Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
Environ Pollut. 2020 Jun;261:114232. doi: 10.1016/j.envpol.2020.114232. Epub 2020 Feb 22.
Microbial assemblages such as biofilms around aquatic plants play a major role in arsenic (As) cycling, which has often been overlooked in previous studies. In this study, arsenite (As(III))-oxidizing, arsenate (As(V))-reducing and As(III)-methylating bacteria were found to coexist in the phyllosphere of Hydrilla verticillata, and their relative activities were shown to determine As speciation, accumulation and efflux. When exposed to As(III), As(III) oxidation was not observed in treatment H(III)-B, whereas treatment H(III)+B showed a significant As(III) oxidation ability, thereby indicating that epiphytic bacteria displayed a substantial As(III) oxidation ability. When exposed to As(V), the medium only contained 5.89% As(III) after 48 h of treatment H(V)-B, while an As(III) content of 86.72% was observed after treatment H(V)+B, thereby indicating that the elevated As(III) in the medium probably originated from As(V) reduction by epiphytic bacteria. Our data also indicated that oxidizing bacteria decreased the As accumulation (by approximately 64.44% compared with that of treatment H(III)-B) in plants, while reducing bacteria played a critical role in increasing As accumulation (by approximately 3.31-fold compared with that of treatment H(V)-B) in plants. Regardless of whether As(III) or As(V) was supplied, As(III) was dominant in the plant tissue (over 75%). Furthermore, the presence of epiphytic bacteria enhanced As efflux by approximately 9-fold. Metagenomic analysis revealed highly diverse As metabolism genes in epiphytic bacterial community, particularly those related to energetic metabolism (aioAB), and As resistance (arsABCR, acr3, arsM). Phylogenetic analysis of As metabolism genes revealed evidence of both vertical inheritance and horizontal gene transfer, which might have contributed to the evolution of the As metabolism genes. Taken together, our research suggested that the diversity of As metabolism genes in epiphytic bacterial community is associated with aquatic submerged macrophytes which may play an important role in As biogeochemistry in aquatic environments.
水生植物叶际微生物群落（如生物膜）在砷（As）循环中起着重要作用，但在以前的研究中往往被忽视。本研究发现，在水鳖叶际中共存着亚砷酸盐（As(III))氧化菌、砷酸盐（As(V))还原菌和 As(III)甲基化菌，它们的相对活性决定了 As 的形态、积累和外排。当暴露于 As(III)时，处理 H(III)-B 中未观察到 As(III)氧化，而处理 H(III)+B 则表现出显著的 As(III)氧化能力，表明附生细菌具有很强的 As(III)氧化能力。当暴露于 As(V)时，处理 H(V)-B 的培养基中 48 小时后仅含有 5.89%的 As(III)，而处理 H(V)+B 后则观察到 86.72%的 As(III)，表明培养基中升高的 As(III)可能来自附生细菌还原 As(V)。我们的数据还表明，氧化菌降低了植物中的 As 积累（与处理 H(III)-B 相比减少了约 64.44%），而还原菌在植物中增加 As 积累方面发挥了关键作用（与处理 H(V)-B 相比增加了约 3.31 倍）。无论供应 As(III)还是 As(V)，植物组织中均以 As(III)为主（超过 75%）。此外，附生细菌使 As 外排增加了约 9 倍。宏基因组分析揭示了附生细菌群落中高度多样化的 As 代谢基因，特别是与能量代谢（aioAB）和 As 抗性（arsABCR、acr3、arsM）相关的基因。As 代谢基因的系统发育分析表明，垂直遗传和水平基因转移都存在证据，这可能有助于 As 代谢基因的进化。综上所述，我们的研究表明，附生细菌群落中 As 代谢基因的多样性与水生沉水植物有关，水生沉水植物可能在水生环境中 As 的生物地球化学过程中发挥重要作用。
