Biogeochemical stability of organic covers and mine wastes under climate change simulated mesocosms.

Mine environments in boreal and sub-boreal zones are expected to experience extreme weather events, increases in temperature, and shifts in precipitation patterns. Climate change impacts on geochemical stability of tailings contaminants and reclamation structures have been identified as important climate-related challenges to Canadian mining sector. Adapting current reclamation strategies for climate change will improve long-term efficiency and viability of mine tailings remediation/restoration strategies under a changing climate. Accordingly, mesocosm experiments were conducted to investigate associations of climate-driven shifts in microbial communities and functions with changes in the geochemistry of organic covers and underlying tailings. Our results show that warming appears to significantly reduce C:N of organic cover and promote infiltration of nitrogen into deeper, unoxidized strata of underlying tailings. We also observed an increase in the abundance of some nitrate reducers and sulfide oxidizers in microbial communities in underlying tailings. These results raise the concern that warming might trigger oxidation of sulfide minerals (linked to nitrate reduction) in deeper unoxidized strata where the oxygen has been eliminated. Therefore, it would be necessary to have monitoring programs to track functionality of covers in response to climate change conditions. These findings have implications for development of climate resilient mine tailings remediation/restoration strategies.

Blended municipal compost and biosolids materials for mine reclamation: Long-term field studies to explore metal mobility, soil fertility and microbial communities.

Application of stable soil amendments is often the key to successful phytostabilization and rehabilitation of mine tailings, and microbial guilds are primary drivers of many geochemical processes promoted by these amendments. Field studies were set up at a tailings management area near Sudbury, Ontario to examine performance of blends of lime stabilized municipal biosolids and compost at nine different rates over thick (1 m) municipal compost covers planted with agricultural crops. Based on biogeochemical variability of the substrates four and ten years after application of the initial compost cover, the experimental plots could be classified into three categories: "Low" rate (0-100 t ha-1 biosolids), "Medium" rate (200-800 t ha-1), and "High" rate (1600-3200 t ha-1) treatments. The addition of biosolids materials to the thick compost cover at rates higher than 100 t ha-1 significantly reduced C:N ratio of the substrates, available phosphorus, and some of the nutrient cations, while notably increasing inorganic carbon and the potential solubility of Ni and Cu. This suggests that increasing biosolids application rates may not equivalently ameliorate soil quality and geochemical stability. Correspondingly, microbial communities were altered by biosolids additions, further intensifying the negative impacts of biosolids on long-term efficiency of the initial compost cover. Abundance of cellulose, hemicellulose, and lignocellulose decomposers (as key drivers of mineralization and humification) was significantly reduced by "Medium" and "High" rate treatments. Most DNA sequences with high affinity to denitrifiers were detected in "High" rate treatments where geochemical conditions were optimal for higher microbial denitrification activities. These findings have implications for improving the long-term efficiency of reclamation and environmental management programs in mine tailings of northern temperate climates.

Ecophysiology of "Halarsenatibacter silvermanii" strain SLAS-1T, gen. nov., sp. nov., a facultative chemoautotrophic arsenate respirer from salt-saturated Searles Lake, California.

Searles Lake occupies a closed basin harboring salt-saturated, alkaline brines that have exceptionally high concentrations of arsenic oxyanions. Strain SLAS-1(T) was previously isolated from Searles Lake (R. S. Oremland, T. R. Kulp, J. Switzer Blum, S. E. Hoeft, S. Baesman, L. G. Miller, and J. F. Stolz, Science 308:1305-1308, 2005). We now describe this extremophile with regard to its substrate affinities, its unusual mode of motility, sequenced arrABD gene cluster, cell envelope lipids, and its phylogenetic alignment within the order Halanaerobacteriales, assigning it the name "Halarsenatibacter silvermanii" strain SLAS-1(T). We also report on the substrate dynamics of an anaerobic enrichment culture obtained from Searles Lake that grows under conditions of salt saturation and whose members include a novel sulfate reducer of the order Desulfovibriales, the archaeon Halorhabdus utahensis, as well as a close homolog of strain SLAS-1(T).

