| As one of the most common heavy metals used in nature, the pollution of copper （Ⅱ） hasbecome one of the most serious environmental problem. Copper （Ⅱ） pollution comes mainlyfrom the industrial and agricultural wastewater, urban waste water, zinc ore mining wastewater, process of discharge and irrigation and copper sulfate pesticides pesticides. Copper （Ⅱ）were released into the atmosphere and soil environment which can cause harm to humanbeings, animals and plants.Aspergillus niger （A. niger） PQ is a strain that widely used to produce polygalacturonase（PG） in fermentation industry. The resistance of A. niger to Copper （Ⅱ） was determined by agrowth inhibition assay, the MTC and MIC of A. niger PQ to copper （Ⅱ） were0.05mmol/Land3mmol/L, respectively. The stress response of A. niger under conditions of3copper （Ⅱ）ion concentrations was investigated by determining the spore germination efficiency, thegrowth of the test fungi, the change in cellular soluble protein levels and antioxidant enzymes,the content of sugar and protein during the production of PG. The study showed that theinfluence of low copper （Ⅱ） concentration was not significant; however, the spore germinationefficiency, the growth of mycelia, the consumption of culture substrate and the production ofPG were significantly inhibited by high copper （Ⅱ） concentration.Meanwhile, a simultaneous increase in the levels of cellular soluble protein andsuperoxide dismutase （SOD） and a strong decrease in catalase （CAT） were induced by highconcentrations of copper （Ⅱ） ions, indicating that the stress response of A. niger PQ to copper（Ⅱ） was correlated with the efficiency of the antioxidative defence system. This study couldoffer useful informations for reducing the negative effect of copper （Ⅱ） on the production ofPG. According to the MTC of A. niger, CuSO4was add to the apple pomace and cottonseedmeal to the copper （Ⅱ） concentration of2.56mg/kg in order to study the effect of lowconcentration copper （Ⅱ） on the solid state fermentation of A. niger, the treatment withoutcopper （Ⅱ） was setted as control. Result showed that the influence of low copper （Ⅱ）concentration was not significant. However, depend on the phenomenon of copper pulutedgroups content of reducing sugar and total sugar in earlier stage of solid-state fermentationprocess were higher than the control, it illustrated that the low concentrations of copper （Ⅱ）has a certain influence to A. niger in early stage of growth, but the influencement disappearedsoon. This study also optimized the culture medium and fermentation conditions of A. nigerPQ to produce polygalacturonase （PG） using copper polluted apple pomace and cottonseedmeal in solid state fermentation with the method of monofactorial and orthogonal experiments.Result showed that when A. niger PQ was cultured at30C for48h in the optimized mediumcontaining10g apple pomace,10g cottonseed meal,0.2g （NH4）2SO4and0.06g K2HPO4inthe optimized conditions of moisture content of solid substrate60%（w/w） and20g drysubstrate/250ml flask, the activity of PG of copper polluted treatment group and controlgroups all reached around300,000U/g.In addition, the article also used crude enzyme solution of PG obtained by the solid-statefermentation on copper polluted medium above to study the enzymatic properties of theoptimum pH, optimum temperature, pH stability, thermal stability and enzymatic reactionkinetics of the copper polluted crude enzyme solution and crude enzyme solution withoutcopper. Result indicated that the enzymatic properties of copper polluted crude enzymesolution of PG and control showed no significant difference. Both of the PG crude enzymesolutions optimum temperature was45C and stable at60C, the optimum pH was5andstable in the acidic environment. This study also proved that using waste pomace insteadbran as the main raw material in the solid-state fermentation of A. niger PQ to produce PGwas feasible, which could not only reduce the cost of raw materials greatly, but also solve theapple pomace recycling problems to some extent. |
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