微生物降解石油源多環(huán)芳香烴的研究進展①

申國蘭，李 利，陳 莎*

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微生物降解石油源多環(huán)芳香烴的研究進展①

申國蘭1，李 利2，陳 莎2*

(1長江大學地球科學學院，武漢 430100；2長江大學生命科學學院，湖北荊州 434025)

石油源多環(huán)芳香烴是存在于石油中的一類致畸、致癌污染物，具有以低環(huán)(2 ~ 3環(huán)) 為主且取代基比例明顯高于其他來源PAHs的組分特征。石油泄露引發(fā)的PAHs污染，其降解主要依賴于微生物的活動。本文對能夠降解PAHs的微生物種類、降解機理、代謝途徑及編碼基因進行了概述。從PAHs作為碳源的角度將微生物降解機理劃分為能以PAHs為唯一碳源進行生長的降解機理和共代謝機理。對與PAHs有關的好氧和厭氧微生物降解途徑及對應的編碼基因簇進行了總結。自然界中細菌、放線菌、真菌及藻類都能夠降解PAHs，由加氧酶催化的苯環(huán)羥基化和還原酶介導的苯環(huán)脫芳烴化是好氧和厭氧降解途徑的關鍵步驟，與降解有關的,,,,和基因簇則分別調控好氧和厭氧降解過程。這些進展有助于系統(tǒng)了解石油源PAHs的降解過程、微生物作用機理和分子遺傳機制，為進一步利用微生物促進環(huán)境生物修復提供理論依據。

石油源多環(huán)芳香烴；微生物降解；機理；代謝途徑；基因

石油是一種含有多種烴類及少量其他有機物的復雜混合物。根據烴類結構特點和成分，可以將石油中的烴類物質分為飽和烴、芳香烴、非烴和瀝青質4種組分[1-2]。石油芳香烴物質中以多環(huán)芳香烴(PAHs) 對環(huán)境污染威脅最大。PAHs是指兩個或兩個以上的苯環(huán)以線性、彎接或簇聚方式構成的一類化學結構穩(wěn)定、難于降解的烴類化合物，其中4環(huán)以上的PAHs容易被土壤或生物體富集而產生毒性，嚴重威脅到人類健康及生物安全[3-4]。PAHs有多種來源，不同來源的PAHs在組分特征上有所差異。石油來源的PAHs以2 ~ 3環(huán)為主，而煤炭、汽油、木材、天然氣等燃料不完全燃燒產生的PAHs以4 ~ 6環(huán)為主[5-6]。另外，石油來源的PAHs取代基比例明顯高于其他來源的PAHs，Buddziński等[7]發(fā)現石油中的單甲基菲含量明顯高于未取代菲，而燃料燃燒產生的PAHs中單甲基和二甲基取代物的含量遠遠小于未被取代的化合物。

石油來源的PAHs一旦進入自然環(huán)境后，光照、雨水淋濾、揮發(fā)和微生物降解等環(huán)境因素會引發(fā)降解，這種降解行為類似于環(huán)境的自我凈化修復。但是微生物對石油源PAHs具有選擇性，Lamberts等[8]分離得到的29株菌株中有11株能夠利用甲基菲，并發(fā)現其中僅有1株鞘氨醇單胞菌能夠降解1-甲基菲和2-甲基菲，其他鞘氨醇單胞菌只能降解1-甲基菲。具有取代基的PAHs在降解開始時取代基團先被氧化，Nadali等[9]分析了2-甲基菲和9-甲基菲的微生物降解產物，發(fā)現2-甲基菲生成2-羥甲基菲和2-菲甲醛，推測甲基基團的氧化是降解開始的第一步。取代基基團氧化后經過脫甲基化變成單體PAHs，后續(xù)的降解過程與PAHs單體的降解途徑一致。Novakovi? 等[10]發(fā)現微生物修復后的土壤中單體菲/甲基菲的比例顯著升高，可能原因是微生物細胞表面的“活性中心”與甲基基團相互作用促使甲基菲的脫甲基化。本文在前人研究的基礎上對能降解PAHs的微生物種類、降解機理、降解途徑及調控基因等方面展開綜述，以期為石油來源的PAHs降解研究提供幫助。

