Isolation of Arsenic Resistant and Arsenopyrite Oxidizing Acidithiobacillus Species from pH Neutral Colombian Mine Effluents

Abstract

Inactive mines provide a great source of bacterial diversity for studying acidophilic communities and their biotechnological applications, but prospecting of these anthropogenic environments in Colombia has been limited. Conventional microbiological methods were used to isolate acidophilic bacterial strains from effluents emanating from the Colombian gold mine ‘El Zancudo’ (Titiribí, Antioquia). Despite the drainage waters having circumneutral pH, all of the isolated strains were phylogenetically related to the extreme acidophile Acidithiobacillus genus. However, based upon 16S rRNA gene sequences the mesophilic sulfur-oxidizing indigenous strains could not be assigned to a species. Pure cultures were selected by screening in medium with soluble inorganic arsenic (III) and their mineral-oxidative activity was evaluated at 30?°C in Erlenmeyer flasks with arsenopyrite ore under rotary shaking conditions. The indigenous strains were able to catalyze arsenopyrite oxidation in a mixed culture with a pulp density of 10%, maintaining their growth in the presence of >80?mM leached arsenic. This research provides information regarding the isolation of arsenic resistant bacterial communities from neutral effluents from El Zancudo mine and the possibility of the isolated strains to be useful in the biooxidation pretreatment of refractory gold-bearing arsenopyrite ores and concentrates.     

Nitrogen and Phosphorus Release from Decomposing Leaves under Sub‐Humid Tropical Conditions1

For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R²= 0.60‐0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R²= 0.69‐0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, y_t= y₀* e‐^kt, from which the specific decay rate constants (k) were calculated for loss of leaf mass (k_B) and release of N (k_N) and P (K_p). Among the plant species, the k values were lowest in Calliandra with k_B= 0.012/d, k_N= 0.017/d and k_p= 0.044/d. Lantana had the highest K values with k_g= 0.067/d and k_p= 0.119/d, but the highest k_N value of 0.109/d occurred in Tithonia. The k_B values for all organic materials were lower than their corresponding k_N and k_p values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the k_B, k_N, and k_p values and total P (r = 0.82‐0.96; P 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia > Senna > Lantana > Sesbania > Croton > Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study.     

Arsenic and antimony release from sediments in a Mediterranean estuary

An ancient realgar mine is responsible for the contamination of a riverine system in central Corsica. Nearby the mine, high As and Sb concentrations are found (up to 2–3 mg l^-1 and 2–3 g l^-1 respectively). A significant increase of the As and Sb concentrations in water is found in the water of the mixing zone of river and sea (Bravona estuary; chlorinity 7000–7800). In the same area, a decrease of As and Sb concentrations in sediments is observed. Fe and Mn exhibit the same behaviour. The possible involvement of redox processes is discussed. However, owing to insufficient reducing capacity and insignificant variation of redox potential values along the various estuarine sites (from 320 down to 280 mV), this scenario is rather doubtful. Desorption from FeOOH particles is the most likely process in the Bravona estuary. The impact of these contaminated waters on the marine environment is discussed. Owing to decrease by dilution, as well as the reduced water flow of the estuary, the net supply of As and Sb to the Tyrrhenian Sea is approximately 5 and 1.5 t y^-1 for As and Sb respectively. The possible harmful influence of the Bravona river should be of local concern only, and the emphasis of this study is, therefore, on a better knowledge of in situ processes.     

Arsenic in Biogenic Iron Minerals from a Contaminated Environment

High arsenic levels have been found in some water samples from the Iron Quadrangle, a main gold, manganese and iron mining region in Brazil. In this work, we used transmission electron microscopy coupled to energy-dispersive X-ray analysis to show arsenic in bacteriogenic iron minerals (BIOS) collected in this region. Two types of iron bacteria stalks and several morphologically different filamentous sheaths of bacteria were found, most containing arsenic. Bacterial stalks were partially coated by spherical precipitates probably deposited after stalk secretion. Arsenic/iron ratios were the same independently of the amount of spherical precipitates, suggesting that arsenic incorporation is independent of bacterial metabolism. Additionally, arsenic seems to be saturated in these minerals, since the arsenic/iron ratio was the same under different arsenic concentrations.     

