微生物降解菲的机理研究进展*

针对微生物降解菲的机理研究进展,论述了细菌、真菌在好氧、厌氧条件下代谢菲的产物以及推测的降解途径;在此基础上概括了催化反应的酶系以及编码酶系的基因簇。简要介绍了基因探针的应用,并结合本实验室的初步研究,指出了该领域有待深入探讨的问题。     

接种功能内生细菌Diaphorobacter sp.Phe15减少蔬菜亚细胞菲积累的体外试验研究

[目的]土壤中的多环芳烃(polycyclic aromatic hydrocarbons, PAHs)可被蔬菜根系吸收并在可食部分积累进而通过食物链威胁人群健康。接种功能内生细菌能有效减低蔬菜中PAHs的积累,而关于其对蔬菜亚细胞组分中PAHs积累的影响却鲜有报道。[方法]采用体外实验,研究了接种具有菲降解功能的菌株Diaphorobacter sp. Phe15对空心菜茎叶亚细胞组分中菲积累的影响及PAHs代谢相关酶活性的响应。[结果]接种Phe15可以可加速空心菜茎叶亚细胞中菲的降解,显著削减空心菜亚细胞组分中菲的含量,接菌后空心菜亚细胞组分中菲降解率达90%以上。此外,接种功能菌Phe15可以影响空心菜亚细胞组分中PAHs代谢相关酶系的活性,空心菜亚细胞水平POD、PPO、C230活性整体得到提高,且酶系活性与空心菜体内菲积累呈负相关关系。[结论]接种具有菲降解功能的菌株Phe15增加了空心菜亚细胞水平PAHs代谢相关酶系活性,进而降低空心菜体内菲的积累,研究结果为利用功能内生细菌削减蔬菜中多环芳烃污染提供了一定的参考和理论依据。     

中度嗜盐菌Martelella sp. AD-3 降解菲过程中水杨酸-5-羟化酶的酶学性质

[目的]研究中度嗜盐菌Martelella sp.AD-3在降解菲过程中水杨酸-5-羟化酶的活性与菲降解效率的关系及其酶学性质.[方法]通过HPLC分析菲的降解效率和AD-3菌粗酶液催化水杨酸的产物,根据NADH在340 nm处的吸光度变化计算水杨酸-5-羟化酶的活性.[结果]水杨酸-5-羟化酶是一种诱导酶,在AD-3菌的对数生长期和稳定初期时活性较高,酶活力大小与该菌对菲的降解速率基本一致.在菲浓度为200 mg/L、生长盐度为3％、pH为9.0的培养条件下,AD-3菌株表达的水杨酸-5-羟化酶的活力最高,为132.8 nmol/(min·mg).水杨酸-5-羟化酶催化水杨酸降解时的最适温度、pH和盐度分别为30℃、7.5和3％,酶的最大反应速率为200 nmol/(min· mg)、米氏常数Km为8.7μmol/L.[结论]AD-3菌在降解菲的过程中表达水杨酸-5-羟化酶,该酶的活性与菲降解速率具有相关性.     

高效木聚糖降解酶系定制的新进展与挑战

木聚糖是植物细胞壁中含量最丰富的非纤维素多糖,大约占陆地生物质资源的20%-35%。不同物种来源的木聚糖结构因取代方式不同而具有广泛的异质性,这对生物质资源向生物燃料和其他高值产品高效转化提出了重大挑战。因此,需要开发由不同类型酶组成的最佳混合物以有效糖化木聚糖类底物。但是针对特定类型的底物设计高效降解酶系十分困难,应考虑底物的类型、底物的组成和物理性质、多糖的聚合度以及不同降解酶组分的生化性质等。本文从不同植物木聚糖的结构异质性与合成复杂性方面展示了其抗降解屏障,同时介绍了木聚糖主链降解酶系及侧链降解酶系的多样性以及协同降解作用,综述了复杂生境中微生物种群产生的混合酶系、降解菌株产生的高效酶系,以及基于特定木聚糖底物改造并定制简化高效的酶系统。随着不同种类木聚糖精细结构和木聚糖降解酶底物特异性的深入研究,针对特定底物类型进行绿色高效木聚糖酶系定制,加速木聚糖类底物的降解,从而实现木质纤维素资源的绿色高值化利用。     