1 降解PAHs化合物的微生物種類

微生物降解是去除環(huán)境中PAHs的最主要途徑[11]。能夠降解PAHs的微生物有細菌、放線菌、真菌和藻類[12]，其中細菌中常見有紅球菌 ()、假單胞菌 ()、棒桿菌 ()、微球菌 ()、產堿桿菌 ()、分支桿菌()以及鞘脂菌()等；放線菌常見的是諾卡氏菌()；PAHs降解真菌又分為木質素降解真菌和非木質素降解真菌，木質素降解真菌常見有平革菌()、側耳()、云芝()等；非木質素降解真菌常見有青霉()、曲霉()及小銀克漢霉()等。部分藻類也具有PAHs降解能力，已經報道的有阿格門氏藻()、顫藻()、柵藻()及月牙藻()等(表1)。

表1 降解PAHs的微生物菌株及其底物

2 能夠以PAHs作為唯一碳源的微生物降解機理

2.1 細菌的降解機理

2.1.1 好氧細菌 細菌降解芳香烴化合物根據降解環(huán)境的氧氣含量可以分為有氧降解和無氧降解。在雙加氧酶作用下PAHs的羥基化是有氧降解的主要途徑。鄰位或間位引入羥基形成反式–二氫-二羥基化合物，提高芳香環(huán)活性，然后繼續(xù)氧化直至芳香環(huán)破裂生成不飽和的直鏈脂肪酸[58]，后續(xù)的降解進入PAHs中心降解途徑與三羧酸循環(huán)中間產物相連[59]。以菲為例，菲是石油污染后在環(huán)境中存在量最大的PAHs之一。細菌有氧降解菲存在多種不同的開環(huán)方式，根據加氧酶作用位點不同，菲一般在1,2位、3,4位和9,10位開環(huán)(圖1)[31, 60-61]。細菌中不同的菌株對應有一條或多條代謝途徑。節(jié)桿菌sp. P1-1和分支桿菌JS19b1T有3條降解菲的途徑，分別從1,2位、3,4位和9,10位開環(huán)[25, 61]。伯克氏菌sp.C3降解菲有兩條途徑，分別從1,2位和3,4位開環(huán)[60]。分支桿菌sp. Strains PYR-1、馬特爾氏菌sp. AD-3 降解菲也有兩條途徑，但是分別從3,4位和9,10位開環(huán)[62-63]。假單胞菌NCIB 9816、鞘氨醇單胞菌sp. PheB4中菲僅有3,4位開環(huán)一條途徑[64-65]。菲1,2位和3,4位環(huán)裂解有著共同的中間產物1,2-二羥萘，該產物對應有兩條降解途徑。對于能夠利用萘的細菌，1,2-二羥萘轉變成水楊酸后經過龍膽酸途徑降解，而不能利用萘的細菌，1,2-二羥萘通過原兒茶酸途徑降解(圖1)。菲也可以在9,10位形成二羥基，繼而生成2,2’-聯苯二酸。

圖1 菲好氧降解的可能途徑[31, 60-61]

2.1.2 厭氧細菌 厭氧細菌降解PAHs的起始步驟主要涉及羧基化和甲基化(圖2)。以萘為例，萘在厭氧環(huán)境中有兩條降解途徑，一條通過甲基化在2號位加上甲基，形成2-甲基萘；另一條通過羧基化也在2號位加上羧基生成2-萘甲酸。甲基化和羧基化產物進一步降解需要輔酶的參與 (琥珀酰輔酶A或輔酶A)，再經過還原酶作用生成烯酰輔酶A，烯酰輔酶A在水合酶作用下與輔酶A相連的芳香環(huán)被打開，后者經過類似于β-氧化的步驟進一步完全降解為乙酰輔酶A和CO2，具體的降解過程見圖2[66]。研究發(fā)現PAHs的完全降解過程中，多種厭氧菌參與其中發(fā)揮著不同的作用。TSAI 等[67]發(fā)現硫酸鹽降解菌會將芴和菲厭氧降解成共同的中間產物苯酚。Fang 等[68]發(fā)現脫硫腸狀菌屬()和梭菌屬()在厭氧條件下將苯酚轉化為苯甲酸鹽，互養(yǎng)菌()能夠進一步將苯甲酸鹽降解為乙酸鹽、H2和CO2，產甲烷菌()最后將乙酸鹽、H2和CO2轉化為甲烷。

