Strain Breeding And Fermentation Conditions Optimization Of The Polysaccharide Produced By Bacillus Mucilaginosus

A new viscosity microbial exopolysacchride named Bacillus mucilaginosuspolysaccharide is produced by Bacillus mucilaginosus in trace nitrogen medium, and wascalled BMPS in this study. Because of its special rheological properties and extraordinarymoister-holding function, it will have a broad application in food, medicine and cosmeticindustry. To improve its production, breeding of B. mucilaginosus for BMPS produced usingcompound mutation and fermentation conditions optimization of high-yield mutation werestudied, and then the properties of the BMPS were analyzed. The main results were asfollows:1. B. mucilaginosus CGMCC5766preserved in our laboratory was used as the originalstrain for stepwise mutations. The mutagenized strain named UD1-6was obtained by UVirradiation of15min and1%(v/v) DES of UV-DES compound mutation. Then the maximumconcentration of BMPS reached6.94g/L, which was25.5%higher than that of original strain.2. The fermentation medium compositions of UD1-6were optimized byPlackett–Burman experiment and response surface analysis after single factor optimization.The optimized medium compositions were determined as (g/L): sucrose61.31, urea0.3,CaCO35.06, K2HPO4·3H2O0.17, MgSO4·7H2O0.6and NaCl0.4. The optimized cultureconditions were:500mL shake flasks containing50mL medium, inoculation age24h,inoculums concentration4%and initial pH7.0at30-32°C for60h. Under the optimizedconditions, the BMPS concentration in5-L fermenter reached23.46±0.76g/L, which was2.4times than that before optimization.3. Study of the BMPS structure showed that it contained both neutral sugar componentsand acid sugar components. As neutral sugar components, the molar ratio of mannose, glucoseand galactose contained in BMPS was2:1.6:1. And as acid sugar components, the proportionof uronic acid contained in BMPS was almost21.3%±3.6. Infrared spectrum analysisdemonstrated the presence of carboxyl groups. Furthermore, the molecular weight of theBMPS was about6×106Da by HPGFC.4. The rheological properties of BMPS was discussed. The solution showed acharacteristic of pseudoplastic non-Newtonian behavior. The viscosity of BMPS solution wasimproved with the concentration increasing and had a good temperature resistance attemperatures from25°C to100°C. The maximum viscosity was observed at pH7.0and itwould become a weak gel at pH12.0. The addition of NaCl, KCl, MgCl2and CaCl2remarkably decreased the viscosity. The precipitation in alkali was attained in the presence ofhigh-priced such as Fe3+and Pb2+. The BMPS had synergy with Sodium alginate, Carrageenan,Locust bean gum, Guar gum, Xanthan gum and Arabia gum. 5. Moisture-absorption and moisture-retention capacity in vitro of BMPS were tested.The results showed that BMPS and hyaluronic acid (HA) performed analogic moisturizingcapacity. At the same time, under the condition of relative humidity (RH) of30%, themoisture-retention capacity of the BMPS was a little higher than that of HA.