Intracellular iron minerals in a dissimilatory iron-reducing bacterium.

Among prokaryotes, there are few examples of controlled mineral formation; the formation of crystalline iron oxides and sulfides [magnetite (Fe3O4) or greigite (Fe3S4)] by magnetotactic bacteria is an exception. Shewanella putrefaciens CN32, a Gram-negative, facultative anaerobic bacterium that is capable of dissimilatory iron reduction, produced microscopic intracellular grains of iron oxide minerals during growth on two-line ferrihydrite in a hydrogen-argon atmosphere. The minerals, formed at iron concentrations found in the soil and sedimentary environments where these bacteria are active, could represent an unexplored pathway for the cycling of iron by bacteria.

Sorption of strontium onto bacteriogenic iron oxides.

Bacteriogenic iron oxides (BIOS) were obtained from a dilute, circumneutral groundwater seep, characterized with respect to mineralogy, and examined for their ability to sorb aqueous Sr2+. BIOS were composed of microbial sheaths encrusted in 2-line ferrihydrite. Sorption experiments indicated that Sr remained completely unbound at pH < 4.5, but sorption increased with increasing pH (maximum of 95% at pH > 7.6). EXAFS analysis of Sr-loaded BIOS failed to elucidate whether Sr sorption occurred on sites specific to the mineral or microbial fraction, but indicated that sorption likely occurred by outer-sphere complexation between BIOS and hydrated Sr2+. Sorption experiments showed that at low ionic strength (I = 0.001 M), sorption followed a Langmuir isotherm (S(max) = 3.41 mol Sr (g of Fe)(1-), K(ads) = 1.26). At higher ionic strength (I = 0.1 M), there was significant inhibition of Sr sorption (S(max) = 1.06 mol Sr (g of Fe)(1-), K(ads) = 1.23), suggesting that sorption to BIOS occurs by outer-sphere complexation. The results suggest that, under dilute circumneutral conditions, BIOS deposits should efficiently sorb dissolved Sr from groundwater flow systems where such deposits exist. This finding has particular relevance to sites impacted by radioactive 90Sr groundwater contamination.

Intracellular manganese granules formed by a subsurface bacterium.

The demonstrated ability of prokaryotes to form internal metal oxide particles during active metabolism has been restricted to Fe. Mineral-bound Mn(IV) is a known electron acceptor during dissimilatory metal reduction by Shewanella putrefaciens, yet no internal deposits of Mn have been reported to form during anaerobic respiration. We observed distinct nanometre-sized Mn-rich granules in the cytoplasm when either birnessite or pyrolusite (beta-MnO(2)) served as the electron acceptor during growth. During rapid Mn reduction, additional precipitates of Mn were also observed in the periplasm together with the cytoplasmic granules. The bacteria did not accumulate detectable Mn in the outer membrane during formation of the internal precipitates. This is the first report of an intracellular Mn solid produced by bacteria and coupled anaerobically to DR.

Structural and spectral features of selenium nanospheres produced by Se-respiring bacteria.

Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate- and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter, approximately 300 nm) of Se(0) having monoclinic crystalline structures. Intracellular packets of Se(0) were also noted. The number of intracellular Se(0) packets could be reduced by first growing cells with nitrate as the electron acceptor and then adding selenite ions to washed suspensions of the nitrate-grown cells. This resulted in the formation of primarily extracellular Se nanospheres. After harvesting and cleansing of cellular debris, we observed large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species. The spectral properties in turn differed substantially from those of amorphous Se(0) formed by chemical oxidation of H(2)Se and of black, vitreous Se(0) formed chemically by reduction of selenite with ascorbate. The microbial synthesis of Se(0) nanospheres results in unique, complex, compacted nanostructural arrangements of Se atoms. These arrangements probably reflect a diversity of enzymes involved in the dissimilatory reduction that are subtly different in different microbes. Remarkably, these conditions cannot be achieved by current methods of chemical synthesis.