Fazi Stefano, Crognale Simona, Casentini Barbara, Amalfitano Stefano, Lotti Francesca, Rossetti Simona
Water Research Institute, National Research Council of Italy (IRSA-CNR), Via Salaria, km 29.300, Monterotondo, RM, 00015, Italy.
Department of Ecological and Biological Sciences (DEB), Tuscia University, Viterbo, Italy.
Microb Ecol. 2016 Jul;72(1):25-35. doi: 10.1007/s00248-016-0768-y. Epub 2016 Apr 18.
Microorganisms play an important role in speciation and mobility of arsenic in the environment, by mediating redox transformations of both inorganic and organic species. Since arsenite [As(III)] is more toxic than arsenate [As(V)] to the biota, the microbial driven processes of As(V) reduction and As(III) oxidation may play a prominent role in mediating the environmental impact of arsenic contamination. However, little is known about the ecology and dynamics of As(III)-oxidizing populations within native microbial communities exposed to natural high levels of As. In this study, two techniques for single cell quantification (i.e., flow cytometry, CARD-FISH) were used to analyze the structure of aquatic microbial communities across a gradient of arsenic (As) contamination in different freshwater environments (i.e., groundwaters, surface and thermal waters). Moreover, we followed the structural evolution of these communities and their capacity to oxidize arsenite, when experimentally exposed to high As(III) concentrations in experimental microcosms. Betaproteobacteria and Deltaproteobacteria were the main groups retrieved in groundwaters and surface waters, while Beta and Gammaproteobacteria dominated the bacteria community in thermal waters. At the end of microcosm incubations, the communities were able to oxidize up to 95 % of arsenite, with an increase of Alphaproteobacteria in most of the experimental conditions. Finally, heterotrophic As(III)-oxidizing strains (one Alphaproteobacteria and two Gammaproteobacteria) were isolated from As rich waters. Our findings underlined that native microbial communities from different arsenic-contaminated freshwaters can efficiently perform arsenite oxidation, thus contributing to reduce the overall As toxicity to the aquatic biota.
微生物通过介导无机和有机砷物种的氧化还原转化，在环境中砷的物种形成和迁移中发挥重要作用。由于亚砷酸盐[As(III)]对生物群的毒性高于砷酸盐[As(V)]，微生物驱动的As(V)还原和As(III)氧化过程可能在介导砷污染的环境影响中发挥重要作用。然而，对于暴露于天然高浓度砷的本地微生物群落中As(III)氧化菌群的生态学和动态知之甚少。在本研究中，采用两种单细胞定量技术（即流式细胞术、催化报告沉积荧光原位杂交技术）分析了不同淡水环境（即地下水、地表水和热水）中砷(As)污染梯度下的水生微生物群落结构。此外，当在实验微宇宙中实验性地暴露于高浓度As(III)时，我们跟踪了这些群落的结构演变及其氧化亚砷酸盐的能力。β-变形菌纲和δ-变形菌纲是在地下水和地表水中检索到的主要菌群，而β-变形菌纲和γ-变形菌纲在热水中的细菌群落中占主导地位。在微宇宙培养结束时，群落能够氧化高达95%的亚砷酸盐，在大多数实验条件下α-变形菌纲有所增加。最后，从富砷水中分离出异养As(III)氧化菌株（一株α-变形菌纲和两株γ-变形菌纲）。我们的研究结果强调，来自不同砷污染淡水的本地微生物群落能够有效地进行亚砷酸盐氧化，从而有助于降低砷对水生生物群的总体毒性。
