Dipartimento di Scienze per gli Alimenti, la Nutrizione e l'Ambiente (DeFENS), Università degli Studi di Milano, via Celoria, 2, 20133, Milan, Italy.
World J Microbiol Biotechnol. 2019 Jul 22;35(8):117. doi: 10.1007/s11274-019-2690-1.
Iron- and sulfur-oxidizing bacteria inhabiting rice rhizoplane play a significant role on arsenic biogeochemistry in flooded rice paddies, influencing arsenic translocation to rice grains. In the present study, the selective pressure of arsenic species on these microbial populations was evaluated. Rice roots from continuously flooded plants were incubated in iron sulfide (FeS) gradient tubes and exposed to either arsenate or arsenite. The biomass developed in the visible iron-oxidation band of the enrichments was analyzed by Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (SEM-EDS) and the bacterial communities were characterized by 16S rRNA gene sequencing. Different Proteobacteria communities were selected depending on exposure to arsenate and arsenite. Arsenate addition favored the versatile iron-oxidizers Dechloromonas and Azospira, associated to putative iron (hydr)oxide crystals. Arsenite exposure decreased the diversity in the enrichments, with the development of the sulfur-oxidizer Thiobacillus thioparus, likely growing on sulfide released by FeS. Whereas sulfur-oxidizers were observed in all treatments, iron-oxidizers disappeared when exposed to arsenite. These results reveal a strong impact of different inorganic arsenics on rhizospheric iron-oxidizers as well as a crucial role of sulfur-oxidizing bacteria in establishing rice rhizosphere communities under arsenic pressure.
在淹水稻田中，栖息在水稻根际的铁硫氧化细菌在砷的生物地球化学中起着重要作用，影响砷向水稻籽粒的迁移。本研究评估了砷物种对这些微生物种群的选择压力。将连续淹水植物的根在硫化亚铁（FeS）梯度管中孵育，并暴露于砷酸盐或亚砷酸盐中。通过扫描电子显微镜和能谱（SEM-EDS）分析在富集物可见铁氧化带中生长的生物量，并通过 16S rRNA 基因测序表征细菌群落。根据暴露于砷酸盐和亚砷酸盐的情况，选择了不同的变形菌群落。砷酸盐的添加有利于多功能铁氧化菌 Dechloromonas 和 Azospira 的生长，它们与可能的铁（氢）氧化物晶体有关。亚砷酸盐暴露降低了富集物中的多样性，硫氧化菌 Thiobacillus thioparus 的生长，可能是在 FeS 释放的硫化物上生长。尽管在所有处理中都观察到了硫氧化菌，但当暴露于亚砷酸盐时，铁氧化菌就消失了。这些结果表明，不同的无机砷化物对根际铁氧化菌有强烈的影响，硫氧化菌在砷压力下建立水稻根际群落中起着至关重要的作用。
