Faculty of Chemistry, Environmental Microbiology and Biotechnology (EMB), Aquatic Microbiology, University of Duisburg-Essen, Universitätsstr. 5, 45141 Essen, Germany.
FEMS Microbiol Ecol. 2022 Feb 10;98(1). doi: 10.1093/femsec/fiac003.
Despite hostile environmental conditions, microbial communities have been found in µL-sized water droplets enclosed in heavy oil of the Pitch Lake, Trinidad. Some droplets showed high sulfate concentrations and surprisingly low relative abundances of sulfate-reducing bacteria in a previous study. Hence, we investigated here whether sulfate reduction might be inhibited naturally. Ion chromatography revealed very high formate concentrations around 2.37 mM in 21 out of 43 examined droplets. Since these concentrations were unexpectedly high, we performed growth experiments with the three sulfate-reducing type strains Desulfovibrio vulgaris, Desulfobacter curvatus, and Desulfococcus multivorans, and tested the effects of 2.5, 8, or 10 mM formate on sulfate reduction. Experiments demonstrated that 8 or 10 mM formate slowed down the growth rate of D. vulgaris and D. curvatus and the sulfate reduction rate of D. curvatus and D. multivorans. Increasing formate concentrations delayed the onsets of growth and sulfate reduction of D. multivorans, which were even inhibited completely while formate was added constantly. Contrary to previous studies, D. multivorans was the only organism capable of formate consumption. Our study suggests that formate accumulates in the natural environment of the water droplets dispersed in oil and that such levels are very likely inhibiting sulfate-reducing microorganisms.
尽管环境条件恶劣，但在特立尼达的Pitch Lake 重油中封闭的 µL 大小的水滴中发现了微生物群落。在之前的一项研究中，一些水滴表现出高硫酸盐浓度和令人惊讶的低硫酸盐还原菌相对丰度。因此，我们在这里研究是否硫酸盐还原可能是自然抑制的。离子色谱法显示，在 43 个检测到的水滴中，有 21 个的甲酸盐浓度约为 2.37 mM。由于这些浓度出人意料地高，我们用三种硫酸盐还原型菌株脱硫弧菌、弯曲脱硫杆菌和脱硫球菌进行了生长实验，并测试了 2.5、8 或 10 mM 甲酸盐对硫酸盐还原的影响。实验表明，8 或 10 mM 甲酸盐减缓了脱硫弧菌和弯曲脱硫杆菌的生长速度以及弯曲脱硫杆菌和脱硫球菌的硫酸盐还原率。增加甲酸盐浓度会延迟脱硫球菌生长和硫酸盐还原的开始，而当持续添加甲酸盐时，甚至会完全抑制其生长和硫酸盐还原。与之前的研究相反，脱硫球菌是唯一能够消耗甲酸盐的生物体。我们的研究表明，甲酸盐在分散在油中的水滴的自然环境中积累，并且这种水平很可能抑制硫酸盐还原微生物。
