Studies On The Screening And Identification Of Bacteria Producing Thermo-inducible Gel And The Physicochemical Properties Of The Product

Systematic studies on the strain Q9415 and its exopolysaccharide PS-9415 were carried out in this dissertation. The results are mainly as following:1. The strain Q9415 was screened by Czapek-Dox medium from soil samples obtained in Hubei province. A white elastic gel was formed by heating its fermented broth to 90℃ and cooling down to ambient temperature. The organism was identified as Agrobacterium radiobacter according to the Bogey's Manual of Systematic Bacteriology.Round, entire, convex, opaque, mucoid and milk white colonies of Q9415 strain appear in 3⁴ days at 30℃ on YM agar, the diameter of the colonies is about 6 mm.The strain Q9415 is a gram-negative, nonsporeforming, immotile, aerobic, rod-shaped organism with 1² subpolar flagellum.The organism grows at temperature between 4℃ and 42 ℃ and at pH value 4 and 9. Pigment production is not observed. The size of cell is about 1.2¹.8μm×0.5⁰.8μm. Oxidase, catalase, ONPG lysase, urease is positive. Citrate is utilized. Arginine dihydrolase, lysine decarboxylase and orinithine decarboxylase is negative. Gelatin, starch, Tween 80 is not hydrolyzed. The test of nitrate reduction, H₂S, indole is negative. V-P test is positive. The strain Q9415 is fermentative. In litmus milk, alkaline is produced, the milk is peptonized and serum circle appeared. Accumulation of poly-beta-hydroxybutyrate (PHB) is observed in later period of incubation.2. The organism Q9415 was found to excrete exopolysaccharide after the logarithmic growth phase was finished which indicated that the fermentation of EPS is non growth-coupled By using the medium containing sucrose 3%, peptone 0.2%, K₂HPO₄0.05%. MgSO₄0.01%, MnSO₄0.01% CaCO₃0.01%, Holo salts 0.01%, Tween 80 0.2%, with pH 7.0⁷.2 and rotation speed of 180r/min, the maximum viscosity and EPS yield of 1.50 Pa s and 14.02 g·L^-1 with carbon conversion efficiency of 46.73% were obtained after incubation in flask at 32℃ in the initial stage (0²0h) and 28℃ in the subsequent stage (21 ⁹6h).The organism was scaJed-up in 5L fermentor with supplemental sucrose and increased inoculum volume and dissolved oxygen, which resulted in a higher output of polysaccharide and a shorter fermentation time of about 50⁶0h.