Microbial Fermentation For The Production Of Poly(Glutamic Acid) And Its Application In Water Treatment

Poly(glutamic acid)is an extracellular polymer produced by microorganisms,which iscomposed of D-glutamic acid,L-glutamic acid or a mixture acid of both.Currently,biosynthesis of PGA has been considered to be a promising new polymer material.PGA is biodegradable,non-toxic,non immunogenicity and so on.Therefore it has been widely used in food,medical,agriculture,environment and other industries.In this study,PGA high-yield strains were screened from a large number of samples.Morphological,molecular biology and physiological and biochemical identification were performed,and the optimal strains were selected as the research object.The fermentation medium and fermentation conditions were optimized.Finally,the application of PGA used as a bioflocculant in the treatment of wastewater containing heavy metal ions was discussed.The main results of this paper were as follows:(1)Two strains T-2 and J-1 were selected for the production of PGA from more than200 strains which isolated from 80 samples.The molecular weight distribution of PGA produced by the two strains were in 10-60 k Da.Morphological observations,physiological and biochemical identification,and 16 S r RNA sequencing analysis were carried out,and the two strains T-2 and J-1 were all identified as Bacillus,and were named DLF-15161 and DLF-15162,respectively.(2)The fermentation medium and fermentation conditions of Bacillus sp.DLF-15161 were optimized by single factor experiment and response surface design.The final optimized medium composition was as follows: sodium glutamate 90 g/L,NH4 Cl 7g/L,K2HPO4 0.5g/L,Mg SO4 0.5g/L,Ca Cl2 0.15g/L,Mn SO4 0.1g/L,trisodium citrate 54g/L,tryptone 44g/L;fermentation conditions: 37?,speed 190 rpm,p H 6.8,Liquid volume 37 m L,inoculation amount of 3%.The average yield of PGA was 118.3g/L in 48 h under the optimal conditions,and the yield of PGA was increased by 75.3g/L compared with that before optimization.(3)The application of PGA in water treatment was preliminarily studied,and the results showed that the products had a certain flocculation activity and metal ions adsorption capacity.With kaolin as the medium,the highest flocculation could be up to 81%.When the initial concentration of Cu2 + was 100?g/m L,the maximum adsorption capacity(6.62mg/g)was reached at 5h,and reached the maximum adsorption capacity(22.28mg/g)at the initial concentration of Cr6 + at 1000mg/L at 6h.After experiment,high yield strains were obtained and the flocculation was verified,which provided the theoretical basis for future application and industrialization.