Roth Spencer, Poulin Brett A, Baumann Zofia, Liu Xiao, Zhang Lin, Krabbenhoft David P, Hines Mark E, Schaefer Jeffra K, Barkay Tamar
Department of Environmental Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States.
Department of Biochemistry and Microbiology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States.
Front Microbiol. 2021 Oct 4;12:741523. doi: 10.3389/fmicb.2021.741523. eCollection 2021.
Climate change dramatically impacts Arctic and subarctic regions, inducing shifts in wetland nutrient regimes as a consequence of thawing permafrost. Altered hydrological regimes may drive changes in the dynamics of microbial mercury (Hg) methylation and bioavailability. Important knowledge gaps remain on the contribution of specific microbial groups to methylmercury (MeHg) production in wetlands of various trophic status. Here, we measured aqueous chemistry, potential methylation rates (k ), volatile fatty acid (VFA) dynamics in peat-soil incubations, and genetic potential for Hg methylation across a groundwater-driven nutrient gradient in an interior Alaskan fen. We tested the hypotheses that (1) nutrient inputs will result in increased methylation potentials, and (2) syntrophic interactions contribute to methylation in subarctic wetlands. We observed that concentrations of nutrients, total Hg, and MeHg, abundance of genes, and rates of methylation in peat incubations (k ) were highest near the groundwater input and declined downgradient. sequences near the input were closely related to those from sulfate-reducing bacteria (SRB), methanogens, and syntrophs. Hg methylation in peat incubations collected near the input source (FPF2) were impacted by the addition of sulfate and some metabolic inhibitors while those down-gradient (FPF5) were not. Sulfate amendment to FPF2 incubations had higher k relative to unamended controls despite no effect on k from addition of the sulfate reduction inhibitor molybdate. The addition of the methanogenic inhibitor BES (25 mM) led to the accumulation of VFAs, but unlike molybdate, it did not affect Hg methylation rates. Rather, the concurrent additions of BES and molybdate significantly decreased k , suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in k with combined addition of BES and molybdate, and accumulation of VFA in peat incubations containing BES, and a high abundance of syntroph-related sequences in peat metagenomes provide evidence for MeHg production by microorganisms growing in syntrophy. Collectively the results suggest that wetland nutrient regimes influence the activity of Hg methylating microorganisms and, consequently, Hg methylation rates. Our results provide key information about microbial Hg methylation and methylating communities under nutrient conditions that are expected to become more common as permafrost soils thaw.
气候变化对北极和亚北极地区产生了巨大影响，由于永久冻土融化，导致湿地养分状况发生变化。水文状况的改变可能会推动微生物汞（Hg）甲基化动态和生物有效性的变化。关于特定微生物群对不同营养状态湿地中甲基汞（MeHg）产生的贡献，仍然存在重要的知识空白。在此，我们在阿拉斯加内陆一个由地下水驱动的养分梯度的沼泽中，测量了水化学、泥炭土培养中的潜在甲基化率（k）、挥发性脂肪酸（VFA）动态以及汞甲基化的遗传潜力。我们检验了以下假设：（1）养分输入将导致甲基化潜力增加，以及（2）互营作用有助于亚北极湿地中的甲基化。我们观察到，在泥炭培养中（k），养分、总汞和甲基汞的浓度、基因丰度以及甲基化率在靠近地下水输入处最高，并沿下游方向下降。输入处附近的序列与硫酸盐还原菌（SRB）、产甲烷菌和互营菌的序列密切相关。在输入源附近（FPF2）收集的泥炭培养物中的汞甲基化受到硫酸盐和一些代谢抑制剂添加的影响，而下游（FPF5）的则不受影响。尽管添加硫酸盐还原抑制剂钼酸盐对k没有影响，但向FPF2培养物中添加硫酸盐相对于未添加对照具有更高的k。添加产甲烷抑制剂BES（25 mM）导致VFA积累，但与钼酸盐不同，它不影响汞甲基化率。相反，同时添加BES和钼酸盐显著降低了k，表明SRB和产甲烷菌之间的相互作用在汞甲基化中起作用。在含有BES的泥炭培养物中，BES和钼酸盐联合添加导致k降低、VFA积累以及泥炭宏基因组中互营菌相关序列的高丰度，这些都为互营生长的微生物产生甲基汞提供了证据。总体而言，结果表明湿地养分状况会影响汞甲基化微生物的活性，进而影响汞甲基化率。我们的结果提供了有关在预计随着永久冻土融化将变得更加普遍的养分条件下微生物汞甲基化和甲基化群落的关键信息。
