Enriching acid rock drainage related microbial communities from surface-deposited oil sands tailings.

Little is known about the microbial communities native to surface-deposited pyritic oil sands tailings, an environment where acid rock drainage (ARD) could occur. The goal of this study was to enrich sulfur-oxidizing organisms from these tailings and determine whether different populations exist at pH levels 7, 4.5, and 2.5. Using growth-based methods provides model organisms for use in the future to predict potential activities and limitations of these organisms and to develop possible control methods. Thiosulfate-fed enrichment cultures were monitored for approximately 1 year. The results showed that the enrichments at pH 4.5 and 7 were established quicker than at pH 2.5. Different microbial community structures were found among the 3 pH environments. The sulfur-oxidizing microorganisms identified were most closely related to Halothiobacillus neapolitanus, Achromobacter spp., and Curtobacterium spp. While microorganisms related to Chitinophagaceae and Acidocella spp. were identified as the only possible iron-oxidizing and -reducing microbes. These results contribute to the general knowledge of the relatively understudied microbial communities that exist in pyritic oil sands tailings and indicate these communities may have a potential role in ARD generation, which may have implications for future tailings management.

Diversity and activity of sulphur-oxidizing bacteria and sulphate-reducing bacteria in landfill cover soils.

UNLABELLED: Sulphur bioconversion in landfill cover soils, including the metabolism of sulphur-oxidizing bacteria (SOB) and sulphate-reducing bacteria (SRB), is one of the important processes affecting H2 S emission from landfills. In this study, two landfills with or without landfill gas collection and utilization system were investigated to characterize the role of biotic and abiotic factors affecting diversity and activity of SOB and SRB in the landfill cover soils. The results revealed that the potential sulphur oxidation rates (SORs) and sulphate reduction rates (SRRs) varied with landfill sites and depths. SOR was significantly correlated with pH and SO4 (2-) , while SRR was significantly related with pH. The populations of both SOB and SRB were low in the acidic landfill cover soils (pH = 4.7-5.37). Cloning and terminal restriction fragment length polymorphism profiles of soxB and dsrB showed that SOB including Halothiobacillus, Thiobacillus, Thiovirga and Bradyrhizobium, and SRB including Desulfobacca, Desulforhabdus and Syntrophobacter dominated in the landfill cover soils, and their distributions were affected mainly by pH value and organic matter contents of soils. SIGNIFICANCE AND IMPACT OF THE STUDY: High diversity of sulphur-oxidizing bacteria (SOB) and sulphate-reducing bacteria (SRB) presented in the landfill cover soils. Among the physicochemical properties of soils (moisture content, pH, organic materials, SO4 (2-) , acid volatile sulphide and total sulphur), pH was the most important factor affecting the diversity and activity of SOB and SRB in the landfill cover soils. Higher pH of landfill cover soils (i.e. neutral or slight alkaline) was favourable for the growth of SOB and SRB, leading to a rapid bioconversion of sulphur. These findings are helpful to optimize sulphur biotransformation in landfill cover soils and to control odour pollution at landfills.

Sulphide oxidation to elemental sulphur in a membrane bioreactor: performance and characterization of the selected microbial sulphur-oxidizing community.

In leather tanning industrial areas sulphide management represents a major problem. However, biological sulphide oxidation to sulphur represents a convenient solution to this problem. Elemental sulphur is easy to separate and the process is highly efficient in terms of energy consumption and effluent quality. As the oxidation process is performed by specialized bacteria, selection of an appropriate microbial community is fundamental for obtaining a good yield. Sulphur oxidizing bacteria (SOB) represent a wide-ranging and highly diversified group of microorganisms with the capability of oxidizing reduced sulphur compounds. Therefore, it is useful to select new microbes that are able to perform this process efficiently. For this purpose, an experimental membrane bioreactor for sulphide oxidation was set up, and the selected microbial community was characterized by constructing 16S rRNA gene libraries and subsequent screening of clones. Fluorescence in situ hybridization (FISH) was then used to assess the relative abundance of different bacterial groups. Sulphide oxidation to elemental sulphur proceeded in an efficient (up to 79% conversion) and stable way in the bioreactor. Both analysis of clone libraries and FISH experiments revealed that the dominant operational taxonomic unit (OTU) in the bioreactor was constituted by Gammaproteobacteria belonging to the Halothiobacillaceae family. FISH performed with the specifically designed probe tios_434 demonstrated that this OTU constituted 90.6+/-1.3% of the bacterial community. Smaller fractions were represented by bacteria belonging to the classes Betaproteobacteria, Alphaproteobacteria, Deltaproteobacteria, Clostridia, Mollicutes, Sphingobacteria, Bacteroidetes and Chlorobia. Phylogenetic analysis revealed that clone sequences from the dominant OTU formed a stable clade (here called the TIOS44 cluster), within the Halothiobacillaceae family, with sequences from many organisms that have not yet been validly described. The data indicated that bacteria belonging to the TIOS44 cluster were responsible for the oxidation process.

