We describe the geochemistry and microbial diversity of a pristine environment that resembles an acid rock drainage (ARD) but it is actually the result of hydrothermal and volcanic influences. We designate this environment, and other comparable sites, as volcanic influenced acid rock drainage (VARD) systems. The metal content and sulfuric acid in this ecosystem stem from the volcanic milieu and not from the product of pyrite oxidation. Based on the analysis of 16S rRNA gene amplicons, we report the microbial community structure in the pristine San Cayetano Costa Rican VARD environment (pH = 2.94–3.06, sulfate ~ 0.87–1.19 g L⁻¹, iron ~ 35–61 mg L⁻¹ (waters), and ~ 8–293 g kg⁻¹ (sediments)). San Cayetano was found to be dominated by microorganisms involved in the geochemical cycling of iron, sulfur, and nitrogen; however, the identity and abundance of the species changed with the oxygen content (0.40–6.06 mg L⁻¹) along the river course. The hypoxic source of San Cayetano is dominated by a putative anaerobic sulfate-reducing Deltaproteobacterium. Sulfur-oxidizing bacteria such as Acidithiobacillus or Sulfobacillus are found in smaller proportions with respect to typical ARD. In the oxic downstream, we identified aerobic iron-oxidizers (Leptospirillum, Acidithrix, Ferrovum) and heterotrophic bacteria (Burkholderiaceae bacterium, Trichococcus, Acidocella). Thermoplasmatales archaea closely related to environmental phylotypes found in other ARD niches were also observed throughout the entire ecosystem. Overall, our study shows the differences and similarities in the diversity and distribution of the microbial communities between an ARD and a VARD system at the source and along the oxygen gradient that establishes on the course of the river.

我们描述了一个原始环境的地球化学和微生物多样性，该环境类似于酸性岩石排泄物（ARD），但实际上是水热和火山影响的结果。我们将此环境和其他类似地点指定为火山影响的酸性岩石排泄（VARD）系统。该生态系统中的金属含量和硫酸源于火山环境，而不是黄铁矿氧化产物。基于对16S rRNA基因的扩增子的分析，我们报告的微生物群落结构在原始圣卡耶塔诺哥斯达黎加VARD环境（pH值= 2.94-3.06，硫酸〜0.87-1.19克L- ^-1，铁〜35-61毫克的L ^{- 1}（水）和〜8–293 g千克^-1（沉积物））。人们发现，圣卡耶塔诺州的微生物主要涉及铁，硫和氮的地球化学循环。然而，沿着河道，物种的身份和丰富度随氧气含量（0.40–6.06 mg L ^-1）而变化。San Cayetano的低氧来源主要是假定的减少厌氧硫酸盐的三角洲变形杆菌。硫氧化细菌如嗜酸或硫化杆菌属在小比例相对于典型ARD找到。在有氧下游，我们确定了好氧铁氧化剂（钩端螺旋体，嗜酸性，铁质）和异养细菌（伯克霍尔德杆菌属细菌，毛球菌），Acidocella）。在整个生态系统中也观察到与其他ARD生态位中的环境系统型密切相关的古细菌。总的来说，我们的研究表明，在源头和沿河流建立的氧气梯度上，ARD和VARD系统之间的微生物群落多样性和分布的差异和相似性。