Microbial community potentially responsible for acid and metal release from an Ostrobothnian acid sulfate soil

Abstract

Soils containing an approximately equal mixture of metastable iron sulfides and pyrite occur in the boreal Ostrobothnian coastal region of Finland, termed ‘potential acid sulfate soil materials’. If the iron sulfides are exposed to air, oxidation reactions result in acid and metal release to the environment that can cause severe damage. Despite that acidophilic microorganisms catalyze acid and metal release from sulfide minerals, the microbiology of acid sulfate soil (ASS) materials has been neglected. The molecular phylogeny of a depth profile through the plough and oxidized ASS layers identified several known acidophilic microorganisms and environmental clones previously identified from acid- and metal-contaminated environments. In addition, several of the 16S rRNA gene sequences were more similar to sequences previously identified from cold environments. Leaching of the metastable iron sulfides and pyrite with an ASS microbial enrichment culture incubated at low pH accelerated metal release, suggesting microorganisms capable of catalyzing metal sulfide oxidation were present. The 16S rRNA gene analysis showed the presence of species similar to Acidocella sp. and other clones identified from acid mine environments. These data support that acid and metal release from ASSs was catalyzed by indigenous microorganisms adapted to low pH.

Impact of mitigation strategies on acid sulfate soil chemistry and microbial community

“…Details of the study area (Åström et al, 2007;Boman et al, 2010) and the physicochemical parameters of the Risöfladan experimental field (Wu et al, 2013) have been previously reported. In brief, the soil below the plow layer consisted of clay with a well-developed structure with an abundance of iron oxide coatings.…”

“…In brief, the soil below the plow layer consisted of clay with a well-developed structure with an abundance of iron oxide coatings. The sulfur content was in the order of ≥ 0.2% (wt/vol) and the pH was~4 in all soil samples due to significant sulfide oxidation (Wu et al, 2013). In total, 24 cores were used in preliminary studies, method development, and the five cores for the experiments reported here.…”

“…The molecular phylogeny of microbial populations from both the untreated and treated soils was analyzed as previously described (Wu et al, 2013) except that the DNA was directly extracted using the PowerSoil DNA isolation kit (MOBIO) according to the manufacturer's instructions. Microbial community DNA was extracted from a thin layer of soil scraped from the surface of cracks within the soil through which the majority of the CaCO 3 and Ca(OH) 2 suspensions flowed.…”

“…These microorganisms need to be able to survive in the low pH and high metal concentrations generated by sulfide mineral dissolution and their pH homeostasis (Slonczewski et al, 2009) and metal resistance (Dopson et al, 2003 strategies have been reviewed. A microbiological study of ASS in boreal environments identified several 16S rRNA gene sequences similar to known acidophilic iron and inorganic sulfur oxidizing microorganisms, suggesting that the acid and metal releases are accelerated by these microorganisms (Wu et al, 2013). In addition, 16S rRNA gene sequence analysis suggested the presence of acidophiles adapted to the low temperatures found in Finland.…”

“…Sulfur-and iron-oxidizing microorganisms are widely found in many acidic environments such as acid mine drainage (Hallberg, 2010), sulfide mine tailings (Rzhepishevska et al, 2005), and ASS (Wu et al, 2013). The role of extreme acidophiles in catalyzing the iron and/or inorganic sulfur compound oxidation leading to the release of acid and metals from metal sulfides is well established (Vera et al, 2013).…”