劉任靜,蔣文濤*,徐凱仁,李忠友,李 瀟,閔 磊,梁 英

流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞活性的影響

劉任靜1,2,3,蔣文濤1,2,3*,徐凱仁1,2,3,李忠友1,2,李 瀟1,2,閔 磊1,2,梁 英1

(1.四川大學(xué)建筑與環(huán)境學(xué)院,四川 成都 610065；2.四川大學(xué),生物力學(xué)工程四川省重點(diǎn)實(shí)驗(yàn)室,四川 成都 610065；3.宜賓四川大學(xué)產(chǎn)業(yè)技術(shù)研究院,四川 宜賓 644000)

為討論流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞活性的影響,本文研究了銅綠微囊藻在0.0,0.3,0.6,0.9Pa切應(yīng)力作用下的生長(zhǎng)情況,并分析了藻細(xì)胞生理指標(biāo)以及藻液指標(biāo)的變化情況.結(jié)果顯示,低于0.6Pa的切應(yīng)力能使藻細(xì)胞密度和光合色素含量不斷增加,從而促進(jìn)銅綠微囊藻的生長(zhǎng)繁殖.其中0.6Pa對(duì)藻細(xì)胞生長(zhǎng)最有利,此條件既能提高藻細(xì)胞光合作用強(qiáng)度和營(yíng)養(yǎng)鹽利用率,又未過度破壞細(xì)胞結(jié)構(gòu).但0.9Pa高切應(yīng)力將通過對(duì)藻細(xì)胞結(jié)構(gòu)的破壞來影響膜滲透性,進(jìn)而抑制銅綠微囊藻生長(zhǎng)與代謝.研究表明,流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞的影響體現(xiàn)為“低促高抑”,即適度切應(yīng)力能夠增強(qiáng)銅綠微囊藻細(xì)胞的活性,而高切應(yīng)力會(huì)抑制其生長(zhǎng).本文結(jié)果將為湖泊水庫等水體銅綠微囊藻水華的預(yù)防和治理提供了新的思路和方案.

水華；切應(yīng)力；銅綠微囊藻；光合作用；細(xì)胞膜

水體富營(yíng)養(yǎng)化導(dǎo)致的藍(lán)藻水華是世界性水環(huán)境問題[1].我國(guó)有三分之一湖泊處于富營(yíng)養(yǎng)化狀態(tài),其中太湖,巢湖,滇池仍為國(guó)家湖泊水華治理的重點(diǎn)[2].藍(lán)藻水華會(huì)消耗水中溶解氧并破壞水生生態(tài)系統(tǒng)平衡,還會(huì)產(chǎn)生劇毒藻毒素威脅飲用水安全,給社會(huì)和經(jīng)濟(jì)的可持續(xù)發(fā)展帶來了不利影響[3-4].

水華的形成受環(huán)境因素和藻細(xì)胞生理結(jié)構(gòu)的制約,其中環(huán)境因素包括水體營(yíng)養(yǎng)鹽濃度,光照和水動(dòng)力條件等[5-6].在環(huán)境因素中,水體營(yíng)養(yǎng)鹽濃度的控制所需周期長(zhǎng),難度大而光照等氣候條件又難以實(shí)現(xiàn)人為調(diào)控,故探究水力擾動(dòng)對(duì)藻類生長(zhǎng)的影響已成為水華治理的重點(diǎn)[7].已有大量研究證實(shí)流動(dòng),流速和擾動(dòng)等水力學(xué)條件對(duì)藻類生長(zhǎng)具有顯著影響[8-10],適度的水體擾動(dòng)能促進(jìn)微囊藻的生長(zhǎng)和菌落數(shù)的增加[11-13].然而,無論是哪種水力擾動(dòng),其本質(zhì)都是水體中動(dòng)力學(xué)環(huán)境的變化,即流體壓強(qiáng)或切應(yīng)力的改變[14].研究發(fā)現(xiàn)藍(lán)藻在0.4MPa靜壓即水下40m處壓強(qiáng)才會(huì)被破壞,而藍(lán)藻水華多發(fā)生在水下5m和淺水湖泊中,由此可見切應(yīng)力是影響藻類生長(zhǎng)的主要因素[15].

