伍玲麗,張曉雪,舒昆慧,司友斌

兩種粒徑納米銀對(duì)的毒性效應(yīng)

伍玲麗,張曉雪,舒昆慧,司友斌*

(安徽農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院,農(nóng)田生態(tài)保育與污染防控安徽省重點(diǎn)實(shí)驗(yàn)室,安徽 合肥 230036)

為明晰不同粒徑納米銀(AgNPs)對(duì)歐洲亞硝化毛桿菌()的毒性效應(yīng),采用室內(nèi)培養(yǎng)方式,探究10nm和50nm的AgNPs對(duì)生長(zhǎng)、氮轉(zhuǎn)化能力、細(xì)胞結(jié)構(gòu)、活性氧生成和功能基因表達(dá)的影響.結(jié)果表明,AgNPs暴露抑制生長(zhǎng),隨著暴露時(shí)間的延長(zhǎng),細(xì)菌生長(zhǎng)抑制率增加,在4h達(dá)到最大值;培養(yǎng)基中NH4+向NO2-轉(zhuǎn)化速率減緩,的銨態(tài)氮轉(zhuǎn)化能力降低;掃描電鏡(SEM)圖像顯示AgNPs造成部分細(xì)菌表面塌陷且有孔洞,細(xì)胞膜受損嚴(yán)重;透射電鏡(TEM)圖像顯示AgNPs造成細(xì)菌內(nèi)部核物質(zhì)消融,細(xì)胞質(zhì)膜界限模糊;流式細(xì)胞儀(FCM)檢測(cè)發(fā)現(xiàn)AgNPs增加細(xì)胞內(nèi)活性氧的生成;qRT-PCR技術(shù)對(duì)AgNPs暴露后功能基因表達(dá)進(jìn)行測(cè)定,發(fā)現(xiàn)AgNPs抑制功能基因的轉(zhuǎn)錄表達(dá).綜上所述,AgNPs通過(guò)與細(xì)胞膜相互作用和產(chǎn)生氧化應(yīng)激損傷,抑制和的表達(dá),進(jìn)而影響銨態(tài)氮轉(zhuǎn)化過(guò)程,且小粒徑AgNPs的毒性強(qiáng)于大粒徑.

納米銀；；氧化應(yīng)激；、、基因豐度；氨氧化

納米銀(AgNPs)是尺寸范圍為1~100nm的原子簇,由約20~15000個(gè)Ag原子組成,與固相Ag相比,具有電導(dǎo)率和熱導(dǎo)率高、化學(xué)性質(zhì)穩(wěn)定、催化活性強(qiáng)等特性[1],廣泛應(yīng)用于電子器件、化妝品、生物醫(yī)學(xué)和紡織業(yè)等方面[2].AgNPs的抗菌作用已被廣泛描述,一些研究認(rèn)為AgNPs釋放的Ag+是其毒性的主要原因,自身的粒子特異性可以忽略不計(jì)[3-5],也有研究表示AgNPs的毒性主要取決于粒徑大小[6].據(jù)報(bào)道,20~80nm AgNPs的毒性主要來(lái)源于Ag+的釋放,而10nm AgNPs由于尺寸較小,更易穿透細(xì)菌的細(xì)胞膜,毒性主要?dú)w于自身的尺寸效應(yīng)[7-8].AgNPs可以與細(xì)胞膜上蛋白質(zhì)結(jié)合,與含有氧、磷、氮或硫原子的電子供體形成絡(luò)合物,導(dǎo)致膜結(jié)合酶等蛋白質(zhì)失活,也可干擾呼吸鏈并阻礙能量的產(chǎn)生[9-10].此外,AgNPs會(huì)造成細(xì)胞膜脂肪酸組成改變,改變膜的流動(dòng)性[11],導(dǎo)致細(xì)胞內(nèi)容物的泄漏[12].AgNPs還可以與細(xì)菌的遺傳物質(zhì)結(jié)合,阻斷翻譯和轉(zhuǎn)錄[13-14],也有研究表明AgNPs進(jìn)入細(xì)胞內(nèi)造成活性氧物質(zhì)(ROS)累積導(dǎo)致膜損傷和基因毒性[15].

