Instituto de Recursos Naturales y Agrobiología de Salamanca (CSIC), Apartado 257, 37071 Salamanca, Spain.
Chemosphere. 2011 Sep;85(1):129-34. doi: 10.1016/j.chemosphere.2011.06.025. Epub 2011 Jul 2.
We studied the bacterial diversity at a single location (the Terrubias mine; Salamanca province, Spain) with a gradient of soil As contamination to test if increasing levels of As would (1) change the preponderant groups of arsenic-resistant bacteria and (2) increase the tolerance thresholds to arsenite [As(III)] and arsenate [As(V)] of such bacteria. We studied the genetic and taxonomic diversity of culturable arsenic-resistant bacteria by PCR fingerprinting techniques and 16S rRNA gene sequencing. Then, the tolerance thresholds to As(III) and As(V) were determined for representative strains and mathematically analyzed to determine relationships between tolerances to As(III) and As(V), as well as these tolerances with the soil contamination level. The diversity of the bacterial community was, as expected, inversely related to the soil As content. The overall preponderant arsenic-resistant bacteria were Firmicutes (mainly Bacillus spp.) followed by γ-Proteobacteria (mainly Pseudomonas spp.), with increasing relative frequencies of the former as the soil arsenic concentration increased. Moreover, a strain of the species Rahnella aquatilis (γ-Proteobacteria class) exhibited strong endurance to arsenic, being described for the first time in literature such a phenotype within this bacterial species. Tolerances of the isolates to As(III) and As(V) were correlated but not with their origin (soil contamination level). Most of the strains (64%) showed relatively low tolerances to As(III) and As(V), but the second most numerous group of isolates (19%) showed increased tolerance to As(III) rather than to As(V), even though the As(V) anion is the prevalent arsenic species in soil solution at this location. To our knowledge, this is the first study to report a shift towards preponderance of Gram-positive bacteria (Firmicutes) related to high concentrations of soil arsenic. It was also shown that, under aerobic conditions, strains with relatively enhanced tolerance to As(III) predominated over the most As(V)-tolerant ones.
我们在一个单一的地点（特鲁比亚斯矿；西班牙萨拉曼卡省）研究了细菌的多样性，该地点的土壤砷污染程度呈梯度分布，以检验是否随着砷含量的增加：（1）会改变砷抗性细菌的优势菌群；（2）会提高这些细菌对亚砷酸盐[As(III)]和砷酸盐[As(V)]的耐受阈值。我们通过 PCR 指纹图谱技术和 16S rRNA 基因测序研究了可培养砷抗性细菌的遗传和分类多样性。然后，我们测定了代表性菌株对 As(III)和 As(V)的耐受阈值，并进行了数学分析，以确定对 As(III)和 As(V)的耐受程度之间的关系，以及这些耐受程度与土壤污染程度之间的关系。正如预期的那样，细菌群落的多样性与土壤砷含量呈负相关。总体上占优势的砷抗性细菌是厚壁菌门（主要是芽孢杆菌属），其次是γ-变形菌门（主要是假单胞菌属），随着土壤砷浓度的增加，前者的相对频率增加。此外，一种水生拉恩氏菌（γ-变形菌门）的菌株表现出对砷的强烈耐受能力，这是在该细菌物种中首次描述这种表型。分离株对 As(III)和 As(V)的耐受程度相关，但与它们的起源（土壤污染水平）无关。大多数菌株（64%）对 As(III)和 As(V)的耐受程度相对较低，但第二多的分离株组（19%）对 As(III)的耐受程度增加，而不是对 As(V)的耐受程度增加，尽管在该地点，土壤溶液中主要的砷物种是 As(V)阴离子。据我们所知，这是第一项报道与高浓度土壤砷相关的革兰氏阳性菌（厚壁菌门）优势地位变化的研究。研究还表明，在需氧条件下，相对增强对 As(III)耐受的菌株占优势，而不是最耐受 As(V)的菌株。