多环芳烃降解菌筛选及其降解特性

通过选择性富集培养,从辽河油田稠油污染土壤4号土样中,获得了能以高浓度菲(2000mg·L^-1)为唯一碳源和能源快速生长的优势菌系和优良菌株ZL5．16S rDNA核苷酸序列分析表明,ZL5菌株归类于鞘氨醇单胞菌属,分得的菌系和菌株有较强的降解菲能力,120h混合菌系降解了投加菲的95．28％,菌株降解了69．24％,但它们对芘的降解能力均较低,外加碳源葡萄糖可提高菌系和菌株的菲、芘降解能力,加量多。提高幅度大,但超过一定量。降解速率开始下降,表现出抑制效应。所以,应用时需控制适宜的浓度。     

乳白耙齿菌F17对共存菲、蒽的降解差异性

【目的】通过对影响乳白耙齿菌F17 (Irpex lacteus)降解共存菲、蒽因素的研究,比较共存的菲和蒽降解性能的不同,并结合降解中间产物的分析,初步探讨其降解途径。【方法】采用GC-MS测定菲和蒽的浓度,并通过质谱图分析降解产物。【结果】共存的菲和蒽在初始浓度均为5 mg/L时生物降解率较高,分别为93%和85%以上。乳白耙齿菌F17在pH 3.0–8.0能较好地降解共存的菲,在pH 4.0–8.0范围内可较好地降解共存的蒽。菲的生物降解过程对低温的适应性比共存的蒽要好,共存体系的最适降解温度是30°C。在酶的作用下,蒽转化成邻苯二甲酸,菲转化为邻苯二甲酸或邻苯二酚。【结论】实验结果表明,当菲和蒽共存时,不同条件下乳白耙齿菌F17对菲的降解效果均比蒽要好,而且菲的总降解速率比蒽要快,作为同分异构体的菲和蒽,由于3个苯环位置的不同而表现出降解性能和降解途径上的差异性。     

石油污染土壤中菲、蒽和正十六烷的微生物降解

在模拟自然条件下,考察了芳香烃(菲、蒽)和脂肪烃(正十六烷)单独存在以及共存于土壤中时,土著微生物对它们降解的影响。结果表明,土著微生物对它们的降解均符合一级反应动力学。菲、蒽或正十六烷单独存在于土壤中时,其微生物降解速率常数分别为0.0226、0.0283和0.0096 d^-1。菲和正十六烷共存时,正十六烷能够作为土著微生物降解菲的共代谢底物,促进菲的降解,使菲的半衰期比其单独存在于土壤中缩短44%;同时,正十六烷的加氧酶被菲诱导,使其活性提高而增强对正十六烷的降解作用,其微生物降解半衰期比其单独存在于土壤中缩短49%。菲和蒽共存促进了土著微生物对菲的降解,却抑制了对蒽的降解。     

黄孢原毛平革菌木素降解酶系的研究进展

黄孢原毛平革菌木素降解酶系主要由木素过氧化物酶、锰过氧化物酶和乙二醛氧化酶组成。由于该酶系特殊的降解机制,除了木质素,它能降解许多种类的有机污染物,因此在环保方面有巨大的应用前景。本文主要综述了国内外对该酶系的研究进展。     