環(huán)境中的氨氧化菌群主要負(fù)責(zé)驅(qū)動(dòng)NH4+-N向NO2--N的轉(zhuǎn)化,由于其獨(dú)特的生理特性對(duì)環(huán)境因子變化較為敏感[16].歐洲亞硝化毛桿菌()為氨氧化模式菌株,一直以來(lái)都作為重點(diǎn)研究對(duì)象[17].AgNPs已經(jīng)被證明對(duì)和其他氨氧化細(xì)菌具有毒性效應(yīng)[18-19].Alito等[20]在一項(xiàng)短期實(shí)驗(yàn)中發(fā)現(xiàn)AgNPs能毒害氨氧化微生物,使活性污泥中的氨氧化速率降低30%左右.Wu等[21]發(fā)現(xiàn)在ZnONPs暴露下膜完整性受到破壞,細(xì)胞生長(zhǎng)和硝化速率受到抑制.Yuan等[22]將暴露在不同粒徑AgNPs中,發(fā)現(xiàn)細(xì)胞壁遭到破壞,且與生物合成、能量產(chǎn)生和與氨氧化過(guò)程有關(guān)的重要蛋白質(zhì)的表達(dá)受到抑制.Choi等[23]發(fā)現(xiàn)AgNPs對(duì)生長(zhǎng)和氨氧化速率的抑制可能與AgNPs誘導(dǎo)造成細(xì)胞體內(nèi)ROS累積有關(guān).目前,已有大量研究表明AgNPs對(duì)氨氧化過(guò)程具有負(fù)面影響,但AgNPs對(duì)氨氧化微生物毒性機(jī)制仍不清楚[24].本研究以為對(duì)象,不僅從細(xì)胞水平探究?jī)煞N粒徑AgNPs對(duì)生長(zhǎng)、細(xì)胞膜損傷、ROS生成的影響,更是從分子水平解析AgNPs對(duì)功能基因表達(dá)的影響,以期揭示AgNPs對(duì)可能的毒性機(jī)制.

1 材料與方法

1.1 實(shí)驗(yàn)材料

1.1.1 供試材料 10nm的AgNPs(Ag10)表面由聚乙烯吡咯烷酮(PVP)包被,購(gòu)于南京先豐納米有限公司,平均粒徑為10±5nm,形態(tài)如圖1A所示.50nm的AgNPs(Ag50)表面無(wú)包被,購(gòu)于南京埃瑞普納米材料有限公司,平均粒徑為50±5nm,形態(tài)如圖1B所示.醋酸銀(CH3COOAg,又名乙酸銀),純度399.5%,密度3.26g/cm3,分子量166.91,CAS號(hào)563-63-3,購(gòu)自西亞試劑.

1.1.2 菌種與培養(yǎng)基(ATCC 19718)由中國(guó)科學(xué)院城市環(huán)境研究所于昌平教授課題組提供.培養(yǎng)基配方:1.32g/L (NH4)2SO4,0.20g/L MgSO4?7H2O,0.02g/L CaCl2?2H2O,0.087g/LK2HPO4, 2.52g/L N-2-羥乙基哌嗪-Ni3-丙磺酸(EPPS),1mg/L C10H12FeN2NaO8?3H2O,0.1mg/L Na2MoO4? 2H2O和ZnSO4?7H2O,0.172mg/L MnSO4,0.04mg/L CoCl2?6H2O, 2.5mg/L酚紅,0.25mg/L CuSO4?5H2O.KHCO3溶液調(diào)節(jié)pH值至6.9~7.5.

圖1 兩種粒徑納米銀TEM圖(A:10nm; B:50nm)

1.2 菌懸液制備

將培養(yǎng)至對(duì)數(shù)生長(zhǎng)期后4000r/min離心收集菌體,KH2PO4緩沖液洗滌殘余培養(yǎng)基,菌體重懸于緩沖液中,4℃避光保存?zhèn)溆?

1.3 N. europaea生長(zhǎng)及NH4+、NO2-含量測(cè)定

將兩種粒徑AgNPs和菌懸液加入高溫滅菌后的培養(yǎng)基中,使AgNPs最終濃度為5,10,20mg/L,同時(shí)控制初始OD600為0.07,于30℃、150r/min恒溫避光培養(yǎng),按時(shí)取樣,每個(gè)處理三個(gè)重復(fù).納氏試劑比色法測(cè)定培養(yǎng)基中NH4+含量,鹽酸N-(1-萘基)-乙二胺比色法測(cè)定NO2-含量.同時(shí)用紫外分光光度計(jì)(UV-2550,菁華,中國(guó))測(cè)定OD600,生長(zhǎng)抑制率(%)=1－處理組OD600/空白組OD600′100%.