Arsenic precipitation by an anaerobic arsenic‐respiring bacterial strain isolated from the polluted sediments of Orbetello Lagoon,Italy

Aims: To isolate and characterize an anaerobic bacterial strain from the deeper polluted lagoon sediment able to use as electron acceptors [As(V)] and sulfate (), using lactate as an electron donor. Methods and Results: Methods for isolation from polluted lagoon sediments included anaerobic enrichment cultures in the presence of As(V) and . Reduction of As(V) to As(III) was observed during the growth of the bacterial strain, and the final concentration of As(III) was lower than the initial As(V) one, suggesting the immobilization of As(III) in the yellow precipitate. The precipitate was identified by energy dispersive spectroscopy X‐ray as arsenic sulfide. Scanning electron microscopy (SEM) revealed rod‐shaped bacterial cells embedded in the precipitate, where net‐like formations strictly related to the bacterial cells were visible. The surface of the precipitate showed the adhesion of bacterial cells, forming clusters. Transmission electron microscopy (TEM) also highlighted precipitates inside the bacterial cells and on their surface. Following 16S rRNA sequencing, the bacterial strain 063 was assigned to the genus Desulfosporosinus. Conclusions: This study reports, for the first time, the isolation from the polluted lagoon sediments of a strain capable of respiring and using As(V) and as electron acceptors with lactate as the sole carbon and energy source with the formation of an arsenic sulfide precipitate. Significance and Impact of the Study: The identification of these properties provides novel insight into the possible use of the anaerobic strain in bioremediation processes and also adds to the knowledge on the biogeochemical cycling of arsenic.     

Near‐natural methods promote restoration of species‐rich grassland vegetation—revisiting a road verge trial after 9 years

The present loss of species‐rich grasslands makes it vital to restore these valuable habitat types, including novel habitat variants such as road verges. Due to the lack of knowledge on long‐term outcomes of restoration initiatives, well‐designed studies comparing different restoration methods are needed. In this study, we examined fine‐scale vegetation recovery patterns over 9 years in a field experiment with several near‐natural restoration methods (adding local seed mixtures, transferring hay from local grasslands using hard or light raking, and natural regeneration) in a road verge. We compared this to standard revegetation (hydroseeding species‐poor commercial seed mixtures). We found major temporal changes in vegetation restored by local seed or hay transfer, before it gradually became more similar to the donor grasslands and seed mixtures, which served as references for the experiment. Natural (spontaneous) regeneration with seed dispersal from surroundings gave similar results, whereas areas revegetated using standard methods became more dissimilar to the reference sites during the study period. The main variation in species composition reflected the contrast between local donor grasslands and seed mixtures and the species‐poor early successional grasslands. We conclude that near‐natural methods (hay transfer and seeding) successfully restored species‐rich grassland, including road verges. This study underlines the importance of comparing several treatments over a sufficiently long period to assess their success in restoring species‐rich grassland.     

Elucidating the Sole Contribution from Electromagnetic Near‐Fields in Plasmon‐Enhanced Cu2O Photocathodes

Despite many promising reports of plasmon‐enhanced photocatalysis, the inability to identify the individual contributions from multiple enhancement mechanisms has delayed the development of general design rules for engineering efficient plasmonic photocatalysts. Herein, a plasmonic photocathode comprised of Au@SiO₂ (core@shell) nanoparticles embedded within a Cu₂O nanowire network is constructed to exclusively examine the contribution from one such mechanism: electromagnetic near‐field enhancement. The influence of the local electromagnetic field intensity is correlated with the overall light‐harvesting efficiency of the device through variation of the SiO₂ shell thickness (5–22 nm) to systematically tailor the distance between the plasmonic Au nanoparticles and the Cu₂O nanowires. A threefold increase in device photocurrent is achieved upon integrating the Au@SiO₂ nanoparticles into the Cu₂O nanowire network, further enabling a 40% reduction in semiconductor film thickness while maintaining photocathode performance. Photoelectrochemical results are further correlated with photoluminescence studies and optical simulations to confirm that the near‐field enhancement is the sole mechanism responsible for increased light absorption in the plasmonic photocathode.     

