微生物降解石油源多环芳香烃的研究进展①

申国兰，李 利，陈 莎*



微生物降解石油源多环芳香烃的研究进展①

申国兰1，李 利2，陈 莎2*

(1长江大学地球科学学院，武汉 430100；2长江大学生命科学学院，湖北荆州 434025)

石油源多环芳香烃是存在于石油中的一类致畸、致癌污染物，具有以低环(2 ~ 3环) 为主且取代基比例明显高于其他来源PAHs的组分特征。石油泄露引发的PAHs污染，其降解主要依赖于微生物的活动。本文对能够降解PAHs的微生物种类、降解机理、代谢途径及编码基因进行了概述。从PAHs作为碳源的角度将微生物降解机理划分为能以PAHs为唯一碳源进行生长的降解机理和共代谢机理。对与PAHs有关的好氧和厌氧微生物降解途径及对应的编码基因簇进行了总结。自然界中细菌、放线菌、真菌及藻类都能够降解PAHs，由加氧酶催化的苯环羟基化和还原酶介导的苯环脱芳烃化是好氧和厌氧降解途径的关键步骤，与降解有关的,,,,和基因簇则分别调控好氧和厌氧降解过程。这些进展有助于系统了解石油源PAHs的降解过程、微生物作用机理和分子遗传机制，为进一步利用微生物促进环境生物修复提供理论依据。

石油源多环芳香烃；微生物降解；机理；代谢途径；基因

石油是一种含有多种烃类及少量其他有机物的复杂混合物。根据烃类结构特点和成分，可以将石油中的烃类物质分为饱和烃、芳香烃、非烃和沥青质4种组分[1-2]。石油芳香烃物质中以多环芳香烃(PAHs) 对环境污染威胁最大。PAHs是指两个或两个以上的苯环以线性、弯接或簇聚方式构成的一类化学结构稳定、难于降解的烃类化合物，其中4环以上的PAHs容易被土壤或生物体富集而产生毒性，严重威胁到人类健康及生物安全[3-4]。PAHs有多种来源，不同来源的PAHs在组分特征上有所差异。石油来源的PAHs以2 ~ 3环为主，而煤炭、汽油、木材、天然气等燃料不完全燃烧产生的PAHs以4 ~ 6环为主[5-6]。另外，石油来源的PAHs取代基比例明显高于其他来源的PAHs，Buddziński等[7]发现石油中的单甲基菲含量明显高于未取代菲，而燃料燃烧产生的PAHs中单甲基和二甲基取代物的含量远远小于未被取代的化合物。

石油来源的PAHs一旦进入自然环境后，光照、雨水淋滤、挥发和微生物降解等环境因素会引发降解，这种降解行为类似于环境的自我净化修复。但是微生物对石油源PAHs具有选择性，Lamberts等[8]分离得到的29株菌株中有11株能够利用甲基菲，并发现其中仅有1株鞘氨醇单胞菌能够降解1-甲基菲和2-甲基菲，其他鞘氨醇单胞菌只能降解1-甲基菲。具有取代基的PAHs在降解开始时取代基团先被氧化，Nadali等[9]分析了2-甲基菲和9-甲基菲的微生物降解产物，发现2-甲基菲生成2-羟甲基菲和2-菲甲醛，推测甲基基团的氧化是降解开始的第一步。取代基基团氧化后经过脱甲基化变成单体PAHs，后续的降解过程与PAHs单体的降解途径一致。Novaković 等[10]发现微生物修复后的土壤中单体菲/甲基菲的比例显著升高，可能原因是微生物细胞表面的“活性中心”与甲基基团相互作用促使甲基菲的脱甲基化。本文在前人研究的基础上对能降解PAHs的微生物种类、降解机理、降解途径及调控基因等方面展开综述，以期为石油来源的PAHs降解研究提供帮助。