2.2 真菌降解PAHs機理

2.2.1 木質素降解真菌 自然界中有一類能夠分泌木質素降解酶系(木質素過氧化物酶、錳過氧化物酶和漆酶)的真菌，這些分泌到細胞外的非特異性酶作用底物范圍廣，能夠降解包括PAHs在內的多種有機污染物，是真菌降解PAHs的獨特機制[69]。有機物的存在能夠誘導激活過氧化物酶和漆酶從而降解PAHs，例如在白腐真菌中添加草酸、丙二酸發(fā)現木質素過氧化物酶的含量升高，含錳的有機物能夠刺激錳過氧化物酶活性提升。木質素降解酶能夠在PAHs特定位點引入羥基。糙皮側耳()降解菲是從9,10位點形成二氫二醇，然后生成2,2’-聯苯二酸，最終降解為CO2，這個過程與好氧細菌降解菲中的9,10位點裂解途徑非常相似[70-71]。

圖2 萘的厭氧降解過程[66]

2.2.2 非木質素降解真菌 有些真菌除了分泌過氧化物酶系和漆酶外，還可以產生類似細胞色素P450單加氧酶的酶系降解PAHs。PAHs在細胞色素P450單加氧酶的作用下首先形成不穩(wěn)定的芳烴氧化產物，然后在環(huán)氧化物酶作用下轉變成為反式-二氫二醇或者酚類物質，繼續(xù)轉化為-葡萄糖苷、-葡萄糖醛酸苷、-硫酸酯、-木糖苷及-甲基進一步分解(圖3)[72]。細胞色素P450單加氧酶對于不同PAHs的起始作用位點各異。糙皮側耳()中細胞色素P450單加氧酶的酶系降解芘和蒽分別生成反式-4,5-芘二醇和反式1,2-蒽二醇、9,10-蒽二醇，但催化芴則在脂肪橋上羥基化和酮基化，生成9-芴醇和9-芴酮[73]。

圖3 非木質素降解真菌降解苯并芘的可能途徑[72]

2.3 放線菌降解PAHs的機理

放線菌降解PAHs的機理與好氧細菌相似。以苯并芘為例，苯并芘有多種起始羥基化位點(圖4)。Schneider 等[28]分離得到了4,5-屈二羧酸，推測分支桿菌(sp. strain RJGⅡ-135)中雙加氧酶作用于苯并芘的4,5- 位點。分支桿菌(PYR-1)降解苯并芘最初從4,5-, 9,10-, 11,12- 位點開始羥基化[30]。PYR-1在苯并芘11,12羥基化生成順式和反式-11,12-二氫-11,12-二羥基苯并芘，推測PYR-1可能同時存在雙加氧酶和單加氧酶[30]。

2.4 藻類降解PAHs的機理

藻類降解PAHs的起始步驟也涉及羥基化。Cerniglia等[54]將阿格門氏藻()接入C14標記的含萘培養(yǎng)基上，發(fā)現可以將萘轉化為1-萘酚，而且檢測到1,2-二羥基-1,2-二氫萘的存在，說明萘的降解涉及羥基化。Safonova等[56]研究柵列藻()降解菲的代謝產物時也檢測到了1,2-二羥基- 1,2-二氫菲。Chan[57]認為藻降解PAHs有單加氧酶和雙加氧酶的參與，該研究利用月牙藻()降解含菲、熒蒽及芘的混合物，發(fā)現4 d內該藻可以降解96% 菲、100% 熒蒽和100% 芘。分析降解產物發(fā)現了4種不同的單羥基菲和3種羥基化的熒蒽和芘產物，分析單羥基產物的出現由單加氧酶途徑產生。同時產物中也檢測到了2種二羥基菲，推測雙加氧酶同時參與了降解過程。