1.4 培養(yǎng)基中AgNPs的Ag+釋放量

將AgNPs(10nm終濃度為5,10mg/L;50nm終濃度為10,20mg/L)暴露在培養(yǎng)基中,培養(yǎng)不同時(shí)間后裝入超濾離心管(Millipore 3kDa,Amicon,美國(guó))中,4500r/min離心過(guò)濾,電感耦合等離子發(fā)射光譜儀(ICP-MS 7500CX, Agilent,美國(guó))測(cè)定濾液中Ag+含量,每組三個(gè)重復(fù).

1.5 N. europaea細(xì)胞形態(tài)觀察

Ag10(10mg/L)和Ag50(20mg/L)處理12h后離心(10000r/min,4℃)收集菌體,0.1mol/L磷酸鹽緩沖液(PBS)漂洗兩次,2.5%戊二醛固定4h,PBS再漂洗3次,乙醇梯度脫水,丙酮替代20min后干燥過(guò)夜,前處理結(jié)束后樣品鍍膜進(jìn)行掃描電鏡SEM(S-4800,日立,日本)觀察.透射電鏡樣品用戊二醛固定后再用1%鋨酸固定1~2h,然后脫水、浸透、包埋、烘干、切片和染色后在透射電鏡TEM(H-7650,日立,日本)下觀察,同時(shí)設(shè)置空白對(duì)照組.

1.6 N. europaea細(xì)胞內(nèi)ROS檢測(cè)

乙酰半胱氨酸(N-acetyl-L-cysteine,NAC)作為抗氧化劑可以清除細(xì)胞內(nèi)多余的ROS,降低AgNPs產(chǎn)生的氧化損傷[25],本實(shí)驗(yàn)添加NAC驗(yàn)證細(xì)胞內(nèi)部ROS的產(chǎn)生.將預(yù)培養(yǎng)1h后10000r/min離心收集菌體,PBS洗滌后加入DCFH-DA探針,按照活性氧檢測(cè)試劑盒(碧云天S0033,上海)的說(shuō)明,于30℃孵育30min后利用流式細(xì)胞儀(FCM, FACSCalibur, BD,美國(guó))于488nm為激發(fā)波長(zhǎng)、525nm為發(fā)射波長(zhǎng)的條件下檢測(cè)熒光強(qiáng)度.試驗(yàn)共5個(gè)處理:空白對(duì)照(CK)、Ag10(10mg/L)、Ag50(20mg/L)、Ag10(10mg/L)+5mmol/L NAC、Ag50(20mg/L)+ 5mmol/L NAC.

1.7 功能基因amoA、hao、merA表達(dá)分析

1.7.1 RNA提取與反轉(zhuǎn)錄 取約108個(gè)菌體,加入溶菌酶消化10min,4℃和12000r/min下離心2min,使用UNIQ-10柱式Ⅰ總RNA抽提試劑盒(生工,上海)提取總RNA,按照TransScript All-in-One First-Stand cDNA Synthesis SupriMix for qPCR(TransGen, 北京)試劑盒進(jìn)行反轉(zhuǎn)錄.RT體系與條件:10μmol/L Random Primer 1μL,RNA 6μL,RNase free dH2O 5μL,混合后70℃熱激3min,冰浴5min,然后繼續(xù)加入dNTP Mixture 2μL,RNase free dH2O 0.5μL,M-MLV 1μL,5′M-MLV Buffer 4μL,RNase Inhibitor 0.5μL,總體積共20μL.將各組分混勻后置于42℃水浴1h,得到第一鏈cDNA.

1.7.2 Real-Time PCR 本實(shí)驗(yàn)根據(jù)Ultra SYBR Mixture(康為世紀(jì), 北京)試劑盒說(shuō)明,采用SYBR Green I法實(shí)時(shí)熒光定量PCR(相對(duì)定量)進(jìn)行mRNA表達(dá)量測(cè)定.20μL反應(yīng)體系為:10μL 2×SYBR Premix EX-Taq Mi,0.5μL 10μmol/L PCR Forward Primer和PCR Reverse Primer,0.4μL ROX (50×),2μL Template cDNA,6.6μL RNase Free dH2O.、、的所用引物如表1所示,每個(gè)樣品3次重復(fù).