圍繞切應(yīng)力對(duì)藻類生長(zhǎng)影響,已有研究發(fā)現(xiàn)螺旋藻和小球藻在相同剪切流中產(chǎn)氧率變化完全相反,表明不同種類的微藻對(duì)切應(yīng)力響應(yīng)與耐受力存在不同規(guī)律,這與Thomas等通過總結(jié)量化得出微藻對(duì)切應(yīng)力的敏感程度為綠藻<藍(lán)藻<硅藻<甲藻的結(jié)論相符[16-17].此外,研究還發(fā)現(xiàn)流體切應(yīng)力會(huì)改變真核細(xì)胞和原核細(xì)胞長(zhǎng)度和形態(tài),且長(zhǎng)時(shí)間切應(yīng)力作用能夠增加微藻產(chǎn)氧量[18-19].由此可見,微藻生長(zhǎng)過程的確會(huì)受切應(yīng)力影響.但近年來國(guó)內(nèi)外針對(duì)切應(yīng)力與藻細(xì)胞關(guān)系的研究主要集中于工業(yè)生產(chǎn)中需要大量繁殖的微藻種類,以獲得不同培養(yǎng)儀器中藻細(xì)胞達(dá)到高生長(zhǎng)率的條件[20-21],而關(guān)于切應(yīng)力對(duì)典型水華藻種生長(zhǎng)影響的研究尚未得到足夠的關(guān)注.

因此本研究選取水華優(yōu)勢(shì)藻種銅綠微囊藻為研究對(duì)象,將切應(yīng)力作為唯一影響參數(shù),通過對(duì)不同切應(yīng)力狀態(tài)下銅綠微囊藻細(xì)胞生長(zhǎng)情況和藻細(xì)胞內(nèi)部生理指標(biāo)變化以及藻細(xì)胞培養(yǎng)液(藻液)指標(biāo)變化來探究切應(yīng)力對(duì)銅綠微囊藻生長(zhǎng)特性和活性的影響,從而為揭示富營(yíng)養(yǎng)化水體中藍(lán)藻水華爆發(fā)原因及其預(yù)防和治理提供參考.

1 材料與方法

1.1 實(shí)驗(yàn)材料與裝置

銅綠微囊藻水華是最常見藍(lán)藻水華之一,BG11培養(yǎng)基為常用微藻培養(yǎng)基,因此選取銅綠微囊藻FACHB-905為實(shí)驗(yàn)對(duì)象,BG11為實(shí)驗(yàn)培養(yǎng)基[22-23],兩者均購(gòu)自中科院水生生物研究所淡水藻種庫.

圖1 剪切流旋轉(zhuǎn)桶裝置與雙桶示意

實(shí)驗(yàn)裝置為剪切流旋轉(zhuǎn)桶裝置,如圖1所示,雙桶為透明亞克力材質(zhì),外桶固定于地面,內(nèi)桶由電機(jī)帶動(dòng)旋轉(zhuǎn),變頻器用于控制旋轉(zhuǎn)桶的速度,取樣口距外桶底部1cm.此裝置可產(chǎn)生穩(wěn)定且均勻切應(yīng)力場(chǎng)[24],桶間切應(yīng)力表達(dá)式見式(1)[16]

式中:為剪切應(yīng)力,Pa;為培養(yǎng)基動(dòng)力粘性系數(shù), Pa·s;為旋轉(zhuǎn)桶角速度(rad/s);1,2分別為旋轉(zhuǎn)桶內(nèi),外半徑;為旋轉(zhuǎn)桶內(nèi)某質(zhì)點(diǎn)距旋轉(zhuǎn)軸的距離(1￡￡2).其中:1=140mm,2=150mm,壁厚均為5mm,即的范圍為140～145mm.將實(shí)驗(yàn)倉中心位置即=142.5mm處的切應(yīng)力代表藻細(xì)胞所受切應(yīng)力,此時(shí)切應(yīng)力的變化不超過1.8%.

