Effect of Remediation Reagents on Bacterial Composition and Ecological Function in Black-Odorous Water Sediments

Black-odorous urban water bodies and sediments pose a serious environmental problem. Herein, we conducted microcosm batch experiments to investigate the effect of remediation reagents (magnesium hydroxide and calcium nitrate) on native bacterial communities and their ecological functions in the black-odorous sediment of urban water. The dominant phyla (Proteobacteria, Actinobacteria, Chloroflexi, and Planctomycetes) and classes (Alpha-, Beta-, and Gamma-proteobacteria, Actinobacteria, Anaerolineae, and Planctomycetia) were determined under calcium nitrate and magnesium hydroxide treatments. Functional groups related to aerobic metabolism, including aerobic chemoheterotrophy, dark sulfide oxidation, and correlated dominant genera (Thiobacillus, Lysobacter, Gp16, and Gaiella) became more abundant under calcium nitrate treatment, whereas functional genes potentially involved in dissimilatory sulfate reduction became less abundant. The relative abundance of chloroplasts, fermentation, and correlated genera (Desulfomonile and unclassified Cyanobacteria) decreased under magnesium hydroxide treatment. These results indicated that calcium nitrate addition improved hypoxia-related reducing conditions in the sediment and promoted aerobic chemoheterotrophy.

Extremely Acidic Eukaryotic (Micro) Organisms: Life in Acid Mine Drainage Polluted Environments—Mini-Review

Acid Mine Drainage (AMD) results from sulfide oxidation, which incorporates hydrogen ions, sulfate, and metals/metalloids into the aquatic environment, allowing fixation, bioaccumulation and biomagnification of pollutants in the aquatic food chain. Acidic leachates from waste rock dams from pyritic and (to a lesser extent) coal mining are the main foci of Acid Mine Drainage (AMD) production. When AMD is incorporated into rivers, notable changes in water hydro-geochemistry and biota are observed. There is a high interest in the biodiversity of this type of extreme environments for several reasons. Studies indicate that extreme acid environments may reflect early Earth conditions, and are thus, suitable for astrobiological experiments as acidophilic microorganisms survive on the sulfates and iron oxides in AMD-contaminated waters/sediments, an analogous environment to Mars; other reasons are related to the biotechnological potential of extremophiles. In addition, AMD is responsible for decreasing the diversity and abundance of different taxa, as well as for selecting the most well-adapted species to these toxic conditions. Acidophilic and acidotolerant eukaryotic microorganisms are mostly composed by algae (diatoms and unicellular and filamentous algae), protozoa, fungi and fungi-like protists, and unsegmented pseudocoelomata animals such as Rotifera and micro-macroinvertebrates. In this work, a literature review summarizing the most recent studies on eukaryotic organisms and micro-organisms in Acid Mine Drainage-affected environments is elaborated.

Biological Desulfurization of Tannery Effluent Using Hybrid Linear Flow Channel Reactors

The tanning process generates a saline effluent with high residual organics, sulfate and sulfide concentrations. The transition from a linear to circular economy requires reimagining of waste streams as potential resources. The organics in tannery effluent have the potential to be converted to renewable energy in the form of biogas if inhibitors to anaerobic digestion are removed. Hybrid linear flow channel reactors inoculated with culture-enriched halophilic sulfate reducing bacteria from saline environments were evaluated as a novel pretreatment step prior to anaerobic digestion for the concurrent removal of sulfur species and resource recovery (elemental sulfur and biogas). During continuous operation of a 4-day hydraulic retention time, the reactors were capable of near-complete sulfide oxidation (>97%) and a sulfate reduction efficiency of 60–80% with the formation of a floating sulfur biofilm containing elemental sulfur. Batch anaerobic digestion tests showed no activity on untreated tannery effluent, while the pretreated effluent yielded 130 mL methane per gram COD consumed.

The pathway of sulfide oxidation to octasulfur globules in the cytoplasm of aerobic bacteria

Sulfur-oxidizing bacteria can oxidize hydrogen sulfide (H 2 S) to produce sulfur globules. Although the process is common, the pathway is unclear. In recombinant Escherichia coli and wild-type Corynebacterium vitaeruminis DSM20294 with SQR but no enzymes to oxidize zero valence sulfur, SQR oxidized H 2 S into short-chain inorganic polysulfide (H 2 S n , n≥2) and organic polysulfide (RS n H, n≥2), which reacted with each other to form long-chain GS n H (n≥2) and H 2 S n before producing octasulfur (S 8 ), the main component of elemental sulfur. GS n H also reacted with GSH to form GSnG (n≥2) and H 2 S; H 2 S was again oxidized by SQR. After GSH was depleted, SQR simply oxidized H 2 S to H 2 S n , which spontaneously generated S 8 . S 8 aggregated into sulfur globules in the cytoplasm. The results highlight the process of sulfide oxidation to S 8 globules in the bacterial cytoplasm and demonstrate the potential of using heterotrophic bacteria with SQR to convert toxic H 2 S into relatively benign S 8 globules. IMPORTANCE Our results support a process of H 2 S oxidation to produce octasulfur globules via SQR catalysis and spontaneous reactions in the bacterial cytoplasm. Since the process is an important event in geochemical cycling, a better understanding facilitates further studies and provides theoretical support for using heterotrophic bacteria with SQR to oxidize toxic H 2 S into sulfur globules for recovery.

