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石油是由烷烃、多环芳烃、以及少量沥青和树脂组成的复杂混合物。在石油开采、炼制等生产过程中产生的废水中含有一定数量的原油,这些石油类污染物质以浮油、分散油、乳化油和溶解油等形式存在于水体中[1],如果不经处理直接排放,会对地表水及土壤等环境介质造成污染。目前对于含油废水的处理主要包括浮选、生物降解、膜分离、高级氧化等技术[2]。其中,在微生物降解基础上发展起来的生物处理法具有操作简单,成本低,不易产生二次污染等优点,是一种环境友好型的处理技术[3-4]。
生物处理法是利用微生物的新陈代谢分解废水中有机物和某些无机毒物(如氰化物、硫化物),并将其转化为稳定无害物质的一种污染处理方法[5]。在利用生物法处理含油废水时,能否筛选出对毒性物质耐受性强且具有降解作用的功能菌是方法成功与否的关键。一些研究工作对于接种降解菌强化处理含油废水进行了报道[6-8]。由于石油烃的复杂性和降解异质性,多数情况下,靠单一的微生物菌种很难实现其完全降解。将不同种属的降解菌进行组合,构建结构稳定、功能广泛的高效微生物菌群,可以弥补接种单株菌强化方法上的不足,有望成为生物法净化含油废水的有效途径。然而,在降解机制探究方面,很难阐明复杂菌群中各种菌株的详细功能作用和细微结构[9-12]。
石油烃降解功能基因是指微生物产生的对于石油烃具有特定降解作用的酶编码基因,通过对功能基因进行测定,可用于分析微生物对石油烃的生物降解潜势[13-15]。在好氧条件下,烷烃单加氧酶基因alkB2和多环芳香烃末端双加氧酶基因Ahd是微生物代谢石油不同组分的主要酶系控制基因[16]。检测石油烃降解功能关键基因是评价石油烃生物降解潜势的重要依据。
本文以采自陕北地区的陈旧性石油污染土壤作为石油烃降解菌源,通过富集培养获得石油烃降解菌群LW-10,通过向高浓度含油废水中接种降解菌群LW-10进行强化处理,探究了石油烃不同组分的生物去除特性、降解菌在含油废水中的生长情况以及石油烃降解关键功能基因的变化规律。研究可为探明水体中石油烃的生物去除特性提供理论基础,同时可为接种降解菌群强化去除水体中原油提供技术支撑。
高浓度含油废水中不同组分烃的生物强化去除特性
Removal efficiencies of different components of crude oil by bioaugmentation
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摘要: 为探究石油烃降解菌群对高浓度含油废水中不同组分烃的生物降解特性,向含油水相中接种石油烃降解菌群LW-10(Accession number: SRR15082184)进行降解实验。利用GC-MS研究了LW-10对原油中不同组分烃的降解性能,采用流式细胞术检测降解体系中的菌量变化。利用qPCR技术对控制不同组分烃降解的关键基因进行检测。结果表明,原油浓度为5000 mg·L−1的含油废水中接种LW-10降解17 d,对原油中烷烃和多环芳烃组分的降解率分别为96.7%和28.4%。体系中的降解菌总浓度与高活性菌浓度由接种时的1.0×108 cfu·mL−1增加至2.1×109 cfu·mL−1和8.3×108 cfu·mL−1。检测的3种石油烃降解功能基因中,烷烃单加氧酶基因alkB2拷贝数由1.06×108 copy·mL−1变为2.84×108 copy·mL−1;芳烃双加氧酶基因Ahd由1.06×108 copy·mL−1降低至1.65×107 copy·mL−1;氧化还原酶基因PA4513由4.09×106 copy·mL−1增加增加至9.26×108 copy·mL−1。结果表明降解菌群LW-10对含油废水中的烷烃组分具有高效降解能力,对多环芳烃组分的降解能力较差。LW-10在降解石油烃过程中通过同化作用发生增殖,不同组分烃的降解效果与石油烃降解功能基因之间存在正相关关系。Abstract: The aim of this study is to investigate the biodegradation efficiencies of different components of crude oil and functional gene shift by inoculating petroleum degrading flora LW-10 (Accession number: SRR15082184) in the oily aqueous phase. The bacterial numbers in the degradation systems were detected by flow cytometry. The copy numbers of functional genes were determined by using real-time polymerase chain reaction (qPCR). Results showed that petroleum-degrading flora LW-10 isolated from the petroleum-contaminated soil was composed by Acinetobacter, Pseudomonas, Pandoraea, Achromobacter, Olivibacter, Rhodococcus, and Leucobacter. After 17 d of inoculation, the numbers of the total bacteria and highly active bacteria in the systems increased from 1.0×108 cfu·mL−1 to 2.1×109 cfu·mL−1 and 8.3×108 cfu·mL−1, respectively. The