Breeding Of γ-Polyglutanic Acid High-yielding Strain And The Research Of Solid-state Fermentation

γ-PGA is a type of macromolecule amino acid polymer which could be deg raded by organisms.Nowadays,the focus on environmental safety draws signifi cant attention to the γ-PGA due to features of innocuity,free from pollution a nd edibility.Furthermore,developmental and applicational prospects of γ-PGA i n the fields of agriculture,medical treatment,materials and food etc.for the e xcellent characters of hygroscopicity,absorbability,biocompatibility and plasticit y.In this research,a higher-yield strain of γ-PGA producing strains was bred by mutagenesis.The solid-state fermentation substrate of strains and process pa rameters were optimized.In the agricultural aspect,the biological effects of sol id-state fermentation of γ-PGA have also been studied.The main research conten ts are as follows:1.Taking the YP-11 stored in laboratory as the original strain which was proc eeded with chemical mutagenesis（EMS）,relatively high-yield YE-5 strain which could produce 20.33 g ·L^﹣1 γ-PGA with 13.3% increased yield compared to ori ginal strain was obtained.The YE-5-2 strain then was conducted by compound mutation（UV-DES）in order to gain higher production.A genetically stable st rain YE-5-2 producing 23.74 g ·L^﹣1 γ-PGA with 16.77% increased production c ompared to YE-5 was obtained through several times of mutagenesis.2.The impact of different substrates and supplemental matrix on γ-PGA solid-s tate fermentation was studied by taking the YE-5-2,a producing strain of γ-PGA,as a strain.The optimum ratio of fermentative matrix is W（soybean flour）: W（straw）= 20:3.The optimum condition of the solid-state fermentation is as follows: initial moisture 60%,initial p H 7～7.5,inoculum size 10%,fermentation temperature 37℃,culture time 64 h.The γ-PGA solid fermentation’s optimum formula of inor ganic salts,carbon and nitrogen sources addition was confirmed hrough single-f actor experiment,orthogonal design analysis and response surface methodology,which is Mg SO₄ · 7H₂O 0.25 g ·L^﹣1,Mn SO₄ · H₂O 0.1 g ·L^﹣1,CaCl₂ 0.15 g ·L^﹣1,Fe Cl₃ · 6H₂O 0.06 g ·L^﹣1,glycerol 10 g·kg^-1,sodium citrate 20.39 g·kg^-1,NH₄NO13.8 g·kg^-1.The yield of γ-PGA was 137.19 g · L^-1under the o ptimal condition of fermentation substrate and culture.3.Biological effects of γ-PGA was preliminary studied by selecting three teste d materials of corn,wheat and calendula.The biomass of the corn seedlings c ould be effectively increased by γ-PGA.The effect of γ-PGA on increasing the biomass and chlorophyll content of corn is more significant under the low-nut rient condition.γ-PGA-soaked wheat shows a significant facilitation on root gro wth and activity.The largest root length and underground dry weight were incr eased roughly by 60%,and the root activity was improved by 22.87%.The e mergence rate of calendula on fermented straw disposed by γ-PGA was greatly enhanced.When the concentration of γ-PGA was 0.005 g · L^-1,the emergence rate reached 91.67%,which is 10% higher than the emergence rate of peat.Th e desire of a low-cost alternative fermented straw to peat was achieved.