Near‐Infrared Light‐Induced Photocurrent from a (NaYF4:Yb‐Tm)/(Cu2O) Composite Thin Film

Utilization of photons of sub‐bandgap energy, mostly near‐infrared (NIR) photo­ns, is highly desirable for photovoltaic devices. We show that (NaYF₄:Yb‐Tm)/(Cu₂O) composite films formed by electrodeposition exhibit robust photoactive current generation under NIR light excitation. The composite films consist of homogeneous crystalline particles of the fluoride and Cu₂O in sub‐micrometer size. From spectroscopic characterization, it is found that the NaYF₄:Yb‐Tm layer in the composite film converts NIR radiation by up‐conversion into visible emission, which is efficiently absorbed by the covering semiconducting Cu₂O film, producing photoelectrons. Accordingly, the composite films exhibit highly photoactive current generation by means of a photoelectrochemical process driven by NIR irradiation. The methodology demonstrated here may have certain implications for the utilization of NIR radiation in solar cells, photocatalysts, and infrared photodetectors.     

Management of a semi‐natural grassland; results from a 15‐year‐old experiment in southern Sweden

Abstract. Vegetation changes in a semi‐natural grassland of wooded meadow type that had been grazed for centuries are described following the introduction of various management regimes: mowing each year, mowing every third year, burning, mechanical removal of woody plants, chemical treatment of woody plants, continuous grazing and abandonment. The experiment was established in southern Sweden in 1972 and has been in progress for 15 years. In 1972, 1980 and 1986 the botanical composition in these plots was investigated in permanent subplots. The study clearly demonstrates that mowing or grazing is necessary to preserve community structure and that mowing is to be preferred in cases where maintaining species richness is of primary concern. Mowing every third year delayed vegetation change and prevented woody species from spreading. Therefore, periodic mowing might be an alternative way to preserve the flora. In contrast, yearly burning does not seem to be a viable management in this type of semi‐natural grassland. To preserve the open landscape regeneration of woody plants has to be prevented. However, in plots where woody plants were removed the typical grassland flora declined. Abandonment resulted in closed forest.     

Efficiency of Some Bacterial Strains in Potassium Release from Mica and Phosphate Solubilization under In Vitro Conditions

Phosphorus and potassium (K) are major essential macronutrients for biological growth and development. Application of beneficial microorganisms to soil is one approach to enhance crop growth. In this study, the ability of five bacterial strains, including four strains of Pseudomonas sp. (S10-3, S14-3, S19-1, and S21-1) and one strain of Azotobacter sp. SP16, to release K from muscovite and biotite was investigated. Furthermore, phosphate solubilization by these strains was measured when an insoluble source of P [Ca₃(PO₄)₂] was added to the medium. Among the bacterial strains, the highest average K release (73% higher than control) was observed with Pseudomonas sp. S14-3. The average amount of K released from biotite was 37% higher than that from muscovite in inoculated treatments. The enhanced release of mineral K might be attributed to the release of organic acids from the bacteria, a mechanism which plays a pivotal role in solubilizing phosphate from inorganic sources. The results confirmed the enhanced phosphate solubilization by the bacterial strains in the presence of muscovite. The highest P solubilizing activity (67% higher than control) was found in S21-1 and S14-3 strains. Concentrations of both K and P in the liquid phase were increased by increasing the time of experiment. X-ray diffraction analysis of muscovite specimens inoculated with S14-3 strain revealed a partial transformation of these minerals through the presence of 19.5 Å peak on the diffractogram of the magnesium-saturated sample. This may be due to the release of K from the interlayer space and subsequent filling with a number of bacterial metabolites. The findings of this research suggest K depletion from mica in the presence of bacteria, but further investigations are needed to clarify the mechanisms involved.     

Drosophila rely on learning while foraging under semi‐natural conditions

Learning is predicted to affect manifold ecological and evolutionary processes, but the extent to which animals rely on learning in nature remains poorly known, especially for short‐lived non‐social invertebrates. This is in particular the case for Drosophila, a favourite laboratory system to study molecular mechanisms of learning. Here we tested whether Drosophila melanogaster use learned information to choose food while free‐flying in a large greenhouse emulating the natural environment. In a series of experiments flies were first given an opportunity to learn which of two food odours was associated with good versus unpalatable taste; subsequently, their preference for the two odours was assessed with olfactory traps set up in the greenhouse. Flies that had experienced palatable apple‐flavoured food and unpalatable orange‐flavoured food were more likely to be attracted to the odour of apple than flies with the opposite experience. This was true both when the flies first learned in the laboratory and were then released and recaptured in the greenhouse, and when the learning occurred under free‐flying conditions in the greenhouse. Furthermore, flies retained the memory of their experience while exploring the greenhouse overnight in the absence of focal odours, pointing to the involvement of consolidated memory. These results support the notion that even small, short lived insects which are not central‐place foragers make use of learned cues in their natural environments.     

