Pathak Ashish, Jaswal Rajneesh, Chauhan Ashvini
Environmental Biotechnology Laboratory, School of the Environment, FSH Science Research Center, Florida A&M University, Tallahassee, FL, United States.
Front Microbiol. 2020 Jan 17;10:3039. doi: 10.3389/fmicb.2019.03039. eCollection 2019.
Nuclear production and industrial activities led to widespread contamination of the Department of Energy (DOE) managed Savannah River Site (SRS), located in South Carolina, United States. The H-02 wetland system was constructed in 2007 for the treatment of industrial and storm water runoff from the SRS Tritium Facility. Albeit at low levels, mercury (Hg) has been detected in the soils of the H-02 wetland ecosystem. In anoxic sediments, Hg is typically methylated by anaerobic microbiota, forming the highly neurotoxic methylmercury (MeHg), which biomagnifies across food webs. However, in surficial oxic wetland soils, microbially mediated demethylation and/or volatilization processes can transform Hg into the less toxic Hg form which is released into the atmosphere, thus circumventing MeHg formation. To obtain a deeper understanding on bacterial Hg volatilization, a robust Hg-resistant (HgR) bacteria, called as strain H-02-3 was isolated from the H-02 soils. A draft genome sequence of this strain was obtained at a coverage of 700×, which assembled in 44 contigs with an N50 of 171,569 bp. The genomic size of the strain H-02-3 was 4,708,612 bp with a total number of 4,240 genes; phylogenomic analysis revealed the strain as an Arthrobacter species. Comparative genomics revealed the presence of 1100 unique genes in strain H-02-3, representing 26.7% of the total genome; many identified previously as metal resistance genes (MRGs). Specific to Hg-cycling, the presence of mercuric ion reductase (), the organomercurial lyase (), and the mercuric resistance operon regulatory protein, were identified. By inference, it can be proposed that the organomercurial lyase facilitates the demethylation of MeHg into Hg which is then reduced to Hg by MerA in strain H-02-3. Furthermore, gene prediction using resistome analysis of strain H-02-3 revealed the presence of several antibiotic resistance genes (ARGs), that statistically correlated with the presence of metal resistant genes (MRGs), suggesting co-occurrence patterns of MRGs and ARGs in the strain. Overall, this study delineates environmentally beneficial traits that likely facilitates survival of sp. H-02-3 within the H-02 wetland soil. Finally, this study also highlights the largely ignored public health risk associated with the co-development of ARGs and MRGs in bacteria native to historically contaminated soils.
核生产和工业活动导致美国南卡罗来纳州能源部（DOE）管理的萨凡纳河场地（SRS）受到广泛污染。H - 02湿地系统于2007年建成，用于处理SRS氚设施的工业和雨水径流。尽管含量较低，但在H - 02湿地生态系统的土壤中已检测到汞（Hg）。在缺氧沉积物中，汞通常由厌氧微生物群甲基化，形成高神经毒性的甲基汞（MeHg），其在食物网中生物放大。然而，在表层有氧湿地土壤中，微生物介导的去甲基化和/或挥发过程可将汞转化为毒性较小的汞形态并释放到大气中，从而避免甲基汞的形成。为了更深入了解细菌汞挥发情况，从H - 02土壤中分离出一种强大的耐汞（HgR）细菌，称为菌株H - 02 - 3。该菌株的基因组草图序列以700×的覆盖度获得，组装成44个重叠群，N50为171,569 bp。菌株H - 02 - 3的基因组大小为4,708,612 bp，共有4,240个基因；系统基因组分析表明该菌株为节杆菌属物种。比较基因组学显示菌株H - 02 - 3中存在1100个独特基因，占基因组总数的26.7%；许多基因先前被鉴定为金属抗性基因（MRGs）。特定于汞循环，鉴定出了汞离子还原酶（）、有机汞裂解酶（）和汞抗性操纵子调节蛋白的存在。由此推断，可以认为有机汞裂解酶促进甲基汞去甲基化为汞，然后在菌株H - 02 - 3中由MerA将其还原为汞。此外，使用菌株H - 02 - 3的抗性组分析进行基因预测发现存在几个抗生素抗性基因（ARGs），这些基因与金属抗性基因（MRGs）的存在具有统计学相关性，表明该菌株中MRGs和ARGs的共现模式。总体而言，本研究描述了可能促进节杆菌属物种H - 02 - 3在H - 02湿地土壤中存活的环境有益特征。最后，本研究还强调了历史污染土壤中天然细菌中ARGs和MRGs共同发展所带来的在很大程度上被忽视的公共卫生风险。