1 降解PAHs化合物的微生物种类

微生物降解是去除环境中PAHs的最主要途径[11]。能够降解PAHs的微生物有细菌、放线菌、真菌和藻类[12]，其中细菌中常见有红球菌 ()、假单胞菌 ()、棒杆菌 ()、微球菌 ()、产碱杆菌 ()、分支杆菌()以及鞘脂菌()等；放线菌常见的是诺卡氏菌()；PAHs降解真菌又分为木质素降解真菌和非木质素降解真菌，木质素降解真菌常见有平革菌()、侧耳()、云芝()等；非木质素降解真菌常见有青霉()、曲霉()及小银克汉霉()等。部分藻类也具有PAHs降解能力，已经报道的有阿格门氏藻()、颤藻()、栅藻()及月牙藻()等(表1)。

表1 降解PAHs的微生物菌株及其底物

2 能够以PAHs作为唯一碳源的微生物降解机理

2.1 细菌的降解机理

2.1.1 好氧细菌 细菌降解芳香烃化合物根据降解环境的氧气含量可以分为有氧降解和无氧降解。在双加氧酶作用下PAHs的羟基化是有氧降解的主要途径。邻位或间位引入羟基形成反式–二氢-二羟基化合物，提高芳香环活性，然后继续氧化直至芳香环破裂生成不饱和的直链脂肪酸[58]，后续的降解进入PAHs中心降解途径与三羧酸循环中间产物相连[59]。以菲为例，菲是石油污染后在环境中存在量最大的PAHs之一。细菌有氧降解菲存在多种不同的开环方式，根据加氧酶作用位点不同，菲一般在1,2位、3,4位和9,10位开环(图1)[31, 60-61]。细菌中不同的菌株对应有一条或多条代谢途径。节杆菌sp. P1-1和分支杆菌JS19b1T有3条降解菲的途径，分别从1,2位、3,4位和9,10位开环[25, 61]。伯克氏菌sp.C3降解菲有两条途径，分别从1,2位和3,4位开环[60]。分支杆菌sp. Strains PYR-1、马特尔氏菌sp. AD-3 降解菲也有两条途径，但是分别从3,4位和9,10位开环[62-63]。假单胞菌NCIB 9816、鞘氨醇单胞菌sp. PheB4中菲仅有3,4位开环一条途径[64-65]。菲1,2位和3,4位环裂解有着共同的中间产物1,2-二羟萘，该产物对应有两条降解途径。对于能够利用萘的细菌，1,2-二羟萘转变成水杨酸后经过龙胆酸途径降解，而不能利用萘的细菌，1,2-二羟萘通过原儿茶酸途径降解(图1)。菲也可以在9,10位形成二羟基，继而生成2,2’-联苯二酸。

图1 菲好氧降解的可能途径[31, 60-61]

2.1.2 厌氧细菌 厌氧细菌降解PAHs的起始步骤主要涉及羧基化和甲基化(图2)。以萘为例，萘在厌氧环境中有两条降解途径，一条通过甲基化在2号位加上甲基，形成2-甲基萘；另一条通过羧基化也在2号位加上羧基生成2-萘甲酸。甲基化和羧基化产物进一步降解需要辅酶的参与 (琥珀酰辅酶A或辅酶A)，再经过还原酶作用生成烯酰辅酶A，烯酰辅酶A在水合酶作用下与辅酶A相连的芳香环被打开，后者经过类似于β-氧化的步骤进一步完全降解为乙酰辅酶A和CO2，具体的降解过程见图2[66]。研究发现PAHs的完全降解过程中，多种厌氧菌参与其中发挥着不同的作用。TSAI 等[67]发现硫酸盐降解菌会将芴和菲厌氧降解成共同的中间产物苯酚。Fang 等[68]发现脱硫肠状菌属()和梭菌属()在厌氧条件下将苯酚转化为苯甲酸盐，互养菌()能够进一步将苯甲酸盐降解为乙酸盐、H2和CO2，产甲烷菌()最后将乙酸盐、H2和CO2转化为甲烷。

2.2 真菌降解PAHs机理

2.2.1 木质素降解真菌 自然界中有一类能够分泌木质素降解酶系(木质素过氧化物酶、锰过氧化物酶和漆酶)的真菌，这些分泌到细胞外的非特异性酶作用底物范围广，能够降解包括PAHs在内的多种有机污染物，是真菌降解PAHs的独特机制[69]。有机物的存在能够诱导激活过氧化物酶和漆酶从而降解PAHs，例如在白腐真菌中添加草酸、丙二酸发现木质素过氧化物酶的含量升高，含锰的有机物能够刺激锰过氧化物酶活性提升。木质素降解酶能够在PAHs特定位点引入羟基。糙皮侧耳()降解菲是从9,10位点形成二氢二醇，然后生成2,2’-联苯二酸，最终降解为CO2，这个过程与好氧细菌降解菲中的9,10位点裂解途径非常相似[70-71]。

