Department of Environmental Science and Engineering, Ewha Womans University, Seoul, 120-750, Republic of Korea.
Environ Sci Pollut Res Int. 2010 Jan;17(1):64-77. doi: 10.1007/s11356-009-0238-x.
BACKGROUND, AIM, AND SCOPE: Hexane, a representative VOC, is used as a solvent for extraction and as an ingredient in gasoline. The degradation of hexane by bacteria is relatively slow due to its low solubility. Moreover, the biodegradation pathway of hexane under aerobic conditions remains to be investigated; therefore, a study relating to aerobic biodegradation mechanisms is required. Consequently, in this study, an effective hexane degrader was isolated and the biodegradation pathway examined for the first time. In addition, the degradation characteristics of a variety of recalcitrant hydrocarbons were qualitatively and quantitatively investigated using the isolate.
A hexane-degrading bacterium was isolated from an enrichment culture using petroleum-contaminated soil as an inoculum with hexane as the sole carbon and energy source. The bacterium was also identified using the partial 16S rRNA gene sequence. To test the hexane-degrading capacity of the isolate, 10 ml of an EH831 cell suspension was inoculated into a 600-ml serum bottle with hexane (7.6-75.8 micromol) injected as the sole carbon source. The rates of hexane degradation were determined by analyzing the concentrations of hexane using headspace gas chromatography. In addition, the hexane biodegradation pathway under aerobic conditions was investigated by identifying the metabolites using gas chromatography-mass spectrometry with solid-phase microextraction. 14C-hexane was used to check if EH831 could mineralize hexane in the same experimental system. The degradabilities of other hydrocarbons were examined using EH831 with methanol, ethanol, acetone, cyclohexane, methyl tert-butyl ether (MTBE), dichloromethane (DCM), trichloroethylene, tetrachloroethylene, benzene, toluene, ethylbenzene, xylene (BTEX), pyrene, diesel, lubricant oil, and crude oil as sole carbon sources.
A bacterium, EH831, was isolated from the enriched hexane-degrading consortium, which was able to degrade hexane and various hydrocarbons, including alcohols, chlorinated hydrocarbons, cyclic alkanes, ethers, ketones, monoaromatic and polyaromatic hydrocarbons, and petroleum hydrocarbons. The maximum hexane degradation rate (V max) of EH831 was 290 micromol g dry cell weight(-1) h(-1), and the saturation constant (K s) was 15 mM. Using 14C-hexane, EH831 was confirmed to mineralize approximately 49% of the hexane into CO2 and, converted approximately, 46% into biomass; the rest (1.7%) remained as extracellular metabolites in the liquid phase. The degradation pathway was assessed through the qualitative analysis of the hexane intermediates due to EH831, which were 2-hexanol, 2-hexanone, 5-hexen-2-one and 2,5-hexanedione, in that order, followed by 4-methyl-2-pentanone, 3-methyl-1-butanol, 3-methyl-1-butanone and butanal, and finally, CO2. EH831 could degrade methanol, ethanol, acetone, cyclohexane, MTBE, DCM, BTEX, pyrene, diesel, and lubricant oil.
EH831 was able to degrade many recalcitrant hydrocarbons at higher degradation rates compared with previous well-known degraders. Furthermore, this study primarily suggested the aerobic biodegradation pathway, which may provide valuable information for researchers and engineers working in the field of environmental engineering.
Rhodococcus sp. EH831 is a promising bioresource for removing hexane and other recalcitrant hydrocarbons from a variety of environments. Moreover, the aerobic biodegradation pathway is reported for the first time in this study, which offers valuable information for understanding the microbial degradation of hexane.
The utility of the strain isolated in this study needs to be proved by its application to biological process systems, such as biofilters and bioreactors, etc., for the degradation of hexane and many other recalcitrant hydrocarbons. Detailed investigations will also be needed to clarify the enzymatic characteristics relating the degradation of both recalcitrant hydrocarbons and hexane.
背景、目的和范围：己烷是一种代表性的挥发性有机化合物，用作萃取溶剂和汽油的成分。由于其低溶解度，细菌对己烷的降解速度相对较慢。此外，有氧条件下己烷的生物降解途径仍有待研究；因此，需要进行与有氧生物降解机制相关的研究。因此，在这项研究中，分离出一种有效的己烷降解菌，并首次研究了其生物降解途径。此外，还使用该分离株定性和定量研究了多种难降解烃的降解特性。
从含有石油污染土壤的富集培养物中分离出一株己烷降解菌，以己烷为唯一碳源和能源。该细菌还通过部分 16S rRNA 基因序列进行鉴定。为了测试分离株的己烷降解能力，将 10ml 的 EH831 细胞悬浮液接种到 600ml 的血清瓶中，用己烷（7.6-75.8µmol）作为唯一的碳源注入。通过顶空气相色谱分析己烷的浓度来确定己烷的降解速率。此外，通过固相微萃取-气相色谱-质谱联用技术鉴定代谢产物，研究了有氧条件下己烷的生物降解途径。使用 14C-己烷检查 EH831 是否可以在相同的实验系统中矿化己烷。使用 EH831 以甲醇、乙醇、丙酮、环己烷、甲基叔丁基醚（MTBE）、二氯甲烷（DCM）、三氯乙烯、四氯乙烯、苯、甲苯、乙苯、二甲苯（BTEX）、芘、柴油、润滑油和原油作为唯一碳源，考察了其他烃类的降解性能。
从富集的己烷降解菌中分离出一株细菌 EH831，它能够降解己烷和各种烃类，包括醇类、氯代烃类、环烷烃类、醚类、酮类、单芳烃和多芳烃类以及石油烃类。EH831 的最大己烷降解速率（Vmax）为 290µmol g 干细胞重量(-1) h(-1)，饱和常数（Ks）为 15mM。使用 14C-己烷，EH831 被证实可将约 49%的己烷矿化为 CO2，并将约 46%转化为生物量；其余（1.7%）仍以液相中的胞外代谢物形式存在。通过对 EH831 产生的己烷中间产物进行定性分析，评估了降解途径，这些中间产物依次为 2-己醇、2-己酮、5-己烯-2-酮和 2,5-己二酮，随后是 4-甲基-2-戊酮、3-甲基-1-丁醇、3-甲基-1-丁酮和丁醛，最后是 CO2。EH831 可以降解甲醇、乙醇、丙酮、环己烷、MTBE、DCM、BTEX、芘、柴油和润滑油。
EH831 能够以比以前已知的降解菌更高的降解速率降解许多难降解的烃类。此外，本研究主要提出了有氧生物降解途径，这可能为从事环境工程领域的研究人员和工程师提供有价值的信息。
Rhodococcus sp. EH831 是一种有前途的生物资源，可用于去除多种环境中的己烷和其他难降解烃类。此外，本研究首次报道了有氧生物降解途径，为理解己烷的微生物降解提供了有价值的信息。
需要通过将分离株应用于生物过程系统（如生物过滤器和生物反应器等）来证明该菌株的实用性，以降解己烷和许多其他难降解烃类。还需要进行详细的研究，以阐明与难降解烃类和己烷降解相关的酶学特性。