1.2 實(shí)驗(yàn)方法

將購(gòu)置的藻種與培養(yǎng)基1:2在無菌室內(nèi)接種后置于光照培養(yǎng)箱中,按照中科院水生生物研究所的方法擴(kuò)大培養(yǎng)后用于實(shí)驗(yàn).實(shí)驗(yàn)開始時(shí),向旋轉(zhuǎn)桶裝置中加入銅綠微囊藻懸浮液800mL,設(shè)置光照強(qiáng)度為 3500lx,室內(nèi)平均溫度為28℃,藻液從培養(yǎng)箱中取出后靜置2h,以確保藻液的溫度與室溫一致,光暗比為 14:10,轉(zhuǎn)速分別為0,100,200,300r/min,其對(duì)應(yīng)切應(yīng)力約0.0,0.3,0.6,0.9Pa,將4種條件實(shí)驗(yàn)組分別定義為靜止組和低,中,高切應(yīng)力組.實(shí)驗(yàn)周期為7d,每2d取樣15mL,用于測(cè)定其藻液指標(biāo)和藻細(xì)胞指標(biāo).在裝置停止后1min內(nèi)完成取樣,以保證取樣的均勻性和實(shí)驗(yàn)的連續(xù)性.藻液指標(biāo)包括pH值,營(yíng)養(yǎng)鹽濃度(總氮濃度TN,總磷濃度TP)和核酸含量;藻細(xì)胞指標(biāo)包括銅綠微囊藻密度,藻細(xì)胞增長(zhǎng)率(藻比增長(zhǎng)率),葉綠素a濃度(Chl-a),類胡蘿卜素濃度(car),藻藍(lán)蛋白濃度(PC),別藻藍(lán)蛋白濃度(APC)和丙二醛濃度(MDA).

1.3 分析測(cè)試方法

采用pH值,TNTP濃度和藻液核酸含量表征藻液指標(biāo)的變化.其中,藻液pH值使用pH計(jì)(PHS-3C)進(jìn)行測(cè)量;TNTP濃度使用總磷測(cè)定儀(5B-6P)和總氮測(cè)定儀(LH-3BN)進(jìn)行測(cè)量;藻液核酸含量采用分光光度法即用260nm處吸光度來評(píng)估藻細(xì)胞滲出的核酸濃度[25].

采用藻密度和藻比增長(zhǎng)率,Chl-a和car濃度,PC和APC濃度,MDA含量表征藻細(xì)胞指標(biāo)變化.其中,銅綠微囊藻密度采用分光光度法即680nm處吸光度來代表藻細(xì)胞密度[26]; Chl-a和car濃度測(cè)定采用甲醇提取的紫外分光光度法[27-28]:取5mL藻液離心(4°C, 13500r/min, 5min),棄去上清液后將藻細(xì)胞重懸于5mL甲醇(90%)中,60°C水浴10min后再次離心,收集上清液并使用紫外可見分光光度計(jì)(UV- 4802)測(cè)量在 470,652,665nm處的吸光度并計(jì)算;PC, APC濃度按照孫曉筠等[29]的方法進(jìn)行測(cè)量;MDA含量采用南京建成生物工程研究所的試劑盒測(cè)定.藻比增長(zhǎng)率計(jì)算如下:

式中:X為當(dāng)天細(xì)胞密度;X-1為前1d細(xì)胞密度;t為X對(duì)應(yīng)培養(yǎng)時(shí)間;t-1為X-1對(duì)應(yīng)培養(yǎng)時(shí)間.

數(shù)據(jù)處理和圖像繪制使用Origin 2023,對(duì)照組和實(shí)驗(yàn)組密度,葉綠素a濃度等指標(biāo)差異采用IBM SPSS Statistics 26單因素方差法(<0.05)進(jìn)行統(tǒng)計(jì)分析.