degradation rates of alkanes and polycyclic aromatic hydrocarbons (PAHs) were 96.7% and 28.4%, respectively. For hydrocarbon degradation functional genes detected, the copy numbers of alkane monooxygenase genes AlkB2 changed from 1.06×108 copy·mL−1 to 2.84×108 copy·mL−1; aromatics dioxygenase genes Ahd decreased from 1.06×108 copy·mL−1 to 1.65×107 copy·mL−1; the oxidoreductase gene PA4513 increased from 4.09×106 copy·mL−1 to 9.26×108 copy·mL−1. Results suggested that flora LW-10 had high degradation capacity towards alkane components in the aqueous phase, but its degradation ability towards PAHs is poor. Also, the flora LW-10 proliferated in the process of degrading petroleum hydrocarbons. There is a positive correlation between the degradation effects of different components and the function genes that encode the enzymes controlling hydrocarbon biodegradation.
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图 3 降解体系中细菌数量变化
Figure 3. The numbers of petroleum-degrading microorganisms in the degradation systems (3-a: Flow cytometry scatter diagram, P5 is the number of total cells in the systems, and P1 is the number of highly active cells in the systems; 3-b: the total number of bacteria and the highly active bacteria in the systems which were calculated according to the flow cytometers diagram)
表 1 土壤基本理化性质[18]
Table 1. Basic physical and chemical properties of the soil
指标
Index含量
Content测定方法
Assay method含水率/% 4.5±0.3 烘干称重法 pH 7.69±0.05 pH电极法 氧化还原电位/mV 137±5 电位法 氨氮/(mg·kg−1) 13.02±0.41 靛酚蓝 硝氮/(mg·kg−1) 0.45±0.03 紫外分光光度法 全氮/(g·kg−1) 0.61±0.10 元素分析仪 石油烃/(mg·kg−1) 26633±325 重量法 表 2 定性PCR扩增引物
Table 2. Qualitative PCR primers
目的基因
Target genes引物序列(5’- 3’)
Primer sequence
(5’-3’)扩增尺寸/bp
Amplicon size退火温度/℃
Annealing temperature参考文献
Reference芳烃双加氧酶基因Ahd F: AACATTGGCACTGATTACGAT 340 54 [24] R: GTAAACTACCGTCAAGTGCAT 氧化还原酶基因PA4513 F: GTGAAGAAAGTCTGGTTCCAGT 58 502 [25] R: GCCAGTCGAAAACCTTGC 烷烃单加氧酶基因alkB2 F: GCGATCTTCTTCCTCGGCCAGT 60 334 [25] R: CGCGCACCTTCGGGTCCATC 表 3 各目的基因标准曲线公式
Table 3. Standard curve formula of h target genes
目的基因
Target genes标准曲线公式
Standard curve formulaR2 E/% 芳烃双加氧酶基因Ahd Ct=−3.462 lgX0+39.395 0.997 94.5 氧化还原酶基因PA4513 Ct=−3.838 lgX0+43.436 0.999 82.2 烷烃单加氧酶基因alkB2 Ct=−3.247 lgX0+35.771 0.996 103.2 表 4 石油烃降解基因变化
Table 4. The changes of petroleum hydrocarbon degradation genes
基因名称
Gene name0 d拷贝数/(copy·mL−1)
0 d Copy number17 d拷贝数/(copy·mL−1)
17 d Copy numberAhd 1.06×108 1.65×107 PA4513 4.09×106 9.26×108 alkB2 1.06×108 2.84×108 -
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