生物质多糖的高效降解与降解酶（系）的精确定制

自然界中多糖类生物质资源十分丰富,然而其复杂的抗降解屏障限制了生物转化的进程.近年来,随着生物质多糖结构的快速解析以及大量多糖降解酶的鉴定研究,针对不同底物结构或产物需求,仿制高效微生物多糖代谢途径,精确定制多糖降解酶系,促进生物质高效转化已成为可能.本文分析中性多糖(纤维素和木聚糖)、碱性多糖(几丁质和壳聚糖)以及酸性多糖(褐藻胶)的精细结构组成与基团性质,总结3类多糖主要降解酶的活性架构特征及其底物精确结合模式.文章还阐述蛋白质工程设计与定制策略,针对酶分子不同功能区的分析,可为酶分子的功能快速设计与改造提供靶点,以获得适宜于工业应用的高效酶分子,此外,根据微生物胞外降解酶系的降解次序与协同关系,可基于应用需求精确定制复杂多糖降解酶系,实现生物质的高效与高值降解转化.     

双加氧酶活力对细菌降解菲的指示作用

在液体培养基中选用两种石油降解细菌进行菲降解实验,研究了菲降解率和双加氧酶活力的变化。结果表明,菲降解率受其浓度的影响,当菲浓度为100mg·L-1时,其降解率为最高。而菲浓度高于100mg·L-1时,其降解率下降。实验发现在菲浓度为50～250mg·L-1条件下,细菌的双加氧酶活力与其菲的降解率存在较好的相关性,对细菌降解菲具有指示作用,可将双加氧酶活力作为菲降解率变化的评价指标。     

Insights into the genome and proteome of <Emphasis Type="Italic">Sphingomonas paucimobilis</Emphasis> strain 20006FA involved in the regulation of polycyclic aromatic hydrocarbon degradation

In order to study the mechanisms regulating the phenanthrene degradation pathway and the intermediate-metabolite accumulation in strain S. paucimobilis 20006FA, we sequenced the genome and compared the genome-based predictions to experimental proteomic analyses. Physiological studies indicated that the degradation involved the salicylate and protocatechuate pathways, reaching 56.3% after 15 days. Furthermore, the strain degraded other polycyclic aromatic hydrocarbons (PAH) such as anthracene (13.1%), dibenzothiophene (76.3%), and fluoranthene. The intermediate metabolite 1-hydroxy-2-naphthoic acid (HNA) accumulated during phenanthrene catabolism and inhibited both bacterial growth and phenanthrene degradation, but exogenous-HNA addition did not affect further degradation. Genomic analysis predicted 126 putative genes encoding enzymes for all the steps of phenanthrene degradation, which loci could also participate in the metabolism of other PAH. Proteomic analysis identified enzymes involved in 19 of the 23 steps needed for the transformation of phenanthrene to trichloroacetic-acid intermediates that were upregulated in phenanthrene cultures relative to the levels in glucose cultures. Moreover, the protein-induction pattern was temporal, varying between 24 and 96 h during phenanthrene degradation, with most catabolic proteins being overexpressed at 96 h—e. g., the biphenyl dioxygenase and a multispecies (2Fe–2S)-binding protein. These results provided the first clues about regulation of expression of phenanthrene degradative enzymes in strain 20006FA and enabled an elucidation of the metabolic pathway utilized by the bacterium. To our knowledge the present work represents the first investigation of genomic, proteomic, and physiological studies of a PAH-degrading Sphingomonas strain.     

Oxidative degradation of phenanthrene by the ligninolytic fungus Phanerochaete chrysosporium.