2 結(jié)果與分析

2.1 流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞培養(yǎng)液的影響

實(shí)驗(yàn)開始時(shí),各組藻液TN,TP,pH值無顯著性差異(圖2) (>0.05),隨著實(shí)驗(yàn)進(jìn)行 TN有不同程度降低(圖2a):靜止組和低,中切應(yīng)力組表現(xiàn)為切應(yīng)力越大,TN越小;而高切應(yīng)力組對(duì)TN的利用率僅高于靜止組,到試驗(yàn)結(jié)束時(shí)其各組TN分別下降13.6%, 24.3%,28.2%和16%.實(shí)驗(yàn)各組TP在第5d才出現(xiàn)顯著性差異(圖2b) (<0.05),其中靜止組和低,中切應(yīng)力組變化趨勢(shì)相同,而高切應(yīng)力組的TP剩余量在實(shí)驗(yàn)結(jié)束時(shí)仍高于其余組.實(shí)驗(yàn)中,雖然各組藻液TN, TP不斷下降,但營(yíng)養(yǎng)鹽濃度始終處于富營(yíng)養(yǎng)化水平,足以維持藻細(xì)胞的正常生長(zhǎng).靜止組和低,中切應(yīng)力組在實(shí)驗(yàn)開始后pH值不斷增加(圖2c),而高切應(yīng)力組的pH值在實(shí)驗(yàn)第3d下降后才上升,但直至實(shí)驗(yàn)結(jié)束其pH值仍低于其余組.

2.2 流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞密度和光合色素的影響

通過銅綠微囊藻密度(圖3a)表征其總生物量,藻比增長(zhǎng)率(圖3b)表征其增長(zhǎng)速率.實(shí)驗(yàn)開始后各組密度呈現(xiàn)出上升趨勢(shì)(圖3a),藻密度從第3d開始出現(xiàn)了明顯的區(qū)別,總體表現(xiàn)為切應(yīng)力組密度高于靜止組但中,高切應(yīng)力組生長(zhǎng)曲線無明顯差異(>0.05).從比增長(zhǎng)率來講,各組都呈現(xiàn)先上升后下降的趨勢(shì),且最大比增長(zhǎng)率出現(xiàn)在中切應(yīng)力組(圖3b).

*代表<0.05;**代表<0.01

銅綠微囊藻細(xì)胞中的光合色素分為脂溶性色素(Chl-a,car)和水溶性蛋白(PC,APC),光能在藻膽體中傳遞的順序?yàn)镻C-APC-Chl-a[30].實(shí)驗(yàn)前各組銅綠微囊藻細(xì)胞的光合色素含量差異不顯著(圖4)(> 0.05).藻細(xì)胞的Chl-a,car濃度隨實(shí)驗(yàn)時(shí)間的增加而增加(圖4a,圖4b),到實(shí)驗(yàn)第5d后,靜止組和低,中切應(yīng)力組Chl-a,car濃度存在顯著性差異(<0.05),實(shí)驗(yàn)結(jié)束時(shí)切應(yīng)力越大,Chl-a,car濃度越高.藻細(xì)胞PC,APC相對(duì)含量呈現(xiàn)先下降后上升的趨勢(shì)(圖4c,圖4d),到實(shí)驗(yàn)結(jié)束時(shí)PC相對(duì)含量表現(xiàn)為切應(yīng)力組高于靜止組,而APC相對(duì)含量在實(shí)驗(yàn)第3d后呈現(xiàn)出隨切應(yīng)力增加而增加并且隨著實(shí)驗(yàn)時(shí)間的增加而增加的規(guī)律.

2.3 流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞膜的影響

各組銅綠微囊藻藻液的核酸含量隨著實(shí)驗(yàn)進(jìn)行呈現(xiàn)出先下降后上升趨勢(shì)(圖5a),實(shí)驗(yàn)進(jìn)行中靜止組藻液核酸含量基本維持原來水平,而切應(yīng)力組核酸含量隨切應(yīng)力的增加而增加,且處理時(shí)間越長(zhǎng),核酸含量越高.實(shí)驗(yàn)第3d切應(yīng)力組藻液核酸含量無明顯差異(>0.05),但靜止組與切應(yīng)力組之間存在明顯差異(<0.05).實(shí)驗(yàn)第5d后各組差異顯著(< 0.05).MDA含量變化與核酸含量變化相似,靜止組MDA含量從第3d開始基本保持不變,而切應(yīng)力組 MDA含量隨切應(yīng)力的增加而上升且隨著處理時(shí)間的增長(zhǎng)而增加(圖5b).

