Heliobacteria Reveal Fermentation As a Key Pathway for Mercury Reduction in Anoxic Environments,Environmental Science & Technology

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Heliobacteria Reveal Fermentation As a Key Pathway for Mercury Reduction in Anoxic Environments
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2018-03-14 00:00:00 , DOI: 10.1021/acs.est.8b00320
D. S. Grégoire ₁ , N. C. Lavoie ₁ , A. J. Poulain ₁

Affiliation

The accumulation of mercury (Hg) in rice, a dietary staple for over half of the world’s population, is rapidly becoming a global food safety issue. Rice paddies support the anaerobic production of toxic methylmercury that accumulates in plant tissue, however the microbial controls of Hg cycling in anoxic environments remain poorly understood. In this study, we reveal a novel reductive Hg metabolism in a representative of the family Heliobacteria (Heliobacterium modesticaldum Ice1) that we confirm in model chemotrophic anaerobes. Heliobacteria served as our initial model because they are a family of spore-forming fermentative photoheterotrophs commonly isolated from terrestrial environments. We observed that H. modesticaldum reduced up to 75% of Hg^II under phototrophic or fermentative conditions. Fermentative Hg^II reduction relied on the ability of cells to oxidize pyruvate whereas phototrophic Hg^II reduction could be supported even in the absence of a carbon source. Inhibiting pyruvate fermentation eliminated Hg^II reduction in all chemotrophic strains tested, whereas phototrophic cells remained unaffected. Here we propose a non mer-operon dependent mechanism for Hg⁰ production in anoxic environments devoid of light where external electron acceptors are limited. These mechanistic details provide the foundation for novel bioremediation strategies to limit the negative impacts of Hg pollution.

中文翻译：

Heliobacteria揭示出发酵是缺氧环境中减少汞的关键途径

大米中的汞是主要食物，而大米是世界上一半以上人口的饮食主粮，它正迅速成为全球食品安全问题。稻田支持厌氧生产在植物组织中积累的有毒甲基汞，但是对在缺氧环境中汞循环的微生物控制仍然知之甚少。在这项研究中，我们揭示了在模型化营养厌氧菌中证实的家族Heliobacteria（HeliobacteriumModesticaldum Ice1）的代表中的一种新型还原性Hg代谢。Heliobacteria成为我们的初始模型，因为它们是通常从陆地环境中分离出来的形成孢子的发酵光异养菌家族。我们观察到，modesticaldum最多减少了Hg ^II的75％在光养或发酵条件下。Hg ^II的发酵还原依赖于细胞氧化丙酮酸的能力，而即使在没有碳源的情况下，也可以支持光养性Hg ^II的还原。抑制丙酮酸发酵消除了所有测试的化学营养菌株中的Hg ^II减少，而光养细胞则不受影响。在这里，我们提出了一种非聚体-operon依赖对Hg机构⁰生产不含轻的缺氧环境，其中外部电子受体的限制。这些机制细节为新型生物修复策略提供了基础，以限制汞污染的负面影响。

更新日期：2018-03-15

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