Real-time PCR擴(kuò)增條件: 95℃預(yù)變性10min,40個(gè)循環(huán)( 95℃變性15s, 61℃退火35s,97℃延伸10s) 最后從65℃升至97℃獲得熔解曲線,采用2-△△Ct法進(jìn)行相對(duì)表達(dá)量計(jì)算.

表1 Real-time PCR實(shí)驗(yàn)所用引物

1.8 數(shù)據(jù)處理與分析

試驗(yàn)數(shù)據(jù)采用SPSS 18.0進(jìn)行統(tǒng)計(jì)分析,并對(duì)不同處理間的數(shù)據(jù)用單因素方差分析. (ANOVA)和Duncan多重比較進(jìn)行顯著性差異(<0.05)檢驗(yàn),再用Origin 9.0繪圖.

2 結(jié)果與分析

2.1 AgNPs對(duì)N. europaea生長(zhǎng)抑制

暴露在兩種粒徑的AgNPs中,細(xì)菌生長(zhǎng)受到顯著抑制(圖2).生長(zhǎng)與AgNPs劑量呈負(fù)相關(guān),且在同等劑量下,10nm AgNPs對(duì)生長(zhǎng)的抑制作用比50nm強(qiáng).生長(zhǎng)抑制率隨著AgNPs暴露時(shí)間的延長(zhǎng)而增加,在4h達(dá)到最大值.4h后抑制率沒(méi)有顯著變化,甚至10nm(5mg/L)和50nm(5、10mg/L)AgNPs處理組抑制率出現(xiàn)降低趨勢(shì),說(shuō)明開始適應(yīng)AgNPs存在.

2.2 AgNPs對(duì)N. europaea銨態(tài)氮轉(zhuǎn)化的影響

隨著培養(yǎng)時(shí)間延長(zhǎng),無(wú)銀對(duì)照組中銨態(tài)氮由于向硝酸鹽氮轉(zhuǎn)化,其含量逐漸降低.不同粒徑、不同劑量AgNPs暴露下銨態(tài)氮轉(zhuǎn)化能力受到抑制(圖3).AgNPs刺激8h后,對(duì)照組中NH4+含量減少了0.10mg/mL.Ag10(5,10,20mg/L)處理組NH4+濃度分別降低0.09,0.07,0.06mg/mL,而Ag50(5,10, 20mg/L)處理組NH4+濃度分別減低0.10,0.09, 0.07mg/mL.由于NH4+的轉(zhuǎn)化,培養(yǎng)液中NO2-含量逐漸增加,與對(duì)照組相比,AgNPs暴露組中NO2-含量明顯降低.其中,Ag10(10,20mg/L),Ag50(20mg/L)處理下,培養(yǎng)液中NO2-含量幾乎不變,而Ag10(5mg/L)和Ag50(5,10mg/L)處理組NO2-含量略有增加,但顯著低于對(duì)照組.

圖2 兩種粒徑納米銀暴露下N. europaea生長(zhǎng)抑制率變化

2.3 AgNPs的Ag+ 釋放

暴露在環(huán)境中的AgNPs容易游離出Ag+,本研究選取10nm(5,10mg/L)和50nm(10,20mg/L)的AgNPs進(jìn)行Ag+釋放量的測(cè)定(圖4).前6h內(nèi)培養(yǎng)基中Ag+含量隨著培養(yǎng)時(shí)間的延長(zhǎng)而增多,6h后趨于穩(wěn)定.暴露12h后,Ag10(5,10mg/L)Ag+釋放量占1.09%、0.75%;Ag50(10、20mg/L)的Ag+釋放量高達(dá)5.41%、4.56%.粒徑為50nm的AgNPs釋放的Ag+量顯著高于10nm的AgNPs,且50nm的AgNPs初始游離出的Ag+較高.