圖5 銅綠微囊藻細(xì)胞膜指標(biāo)

*代表<0.05;**代表<0.01

3 討論

微囊藻水華是最常見的水華藻屬,研究證明水動(dòng)力擾動(dòng)對(duì)微囊藻生長(zhǎng)有直接影響[22].本文以切應(yīng)力為水動(dòng)力擾動(dòng)參數(shù),在光照強(qiáng)度,營(yíng)養(yǎng)鹽濃度等環(huán)境因素保持一致的前提下,利用剪切流旋轉(zhuǎn)桶裝置對(duì)銅綠微囊藻細(xì)胞施加不同強(qiáng)度切應(yīng)力(0,0.3,0.6, 0.9Pa)來探究藻細(xì)胞在切應(yīng)力作用下生長(zhǎng)變化情況,為揭示流體力學(xué)應(yīng)力對(duì)銅綠微囊藻水華的影響提供理論依據(jù).

結(jié)果顯示,藻細(xì)胞在經(jīng)過短暫適應(yīng)期后便迅速繁殖進(jìn)入對(duì)數(shù)增長(zhǎng)期,流體切應(yīng)力對(duì)銅綠微囊藻生長(zhǎng)有顯著影響,小于0.6Pa的切應(yīng)力組較靜止組表現(xiàn)為促生長(zhǎng)作用.究其原因,首先在實(shí)驗(yàn)中光合色素含量均較靜止組顯著上升,而脂溶性色素Chl-a,水溶性蛋白PC,APC含量的增加能強(qiáng)化藻細(xì)胞對(duì)光能的捕獲,吸收與傳遞,car又能起到防止葉綠素分子被破壞,維持光合機(jī)能的運(yùn)作[31],兩個(gè)方面共同作用進(jìn)而增強(qiáng)光合作用促進(jìn)藻細(xì)胞生長(zhǎng).其次,實(shí)驗(yàn)設(shè)置的光照強(qiáng)度為3500lx,小于銅綠微囊藻的光飽和點(diǎn)40000lx[32].當(dāng)光照強(qiáng)度低于光飽和點(diǎn)時(shí),切應(yīng)力可通過改變?cè)寮?xì)胞的光照機(jī)制來增強(qiáng)細(xì)胞的分裂過程[33-34],這可能是切應(yīng)力通過光合作用促進(jìn)藻細(xì)胞生長(zhǎng)的另一種方式.故切應(yīng)力條件可以從兩個(gè)不同的角度促進(jìn)藻細(xì)胞光合作用的進(jìn)行,這是出現(xiàn)促進(jìn)作用的原因之一.

從另外一方面來看,在0～0.6Pa范圍內(nèi),藻細(xì)胞對(duì)TN,TP吸收利用率隨切應(yīng)力的增加而增加,這一實(shí)驗(yàn)結(jié)果與其他研究中切應(yīng)力能提高營(yíng)養(yǎng)鹽傳遞速率的結(jié)果一致[35],銅綠微囊藻需要這些外源性氮來維持生長(zhǎng)代謝及產(chǎn)毒,并利用水體中的外源性磷來用于胞內(nèi)核酸,ATP和細(xì)胞膜上磷脂等生理組織的合成及生理代謝[36-37].因此,切應(yīng)力條件還能通過提高營(yíng)養(yǎng)物質(zhì)吸收利用率來促進(jìn)藻細(xì)胞的生長(zhǎng).

最后,銅綠微囊藻是一種自養(yǎng)型生物,二氧化碳是其主要碳源,而切應(yīng)力造成的水體流動(dòng)混合既可使水中二氧化碳梯度隨著水體混合強(qiáng)度的增高(即切應(yīng)力的增大)而減小[38],促進(jìn)藻細(xì)胞對(duì)二氧化碳的吸收;又可降低藻細(xì)胞周圍分泌和代謝產(chǎn)物濃度,減少其對(duì)藻細(xì)胞生長(zhǎng)的抑制作用,進(jìn)而提高藻細(xì)胞的生長(zhǎng)速率[39].

