Table_1_Genomic Variation and Arsenic Tolerance Emerged as Niche Specific Adaptations by Different Exiguobacterium Strains Isolated From the Extreme Salar de Huasco Environment in Chilean – Altiplano.XLSX

Polyextremophilic bacteria can thrive in environments with multiple stressors such as the Salar de Huasco (SH). Microbial communities in SH are exposed to low atmospheric pressure, high UV radiation, wide temperature ranges, salinity gradient and the presence of toxic compounds such as arsenic (As). In this work we focus on arsenic stress as one of the main adverse factors in SH and bacteria that belong to the Exiguobacterium genus due to their plasticity and ubiquity. Therefore, our aim was to shed light on the effect of niche conditions pressure (particularly arsenic), on the adaptation and divergence (at genotypic and phenotypic levels) of Exiguobacterium strains from five different SH sites. Also, to capture greater diversity in this genus, we use as outgroup five As(III) sensitive strains isolated from Easter Island (Chile) and The Great Salt Lake (United States). For this, samples were obtained from five different SH sites under an arsenic gradient (9 to 321 mg/kg: sediment) and isolated and sequenced the genomes of 14 Exiguobacterium strains, which had different arsenic tolerance levels. Then, we used comparative genomic analysis to assess the genomic divergence of these strains and their association with phenotypic differences such as arsenic tolerance levels and the ability to resist poly-stress. Phylogenetic analysis showed that SH strains share a common ancestor. Consequently, populations were separated and structured in different SH microenvironments, giving rise to multiple coexisting lineages. Hence, this genotypic variability is also evidenced by the COG (Clusters of Orthologous Groups) composition and the size of their accessory genomes. Interestingly, these observations correlate with physiological traits such as growth patterns, gene expression, and enzyme activity related to arsenic response and/or tolerance. Therefore, Exiguobacterium strains from SH are adapted to physiologically overcome the contrasting environmental conditions, like the arsenic present in their habitat.

多重极端嗜极菌（polyextremophilic bacteria）可在多重胁迫环境中存活，例如瓦斯科盐沼（Salar de Huasco, SH）。该盐沼中的微生物群落面临低气压、强紫外辐射、宽温度波动、盐度梯度以及砷（As）等有毒化合物的胁迫。本研究聚焦于瓦斯科盐沼中主要逆境因子之一的砷胁迫，以及因具备代谢可塑性和广泛分布性而被选为研究对象的小杆菌属（Exiguobacterium）细菌。

因此，本研究旨在阐明生境条件压力（尤其是砷胁迫）对取自瓦斯科盐沼5个不同采样点的小杆菌属菌株在基因型与表型层面的适应与分化的影响。此外，为了更全面地捕获该属的物种多样性，本研究引入5株对三价砷（As(III)）敏感的菌株作为外类群（outgroup），这些菌株分别分离自智利复活节岛与美国大盐湖。

为此，研究人员从砷含量梯度为9~321 mg/kg的5个瓦斯科盐沼沉积物采样点获取样本，分离得到14株具有不同砷耐受水平的小杆菌属菌株并完成其基因组测序。随后，本研究通过比较基因组学分析，评估了这些菌株的基因组分化程度，及其与砷耐受水平、多重胁迫抗性等表型差异之间的关联。

系统发育分析结果显示，瓦斯科盐沼的小杆菌属菌株拥有共同的祖先。由此，种群在瓦斯科盐沼的不同微生境中发生分化并形成结构化种群，进而产生了多个共存的进化支系。这种基因型变异也可通过直系同源簇（Clusters of Orthologous Groups, COG）的组成特征以及附属基因组的大小得到佐证。

有趣的是，这些基因组层面的观测结果与砷响应/耐受相关的生长模式、基因表达及酶活性等生理特征高度相关。综上，瓦斯科盐沼中的小杆菌属菌株已在生理层面适应并克服了其生境中的极端环境条件，例如栖息地中存在的砷污染物。