圖4 培養(yǎng)基中AgNPs的Ag+釋放量

2.4 AgNPs對(duì)N.europaea細(xì)胞形態(tài)及結(jié)構(gòu)的影響

通過(guò)SEM和TEM觀察AgNPs處理12h后細(xì)胞形態(tài)與內(nèi)部結(jié)構(gòu)的變化,其中圖A、C、E放大40000倍,圖B、F放大12000倍,圖D放大15000倍.空白組(圖5A、B)中細(xì)胞飽滿且表面光滑,結(jié)構(gòu)清晰完整,細(xì)胞內(nèi)部物質(zhì)分布均勻.掃描電鏡圖像(圖5C、E)顯示AgNPs處理造成細(xì)胞膜表面出現(xiàn)塌陷,且有大小不一的孔洞,細(xì)胞內(nèi)容物流出.透射電鏡圖像(圖5D、F)顯示AgNPs處理造成細(xì)胞內(nèi)核解體且中央出現(xiàn)大片空白區(qū)域,細(xì)胞器聚集于細(xì)胞邊緣,細(xì)胞質(zhì)壁界限模糊.

A、B:空白對(duì)照; C、D:10mg/LAg10; E、F:20mg/LAg50

2.5 AgNPs對(duì)N.europaea的氧化應(yīng)激作用

暴露在兩種粒徑AgNPs中細(xì)胞內(nèi)ROS含量顯著上升(圖6).空白組中細(xì)胞內(nèi)平均熒光強(qiáng)度為6.7,Ag10(10mg/L)和Ag50(20mg/L)處理組中細(xì)胞內(nèi)平均熒光強(qiáng)度升高到35.2和28.1,添加NAC后熒光強(qiáng)度又顯著降低為12.7和12.5.說(shuō)明AgNPs能刺激內(nèi)部ROS的產(chǎn)生和累積,AgNPs氧化應(yīng)激作用可能是對(duì)產(chǎn)生毒性效應(yīng)的原因之一.

圖6 兩種粒徑納米銀暴露后N. europaea細(xì)胞內(nèi)ROS含量變化

Ag10為10mg/L;Ag50為20mg/L;NAC為5mmol/L

圖中標(biāo)有不同小寫字母者為Duncan檢測(cè)下差異顯著(<0.05),下同

2.6 AgNPs對(duì)N. europaea功能基因表達(dá)的影響

負(fù)責(zé)編碼氨氧加氧酶,主要調(diào)控NH4+到NH2OH的轉(zhuǎn)化,負(fù)責(zé)編碼羥氨氧化還原酶,主要調(diào)控NH2OH到NO2-轉(zhuǎn)化過(guò)程[26],merA調(diào)控重金屬應(yīng)激[27].本研究以的16S RNA為參照基因,以無(wú)銀處理為對(duì)照組,AgNPs和Ag+暴露12h后功能基因、、表達(dá)如圖7所示.基因表達(dá)下調(diào)為負(fù)性調(diào)控(抑制表達(dá)),表達(dá)上調(diào)則為正性調(diào)控(促進(jìn)表達(dá)).Ag+處理組中、、表達(dá)與對(duì)照相比分別下調(diào)23.26、1.96、12.82倍;Ag10(10mg/L)處理組、表達(dá)分別下調(diào)13.33、8.06倍,表達(dá)上調(diào)1.46倍;Ag50(20mg/L)處理組、表達(dá)分別下調(diào)1.37、2.79倍,則上調(diào)了1.90倍.說(shuō)明Ag+能顯著抑制、、表達(dá),AgNPs處理下、表達(dá)下調(diào),輕微上調(diào).

圖7 納米銀和銀離子脅迫下N. europaea基因表達(dá)量變化

3 討論

3.1 AgNPs對(duì)N. europaea生長(zhǎng)抑制與其釋放的Ag+量相關(guān)

.對(duì)環(huán)境因子的變化較為敏感.本研究發(fā)現(xiàn)AgNPs抑制生長(zhǎng),培養(yǎng)基中NH4+向NO2-轉(zhuǎn)化過(guò)程受阻,氨氧化過(guò)程減緩,且10nm比50nm的AgNPs影響更大. Radniecki等[28]得出類似結(jié)論,并發(fā)現(xiàn)對(duì)小粒徑AgNPs的敏感性增加是由于其表面積與體積比較大,AgNPs的毒性與其顆粒大小有關(guān).納米材料與細(xì)胞直接接觸被廣泛認(rèn)為是其生物毒性來(lái)源之一[29],也有大量文獻(xiàn)證實(shí)AgNPs對(duì)氨氧化微生物的毒性與釋放的Ag+密切相關(guān)[30-31].本研究中50nm的AgNPs釋放的Ag+高于10nm的AgNPs,12h后50nm(20mg/L)的AgNPs釋放的Ag+高達(dá)1mg/L,而10nm的AgNPs Ag+釋放量只有幾十μg/L,可能是因?yàn)?0nm的AgNPs表面由PVP包被,在液體環(huán)境中較為穩(wěn)定,而50nm的AgNPs表面無(wú)包被,更易釋放Ag+,這與Arnaout和Gunsch[32]的研究結(jié)果相近.

