铜离子对混合菌群降解三氯乙烯的影响与机制分析

Effects of copper on biodegradation mechanism of trichloroethylene by mixed microorganisms

在三氯乙烯(TCE)胁迫条件下,从生活垃圾填埋场覆盖土中富集得到了可高效降解TCE的混合菌群SWA1。考察了铜离子浓度0-15μmol/L范围内混合菌群对TCE的降解,当铜离子浓度为0.03μmol/L时,降解速率最大为29.60 nmol/min,降解率达95.75%。此条件下的pmo A和mmo X表达量均达最大值,pmo A的相对表达量(4.22 E-03)比mmo X(9.30 E-06)和Lmp H(0)高3个数量级。在0-0.75μmol/L和1-15μmol/L两个铜离子浓度区间,分别出现了TCE降解峰值,高通量测序结果表明,甲基孢囊菌科Methylocystaceae的甲烷氧化菌为优势微生物。随着铜离子浓度提高,混合菌群SWA1生物多样性显著降低。铜离子浓度的变化影响了混合菌群的结构和活性,进而影响了TCE降解机制。当铜离子浓度为0.03μmol/L时,降解机制包括TCE直接降解和甲烷氧化菌共代谢降解。当铜离子浓度为5μmol/L时,降解率可达到84.75%。此时,降解机制包括TCE直接降解以及甲烷氧化菌和含苯酚羟化酶菌群的共代谢降解。

We isolated and enriched mixed microorganisms SWA1 from landfill cover soils supplemented with trichloroethylene（TCE）. The microbial mixture could degrade TCE effectively under aerobic conditions. Then, we investigated the effect of copper ion（0 to 15 μmol/L） on TCE biodegradation. Results show that the maximum TCE degradation speed was 29.60 nmol/min with 95.75% degradation when copper ion was at 0.03 μmol/L. In addition, genes encoding key enzymes during biodegradation were analyzed by Real-time quantitative reverse transcription PCR（RT-q PCR）. The relative expression abundance of pmo A gene（4.22E-03） and mmo X gene（9.30E-06） was the highest when copper ion was at 0.03 μmol/L. Finally, we also used Mi Seq pyrosequencing to investigate the diversity of microbial community. Methylocystaceae that can co-metabolic degrade TCE were the dominant microorganisms; other microorganisms with the function of direct oxidation of TCE were also included in SWA1 and the microbial diversity decreased significantly along with increasing of copper ion concentration. Based on the above results, variation of copper ion concentration affected the composition of SWA1 and degradation mechanism of TCE. The degradation mechanism of TCE included co-metabolism degradation of methanotrophs and oxidation metabolism directly at copper ion of 0.03 μmol/L. When copper ion at 5 μmol/L（biodegradation was 84.75%）, the degradation mechanism of TCE included direct-degradation and co-metabolism degradation of methanotrophs and microorganisms containing phenol hydroxylase. Therefore, biodegradation of TCE by microorganisms was a complicated process, the degradation mechanism included co-metabolism degradation of methanotrophs and bio-oxidation of non-methanotrophs.