但是在高切應(yīng)力組(>0.9Pa),并未出現(xiàn)與低/中切應(yīng)力組一致的生長(zhǎng)情況.因?yàn)橐延醒芯孔C實(shí)藻細(xì)胞受損后會(huì)釋放大量胞內(nèi)酸性物質(zhì)和內(nèi)源性營(yíng)養(yǎng)物質(zhì)[40],同時(shí)降低藻細(xì)胞對(duì)營(yíng)養(yǎng)鹽的利用率[35],因此核酸外滲量和MDA的累積量可用于表征藻細(xì)胞損傷水平和細(xì)胞膜脂質(zhì)過氧化的程度[41].高切應(yīng)力組結(jié)果顯示這兩個(gè)指標(biāo)含量與切應(yīng)力成正相關(guān)且在高切應(yīng)力條件下顯著增大,表明高切應(yīng)力會(huì)導(dǎo)致細(xì)胞膜遭受不可逆損傷而抑制藻細(xì)胞的生長(zhǎng)代謝.其他學(xué)者的研究也表明銅綠微囊藻在高混合培養(yǎng)環(huán)境中所積累的MDA是銅綠微囊藻生長(zhǎng)減慢的原因[42-44].此外,高切應(yīng)力組pH值和營(yíng)養(yǎng)鹽(TN,TP)的變化規(guī)律與藻細(xì)胞損傷后的結(jié)果規(guī)律也一致,進(jìn)一步證實(shí)藻細(xì)胞在高切應(yīng)力作用下將產(chǎn)生不可逆損傷.

綜上所述,切應(yīng)力在較低范圍內(nèi)(本文<0.6Pa)能通過改善藻細(xì)胞光照機(jī)制和提高二氧化碳利用率來增強(qiáng)光合作用,通過均衡營(yíng)養(yǎng)鹽分布來促進(jìn)總磷,總氮吸收,適當(dāng)?shù)乃w流動(dòng)混合還能降低藻細(xì)胞周圍代謝物濃度,最終起到促進(jìn)藻細(xì)胞生長(zhǎng)的作用.而在高切應(yīng)力(本文>0.9Pa)條件下,切應(yīng)力將對(duì)藻細(xì)胞的結(jié)構(gòu)產(chǎn)生破壞,影響細(xì)胞膜滲透性和生理功能,進(jìn)而抑制藻細(xì)胞生長(zhǎng).由此趨勢(shì)可判斷,切應(yīng)力的持續(xù)增加將進(jìn)一步對(duì)藻細(xì)胞膜產(chǎn)生更嚴(yán)重的損傷,會(huì)更顯著的抑制藻細(xì)胞生長(zhǎng)甚至直接導(dǎo)致藻細(xì)胞的機(jī)械破碎,這與已有的高速流動(dòng)和強(qiáng)水力擾動(dòng)對(duì)水華具有抑制和消亡作用等研究結(jié)果相吻合[8,45].事實(shí)上流體切應(yīng)力對(duì)細(xì)胞的影響在很多領(lǐng)域均已被證實(shí):醫(yī)學(xué)研究發(fā)現(xiàn)低的壁面切應(yīng)力(<0.6Pa)對(duì)內(nèi)皮細(xì)胞的作用是發(fā)生動(dòng)脈粥樣硬化的重要原因[46-47];植物學(xué)研究也表明,高剪切力會(huì)使得植物細(xì)胞生長(zhǎng)率,產(chǎn)量和細(xì)胞聚集體的大小都有所下降,當(dāng)切應(yīng)力高達(dá)100Pa時(shí),會(huì)直接使植物細(xì)胞分散[48-49];微生物學(xué)研究也同樣發(fā)現(xiàn)在10.9～14.5Pa高切應(yīng)力下大腸桿菌細(xì)胞會(huì)發(fā)生長(zhǎng)度變化和不對(duì)稱分裂[19].以上證據(jù)表明切應(yīng)力是一個(gè)影響動(dòng)植物和微生物細(xì)胞生長(zhǎng)的重要因素.由此可見,已有的水力擾動(dòng)研究中無論是最佳轉(zhuǎn)速,最佳水力強(qiáng)度還是最佳生長(zhǎng)流速等均是在一定切應(yīng)力作用下產(chǎn)生的結(jié)果.

