不同形态铁对脱色希瓦氏菌S12偶氮还原的影响

Effects of Iron on Azoreduction by Shewanella decolorationis S12

以脱色希瓦氏菌(Shewanella decolorationis)S12为材料,研究了不同形态铁对其厌氧偶氮还原的影响.结果表明,Fe(Ⅲ)对偶氮还原的影响与其形态及浓度直接相关.不可溶性Fe(Ⅲ)对偶氮还原表现延缓作用,0.05～2 mmol/L的Fe2O3均延缓0.2mmol/L的苋菜红还原,但作用效果不随Fe2O3浓度的增加而成比例强化.而对于可溶性Fe(Ⅲ),0.4 mmol/L浓度以下对0.2mmol/L的苋菜红还原具有一定的促进作用,作用效果与其浓度变化不呈线性关系.1 mmol/L浓度以上则表现为抑制作用,浓度越高其抑制作用越强,这种现象在电子供体不足的情况下尤为明显.进一步研究发现,可溶性Fe(Ⅱ)和Fe(Ⅲ)均具有缓解双香豆素对醌循环的抑制作用而促进偶氮还原.由此推测,可溶性铁对偶氮还原的促进作用是由于这些化合物的细胞透过性,在低浓度条件下形成Fe(Ⅱ)Fe(Ⅲ)氧化还原循环,充当电子传递的中间媒介,通过发挥电子穿梭功能从而促进细菌的偶氮还原.而高浓度条件下可溶性Fe(Ⅲ)优先大量接受来自电子供体的电子而与偶氮化合物竞争,其电子穿梭功能被掩盖,从而抑制偶氮还原.对于不可透过细胞的不可溶性Fe(Ⅲ),只是作为胞外电子受体与强极性的偶氮化合物竞争电子从而仅仅呈现延缓作用.通过对铁的形态及浓度的适当选择与控制可以获得更高效的偶氮还原效率.

The effects of soluble and insoluble Fe（Ⅲ） on anaerobic azoreduction by Shewanella decolorationis S12 were examined in a series of experiments.Results showed that the effects of iron on anaerobic azoreduction depended on the solubility and concentration of the compounds.Azoreduction was inhibited by insoluble Fe（Ⅲ） and 0.05-2 mmol/L Fe2O3 all decelerated the azoreduction activity of 0.2 mmol/L amaranth,but the increase in the concentrations of Fe2O3 did not cause an increasing inhibition.Soluble Fe（Ⅲ） of which concentration less than 0.4 mmol/L enhanced azoreduction activity of 0.2 mmol/L amaranth but there was no linear relationship between the concentration of soluble Fe（Ⅲ） and azoreduction activity.Soluble Fe（Ⅲ） of which concentration more than 1 mmol/L inhibited azoreduction activity of 0.2 mmol/L amaranth and an increasing concentration resulted in an increased inhibition.The inhibition was strengthened under the conditions of limited electron donor.On the other hand,soluble Fe（Ⅲ） and Fe（Ⅱ） could relieve the inhibition of azoreduction by dicumarol which blocked quinone cycle.It suggests that in addition to quinone cycle,there is a Fe（Ⅲ）←→Fe（Ⅱ） cycle shuttling electrons in cytoplasmic and periplasmic environment.That is the reason why low concentration of soluble Fe（Ⅲ） or Fe（Ⅱ） can enhance azoreduction of S.decolorationis S12.It also indicates that insoluble Fe（Ⅲ） and high concentration of soluble Fe（Ⅲ） do compete with azo dye for electrons once it acts as electron acceptor.Thus,when iron and azo dye coexisted,iron could serve as an electron transfer agent or electron competitive inhibitor for anaerobic azoreduction under different conditions.High efficiency of azoreduction can be achieved through controlling the solubility and concentration of irons.