Study On Poly-Г-Gutamic Acid Produced By Bacillus Subtilis ZJUTZY And Its Flocculating Character

Poly-γ-gutamic acid (y-PGA) was a compound of equal poly amino acid produced by microbe, was condensed by singleγ-glutamic acid, and was a new biopolymer materials due to its water-soluble and biodegradable characters. Recent years, it was widely used as a thickener, moisturizing agent and drug deliver in the area of industry, and was a multifunctional biological products with great prospect and development value.In this study a novel poly-γ-glutamic acid producing strain was isolated from natto and strains preserved in lab on the basis of broth viscidity as a marker of isolation. The product obtained from the broth of this novel isolate by organic solvent deposition and original purification was identified to be formed from glutamic acid through the process of hydrolyze and HPLC. This isolate named ZJUTZY was identified as a member of the genus Bacillus subtilis on the basis of standard morphological and physiological characters and nucleotide sequence analysis of 16S rDNA (GenBank database accession number EF694950). The result of SDS-PAGE showed that molecular weight of y-PGA was in the range from 40 kDa to 110 kDaA new method of examination was established using the character of reaction between 2, 4-dinitrofluorobenzene and amido, and absorption under 356 nm (uv). This method can determine the average quality and yield of poly-γ-glutamic acid synchronly. Then the effects of the fermentation conditions were studied by single factor test. The results showed that the optimum temperature, rotation speed and initial pH were 28℃, 200 r/min and 7.0 respectively. The optimum medium was glycerin 60 g/L, peptone 60 g/L, glutamic acid 160 g/L, K₂HPO₄ 0.5 g/L. The amount and average molecule weight of poly-γ-glutamic acid was 56.07 g/L and 59k Da, respectively.The flocculating activity of a bioflocculants poly-γ-gutamic acid (γ-PGA) were studied using Ca(OH)₂ as flocculating median .The result showed that the optimum flocculating condition was as following: y- PGA additional concentration 0.08 g/L, system pH 6.0, temperature 40℃. It was found that Mg²⁺,Ca²⁺,K⁺ could improve the flocculating activity ofγ-PGA. However, Fe³⁺,Co²⁺,Mn²⁺ would inhibit the flocculating activity ofγ-PGA. The maximal flocculating efficiency could reach 46.99 %.