圖4 放線菌降解苯并芘的可能途徑[30]

3 不能以PAHs為唯一碳源的(共代謝)降解機理

共代謝現象最早是Leadbetter和Foster[74]在甲烷假單胞菌()中發(fā)現的，該菌不能利用乙烷、丙烷和丁烷作為碳源生長，但是添加外加碳源甲烷后該菌能夠氧化上述3種碳源。Leadbetter和Foster將此現象稱之為共氧化(Co-oxidation)，認為在生長基質(甲烷)存在的情況下，在微生物的作用下非生長基質(乙烷、丙烷和丁烷) 發(fā)生氧化。隨后，Jesnsen[75]提出用共代謝(Co-metabolism)的概念來替代共氧化，認為在生長基質存在時，微生物對非生長基質的轉化不僅有氧化，還有還原作用，都應該屬于代謝的范疇?，F在PAHs共代謝是指在外加碳源情況下，難生物降解的PAHs有可能被微生物轉化甚至完全降解[76]。Gibson 等[77]發(fā)現盡管strain B-836不能利用苯并芘作為碳源生長，但是有琥珀酸和聯苯的存在下，能夠將苯并芘氧化生成二氫二醇化合物。另外，有研究報道某些真菌能夠利用PAHs作為生長碳源，但是添加某些有機物后PAHs降解效率顯著提高，這些研究把它歸結為共代謝[78]。微生物以共代謝方式降解PAHs可能有以下幾種原因：①缺少進一步降解的酶系。當某種易降解物加入后，微生物在代謝易降解物過程中誘導產生某種專一性較差的酶，這種酶的作用導致了PAHs的降解。缺少這類酶時，降解反應無法繼續(xù)進行。②由于中間產物的抑制。③需要另外的基質誘導代謝酶或提供細胞反應中不能充分供應的物質[79]。有研究認為土壤中微生物代謝產生的多酚氧化酶參與了共代謝降解PAHs的過程，劉世亮等[80]發(fā)現，當苯并芘加入土壤7 d后，加有共代謝底物的組分(水楊酸、鄰苯二甲酸、琥珀酸鈉)中多酚氧化酶活性明顯高于對照組，到第35天，加有水楊酸和琥珀酸鈉的處理組多酚氧化酶活性明顯高于其他2個處理，與土壤中苯并芘的降解率相一致。

4 微生物降解PAHs 的途徑及其調控基因

PAHs的微生物降解是復雜的降解過程，好氧細菌及真菌分解依靠加氧酶等一系列酶催化PAHs生成一些關鍵中間代謝物(原兒茶酸、水楊酸、龍膽酸、鄰苯二酚)[81]。厭氧細菌則借助硫酸鹽、硝酸鹽、甲烷等電子受體將PAHs逐步降解為苯甲酸鹽。這些中間產物再通過相應的降解途徑徹底分解。目前已知的中間產物主要有鄰苯二酚、3,4-二羥基苯甲酸、龍膽酸(1,5-二羥基苯甲酸)、1,2,4-苯三酚、6-氯-1,2,4-苯三酚、對苯二酚、氯代對苯二酚、苯甲酰輔酶A等，這些物質主要通過β-酮己二酸途徑、苯乙酸途徑和龍膽酸途徑以及苯甲酰輔酶A途徑等進行降解[82]。