3.2 AgNPs造成N. europaea的細(xì)胞結(jié)構(gòu)損傷及細(xì)胞內(nèi)活性氧的累積

掃描電鏡(SEM)和透射電鏡(TEM)圖像顯示,AgNPs造成細(xì)胞表面塌陷且有孔洞,細(xì)菌內(nèi)部核物質(zhì)消融且質(zhì)膜界限不明顯,AgNPs與細(xì)菌表面直接作用可能是AgNPs導(dǎo)致死亡的原因之一.通過(guò)染色進(jìn)行電鏡觀察已成為一種普遍方法,本研究得出在銀脅迫下細(xì)胞膜遭到破壞與他人在文獻(xiàn)中描述的一樣[9].AgNPs不僅可以直接破壞細(xì)胞結(jié)構(gòu)損傷細(xì)胞,還可以誘導(dǎo)細(xì)胞體內(nèi)ROS的累積,對(duì)造成氧化損傷.ROS主要包括羥基自由基(·OH)、超氧陰離子(·O2-)、單線態(tài)氧(1O2)、過(guò)氧化氫(H2O2)等具有殺菌作用的自由基[33].電子自旋共振光譜(EPR)被認(rèn)為是證明ROS存在的有效工具,我們前期工作已檢測(cè)到AgNPs產(chǎn)生的自由基為·OH[34].當(dāng)微生物體內(nèi)ROS含量超過(guò)自身抗氧化防御能力會(huì)導(dǎo)致生物體谷胱甘肽(GSH)的耗竭以及多種抗氧化酶活性的改變,是AgNPs毒性作用的可能機(jī)制之一[35].AgNPs暴露下內(nèi)部ROS含量測(cè)定結(jié)果顯示兩種粒徑AgNPs暴露后細(xì)胞內(nèi)ROS含量均明顯增高,NAC處理后細(xì)胞內(nèi)ROS顯著降低,進(jìn)一步印證了AgNPs的氧化應(yīng)激作用.氧化應(yīng)激是AgNPs毒性機(jī)制中報(bào)道最多的,ROS的產(chǎn)生會(huì)導(dǎo)致細(xì)胞壁損傷、細(xì)胞膜破壞、蛋白質(zhì)損傷和電子傳遞中斷[36].

3.3 AgNPs對(duì)N. europaea功能基因amoA、hao和merA表達(dá)的影響

qRT-PCR測(cè)定結(jié)果顯示兩種粒徑AgNPs均抑制和表達(dá),輕微上調(diào).其中負(fù)責(zé)調(diào)控氨氧化過(guò)程第一步的基因受AgNPs影響最大,這可能是AgNPs影響銨態(tài)氮轉(zhuǎn)化的主要原因,與Michels等[26]研究結(jié)果類似.也有文獻(xiàn)報(bào)道AgNPs雖然抑制硝化作用,的表達(dá)卻沒(méi)有改變,AgNPs不影響的轉(zhuǎn)錄[32].用于NADPH還原,在重金屬存在時(shí)傾向于上調(diào)[37],本研究發(fā)現(xiàn)AgNPs暴露下表達(dá)受抑制,說(shuō)明AgNPs對(duì)的影響與一般重金屬應(yīng)激機(jī)制不同.10nm的AgNPs對(duì)功能基因表達(dá)的抑制效果比50nm的AgNPs強(qiáng),可能是小粒徑AgNPs更易進(jìn)入細(xì)胞內(nèi)部,與細(xì)胞內(nèi)物質(zhì)(包括核酸)結(jié)合,破壞細(xì)胞內(nèi)部結(jié)構(gòu)[38].Choi等[39]同樣發(fā)現(xiàn)小粒徑AgNPs對(duì)氨氧化細(xì)菌基因的損傷較嚴(yán)重.根據(jù)nAg50(20mg/L)12h釋放的Ag+量,選擇1mg/L Ag+暴露下對(duì)功能基因表達(dá)的影響,發(fā)現(xiàn)Ag+對(duì)、、表達(dá)抑制較明顯.10nm的由PVP包被的AgNPs釋放的Ag+較少但對(duì)基因的影響依舊很大,其中PVP作為一種涂層材料是無(wú)毒的[40],說(shuō)明AgNPs對(duì)基因的表達(dá)與粒徑大小有關(guān).50nm的AgNPs的毒性可能部分來(lái)自釋放的Ag+,部分由于本身的特異抗菌性,10nm AgNPs的毒性主要是自身作用的結(jié)果[41].AgNPs的毒性大小與其濃度及粒徑有關(guān).

