Wang Lanjing, Liu Hang, Wang Feng, Wang Yongmin, Xiang Yuping, Chen Yongyi, Wang Jiwu, Wang Dingyong, Shen Hong
College of Resources and Environment, Southwest University, Chongqing, China.
Research Center of Biology, Southwest University, Chongqing, China.
Front Microbiol. 2024 Jul 2;15:1376844. doi: 10.3389/fmicb.2024.1376844. eCollection 2024.
In nature, methylmercury (MeHg) is primarily generated through microbial metabolism, and the ability of bacteria to methylate Hg(II) depends on both bacterial properties and environmental factors. It is widely known that, as a metabolic analog, molybdate can inhibit the sulfate reduction process and affect the growth and methylation of sulfate-reducing bacteria (SRB). However, after it enters the cell, molybdate can be involved in various intracellular metabolic pathways as a molybdenum cofactor; whether fluctuations in its concentration affect the growth and methylation of aerobic mercury methylating strains remains unknown. To address this gap, aerobic γ-Proteobacteria strains TGRB3 (B3) and TGRB4 (B4), as well as an obligate anaerobic δ-Proteobacteria strain of the SRB CGMCC 1.3481 (DE), were used as experimental strains. The growth and methylation ability of each strain were analyzed under conditions of 500 ng·L Hg(II), 0 and 21% of oxygen, and 0, 0.25, 0.50, and 1 mM of MoO . In addition, in order to explore the metabolic specificity of aerobic strains, transcriptomic data of the facultative mercury-methylated strain B3 were further analyzed in an aerobic mercuric environment. The results indicated that: (a) molybdate significantly inhibited the growth of DE, while B3 and B4 exhibited normal growth. (b) Under anaerobic conditions, in DE, the MeHg content decreased significantly with increasing molybdate concentration, while in B3, MeHg production was unaffected. Furthermore, under aerobic conditions, the MeHg productions of B3 and B4 were not influenced by the molybdate concentration. (c) The transcriptomic analysis showed several genes that were annotated as members of the molybdenum oxidoreductase family of B3 and that exhibited significant differential expression. These findings suggest that the differential expression of molybdenum-binding proteins might be related to their involvement in energy metabolism pathways that utilize nitrate and dimethyl sulfoxide as electron acceptors. Aerobic bacteria, such as B3 and B4, might possess distinct Hg(II) biotransformation pathways from anaerobic SRB, rendering their growth and biomethylation abilities unaffected by molybdate.
在自然界中，甲基汞（MeHg）主要通过微生物代谢产生，细菌将汞（II）甲基化的能力取决于细菌特性和环境因素。众所周知，作为一种代谢类似物，钼酸盐可以抑制硫酸盐还原过程，并影响硫酸盐还原菌（SRB）的生长和甲基化。然而，钼酸盐进入细胞后，可以作为钼辅因子参与各种细胞内代谢途径；其浓度波动是否会影响好氧汞甲基化菌株的生长和甲基化仍不清楚。为了填补这一空白，将好氧γ-变形菌菌株TGRB3（B3）和TGRB4（B4），以及SRB的专性厌氧δ-变形菌菌株CGMCC 1.3481（DE）用作实验菌株。在500 ng·L汞（II）、0和21%氧气以及0、0.25、0.50和1 mM钼酸盐的条件下，分析了各菌株的生长和甲基化能力。此外，为了探索好氧菌株的代谢特异性，在好氧汞环境中进一步分析了兼性汞甲基化菌株B3的转录组数据。结果表明：（a）钼酸盐显著抑制DE的生长，而B3和B4表现出正常生长。（b） 在厌氧条件下，在DE中，MeHg含量随钼酸盐浓度的增加而显著降低，而在B3中，MeHg的产生不受影响。此外，在好氧条件下，B3和B4的MeHg产生不受钼酸盐浓度的影响。（c） 转录组分析显示，B3中有几个基因被注释为钼氧化还原酶家族成员，并表现出显著的差异表达。这些发现表明，钼结合蛋白的差异表达可能与其参与利用硝酸盐和二甲基亚砜作为电子受体的能量代谢途径有关。好氧细菌，如B3和B4，可能具有与厌氧SRB不同的汞（II）生物转化途径，使其生长和生物甲基化能力不受钼酸盐的影响。