图2 萘的厌氧降解过程[66]

2.2.2 非木质素降解真菌 有些真菌除了分泌过氧化物酶系和漆酶外，还可以产生类似细胞色素P450单加氧酶的酶系降解PAHs。PAHs在细胞色素P450单加氧酶的作用下首先形成不稳定的芳烃氧化产物，然后在环氧化物酶作用下转变成为反式-二氢二醇或者酚类物质，继续转化为-葡萄糖苷、-葡萄糖醛酸苷、-硫酸酯、-木糖苷及-甲基进一步分解(图3)[72]。细胞色素P450单加氧酶对于不同PAHs的起始作用位点各异。糙皮侧耳()中细胞色素P450单加氧酶的酶系降解芘和蒽分别生成反式-4,5-芘二醇和反式1,2-蒽二醇、9,10-蒽二醇，但催化芴则在脂肪桥上羟基化和酮基化，生成9-芴醇和9-芴酮[73]。

图3 非木质素降解真菌降解苯并芘的可能途径[72]

2.3 放线菌降解PAHs的机理

放线菌降解PAHs的机理与好氧细菌相似。以苯并芘为例，苯并芘有多种起始羟基化位点(图4)。Schneider 等[28]分离得到了4,5-屈二羧酸，推测分支杆菌(sp. strain RJGⅡ-135)中双加氧酶作用于苯并芘的4,5- 位点。分支杆菌(PYR-1)降解苯并芘最初从4,5-, 9,10-, 11,12- 位点开始羟基化[30]。PYR-1在苯并芘11,12羟基化生成顺式和反式-11,12-二氢-11,12-二羟基苯并芘，推测PYR-1可能同时存在双加氧酶和单加氧酶[30]。

2.4 藻类降解PAHs的机理

藻类降解PAHs的起始步骤也涉及羟基化。Cerniglia等[54]将阿格门氏藻()接入C14标记的含萘培养基上，发现可以将萘转化为1-萘酚，而且检测到1,2-二羟基-1,2-二氢萘的存在，说明萘的降解涉及羟基化。Safonova等[56]研究栅列藻()降解菲的代谢产物时也检测到了1,2-二羟基- 1,2-二氢菲。Chan[57]认为藻降解PAHs有单加氧酶和双加氧酶的参与，该研究利用月牙藻()降解含菲、荧蒽及芘的混合物，发现4 d内该藻可以降解96% 菲、100% 荧蒽和100% 芘。分析降解产物发现了4种不同的单羟基菲和3种羟基化的荧蒽和芘产物，分析单羟基产物的出现由单加氧酶途径产生。同时产物中也检测到了2种二羟基菲，推测双加氧酶同时参与了降解过程。

图4 放线菌降解苯并芘的可能途径[30]