New Data on Hydrogeochemical and Isotopic Composition of Natural Waters of the Baidar Valley (Crimean Peninsula)

—Results of study of natural waters of the Baidar valley (southwestern Crimean Peninsula) obtained during the 2018–2019 field works are presented. Major groundwater resources of the study area are confined to the Upper Jurassic aquifer complex, which serves as a recharge source for the aquifer systems of the Plain Crimean and the Azov–Kuban’ artesian basins and hydrogeologic folded region of the Crimean Mountains mega-anticlinorium. The regional waters are fresh and ultrafresh, predominantly of calcium bicarbonate composition, with TDS varying from 208 to 1269 mg/dm3. The study enabled their classification into eight geochemical groups: (1) waters of a regional fracture zone in carbonate-terrigenous rocks affected by continental salinization; (2) waters of a regional fracture zone affected by leaching of aluminosilicates and sulfide oxidation; (3) waters of a regional fracture zone dominated by sodium aluminosilicates in the fracture filling (long-term interaction in the water–rock system), affected by continental salinization; (4) regional fracture zones dominated by sodium aluminosilicates affected by anthropogenic continental salinization; (5) groundwaters in fracture–vein aquifers affected by leaching of aluminosilicates and sulfide oxidation; (6) fracture–vein aquifers affected by leaching of sodium aluminosilicates (long-term interaction in the water–rock system); (7) waters in fractured karst aquifers; and (8) surface waters subjected to continental salinization. Fracture karst waters, which were found to be most protected against human impact and continental salinization processes, are slightly alkaline (pH = 7.7), fresh (with average TDS = 444 mg/dm3), with low silicon concentrations (2.23 mg/dm3), and of calcium bicarbonate composition. Waters residing in regional fracture and fracture–vein zones are affected by continental salinization and anthropogenic load and are neutral to alkaline (pH = 7.1–8.6), predominantly fresh (TDS = 269–1269 mg/dm3), with average silicon concentrations of 4.61–4.70 mg/dm3, of calcium bicarbonate composition, with high concentrations of sulfate ion, magnesium, and sodium. The waters of the Chernaya River, Chernorechensk reservoir, and lakes, which are also affected by continental salinization, are slightly alkaline (pH = 8.3), brackish (TDS = 207–364 mg/dm3), with an average silicon concentration of 1.18 mg/dm3, of calcium bicarbonate composition, with high concentrations of chlorine ion, magnesium, and sodium. The calculated intensity of chemical-element migration in waters of the background composition follows the descending order: very strong, I17.7 > Br14.4; strong, Se2.83 > B2.22 > Sr1.46 > Sb1.12 > Be1.07 > Hg1.06; moderately strong, Zn0.74 > Mo0.50 > Li0.46 > Sc0.41 > Ag0.18 > As0.16 > Si0.123 > Ba0.122; weak, Cr0.10 > Cu0.096 > Bi0.080 > Sn0.068 > Tl0.067 > P0.062 > Ni0.043 > Ta0.040 > Ge0.034 > Cd0.028 > Fe0.026 > Rb0.024 > Co0.023 > Pb0.020 > W0.017 > V0.012; very weak (inert), Nb0.008 > Hf0.0033 > Mn0.0031 > La0.0029 > Cs0.0022 > Ti0.0018 > Ga0.0016 > Y0.0013 > Al0.0008 > Zr0.0008. All the studied waters are found to be of atmospheric origin and located along the global (GMWL) and local (LMWL) meteoric water lines. Their δ18O value varies from –9.9 to –3.3‰, and δD value, from –64.2 to –32.5‰. Sedimentary carbonate rocks, atmospheric carbon dioxide, organic compounds, and hydrolysis of aluminosilicate minerals serve as the source of δ13C bicarbonate ion in natural waters of the Baidar valley. Surface waters have a heavier carbon isotope composition (δ13C = –9.2 to –6.2‰), which is due to atmospheric CO2, plant growth, and associated microbial activity. Fracture karst waters are characterized by a lighter carbon isotope composition (δ13C = –12.8 to –11.0‰) because of their interaction with dispersed organic matter. Waters of the regional fracture and fracture–vein zones display the widest variation in δ13C (–15.5 to –6.9‰), which is associated with a mixed type of “isotope supply” to the waters. A complex hydrogeochemical field that has formed in the Baidar valley tends to be increasingly affected by the anthropogenic factor.

