Study On Mutation Breeding Of Gellan Gum-producing Bacteria And Its Fermentation Technigues

As a new microbial exocellular polysaccharide, gellan gum is produced by aerobic fermentationof Sphingomonas paucimobilis ATCC31461. Compared with agar and carrageenan, gellan gum hasadvantages of low consumption, thermal stability, superior taste properties, high transparency, good acidresistance, etc, and it’s already widely used in food, agriculture, chemical, medicine and other fields. Butnow there are still some problems in industrial production of gellan gum, which lead to the high productioncost, and limited the application. Therefore proper fermentation technique to reduce the cost and improvegellan gum’s quality and output is extremely needed.Sphingomonas paucimobilis FJ-09is used as original bacterial strain in this paper, yield of crudegum and viscosity of fermentation broth are settled as detection parameters in this experiment, single factormutagenesis and composite mutagenesis are done to this strain, and finally we got mutant strain namedFJ-H6with high gellan gum yield. Then, we optimized seed culture medium composition, cultivationcondition, initial carbon sources of fermentation medium, method of carbon sources addition. The maincontents are as follows:(1) With FJ-09as the target, we did mutation breeding research. Ultraviolet rays, microwaveand diethyl sulfate were all proved effective in this mutagenesis, and on this basis, strategy of compositemutagenesis was designed, as a result, FJ-H6with gellan gum yield of9.03g/L was obtained, this value was21.0percent higher than the original strain. and this strain had a good genetic stability.(2) Determination of FJ-H6growth curve, provided process parameters for later fermentationoptimization. By method of single factor and orthogonal test, we optimized seed culture mediumcomposition. Finally, it determined that seed culture medium composition of:2.5%glucose,0.5%solublestarch,0.5%peptone,0.3%sodium nitrate,0.5%NaCl, and at pH7.0, we could get the maximum gellangum yield.(3) By method of single factor and orthogonal test, we optimized fermentation conditions ofFJ-H6. Finally, it determined that the optimized condition was: seed cultivation time of18h, inoculatingquantity of8%, liquid medium volume of25mL/250mL, initial pH of7.5, fermentation temperature of 28℃, speed of220r/min.(4) By study of initial carbon source of fermentation medium and method of carbon sourceaddition, we determined that the best initial carbon source was6%maltose, the best method of carbonsource addition was adding2.5%maltose after fermentation time of18h, and the gellan gum yield was13.86g/L, it’s18.8%higher than the control group.