需要注意的是,本文的結(jié)果是在平均溫度28℃,光強(qiáng)3500lx,光暗比為14:10且營(yíng)養(yǎng)鹽充分等有利于銅綠微囊藻生長(zhǎng)的條件下獲得的,而在湖泊水庫中水華的休眠與復(fù)蘇與其水質(zhì)氣候等環(huán)境因素緊密相關(guān)[50-51].因此,若要將切應(yīng)力對(duì)藻細(xì)胞的影響規(guī)律應(yīng)用到治理水華實(shí)例中,還應(yīng)考慮其所處環(huán)境條件“因地制宜”.以溫度為例,低溫(15℃)比適宜溫度(25℃)對(duì)藻類帶來的抑制作用會(huì)更為顯著[52],即在相對(duì)低溫的環(huán)境下,所需的可產(chǎn)生抑制效果的臨界切應(yīng)力可能會(huì)更小,反之,酷暑高溫環(huán)境下,所需的臨界切應(yīng)力可能會(huì)更大.因此,還需要根據(jù)不同湖泊富營(yíng)養(yǎng)化程度和溫度變化情況等環(huán)境因素綜合考慮后分析切應(yīng)力的最優(yōu)抑制效果.同樣也提示,不同水質(zhì),溫度和富營(yíng)養(yǎng)等條件下切應(yīng)力對(duì)藻細(xì)胞的影響規(guī)律還需要更加深入的研究.

4 結(jié)語

本文以銅綠微囊藻為研究對(duì)象,在光照和溫度等外部環(huán)境因素保持一致的前提下,對(duì)藻細(xì)胞施加不同強(qiáng)度的均勻切應(yīng)力,旨在探究流體切應(yīng)力對(duì)銅綠微囊藻細(xì)胞生長(zhǎng)的影響.結(jié)果清晰的展示了銅綠微囊藻在不同切應(yīng)力作用下生長(zhǎng)變化情況,驗(yàn)證了流體切應(yīng)力是影響藻細(xì)胞活性的直接因素,獲得了實(shí)驗(yàn)室條件下銅綠微囊藻細(xì)胞對(duì)切應(yīng)力的耐受范圍,同時(shí)發(fā)現(xiàn)切應(yīng)力對(duì)銅綠微囊藻細(xì)胞的影響體現(xiàn)為“低促高抑”,即低切應(yīng)力能提高藻細(xì)胞活性而高切應(yīng)力會(huì)抑制藻細(xì)胞生長(zhǎng)與代謝.

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Effect of fluid shear stress on activity ofcells.

LIU Ren-jing1,2,3, JIANG Wen-tao1,2,3*, XU Kai-ren1,2,3, LI Zhong-you1,2, LI Xiao1,2, MIN Lei1,2, LIANG Ying1

(1.College of Architecture and Environment, Sichuan University, Chengdu 610065, China；2.Key Laboratory for Biomechanical Engineering of Sichuan University, Chengdu 610065, China；3.Yibin Industrial Technology Research Institute of Sichuan University, Yibin 644000, China)., 2023,43(2)：896～903

To study the effect of the shear stress on the cell activity of, its growth under shear stresses, 0.0, 0.3, 0.6 and 0.9 Pa, was investigated accordingly, and the changes of the algal-cell physiological indicator and the algal-fluid indicator were analyzed. The results indicated that the shear stress below 0.6 Pa can cause the density and photosynthetic pigment content of Microcystis aeruginosa cells increase, promoting their growth and reproduction.The photosynthetic intensity and the nutrient utilization were enhanced by the most favorable shear-stress condition (0.6Pa) for growth, while the cell structure was not excessively damaged. However, the high shear stress, 0.9Pa, would affect the membrane permeability of the algal cells by breaking their structure, thereby inhibiting their growth and metabolism.The results demonstrated that the growth ofcells was affected by the fluid shear stress, manifested as “l(fā)ow promotion and high inhibition”, where their activity was enhanced by moderate shear stress, and their growth was inhibited by the high shear stress. The findings provided a hint or an approach for preventing and managingblooms in water bodies, such as lakes and reservoirs.

water bloom；shear stress；Microcystis aeruginosa；photosynthesis；cell membrane

X172

A

1000-6923(2023)02-0896-08

劉任靜(1998–),女,四川樂山人,四川大學(xué)建筑與環(huán)境學(xué)院環(huán)境系碩士研究生,主要從事湖泊富營(yíng)養(yǎng)化水體研究.

2022-07-18

國(guó)家自然科學(xué)基金資助項(xiàng)目(11972239;12102281),四川省自然科學(xué)基金(2022NSFSC1967)

* 責(zé)任作者, 教授, scubme_jwt@outlook.com