The Role of Microorganisms in the Formation, Dissolution, and Transformation of Secondary Minerals in Mine Rock and Drainage: A Review

Mine waste rock and drainage pose lasting environmental, social, and economic threats to the mining industry, regulatory agencies, and society as a whole. Mine drainage can be alkaline, neutral, moderately, or extremely acidic and contains significant levels of sulfate, dissolved iron, and, frequently, a variety of heavy metals and metalloids, such as cadmium, lead, arsenic, and selenium. In acid neutralization by carbonate and silicate minerals, a range of secondary minerals can form and possibly scavenge these potentially harmful elements. Apart from the extensively studied microbial-facilitated sulfide oxidation, the diverse microbial communities present in mine rock and drainage may also participate in the formation, dissolution, and transformation of secondary minerals, influencing the mobilization of these metals and metalloids. This article reviews major microbial-mediated geochemical processes occurring in mine rock piles that affect drainage chemistry, with a focus on the role of microorganisms in the formation, dissolution, and transformation of secondary minerals. Understanding this is crucial for developing biologically-based measures to deal with contaminant release at the source, i.e., source control.

Quantifying the Seawater Sulfate Concentration in the Cambrian Ocean

Although the earliest animals might have evolved in certain “sweet spots” in the last 10 million years of Ediacaran (550–541 Ma), the Cambrian explosion requires sufficiently high levels of oxygen (O2) in the atmosphere and diverse habitable niches in the substantively oxygenated seafloor. However, previous studies indicate that the marine redox landscape was temporally oscillatory and spatially heterogeneous, suggesting the decoupling of atmospheric oxygenation and oceanic oxidation. The seawater sulfate concentration is controlled by both the atmospheric O2 level and the marine redox condition, with sulfide oxidation in continents as the major source, and sulfate reduction and pyrite burial as the major sink of seawater sulfate. It is thus important to quantify the sulfate concentration on the eve of the Cambrian explosion. In this study, we measured the pyrite contents and pyrite sulfur isotopes of black shale samples from the Yurtus Formation (Cambrian Series 2) in the Tarim Block, northwestern China. A numerical model is developed to calculate the seawater sulfate concentration using the pyrite content and pyrite sulfur isotope data. We first calibrate some key parameters based on observations from modern marine sediments. Then, the Monte Carlo simulation is applied to reduce the uncertainty raised by loosely confined parameters. Based on the geochemical data from both Tarim and Yangtze blocks, the modeling results indicate the seawater sulfate concentration of 8.9–14 mM, suggesting the seawater sulfate concentration was already 30–50% of the present level (28 mM). High seawater sulfate concentration might be attributed to the enhanced terrestrial sulfate input and widespread ocean oxygenation on the eve of the Cambrian explosion.

Aqueous system-level processes and prokaryote assemblages in the ferruginous and sulfate-rich bottom waters of a post-mining lake

In the aqueous oligotrophic ecosystem of a post-mining lake (Lake Medard, Czechia), reductive Fe(II) dissolution outpaces sulfide generation from microbial sulfate reduction (MSR), and ferruginous conditions occur without quantitative sulfate depletion. An isotopically constrained estimate of the rates of sulfate reduction (SRR) suggests that despite a high genetic potential, this respiration pathway is limited by the rather low amounts of metabolizable organic carbon. This points to substrate competition exerted by iron and nitrogen respiring prokaryotes. Yet, the microbial succession across the nitrogenous and ferruginous zones of the bottom water column also indicates sustained genetic potential for chemolithotrophic sulfur oxidation. Therefore, our isotopic SRR estimates could be rather portraying high rates of anoxic sulfide oxidation to sulfate, probably accompanied by microbially induced disproportionation of S intermediates. Near and at the anoxic sediment-water interface, vigorous sulfur cycling can be fuelled by ferric and manganic particulate matter and redeposited siderite stocks. Sulfur oxidation and disproportionation then appear to prevent substantial stabilization of iron monosulfides as pyrite but can enable the interstitial precipitation of small proportions of equant microcrystalline gypsum. This latter mineral isotopically fingerprints sulfur oxidation proceeding at near equilibrium with the ambient anoxic waters, whilst authigenic pyrite-sulfur displays a 38 to 27 ‰ isotopic offset from ambient sulfate, suggestive of incomplete MSR and likely reflective also of an open sulfur cycling system. Pyrite-sulfur fractionation decreases with increased reducible reactive iron in the sediment. In the absence of ferruginous coastal zones today, the current water column redox stratification in the post-mining Lake Medard has scientific value for (i) testing emerging hypotheses on how a few interlinked biogeochemical cycles operated in nearshore paleoenvironments during redox transitional states; and (ii) to acquire insight on how similar early diagenetic redox proxy signals developed in sediments affected by analogue transitional states in ancient water columns.