Metformin in contrast to berberine reversed arsenic‐induced oxidative stress in mitochondria from rat pancreas probably via Sirt3‐dependent pathway

Exposure to arsenic has been linked to the development of type 2 diabetes though its mechanism of toxicity remains unresolved. In this study berberine (BBR) effects on arsenic‐induced sirtuin 3 (Sirt3) modifications in isolated mitochondria from rat pancreas were evaluated and compared with metformin (MET). With arsenic, mitochondrial reactive oxygen species (ROS), oxidative stress, and insulin resistance were obtained higher than control. From our results and in the presence of arsenic trioxide, insulin resistance and Sirt3 levels were found to be predominantly elevated that could be the result of compensating mechanisms. Apparently, BBR and MET recruit both direct (as an antioxidant) and indirect mechanisms (Sirt3 content) to deal with arsenic trioxide toxicity. Metformin compared with BBR exhibited a less significant effect on ROS levels and since its direct antioxidant property is minor, depressed the ROS level mainly through the Sirt3 modification.     

Phase‐Field Model of Electrothermal Breakdown in Flexible High‐Temperature Nanocomposites under Extreme Conditions

Polymer‐based dielectrics are attracting increasing attention due to their high‐density energy storage. However, mitigating the heat generation in real capacitors has been a challenge. Here an electrothermal breakdown phase‐field model is developed to fundamentally understand the thermal effects on the dielectric breakdown of polymer‐based dielectrics in real capacitor configurations including the increase in the dielectric loss and the decrease in the breakdown strength. While both enhancing the thermal conductivity and reducing the electrical conductivity of the polymer nanocomposites can reduce the thermal effects, it is found that reducing the electrical conductivity is more effective. This work is expected to not only stimulate attention to the thermal effects in polymer‐based dielectrics but also provide a fundamental guidance to mitigate the heat‐induced deterioration of breakdown strength.     

Genetic‐based dissection of arsenic accumulation in maize using a genome‐wide association analysis method

Understanding the mechanism of arsenic (As) accumulation in plants is important in reducing As's toxicity to plants and its potential risks to human health. Here, we performed a genome‐wide association study to dissect the genetic basis of the As contents of different maize tissues in Xixian, which was irrigated with As‐rich surface water, and Changge using an association population consisting of 230 representative maize inbred lines. Phenotypic data revealed a wide normal distribution and high repeatability for the As contents in maize tissues. The As concentrations in maize tissues followed the same trend in the two locations: kernels < axes < stems < bracts < leaves. In total, 15, 16 and 15 non‐redundant quantitative trait loci (QTL s) associated with As concentrations were identified (P  ≤ 2.04 × 10^?6) in five tissues from Xixian, Changge, and the combination of the locations, respectively, explaining 9.70%–24.65% of the phenotypic variation for each QTL , on average. Additionally, four QTL s [involving 15 single nucleotide polymorphisms (SNP s)] were detected in the single and the combined locations, indicating that these loci/SNP s might be stable across different environments. The candidate genes associated with these four loci were predicted. In addition, four non‐redundant QTL s (6 SNP s), including a QTL that was detected in multiple locations according to the genome‐wide association study, were found to co‐localize with four previously reported QTL intervals. These results are valuable to understand the genetic architecture of As mechanism in maize and facilitate the genetic improvement of varieties without As toxicity.     

Brief communication: Additional cases of maxillary canine‐first premolar transposition in several prehistoric skeletal assemblages from the Santa Barbara Channel Islands of California