The ligninolytic fungus Phanerochaete chrysosporium oxidized phenanthrene and phenanthrene-9,10-quinone (PQ) at their C-9 and C-10 positions to give a ring-fission product, 2,2'-diphenic acid (DPA), which was identified in chromatographic and isotope dilution experiments. DPA formation from phenanthrene was somewhat greater in low-nitrogen (ligninolytic) cultures than in high-nitrogen (nonligninolytic) cultures and did not occur in uninoculated cultures. The oxidation of PQ to DPA involved both fungal and abiotic mechanisms, was unaffected by the level of nitrogen added, and was significantly faster than the cleavage of phenanthrene to DPA. Phenanthrene-trans-9,10-dihydrodiol, which was previously shown to be the principal phenanthrene metabolite in nonligninolytic P. chrysosporium cultures, was not formed in the ligninolytic cultures employed here. These results suggest that phenanthrene degradation by ligninolytic P. chrysosporium proceeds in order from phenanthrene----PQ----DPA, involves both ligninolytic and nonligninolytic enzymes, and is not initiated by a classical microsomal cytochrome P-450. The extracellular lignin peroxidases of P. chrysosporium were not able to oxidize phenanthrene in vitro and therefore are also unlikely to catalyze the first step of phenanthrene degradation in vivo. Both phenanthrene and PQ were mineralized to similar extents by the fungus, which supports the intermediacy of PQ in phenanthrene degradation, but both compounds were mineralized significantly less than the structurally related lignin peroxidase substrate pyrene was.     

Identification of metabolites from phenanthrene oxidation by phenoloxidases and dioxygenases of Polyporus sp. S133

Phenanthrene degradation by Polyporus sp. S133, a new phenanthrene-degrading strain, was investigated in this work. The analysis of degradation was performed by calculation of the remaining phenanthrene by gas chromatography-mass spectrometry. When cells were grown in phenanthrene culture after 92 h, all but 200 and 250 mg/l of the phenanthrene had been degraded. New metabolic pathways of phenanthrene and a better understanding of the phenoloxidases and dioxygenase mechanism involved in degradation of phenanthrene were explored in this research. The mechanism of degradation was determined through identification of the several metabolites; 9,10-phenanthrenequinone, 2,2'-diphenic acid, salicylic acid, and catechol. 9,10-Oxidation and ring cleavage to give 9,10-phenanthrenequinone is the major fate of phenanthrene in ligninolytic Polyporus sp. S133. The identification of 2,2'-diphenic acid in culture extracts indicates that phenanthrene was initially attacked through dioxigenation at C9 and C10 to give cis-9,10-dihydrodiol. Dehydrogenation of phenanthrene-cis-9,10-dihydrodiol to produce the corresponding diol, followed by ortho-cleavage of the oxygenated ring, produced 2,2'-diphenic acid. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase, and 2,3-dioxygenase) produced by Polyporus sp. S133 was detected during the incubation. The highest level of activity was shown at 92 h of culture.     

Identification of pyrene-induced proteins in Mycobacterium sp. strain 6PY1: evidence for two ring-hydroxylating dioxygenases

In this study, the enzymes involved in polycyclic aromatic hydrocarbon (PAH) degradation were investigated in the pyrene-degrading Mycobacterium sp. strain 6PY1. [(14)C]pyrene mineralization experiments showed that bacteria grown with either pyrene or phenanthrene produced high levels of pyrene-catabolic activity but that acetate-grown cells had no activity. As a means of identifying specific catabolic enzymes, protein extracts from bacteria grown on pyrene or on other carbon sources were analyzed by two-dimensional gel electrophoresis. Pyrene-induced proteins were tentatively identified by peptide sequence analysis. Half of them resembled enzymes known to be involved in phenanthrene degradation, with closest similarity to the corresponding enzymes from Nocardioides sp. strain KP7. The genes encoding the terminal components of two distinct ring-hydroxylating dioxygenases were cloned. Sequence analysis revealed that the two enzymes, designated Pdo1 and Pdo2, belong to a subfamily of dioxygenases found exclusively in gram-positive bacteria. When overproduced in Escherichia coli, Pdo1 and Pdo2 showed distinctive selectivities towards PAH substrates, with the former enzyme catalyzing the dihydroxylation of both pyrene and phenanthrene and the latter preferentially oxidizing phenanthrene. The catalytic activity of the Pdo2 enzyme was dramatically enhanced when electron carrier proteins of the phenanthrene dioxygenase from strain KP7 were coexpressed in recombinant cells. The Pdo2 enzyme was purified as a brown protein consisting of two types of subunits with M(r)s of about 52,000 and 20,000. Immunoblot analysis of cell extracts from strain 6PY1 revealed that Pdo1 was present in cells grown on benzoate, phenanthrene, or pyrene and absent in acetate-grown cells. In contrast, Pdo2 could be detected only in PAH-grown cells. These results indicated that the two enzymes were differentially regulated depending on the carbon source used for growth.     

