Department of Isotope Biogeochemistry, Department of Environmental Microbiology, Helmholtz Centre for Environmental Research-UFZ, Permoserstrasse 15, 04318 Leipzig, Germany.
Environ Sci Technol. 2010 Jan 1;44(1):309-15. doi: 10.1021/es902491d.
Laboratory experiments were performed with two aerobic MTBE degrading strains ( Methylibium sp. PM1 and Aquincola tertiaricarbonaris L108) in order to determine whether conditions of low oxygen availability, typically found in fuel-contaminated aquifers, can influence stable isotope fractionation of MTBE. Although single carbon and hydrogen enrichment factors of the two strains were not significantly or were only slightly (L108) affected by low oxygen concentrations (fully oxic incubation with initial 21% O2 in the headspace tested versus hypoxic conditions always <2% O2), the experiments showed indirect effects caused by competition interactions in mixed cultures. In a mixed culture of PM1 and L108 under oxic and even more so under hypoxic conditions, the total observed carbon isotope enrichment factor was significantly reduced, while hydrogen fractionation was not detectable. This indicates that the low fractionating model strain L108 is more competitive in degrading MTBE compared to strain PM1. Consistently, higher oxygen affinities during MTBE degradation were observed for strain L108. These first studies, conducted with resting cells, may explain the low isotope fractionation observed in some field studies that are not necessarily related to a lack of biodegradation.
实验室实验使用两种好氧 MTBE 降解菌株（甲基杆菌 PM1 和 Aquincola tertiaricarbonaris L108）进行，以确定低氧条件（通常存在于受燃料污染的含水层中）是否会影响 MTBE 的稳定同位素分馏。尽管两种菌株的单碳和单氢富集因子不受低氧浓度的显著或仅轻微影响（在顶空初始 21%O2 的完全好氧孵育与始终<2%O2 的缺氧条件下进行测试），但实验表明混合培养物中的竞争相互作用会产生间接影响。在 PM1 和 L108 的混合培养物中，无论是在好氧条件下还是在缺氧条件下，总观察到的碳同位素富集因子显著降低，而氢分馏则不可检测。这表明与 PM1 菌株相比，低分馏模型菌株 L108 在降解 MTBE 方面更具竞争力。一致地，在 MTBE 降解过程中观察到 L108 菌株具有更高的氧气亲和力。这些首次使用静止细胞进行的研究可能解释了一些野外研究中观察到的低同位素分馏现象，这些现象不一定与缺乏生物降解有关。