Halothiobacillus neapolitanus strain OSWA isolated from "The Old Sulphur Well" at Harrogate (Yorkshire, England).

The "Old Sulphur Well" has a subterranean input of water containing 5.5mM total sulfide, which would be inhibitory to the growth of most bacteria. The obligately chemolithoautotrophic Halothiobacillus neapolitanus is a sulfur bacterium known to tolerate and metabolize high sulfide concentrations, and we report the isolation of H. neapolitanus strain OSWA from this source. Strain OSWA grows well on thiosulfate and tetrathionate as energy sources, and tolerates at least 5mM sulfide. Its specific growth rates and yields in batch culture were 0.22h(-1) and 5.3 gmol(-1) (thiosulfate), and 0.23 h(-1) and 9.5 gmol(-1) (tetrathionate). Its 16S rRNA gene sequence shows >99% identity to reference sequences of H. neapolitanus, and it shares morphological and physiological characteristics typical of the species. It is one of a very small number of strains of H. neapolitanus described to date, and the first to be isolated from an ancient sulfide-rich natural spa.

Isolation and characterization of an obligately chemolithoautotrophic Halothiobacillus strain capable of growth on thiocyanate as an energy source.

Molecular and microbiological analysis of a laboratory bioreactor biomass oxidizing thiocyanate at autotrophic conditions and at 1 M NaCl showed a domination of a single chemolithoautotrophic sulfur-oxidizing bacterium (SOB) capable of using thiocyanate as an energy source. The bacterium was isolated in pure cultures and identified as a member of the Halothiobacillus halophilus/hydrothermalis clade. This clade includes moderately halophilic chemolithoautotrophic SOB from marine and hypersaline habitats for which the ability to utilize thiocyanate as an electron donor has not been previously demonstrated. Halothiobacillus sp. strain SCN-R1 grew with thiocyanate as the sole energy and nitrogen source oxidizing it to sulfate and ammonium via the cyanate pathway. The pH range for thiocyanate oxidation was within a neutral region between 7 and 8 and the range of salinity was from 0.2 to 1.5 M NaCl, with an optimum at 0.5 M. Despite the close phylogenetic relatedness, none of the tested type strains and other isolates from the H. halophilus/hydrothermalis group exhibited thiocyanate-oxidizing capacity.

Isolation, characterization, and in situ detection of a novel chemolithoautotrophic sulfur-oxidizing bacterium in wastewater biofilms growing under microaerophilic conditions.

We successfully isolated a novel aerobic chemolithotrophic sulfur-oxidizing bacterium, designated strain SO07, from wastewater biofilms growing under microaerophilic conditions. For isolation, the use of elemental sulfur (S(0)), which is the most abundant sulfur pool in the wastewater biofilms, as the electron donor was an effective measure to establish an enrichment culture of strain SO07 and further isolation. 16S rRNA gene sequence analysis revealed that newly isolated strain SO07 was affiliated with members of the genus Halothiobacillus, but it was only distantly related to previously isolated species (89% identity). Strain SO07 oxidized elemental sulfur, thiosulfate, and sulfide to sulfate under oxic conditions. Strain SO07 could not grow on nitrate. Organic carbons, including acetate, propionate, and formate, could not serve as carbon and energy sources. Unlike other aerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 150 mM was negligible. In situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells hybridized with a probe specific for strain SO07 were mainly present in the oxic biofilm strata (ca. 0 to 100 micro m) and that they often coexisted with sulfate-reducing bacteria in this zone. These results demonstrated that strain SO07 was one of the important sulfur-oxidizing populations involved in the sulfur cycle occurring in the wastewater biofilm and was primarily responsible for the oxidation of H(2)S and S(0) to SO(4)(2-) under oxic conditions.