Genetics of naphthalene and phenanthrene degradation by Comamonas testosteroni

Naphthalene and phenanthrene have long been used as model compounds to investigate the ability of bacteria to degrade polycyclic aromatic hydrocarbons. The catabolic pathways have been determined, several of the enzymes have been purified to homogeneity, and genes have been cloned and sequenced. However, the majority of this work has been performed with fast growing Pseudomonas strains related to the archetypal naphthalene-degrading P. putida strains G7 and NCIB 9816-4. Recently Comamonas testosteroni strains able to degrade naphthalene and phenanthrene have been isolated and shown to possess genes for polycyclic aromatic hydrocarbon degradation that are different from the canonical genes found in Pseudomonas species. For instance, C. testosteroni GZ39 has genes for naphthalene and phenanthrene degradation which are not only different from those found in Pseudomonas species but are also arranged in a different configuration. C. testosteroni GZ42, on the other hand, has genes for naphthalene and phenanthrene degradation which are arranged almost the same as those found in Pseudomonas species but show significant divergence in their sequences. Received 10 August 1997/ Accepted in revised form 15 August 1997     

Versatile catechol dioxygenases in <Emphasis Type="Italic">Sphingobium scionense</Emphasis> WP01<Superscript>T</Superscript>

The objective was to understand the roles of multiple catechol dioxygenases in the type strain Sphingobium scionense WP01^T (Liang and Lloyd-Jones in Int J Syst Evol Microbiol 60:413–416, 2010a) that was isolated from severely contaminated sawmill soil. The dioxygenases were identified by sequencing, examined by determining the substrate specificities of the recombinant enzymes, and by quantifying gene expression following exposure to model priority pollutants. Catechol dioxygenase genes encoding an extradiol xylE and two intradiol dioxygenases catA and clcA that are highly similar to sequences described in other sphingomonads are described in S. scionense WP01^T. The distinct substrate specificities determined for the recombinant enzymes confirm the annotated gene functions and suggest different catabolic roles for each enzyme. The role of the three enzymes was evaluated by analysis of enzyme activity in crude cell extracts from cells grown on meta-toluate, benzoate, biphenyl, naphthalene and phenanthrene which revealed the co-induction of each enzyme by different substrates. This was corroborated by quantifying gene expression when cells were induced by biphenyl, naphthalene and pentachlorophenol. It is concluded that the ClcA and XylE enzymes are recruited in pathways that are involved in the degradation of chlorinated aromatic compounds such as pentachlorophenol, the XylE and ClcA enzymes will also play a role in degradation pathways that produce alkylcatechols, while the three enzymes ClcA, XylE and CatA will be simultaneously involved in pathways that generate catechol as a degradation pathway intermediate.     

降解性细菌对菲诱导的蛋白及酶活性应答反应

测定了3株以菲为唯一碳源的芽孢杆菌属(Bacillus)菌株(BA11、BA19和BA27)的降解能力、多酚氧化酶和过氧化氢酶的活性及蛋白变化．结果表明,当菲浓度在200mg·L^-1以下时,3株菌多酚氧化酶和过氧化氢酶的活性随菲浓度的提高变化不大,其中BA19和BA27菌株表现出较高的稳定性．当菲浓度为200mg·L^-1时,BA27诱导表达了一条分子量为27000道尔顿的新蛋白条带,同时有些蛋白的合成受到抑制．因此可以认为,诱导产生的新蛋白与其污染条件下的细菌降解能力及稳定性有关．