4.1 β-酮己二酸途徑及其調控基因

β-酮己二酸(ketoadipate)途徑 (鄰位裂解途徑)是芳香烴降解的一條重要途徑，好氧細菌和真菌中都具有這條降解途徑。該途徑有鄰苯二酚和原兒茶酸(3,4-二羥基苯甲酸) 兩個中間產物，對應著兩條并行的降解支路，兩條支路分別通過鄰苯二酚1,2-雙加氧酶和原兒茶酸3,4-雙加氧酶在鄰位羥基位點將芳香環(huán)打開，然后經過異構、脫羧形成共同的代謝中間產物β-酮己二酸烯醇內酯，再經過水解、輔酶A轉移、硫解等步驟生成了乙酰輔酶A和琥珀酰輔酶A。β-酮己二酸途徑主要是受和基因簇調控，其中基因簇(調控原兒茶酸支路)存在于考克氏菌屬(spp.)、不動桿菌屬(spp.)、棒桿菌屬(spp.)、鏈霉屬(spp.)、紅球菌屬(spp.)及假單胞菌屬(spp.)的一些菌株[83-87]。基因簇數量不同種屬的細菌中有所區(qū)別，即使相同屬的細菌基因簇數量也有不同?？伎耸暇鶧C2201、不動桿菌sp. ADP1、新月柄桿菌只有一個單獨的基因簇，而sp. strain RHA1存在兩個基因簇，分別由兩個不同的操縱子調控(JI和H-GBLRF)，KT2440中存在3個基因簇(RKFTBDCP、IJ和GH)[83,87-91]。多個基因簇有可能分布在一個染色體上，也有可能分布于不同染色體，和中多個基因簇分布在兩條不同染色體，而中基因簇則分布在一條染色體上[87]。基因 (調控鄰苯二酚支路) 多集中在一個基因簇上[90]，但、、中有多個基因簇，且分布在不同染色體上[87]?；虼刂惺寝D錄調控子，調控相鄰基因的轉錄表達。節(jié)細菌屬中是LysR型轉錄調控子，通過-粘康酸誘導激活相鄰基因的轉錄，而紅球菌中是IclR型調控子，控制原兒茶酸的代謝調控[92-94]。

4.2 苯乙酸途徑(PAA) 及其調控基因

作為該途徑的中間代謝產物苯乙酸沒有采取脂肪烴降解方式降解為苯甲酸進入β-酮己二酸途徑，而是先連接上輔酶A，形成苯乙酰輔酶A，然后在芳香環(huán)2,3位上引入羥基形成順式-二氫二醇，再經過環(huán)裂解、水合、氧化硫酯、脫氫步驟分解為乙酰輔酶A和琥珀酰輔酶A，進入TCA循環(huán)。苯乙酸途徑受基因簇調控?；虼氐臄盗吭诓煌N屬中有所不同，紅球菌PR4和假單胞菌KT 2440/U中有兩個基因簇，而鏈霉菌A3中基因簇數量超過3個[82]。RHA1、PR4及KT 2440/U菌株中基因簇中均含有兩個連續(xù)的核心功能區(qū)域：GHIJK (編碼芳香環(huán)羥基化) 和( 編碼β-氧化)。多個基因簇在染色體上的位置不一定連續(xù)。PR4的兩個基因簇為連續(xù)分布，而RHA1的基因簇則存在2.6 kb的間隔，A3也有類似情況出現[82]。

4.3 龍膽酸途徑(GEN)及其調控基因

sp. Strain U2菌株中萘被降解為水楊酸后沒有轉化為兒茶酚為進入β-酮己二酸途徑，而是繼續(xù)被氧化為龍膽酸，在龍膽酸1,2-雙加氧酶催化開環(huán)，通過后續(xù)代謝進入TCA循環(huán)，這條途徑被稱為龍膽酸途徑[95]。許多PAHs在分解過程中產生的萘、水楊酸、3-羥基苯甲酸和鄰氨基苯甲酸等產物都可以通過龍膽酸途徑轉變?yōu)楸岷脱雍魉?，進入TCA循環(huán)[96]。該途徑受基因簇的調控，假單胞菌G7的NAH7質粒中基因簇上游操縱子(AaAbAcAdBFCQED)負責編碼由萘轉為水楊酸的酶系，下游操縱子(GTHINLOMKJXY) 負責編碼水楊酸轉變?yōu)楸岷鸵胰?，操縱子R處于上、下游操縱子之間，是調節(jié)基因，調節(jié)上、下操縱子的表達，水楊酸可以誘導激活R，導致基因簇的高效表達[97]。假單胞菌屬的不同菌中均存在下游操縱子的部分序列(THINLOMKJ)[98]。

