| 94 strains sheathed bacteria were successfully isolated from 150 water samples by two enrichment methods combined with three isolation methods. the experiment showed that when the quantity of sheathed bacteria in water sample is low, enrichment method is better for isolation, whereas when the quantity of sheathed bacteria in water sample is high, plate streaking and plate dropping maybe more effective. If there is more Gram-positive bacteria in water sample, putting 0.5u/L Penicillin in the enrichment medium is good for isolation.Rapid screening of sheathed bacteria with Fe2+ oxidizing activity was done by Winogradsky liquid tube method, and 24 strains were selected .In the 24 strains mentioned above, FC9901 was the best strain which can produce oxidizing enzyme with the highest activity by further screening. The study showed that rapid screening result is consistent with further screening result. It showed that Winogradsky liquid tube method can be used as a basis to judge oxidizing ability of strain.The morphological, culture and physiological features of the strain were studied by poly- characterization method. and based on Bergy,s Manual of Determinative Bacteriology(9thed), FC9901 was identified as Sphaerotilus natans in the Sphaerotilus genus. The study on some preservation methods of sheathed bacteria showed that distilled-water preservation method is a effective and simple method. Study on the Fe2+ oxidizing mechanism of sheathed bacteria showed that the trophy kind of sheathed bacteria is chemoorganotrophs. The energy is come from oxidize of organic, not gain energy from Fe2+ oxidation .Fe2+ oxidizing activity in the spent culture medium was sensitive to pH, heat, NaN3, pronase, SDS, NaCl, HgCl2. It showed that Fe2+oxidation is a kind of enzyme catalyzed process. The study on localization of activity showed that Fe2+ oxidizing activity is a extra cellular enzyme. Based on above experiment ,We study the optimal medium and condition of enzyme production. The optimum medium consisted of 10g citrate per litre ,1.2g NaNO3 per litre ,0.5gMgSO4 per litre,0.5g K2HPO4?7H2O per litre ,0.005g CaCl2per litre,0.0005gZnSO4?7H2O per litre. The optimum condition of shaking flask producing enzyme were the temperature 30℃ ,initial pH 7.0, medium volume 50ml medium /150ml flask, inoculum's concentration is 2%, rate of shaking is 150rpm,culture period 72 hours. The enzyme producing activity could reached maximum level, oxidation rate could reached 91.5% after modification of medium and condition. It was increased 30% to first. Crude oxidizing enzyme was obtained from ammonium sulfate precipitation and dialyze. Biochemical properties of the enzyme were examined as follows, the optimum temperature and pH for oxidizing activity was 30℃ and7.5.The enzyme was easy to lose activity in strong acid or strong alkaline circumstance . The enzyme could keep its original activity after 150min at 30℃.But it was sensitive to high temperature. About 65% activity of the original activity is lost after 5 min at 50℃. Different metal ions showed different effects on the oxidizing activity :Ca2+ ,Mg2+ ,Zn2+ increased the oxidizing activity ,whereas Cu2+,Hg2+ ,Al3+ cause inhibition .K+ ,Na+ ,Fe2+ effected on the activity is not obvious.
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