3 不能以PAHs为唯一碳源的(共代谢)降解机理

共代谢现象最早是Leadbetter和Foster[74]在甲烷假单胞菌()中发现的，该菌不能利用乙烷、丙烷和丁烷作为碳源生长，但是添加外加碳源甲烷后该菌能够氧化上述3种碳源。Leadbetter和Foster将此现象称之为共氧化(Co-oxidation)，认为在生长基质(甲烷)存在的情况下，在微生物的作用下非生长基质(乙烷、丙烷和丁烷) 发生氧化。随后，Jesnsen[75]提出用共代谢(Co-metabolism)的概念来替代共氧化，认为在生长基质存在时，微生物对非生长基质的转化不仅有氧化，还有还原作用，都应该属于代谢的范畴。现在PAHs共代谢是指在外加碳源情况下，难生物降解的PAHs有可能被微生物转化甚至完全降解[76]。Gibson 等[77]发现尽管strain B-836不能利用苯并芘作为碳源生长，但是有琥珀酸和联苯的存在下，能够将苯并芘氧化生成二氢二醇化合物。另外，有研究报道某些真菌能够利用PAHs作为生长碳源，但是添加某些有机物后PAHs降解效率显著提高，这些研究把它归结为共代谢[78]。微生物以共代谢方式降解PAHs可能有以下几种原因：①缺少进一步降解的酶系。当某种易降解物加入后，微生物在代谢易降解物过程中诱导产生某种专一性较差的酶，这种酶的作用导致了PAHs的降解。缺少这类酶时，降解反应无法继续进行。②由于中间产物的抑制。③需要另外的基质诱导代谢酶或提供细胞反应中不能充分供应的物质[79]。有研究认为土壤中微生物代谢产生的多酚氧化酶参与了共代谢降解PAHs的过程，刘世亮等[80]发现，当苯并芘加入土壤7 d后，加有共代谢底物的组分(水杨酸、邻苯二甲酸、琥珀酸钠)中多酚氧化酶活性明显高于对照组，到第35天，加有水杨酸和琥珀酸钠的处理组多酚氧化酶活性明显高于其他2个处理，与土壤中苯并芘的降解率相一致。

4 微生物降解PAHs 的途径及其调控基因

PAHs的微生物降解是复杂的降解过程，好氧细菌及真菌分解依靠加氧酶等一系列酶催化PAHs生成一些关键中间代谢物(原儿茶酸、水杨酸、龙胆酸、邻苯二酚)[81]。厌氧细菌则借助硫酸盐、硝酸盐、甲烷等电子受体将PAHs逐步降解为苯甲酸盐。这些中间产物再通过相应的降解途径彻底分解。目前已知的中间产物主要有邻苯二酚、3,4-二羟基苯甲酸、龙胆酸(1,5-二羟基苯甲酸)、1,2,4-苯三酚、6-氯-1,2,4-苯三酚、对苯二酚、氯代对苯二酚、苯甲酰辅酶A等，这些物质主要通过β-酮己二酸途径、苯乙酸途径和龙胆酸途径以及苯甲酰辅酶A途径等进行降解[82]。

4.1 β-酮己二酸途径及其调控基因

β-酮己二酸(ketoadipate)途径 (邻位裂解途径)是芳香烃降解的一条重要途径，好氧细菌和真菌中都具有这条降解途径。该途径有邻苯二酚和原儿茶酸(3,4-二羟基苯甲酸) 两个中间产物，对应着两条并行的降解支路，两条支路分别通过邻苯二酚1,2-双加氧酶和原儿茶酸3,4-双加氧酶在邻位羟基位点将芳香环打开，然后经过异构、脱羧形成共同的代谢中间产物β-酮己二酸烯醇内酯，再经过水解、辅酶A转移、硫解等步骤生成了乙酰辅酶A和琥珀酰辅酶A。β-酮己二酸途径主要是受和基因簇调控，其中基因簇(调控原儿茶酸支路)存在于考克氏菌属(spp.)、不动杆菌属(spp.)、棒杆菌属(spp.)、链霉属(spp.)、红球菌属(spp.)及假单胞菌属(spp.)的一些菌株[83-87]。基因簇数量不同种属的细菌中有所区别，即使相同属的细菌基因簇数量也有不同。考克氏菌DC2201、不动杆菌sp. ADP1、新月柄杆菌只有一个单独的基因簇，而sp. strain RHA1存在两个基因簇，分别由两个不同的操纵子调控(JI和H­GBLRF)，KT2440中存在3个基因簇(RKFTBDCP、IJ和GH)[83,87-91]。多个基因簇有可能分布在一个染色体上，也有可能分布于不同染色体，和中多个基因簇分布在两条不同染色体，而中基因簇则分布在一条染色体上[87]。基因 (调控邻苯二酚支路) 多集中在一个基因簇上[90]，但、、中有多个基因簇，且分布在不同染色体上[87]。基因簇中是转录调控子，调控相邻基因的转录表达。节细菌属中是LysR型转录调控子，通过-粘康酸诱导激活相邻基因的转录，而红球菌中是IclR型调控子，控制原儿茶酸的代谢调控[92-94]。

