State Key Laboratory of Crop Genetics and Germplasm Enhancement, Jiangsu Provincial Key Laboratory for Organic Solid Waste Utilization, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
State Key Laboratory of Crop Genetics and Germplasm Enhancement, Jiangsu Provincial Key Laboratory for Organic Solid Waste Utilization, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
Environ Pollut. 2022 Sep 15;309:119825. doi: 10.1016/j.envpol.2022.119825. Epub 2022 Jul 20.
Rice growing in flooded paddy soil often accumulates considerable levels of inorganic and organic arsenic (As) species, which may cause toxicity to plants and/or pose a risk to human health. The bioavailability and toxicity of As in soil depends on its chemical species, which undergo multiple transformations driven primarily by soil microbes. However, the role of endophytes inside rice roots in As species transformation remains largely unknown. We quantified the abundances of microbial functional genes involved in As transformation in the endosphere and rhizosphere of rice roots growing in three paddy soils in a pot experiment. We also isolated 46 different bacterial endophytes and tested their abilities to transform various As species. The absolute abundances of the arsenate reductase gene arsC and the dissimilatory arsenate reductase gene arrA in the endosphere were comparable to those in the rhizosphere, whereas the absolute abundances of the arsenite methylation gene arsM and arsenite oxidation gene aioA in the endosphere were lower. After normalization based on the bacterial 16S rRNA gene, all four As transformation genes showed higher relative abundances in the endosphere than in the rhizosphere. Consistent with the functional gene data, all of the 30 aerobic endophytic isolates were able to reduce arsenate, but only 3 strains could oxidize arsenite. Among the 16 anaerobic endophytic isolates, 4 strains belonging to Desulfovibrio, Terrisporobacter or Clostridium could methylate arsenite and/or methylarsenite. Six strains of aerobic endophytes could demethylate methylarsenite, among which three strains also could reduce and demethylate methylarsenate. None of the isolates could demethylate dimethylarsenate. These results suggest that diverse endophytes living inside rice roots could participate in As species transformation and affect As accumulation and species distribution in rice plants.
在水淹稻田中生长的水稻通常会积累相当数量的无机和有机砷（As）物种，这可能对植物产生毒性和/或对人类健康构成风险。土壤中 As 的生物有效性和毒性取决于其化学形态，这些形态主要受土壤微生物的驱动而发生多种转化。然而，根内内生菌在 As 物种转化中的作用在很大程度上尚不清楚。我们在盆栽实验中定量了生长在三种稻田土壤中的水稻根内球和根际中参与 As 转化的微生物功能基因的丰度，还分离了 46 种不同的细菌内生菌，并测试了它们转化各种 As 物种的能力。砷酸盐还原酶基因 arsC 和异化砷酸盐还原酶基因 arrA 在根内的绝对丰度与根际相当，而砷酸盐甲基化基因 arsM 和亚砷酸盐氧化基因 aioA 在根内的绝对丰度较低。基于细菌 16S rRNA 基因归一化后，所有四个 As 转化基因在内球中的相对丰度均高于根际。与功能基因数据一致，所有 30 种需氧内生菌均能还原砷酸盐，但只有 3 株能氧化亚砷酸盐。在 16 种厌氧内生菌中，4 株属于脱硫弧菌、栖热菌或梭菌的菌株能够甲基化亚砷酸盐和/或甲基砷酸盐。6 株需氧内生菌能够去甲基化甲基砷酸盐，其中 3 株还能够还原和去甲基化甲基砷酸盐。没有分离株能够去甲基化二甲基砷酸盐。这些结果表明，生活在水稻根内的多种内生菌可以参与 As 物种转化，并影响水稻植株中 As 的积累和形态分布。
