硝酸盐促进有机物污染底泥修复过程中的微生物群落响应机理

Microbiota play an important role in degradation of organic pollutants in contaminated sediments. However, lock of available electron acceptors restricts the metabolic activity and biodegradation rate of organic pollutants in the sediments. Addition of nitrate, a common electron acceptor under anaerobic condition, can strengthen the microbial biodegradation of the organic pollutants. However, the molecular mechanisms of nitrate simultaneously enhancing the biodegradation of organic electron donors (OEDs) and organic electron acceptors (OEAs) are still unclear. Combining previous knowledge about the anaerobic respiration of microbiota and the biodegradation of the OEDs and OEAs, we propose a hypothesis to elucidate the mechanisms as follows: nitrate firstly couples with OED and enhances the anaerobic respiration and ATP production of microbiota. Then the reproductions of microorganisms with respiratory versatility are promoted and the community structures and metabolic properties are changed. Simultaneously, the transcriptions of dehalogenase genes are induced by nitrate via the CprK pathway. Ultimately, the biodegradation of OEA is promoted. In order to verify the hypothesis, we choose naphthalene and decabromodiphenyl ether as representatives of OED and OEA, respectively, and build micro-cosmic systems to conduct the biodegradation experiments. We intend to monitor the changes of ATP production, metabolic activity, community structure, functional gene composition and expression of the microbiota via biological kits, SSU rRNA gene high-throughput sequencing, metagenomic/metatranscriptomic sequencing, and RT-PCR. Combining with detecting of physical and chemical indexes, the results will illustrate the molecular mechanisms of nitrate simultaneously enhancing the biodegradation of OEDs and OEAs.

微生物群落在去除底泥有机污染物过程中发挥重要作用，但因污染底泥中缺乏可利用的电子受体而限制了微生物群落的代谢活性和降解有机物的能力。投加作为电子受体的硝酸盐能促进微生物群落厌氧降解有机物，但硝酸盐同时促进微生物群落厌氧降解电子供体类有机物（OED）和电子受体类有机物（OEA）的分子机理尚不清楚。结合已有知识，我们认为硝酸盐首先耦合OED促进微生物群落厌氧呼吸产能，进而促使复合呼吸功能微生物繁殖，改变微生物群落结构和代谢特性，同时硝酸盐通过CprK诱导脱卤微生物还原脱卤酶基因表达，最终促使微生物群落降解OEA。为了验证该假说，我们拟以萘和十溴二苯醚为代表，通过微宇宙系统中微生物群落核糖体小亚基DNA高通量测序、宏基因组/宏转录组测序和RT-PCR技术，结合理化指标分析微生物群落结构、功能基因组成和表达变化，以期阐明硝酸盐促进微生物群落降解污染河涌底泥中有机物的分子机理。

随着我国工业化和城市化进程的不断推进，人民生活水平不断提高的同时，工农业生产也带来了严重的环境污染，其中珠三角地区电子电器工业园区河涌底泥有机污染因导致严重的河涌“黑臭”问题而成为工业污染的典型代表，不仅影响整个城市的景观，还对城市居民的身心健康造成严重的不良影响。因此，有机污染物污染河涌底泥的修复问题成为当前城市河道水体修复的核心问题，而生物修复因其成本低、易操作、二次污染风险小等优势近年来受到广泛关注，但又因其修复效率低、修复周期长等问题限制了其在城市污染河涌修复中的应用。为了解决生物修复效率低、修复周期长的问题，本项目通过研究硝酸钙作为厌氧条件下的电子受体促进污染河涌底泥微生物群落的厌氧呼吸产能，激活污染河涌底泥中微生物的代谢活性，促进污染河涌底泥微生物群落对有机污染物的代谢降解效率，从而达到提高生物修复污染河涌底泥的目的。研究发现投加硝酸盐能够显著改善微生物的群落结构，将微生物群落由厌氧发酵异养氧化产能转化为硝酸盐厌氧呼吸产能，从而提高了产能效率，有效促进了微生物群落的代谢活性，加速了污染河涌底泥中有机污染物的降解，投加硝酸盐1个月内底泥表层呈现土黄色，不再有“黑臭”问题，修复8个月后的底泥全部呈现土黄色，有机污染物显著降解，但修复后上覆水中亚硝酸盐浓度和硫酸盐浓度显著提高，尚需深入研究硝酸盐与有机污染物的摩尔分子量比例问题，以避免因过量投加硝酸盐导致的二次氮污染问题。本项目的研究基本阐明了硝酸盐促进污染河涌底泥有机污染物降解的分子机制，为后续利用硝酸盐激活河涌底泥土著微生物加速河涌底泥修复提供重要的理论指导。

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