4.2 苯乙酸途径(PAA) 及其调控基因

作为该途径的中间代谢产物苯乙酸没有采取脂肪烃降解方式降解为苯甲酸进入β-酮己二酸途径，而是先连接上辅酶A，形成苯乙酰辅酶A，然后在芳香环2,3位上引入羟基形成顺式-二氢二醇，再经过环裂解、水合、氧化硫酯、脱氢步骤分解为乙酰辅酶A和琥珀酰辅酶A，进入TCA循环。苯乙酸途径受基因簇调控。基因簇的数量在不同种属中有所不同，红球菌PR4和假单胞菌KT 2440/U中有两个基因簇，而链霉菌A3中基因簇数量超过3个[82]。RHA1、PR4及KT 2440/U菌株中基因簇中均含有两个连续的核心功能区域：GHIJK (编码芳香环羟基化) 和( 编码β-氧化)。多个基因簇在染色体上的位置不一定连续。PR4的两个基因簇为连续分布，而RHA1的基因簇则存在2.6 kb的间隔，A3也有类似情况出现[82]。

4.3 龙胆酸途径(GEN)及其调控基因

sp. Strain U2菌株中萘被降解为水杨酸后没有转化为儿茶酚为进入β-酮己二酸途径，而是继续被氧化为龙胆酸，在龙胆酸1,2-双加氧酶催化开环，通过后续代谢进入TCA循环，这条途径被称为龙胆酸途径[95]。许多PAHs在分解过程中产生的萘、水杨酸、3-羟基苯甲酸和邻氨基苯甲酸等产物都可以通过龙胆酸途径转变为丙酮酸和延胡索酸，进入TCA循环[96]。该途径受基因簇的调控，假单胞菌G7的NAH7质粒中基因簇上游操纵子(AaAbAcAdBFCQED)负责编码由萘转为水杨酸的酶系，下游操纵子(GTHINLOMKJXY) 负责编码水杨酸转变为丙酮酸和乙醛，操纵子R处于上、下游操纵子之间，是调节基因，调节上、下操纵子的表达，水杨酸可以诱导激活R，导致基因簇的高效表达[97]。假单胞菌属的不同菌中均存在下游操纵子的部分序列(THINLOMKJ)[98]。

另外，在不同种属的菌株中还发现一些基因与. putida G7的NAH7质粒中基因簇非常相似，且高度保守，因此通常被称为“经典的基因”。这些编码降解PAHs关键酶的基因有的位于质粒上，有的位于染色体上，如.NCIB9816质粒中基因簇ABC，sp.strain C18菌株中的基因簇ABDEFGHIJ，OUS82染色体中的基因簇AaAbAcAdBFCQED和PaK1菌株中的基因簇A1­A2A3A4BFCQED以及AN10菌株中的基因簇AaAbAcAdBFCED与G7的NAH7质粒中基因簇非常相似[99-103]。

