effective at neutral pH ranges. The high productivity and versatile application of γ-PGA make its development as a new biodegradable harmless bioflocculant economical and advantageous.