Thiomonas bacteria are ubiquitous at acid mine drainage sites and play key roles in the remediation of water at these locations by oxidizing arsenite to arsenate, favouring the sorption of arsenic by iron oxides and their coprecipitation. Understanding the adaptive capacities of these bacteria is crucial to revealing how they persist and remain active in such extreme conditions. Interestingly, it was previously observed that after exposure to arsenite, when grown in a biofilm, some strains of Thiomonas bacteria develop variants that are more resistant to arsenic. Here, we identified the mechanisms involved in the emergence of such variants in biofilms. We found that the percentage of variants generated increased in the presence of high concentrations of arsenite (5.33 mM), especially in the detached cells after growth under biofilm-forming conditions. Analysis of gene expression in the parent strain CB2 revealed that genes involved in DNA repair were upregulated in the conditions where variants were observed. Finally, we assessed the phenotypes and genomes of the subsequent variants generated to evaluate the number of mutations compared to the parent strain. We determined that multiple point mutations accumulated after exposure to arsenite when cells were grown under biofilm conditions. Some of these mutations were found in what is referred to as ICE19, a genomic island (GI) carrying arsenic-resistance genes, also harbouring characteristics of an integrative and conjugative element (ICE). The mutations likely favoured the excision and duplication of this GI. This research aids in understanding how Thiomonas bacteria adapt to highly toxic environments, and, more generally, provides a window to bacterial genome evolution in extreme environments.

中文翻译：

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亚砷酸盐和生物膜条件下的生长对硫单胞菌进化的影响。CB2

硫单 胞菌在酸性矿山排水地点无处不在，通过将亚砷酸盐氧化为砷酸盐，有利于铁氧化物吸附砷及其共沉淀，在这些地点的水修复中发挥关键作用。了解这些细菌的适应能力对于揭示它们如何在这种极端条件下持续存在并保持活跃至关重要。有趣的是，先前观察到，在接触亚砷酸盐后，当在生物膜中生长时，某些硫单胞菌菌株 细菌会发展出对砷更具抗性的变体。在这里，我们确定了在生物膜中出现此类变体所涉及的机制。我们发现在高浓度亚砷酸盐 (5.33 mM) 存在下产生的变体百分比增加，尤其是在生物膜形成条件下生长后的分离细胞中。对亲本菌株 CB2 中基因表达的分析表明，在观察到变异的条件下，参与 DNA 修复的基因上调。最后，我们评估了后续产生的变异的表型和基因组，以评估与亲本菌株相比的突变数量。我们确定，当细胞在生物膜条件下生长时，暴露于亚砷酸盐后会积累多个点突变。其中一些突变是在所谓的 ICE19 中发现的，ICE19 是一个基因组岛 (GI)，携带抗砷基因，也具有整合和接合元件 (ICE) 的特征。突变可能有利于该 GI 的切除和复制。这项研究有助于了解如何 硫单 胞菌细菌适应剧毒环境，更一般地说，为极端环境中的细菌基因组进化提供了一个窗口。