另外，在不同種屬的菌株中還發(fā)現一些基因與. putida G7的NAH7質粒中基因簇非常相似，且高度保守，因此通常被稱為“經典的基因”。這些編碼降解PAHs關鍵酶的基因有的位于質粒上，有的位于染色體上，如.NCIB9816質粒中基因簇ABC，sp.strain C18菌株中的基因簇ABDEFGHIJ，OUS82染色體中的基因簇AaAbAcAdBFCQED和PaK1菌株中的基因簇A1-A2A3A4BFCQED以及AN10菌株中的基因簇AaAbAcAdBFCED與G7的NAH7質粒中基因簇非常相似[99-103]。

4.4 苯甲酰輔酶A降解途徑及其調控基因

Tsai等[68]發(fā)現硫酸鹽降解菌會將芴和菲厭氧降解成共同的中間產物苯酚。Fang等[68]發(fā)現脫硫腸狀菌屬()和梭菌屬()在厭氧條件下將苯酚轉化為苯甲酸鹽。PAHs的厭氧降解又需要輔酶的參與，因此推測苯甲酰輔酶A 是PAHs厭氧降解的中間產物。苯甲酰輔酶A的完全降解又分為上游降解途徑和下游降解途徑(圖5)。上游降解途徑是指從苯甲酰輔酶A經過一系列酶促反應催化降解為7-羧基-庚酰輔酶A的過程，整個上游降解途徑可分為兩個重要的降解步驟：一是脫芳烴化，脫芳烴化是指苯甲酰輔酶A在ATP和H供體的存在下，被苯甲酰輔酶A還原酶(BCR)催化下生成1,5環(huán)己二烯酰輔酶A。二是在1,5環(huán)己二烯酰輔酶A水合酶、脫氫酶和水解酶的作用下生成7-羧基-庚酰輔酶A或3-羥基-7羧基-庚酰輔酶A，這個過程類似β-氧化過程(圖5中的a、b)[104]。苯酰輔酶A降解途徑涉及到眾多降解基因或基因簇，其中兼性厭氧菌編碼苯環(huán)脫芳烴化的苯甲酰輔酶A還原酶(BCR)在陶厄氏菌 ()中已經研究得比較清楚，該BCR酶由αβγδ四聚體組成，分別由基因編碼。BCR酶有兩個功能不同的結構域：由編碼的αδ亞基上有兩個ATP結合位點和鐵硫聚合物的電子結合位點；βγ亞基由編碼，起到結合一個苯甲酰輔酶A和協調鐵硫聚合物的作用[105-107]。磁螺菌屬(spp.)的不同菌株中編碼BCR酶的基因也有與陶厄氏菌 ()相似的基因簇[108-109]。紅假單胞菌()中分離得到的BCR也由αβγδ四聚體組成，由基因編碼，但基因編碼的產物氨基酸序列與基因只有64% ~ 76% 的相似性[109-110]。固氮弧菌屬() 中BCR四聚體由基因編碼與和基因產物僅有22% ~ 43% 的相似性[111]。專性厭氧菌有著與兼性厭氧菌不同的脫芳烴化酶系，研究已經證實專性厭氧菌中互養(yǎng)菌()和地桿菌()缺乏兼性厭氧菌中典型的BCR結構[112-113]。地桿菌()中基因簇編碼苯甲酰輔酶A脫芳烴化的酶系，互養(yǎng)菌()中編碼苯甲酰輔酶A脫芳烴化的酶系也由基因簇控制，兩個基因簇有高度相似性(氨基酸水平＞50% 相似性)[113]。

圖5 苯和苯乙酰輔酶A的厭氧降解途徑[104]

