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Sulfur oxidizing bacteria (SOB) play a key role in sulfur cycling in mine tailings impoundment (TI) waters, where sulfur concentrations are typically high. However, our understanding of SOB sulfur cycling via potential S oxidation pathways (sox, rdsr, and S4I) in these globally ubiquitous contexts, remains limited. Here, we identified TI water column SOB community composition, metagenomics derived metabolic repertoires, physicochemistry, and aqueous sulfur concentration and speciation in four Canadian base metal mine, circumneutral-alkaline TIs over four years (2016 - 2019). Identification and examination of genomes from nine SOB genera occurring in these TI waters revealed two pH partitioned, metabolically distinct groups, which differentially influenced acid generation and sulfur speciation. Complete sox (csox) dominant SOB (e.g., Halothiobacillus spp., Thiomonas spp.) drove acidity generation and S2O32- consumption via the csox pathway at lower pH (pH ~5 to ~6.5). At circumneutral pH conditions (pH ~6.5 to ~8.5), the presence of non-csox dominant SOB (hosting the incomplete sox, rdsr, and/or other S oxidation reactions; e.g. Thiobacillus spp., Sulfuriferula spp.) were associated with higher [S2O32-] and limited acidity generation. The S4I pathway part 1 (tsdA; S2O32- to S4O62-), was not constrained by pH, while S4I pathway part 2 (S4O62- disproportionation via tetH) was limited to Thiobacillus spp. and thus circumneutral pH values. Comparative analysis of low, natural (e.g., hydrothermal vents and sulfur hot springs) and high (e.g., Zn, Cu, Pb/Zn, and Ni tailings) sulfur systems literature data with these TI results, reveals a distinct TI SOB mining microbiome, characterized by elevated abundances of csox dominant SOB, likely sustained by continuous replenishment of sulfur species through tailings or mining impacted water additions. Our results indicate that under the primarily oxic conditions in these systems, S2O32- availability plays a key role in determining the dominant sulfur oxidation pathways and associated geochemical and physicochemical outcomes, highlighting the potential for biological management of mining impacted waters via pH and [S2O32-] manipulation. [ABSTRACT FROM AUTHOR]

Environmental context: High-quality ecotoxicology data are required to derive reliable water quality guideline values that ensure long-term protection of marine biota from arsenate. Tropical and temperate marine biota have sensitivity to arsenate covering three to four orders of magnitude due to the range of arsenate detoxification mechanisms used to reduce toxicity. The water quality guideline values derived in this study will contribute to robust risk assessments of arsenate in marine environments. Rationale: There are very few high-quality chronic inorganic arsenate (AsV) toxicity data to assess the risks to marine ecosystems. We aimed to determine the range in chronic toxicity of AsV to marine biota and derive reliable water quality guideline values (GVs) for the long-term protection of marine ecosystems. Methodology: We generated chronic toxicity data based on measured dissolved (<0.45 µm filtered) AsV concentrations for 13 marine species representing seven taxonomic groups from temperate and tropical environments. Effect concentrations at the 10% level (EC10) were used in a species sensitivity distribution (SSD) to derive water quality GVs. Results: The range of concentrations causing chronic 10, 20 and 50% adverse effects were 13–26 000, 18–34 000 and 32–330 000 µg AsV L–1, respectively. Increased phosphate and nitrate concentrations were found to reduce the toxicity of AsV to certain microalgal, sea urchin and bivalve species. The range in effect concentrations for tropical versus temperate species overlapped at all effect levels. The GVs for the long-term protection of 80, 90, 95 and 99% of marine biota were: 48, 22, 12 and 4.8 µg AsV L–1, respectively. Discussion: Recommendations on performing toxicity tests with arsenic to prevent artefacts associated with arsenic speciation were made to improve future research on arsenic toxicity. The new data will improve the reliability status of the Australian and New Zealand AsV GVs for marine water quality and fill a data gap for global risk assessments of AsV for marine biota. Environmental context. High-quality ecotoxicology data are required to derive reliable water quality guideline values that ensure long-term protection of marine biota from arsenate. Tropical and temperate marine biota have sensitivity to arsenate covering three to four orders of magnitude due to the range of arsenate detoxification mechanisms used to reduce toxicity. The water quality guideline values derived in this study will contribute to robust risk assessments of arsenate in marine environments. [ABSTRACT FROM AUTHOR]

Micronutrients play key roles in numerous metabolic processes in cyanobacteria. However, our understanding of whether the micronutrient cobalt influences the productivity of freshwater systems or the occurrence of cyanobacterial blooms is limited. This study aimed to quantify the concentration of Co necessary for optimal cyanobacterial growth by exposing Microcystis aeruginosa to a range of Co concentrations under culture conditions. Extended exposure to concentrations below ˜0.06 μg · L−1 resulted in notable inhibition of M. aeruginosa growth. A clear negative relationship was observed between Co concentration in solution and intracellular Fe quota of M. aeruginosa, possibly due to decreased transport of Fe at higher Co concentrations. Cyanocobalamin and any Co within the structure of cyanocobalamin appears to be non‐bioavailable to M. aeruginosa, instead they likely rely on the synthesis of a structural variant – pseudocobalamin, which may have implications for the wider algal community as the variants of cobalamin are not necessarily functionally exchangeable. To evaluate the likelihood of Co limitation of cyanobacterial growth under field conditions, a survey of 10 freshwater reservoirs in South‐Eastern Australia was conducted. Four of the ten sites had dissolved Co concentrations below the 0.06 μg · L−1 threshold value. All four of these sites rarely undergo cyanobacterial blooms, strengthening evidence of the potential for Co to limit growth, perhaps either alone or in combination with phosphorus. [ABSTRACT FROM AUTHOR]