雖然本文利用兩種不同粒徑的AgNPs探討了對(duì)的毒性作用,并發(fā)現(xiàn)AgNPs通過(guò)直接破壞細(xì)胞結(jié)構(gòu)、產(chǎn)生氧化應(yīng)激和影響和基因表達(dá)進(jìn)而影響銨態(tài)氮的轉(zhuǎn)化,但是關(guān)于AgNPs對(duì)毒性作用及其影響機(jī)理還有待進(jìn)一步的研究.

4 結(jié)論

4.1 AgNPs抑制了生長(zhǎng),導(dǎo)致銨態(tài)氮轉(zhuǎn)化過(guò)程延緩,且粒徑越小抑制作用越強(qiáng).

4.2 AgNPs對(duì)的毒性作用主要有兩條途徑:AgNPs能直接作用于表面,破壞細(xì)胞膜,導(dǎo)致胞內(nèi)物質(zhì)流出,核物質(zhì)消融且質(zhì)膜界限不明顯;刺激細(xì)菌體內(nèi)ROS生成,ROS累積造成氧化損傷.

4.3 實(shí)時(shí)熒光定量PCR結(jié)果顯示,AgNPs抑制和表達(dá),對(duì)的表達(dá)影響較小.

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Toxicity of two sizes of silver nanoparticles to.

WU Ling-li, ZHANG Xiao-xue, SHU Kun-hui, SI You-bin*

(Anhui Province Key Laboratory of Farmland Ecological Conservation and Pollution Prevention, School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China)., 2019,39(10)：4401~4408

The laboratory incubation experiments were conducted to study the toxicity of silver nanoparticles with different particle sizes on, and the effects of two sizes of nanosilver (10nm and 50nm) on the bacterial growth, nitrogen transformation, cellular structure, reactive oxygen generation and gene expression were investigated. The results showed that nanosilver inhibited the growth of. With the extension of exposure time, the inhibition rate of bacterial growth activity increased and reached to maximum at 4h. In the medium, the transformation rate of NH4+to NO2-was slowed down, and the nitrogen transformation ability bywas reduced. Scanning electron microscopy (SEM) images showed that nanosilver heavily damaged the cell membrane by causing holes on the surface of bacteria. Transmission electron microscope (TEM) images showed that the nuclear material inside the bacteria was disappeared and the boundary of the cytoplasmic membrane was blurred. Flow cytometry (FCM) was employed to detect that nanosilver could generate intracellular reactive oxygen (ROS) in the cells. qRT-PCR technology was used to determine the expression ofandofafter the exposure to nanosilver, and it was found that nanosilver inhibited the expression of the functional genes. In conclusion, nanosilver could interact with cell membrane, generated oxidative stress damage and inhibited the expression of functional genesandof, which further affected the transformation process of ammonium nitrogen. In addition, the toxicity of nanosilver with small particle size was stronger than that of large particle size.

nanosilver；；oxidative stress；gene expression of,, and；ammoxidation

X171.5

A

1000-6923(2019)10-4401-08

伍玲麗(1994-),女,安徽蕪湖人,安徽農(nóng)業(yè)大學(xué)碩士研究生,主要研究方向?yàn)槲⑸锒纠?

2019-03-11

國(guó)家自然科學(xué)基金重點(diǎn)項(xiàng)目(41430752);安徽農(nóng)業(yè)大學(xué)研究生創(chuàng)新基金(2019ysj-67)

* 責(zé)任作者, 教授, youbinsi@ahau.edu.cn