4.4 苯甲酰辅酶A降解途径及其调控基因

Tsai等[68]发现硫酸盐降解菌会将芴和菲厌氧降解成共同的中间产物苯酚。Fang等[68]发现脱硫肠状菌属()和梭菌属()在厌氧条件下将苯酚转化为苯甲酸盐。PAHs的厌氧降解又需要辅酶的参与，因此推测苯甲酰辅酶A 是PAHs厌氧降解的中间产物。苯甲酰辅酶A的完全降解又分为上游降解途径和下游降解途径(图5)。上游降解途径是指从苯甲酰辅酶A经过一系列酶促反应催化降解为7-羧基-庚酰辅酶A的过程，整个上游降解途径可分为两个重要的降解步骤：一是脱芳烃化，脱芳烃化是指苯甲酰辅酶A在ATP和H供体的存在下，被苯甲酰辅酶A还原酶(BCR)催化下生成1,5环己二烯酰辅酶A。二是在1,5环己二烯酰辅酶A水合酶、脱氢酶和水解酶的作用下生成7-羧基-庚酰辅酶A或3-羟基-7羧基-庚酰辅酶A，这个过程类似β-氧化过程(图5中的a、b)[104]。苯酰辅酶A降解途径涉及到众多降解基因或基因簇，其中兼性厌氧菌编码苯环脱芳烃化的苯甲酰辅酶A还原酶(BCR)在陶厄氏菌 ()中已经研究得比较清楚，该BCR酶由αβγδ四聚体组成，分别由基因编码。BCR酶有两个功能不同的结构域：由编码的αδ亚基上有两个ATP结合位点和铁硫聚合物的电子结合位点；βγ亚基由编码，起到结合一个苯甲酰辅酶A和协调铁硫聚合物的作用[105-107]。磁螺菌属(spp.)的不同菌株中编码BCR酶的基因也有与陶厄氏菌 ()相似的基因簇[108-109]。红假单胞菌()中分离得到的BCR也由αβγδ四聚体组成，由基因编码，但基因编码的产物氨基酸序列与基因只有64% ~ 76% 的相似性[109-110]。固氮弧菌属() 中BCR四聚体由基因编码与和基因产物仅有22% ~ 43% 的相似性[111]。专性厌氧菌有着与兼性厌氧菌不同的脱芳烃化酶系，研究已经证实专性厌氧菌中互养菌()和地杆菌()缺乏兼性厌氧菌中典型的BCR结构[112-113]。地杆菌()中基因簇编码苯甲酰辅酶A脱芳烃化的酶系，互养菌()中编码苯甲酰辅酶A脱芳烃化的酶系也由基因簇控制，两个基因簇有高度相似性(氨基酸水平＞50% 相似性)[113]。

图5 苯和苯乙酰辅酶A的厌氧降解途径[104]

苯甲酰辅酶A下游降解途径是指从7-羧基-庚酰辅酶A或3-羟基-7羧基-庚酰辅酶A开始经过一系列酶促反应最终降解为乙酰辅酶A和CO2的过程。固氮弧菌属()、地杆菌()、陶厄氏菌 ()、磁螺菌属(spp.)、互养菌() 中苯甲酰辅酶A经过酶促反应苯环开链生成3-羟基-7羧基-庚酰辅酶A，而红假单胞菌()的产物为7-羧基-庚酰辅酶A，在脱氢酶和水合酶的作用下，7-羧基-庚酰辅酶A羟基化生成3-羟基-7羧基-庚酰辅酶A。在有NAD+存在下，3-羟基-7羧基-庚酰辅酶A被还原生成3-羰基-7羧基-庚酰辅酶A，然后在CoA参与下脱去1分子乙酰辅酶A生成5-羧基-戊二酰辅酶A，在戊二酰辅酶A脱氢酶作用下脱去2H+和1 CO2生成巴豆酰辅酶A(丁烯酰辅酶A)，在3-羟基丁酰辅酶A脱氢酶和1 H2O催化下生成3-羟基丁酰辅酶A，在脱氢酶的作用下最终降解生成2分子乙酰辅酶A[104]。

5 展望

伴随着经济全球化的进程，石油及其产品已经遍及全球各个角落。石油及其产品的开采、炼制、储运和使用都可能会产生PAHs。PAHs具有高度稳定性、耐降解性和环境毒性，给生态环境及人类生活带来极大的威胁。利用微生物降解因石油泄露残留在环境中的PAHs是绿色、安全、低耗能的办法，已经成为了世界性的研究课题，相关研究已经在不同微生物中PAHs的降解途径、功能酶系、编码基因及信号调控方面展开，其中单环芳香烃的开环、好氧降解途径以及相关的编码基因已经研究得比较清楚，低分子量(≤3环)的PAHs好氧降解机理、代谢途径以及编码基因也逐渐明了，高分子量(≥4环)PAHs的微生物降解尽管已成为当前研究热点，但相关降解途径及编码基因还不甚清楚。另外，PAHs的厌氧降解途径的了解还十分有限，厌氧降解途径的相关基因以及调控机理已经成为目前的研究热点。与细菌相比，真菌特别是非木质素降解真菌对PAHs降解的机理目前也不清楚，这方面的研究也逐渐开始成为未来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

国家自然科学基金项目(31501453)资助。

(chensuo9803@126.com)

申国兰 (1983— )，女，河北石家庄人，硕士研究生，主要从事地质环境生态学方面研究。E-mail: 270968223@qq.com

10.13758/j.cnki.tr.2018.01.003

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