This article identifies and discusses seven new cases of complete maxillary canine‐premolar transposition in ancient populations from the Santa Barbara Channel region of California. A high frequency of this tooth transposition has been previously documented within a single prehistoric cemetery on one of the Channel Islands. A total of 966 crania representing 30 local sites and about 7,000 years of human occupation were examined, revealing an abnormally high prevalence of this transposition trait among islanders during the Early period of southern California prehistory (～5500–600 B.C.). One of the affected crania is from a cemetery more than 7,000‐years‐old and constitutes the earliest case of tooth transposition in humans so far reported. The results are consistent with findings by other studies that have indicated inbreeding among the early Channel Islands groups. Together with the normal transposition rates among mainland populations, the decreasing prevalence of maxillary canine‐first premolar transposition among island populations across the Holocene suggests that inbreeding on the northern Channel Islands had all but ceased by the end of the first millennium B.C., most likely as a result of increased cross‐channel migration and interaction. Am J Phys Anthropol 143:155–160, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of Bioavailable Heavy Metal Species,Arsenic, and Acid Drainage from Mine Tailings on a Microbial Community Sampled Along a Pollution Gradient in a Freshwater Ecosystem

Sediment and water samples representing a pollution gradient in a long, narrow lake polluted at one end by heavy metals, arsenic, and acid drainage from mine tailings, together with samples from an unpolluted reference lake, were analyzed to determine effects of pollutants on the microbial community of the polluted lake. Ribosomal ribonucleic acid, fatty acid, and phospholipid analyses, along with assays of CO₂ production, denitrification, and enzyme activities, were performed to characterize the microflora; and environmental conditions were defined by various physicochemical analyses, including determination of bioavailable metal species. Mine waste pollution fostered the growth of Holophagal Acidobacteria, green sulphur bacteria, and α-Proteobacteria but inhibited numerous other types of microorganisms, reducing the overall productivity, biomass, and biodiversity of the microflora. The beneficial effects imply toleration of pollutants, suppression of competing or antagonistic species, and utilization of biogenic sulphide; and the toxic effects are attributable to bioavailable metals, arsenic, and sulphuric acid produced by oxidation of sulphides. The bioavailability and toxicity of sediment-bound metals were evidently increased by acidification, elevation of sediment Eh, and inhibition of metal-immobilizing bacteria by pollutants but were decreased by metal-scavenging oxyhydroxides, sulphide, and organic matter. Metal toxicity also depended on specific metal properties (e.g., electronegativity), providing a basis for inferring mechanisms of toxicity and oxidation states of metals and explaining differences in relative toxicity. The pollutants harmed the ecosystem as a whole by inhibiting microorganisms that performed crucial ecological functions, notably oxygen-releasing photosynthesis, decomposition and humification of organic matter, nutrient recycling, and control of metal availability.     

Release from Parasites as Natural Enemies: Increased Performance of a Globally Introduced Marine Crab

Introduced species often seem to perform better than conspecifics in their native range. This is apparent in the high densities they may achieve or the larger individual sizes they attain. A prominent hypothesis explaining the success of introduced terrestrial species is that they are typically free of or are less affected by the natural enemies (competitors, predators, and parasites) they encounter in their introduced range compared to their native range. To test this hypothesis in a marine system, we conducted a global assessment of the effect of parasitism and predation on the ecological performance of European green crab populations. In Europe, where the green crab is native, crab body size and biomass were negatively associated with the prevalence of parasitic castrators. When we compared native crab populations with those from introduced regions, limb loss (an estimator of predation) was not significantly lower in introduced regions, parasites infected introduced populations substantially less and crabs in introduced regions were larger and exhibited a greater biomass. Our results are consistent with the general prediction that introduced species suffer less from parasites compared to populations where they are native. This may partly explain why the green crab is such a successful invader and, subsequently, why it is a pest in so many places.     

Brief communication: Population data support the adaptive nature of HACNS1 sapiens/neandertal‐chimpanzee differences in a limb expression domain

The 546‐base pair enhancer of limb expression HACNS1, which is highly constrained in all terrestrial vertebrates, has accumulated 16 human‐specific changes after the human‐chimpanzee split. There has been discussion whether this process was driven by positive selection or biased gene conversion, without considering population data. We studied 83 South Amerindian, 11 Eskimo, 35 Europeans, 37 Bantu, and non‐Bantu Sub‐Saharan speakers, and 28 Brazilian mestizo samples and found no variation in this DNA region. Similar lack of variability in this region was found in four Africans, five Europeans or Euro‐derived, two Asians, one Paleo‐Eskimo, and one Neandertal sequence, whose whole genomes are publicly available. No difference was found. This result favors the interpretation of past positive and present conservative selection, as would expected in a region which influences Homo‐specific traits as important as opposable thumbs, manual dexterity, and bipedal walking. Am J Phys Anthropol, 2010. © 2010 Wiley‐Liss, Inc.