苯甲酰輔酶A下游降解途徑是指從7-羧基-庚酰輔酶A或3-羥基-7羧基-庚酰輔酶A開始經過一系列酶促反應最終降解為乙酰輔酶A和CO2的過程。固氮弧菌屬()、地桿菌()、陶厄氏菌 ()、磁螺菌屬(spp.)、互養(yǎng)菌() 中苯甲酰輔酶A經過酶促反應苯環(huán)開鏈生成3-羥基-7羧基-庚酰輔酶A，而紅假單胞菌()的產物為7-羧基-庚酰輔酶A，在脫氫酶和水合酶的作用下，7-羧基-庚酰輔酶A羥基化生成3-羥基-7羧基-庚酰輔酶A。在有NAD+存在下，3-羥基-7羧基-庚酰輔酶A被還原生成3-羰基-7羧基-庚酰輔酶A，然后在CoA參與下脫去1分子乙酰輔酶A生成5-羧基-戊二酰輔酶A，在戊二酰輔酶A脫氫酶作用下脫去2H+和1 CO2生成巴豆酰輔酶A(丁烯酰輔酶A)，在3-羥基丁酰輔酶A脫氫酶和1 H2O催化下生成3-羥基丁酰輔酶A，在脫氫酶的作用下最終降解生成2分子乙酰輔酶A[104]。

5 展望

伴隨著經濟全球化的進程，石油及其產品已經遍及全球各個角落。石油及其產品的開采、煉制、儲運和使用都可能會產生PAHs。PAHs具有高度穩(wěn)定性、耐降解性和環(huán)境毒性，給生態(tài)環(huán)境及人類生活帶來極大的威脅。利用微生物降解因石油泄露殘留在環(huán)境中的PAHs是綠色、安全、低耗能的辦法，已經成為了世界性的研究課題，相關研究已經在不同微生物中PAHs的降解途徑、功能酶系、編碼基因及信號調控方面展開，其中單環(huán)芳香烴的開環(huán)、好氧降解途徑以及相關的編碼基因已經研究得比較清楚，低分子量(≤3環(huán))的PAHs好氧降解機理、代謝途徑以及編碼基因也逐漸明了，高分子量(≥4環(huán))PAHs的微生物降解盡管已成為當前研究熱點，但相關降解途徑及編碼基因還不甚清楚。另外，PAHs的厭氧降解途徑的了解還十分有限，厭氧降解途徑的相關基因以及調控機理已經成為目前的研究熱點。與細菌相比，真菌特別是非木質素降解真菌對PAHs降解的機理目前也不清楚，這方面的研究也逐漸開始成為未來PAHs降解的研究方向之一。

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Microbial Degradation of Polycyclic Aromatic Hydrocarbons from Crude Oils: A Review

SHEN Guolan1, LI Li2, CHEN Suo2*

(1 College of Geosciences, Yangtze University, Wuhan 430100, China; 2 College of Life Science, Yangtze University, Jingzhou, Hubei 434025, China)

Polycyclic aromatic hydrocarbons (PAHs) from crude oils is a kind of teratogenic and carcinogenic contaminant, in which the low aromatic nucleus ring (2–3 ring) are the dominated components and the substituent group ratio is significantly higher than those from other origins. The degradation of PAHs caused by oils leakage are mainly dependent on microbial activities. This paper summarizes the microbial species, degradation mechanisms, metabolic pathways and coding genes with relation to PAHs biodegradation. The degradation mechanisms are divided into co-metabolism mechanism and the mechanism in which PAHs could be acted as the only carbon source of microbial population from the perspective of carbon source. The degradation pathways of aerobic and anaerobic microorganisms associated with PAHs and corresponding encoding gene clusters are also elaborated in this paper. In natural environment, bacteria, actinomycetes, fungi and algae can degrade PAHs. The hydroxylation and dearomatization of benzene respectively catalyzed by oxygenases and reductases are the key steps in aerobic and anaerobic degradation pathways. Moreover,,,,,andgene clusters associated with degradation regulate the aerobic and anaerobic degradation process respectively. These advances can contribute to systematically understand the PAHs degradation process, the mechanism of microbial action and molecular genetic mechanisms, and thus can provide a theoretical basis for further utilization of microorganisms in environmental bioremediation.

Polycyclic aromatic hydrocarbons from crude oils; Microbial degradation; Mechanism; Degradation pathways; Genes

國家自然科學基金項目(31501453)資助。

(chensuo9803@126.com)

申國蘭 (1983— )，女，河北石家莊人，碩士研究生，主要從事地質環(huán)境生態(tài)學方面研究。E-mail: 270968223@qq.com

10.13758/j.cnki.tr.2018.01.003

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