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Microbial arsenite oxidation was observed byAcinetobactersp. XS21, this strain oxidised arsenite As(III) up to 80 mM within 48–72 h of incubation. The present strain XS21 oxidised As(III) at a very high concentration in a shorter interval of time than any of the previous reported microbes. Further, XS21 was applied to the soil to observe its ability in reducing the mobility of As(III), and we found thatAcinetobactersp. XS21 efficiently removed arsenite from soluble-exchangeable fraction and removed 70% of the arsenite as compared to control. This feature makes it a potential candidate for bioremediation. Arsenic-resistant bacteria with strong As(III)-oxidising ability may have potential to improve bioremediation of As(III)-contaminated sites. To understand their basis of resistance and transformation we found the As(III) oxidase gene using degenerate primer and amplified ∼550 bp ofaioAgene. AmplifiedaioAgene sequence exhibiting 52% identity in terms of gene and deduced protein sequence toUncultured bacterium, andAchromobactersp. arsenite oxidase of larger subunit. Arsenite oxidase, an enzyme, was also observed in this isolate, which may provide a resistance and transforming ability. This bacterium was identified asAcinetobactersp., by sequencing 16s rRNA gene sequence analysis. [ABSTRACT FROM AUTHOR]

Metal and mineral transformations are a cornerstone of geomicrobiological processes. Of central importance are the mechanisms by which microorganisms alter the speciation and mobility of metals, including their properties of mineral dissolution or mineral formation. Such processes underpin natural biogeochemical cycles for metals, and related elements such as metalloids, and metal radionuclides, as well as those elements that may be commonly associated with metal compounds and minerals, e.g., P and S. They may also determine the fate of contaminant toxic metals and radionuclides when introduced or redistributed in the environment as a result of natural or anthropogenic activities. Such contamination is an increasing problem, and microbe-based systems are increasingly viewed as potentially useful approaches for bioremediation, as well as for element biorecovery. Biomineralization is a general term for the processes by which living organisms form minerals, and this can result in metal removal from solution providing a means of detoxification as well as biorecovery. Dead biota and derived products may also provide a template for mineral deposition, the reversibility, or otherwise, of the reaction depending on physico-chemical conditions. The most common biominerals precipitated by microbes include oxides, phosphates, sulfides and oxalates, and these can have special chemical properties such as high metal sorption capacities and redox catalysis. Furthermore, some biominerals may be deposited in nanoscale dimensions, providing further significant physical, chemical and biological properties of applied significance. The purpose of this Special Issue of theGeomicrobiology JournalonBiomineralization, Bioremediation and Biorecoveryis to bring together and highlight some specific examples of metal and radionuclide biomineralization by microorganisms from the different major microbial groups such as cyanobacteria, bacteria, microalgae and fungi. A range of elements and organisms are covered together with a variety of environmental and industrial contexts where a biomineralization approach may assist bioremediation, metal biorecovery or substrate stability. [ABSTRACT FROM AUTHOR]

Heavy metal contamination of mine tailings is one of the most serious environmental challenges facing the mining industry worldwide. Conventional technologies used for the treatment of such tailing soils are expensive both in terms of operation and capital costs as well as being not so effective. In the present study, an indigenous calcifying urease producing bacterial strain was isolated from copper mine tailing soil and used for bioimmobilization of copper, lead and cadmium in contaminated mine tailing soils. Phylogenetic analysis of the 16S rRNA gene sequence identified it asBacillus firmus. The efficiency of metal bioimmobilization was based on microbially induced calcite precipitation (MICP). A five-stage sequential soil extraction procedure was carried out to obtain distribution patterns for the different metals. The mobility of the toxic metals was found to be significantly reduced in the exchangeable fraction with their concentrations markedly increasing in the carbonated fraction after bioremediation. Scanning electron microscopy showed the precipitation of calcite in association with the bacterial cells. Calcium carbonate minerals such as calcite, gwihabaite and aragonite were identified in the bioremediated tailings soils using X-ray diffraction (XRD). It is concluded that MICP holds considerable promise for the remediation of mine tailing soils by efficient immobilization of toxic metals such as copper, lead and cadmium. [ABSTRACT FROM AUTHOR]

Sand storms have become a growing global environmental issue and there is an urgent need to explore cost-effective green technologies to stabilize the sands of desert regions. In this study, the performance of a ureolyticBacillussp. for stabilization of sands was evaluated. TheBacillussp. could efficiently consolidate sand particles by hydrolysis of urea and the subsequent production of calcite and aragonite minerals. The biostabilized sands had a high resistance to erosion by a 33 m s−1wind speed even after 12-d exposure to freeze-thaw cycles. The compressive strength of biostabilized sands was dependent on the applied cell density and concentrations of Ca2+and urea. High cell densities, urea and Ca2+concentrations reduced the compressive strength. The optimal cell density, Ca2+and urea concentrations were OD6000.4, 15 mM and 20 g L−1, respectively, when performance and cost were considered. This study shows that biostabilization of sand based on microbially induced carbonate precipitation (MICP) has potential for the prevention of sand storms and wind erosion of soil. [ABSTRACT FROM AUTHOR]

Salinity and pH are two water chemical factors that vary drastically—seasonally or daily—in a variety of aquatic environments. Drastic change of salinity and pH may have a significant impact on adsorption of microbial extracellular polymers (EPS) to sediment minerals and thus influence many other important elemental geochemical processes. However, how salinity and pH changes affect EPS adsorption to minerals is poorly known. In the present study, adsorption of EPS from a hypersaline microbial mat to goethite at different pH values (4, 7 and 10) and salinity (0.15‰, 35‰ and 70‰) was monitored online using a quartz crystal microbalance (QCM) with EEM fluorescence spectroscopy as a complementary method. The adsorption kinetics were well described by an exponential function. The adsorption capacity of EPS to goethite significantly increased as the pH and salinity increased. The pH and salinity dependence of EPS adsorption to goethite is of great importance for understanding the environmental geochemistry of heavy metals in aquatic environments. In inland lakes and estuary zones, the seasonal or daily pulse of hydrological events will drastically alter water salinity and pH and consequently exert significant influences on the mobility, chemical species and ecotoxicity of heavy metals through the EPS pathway. It is necessary to systematically investigate the geochemical behavior of EPS in such dynamic aquatic environments and their potential effects on other geochemical processes. [ABSTRACT FROM AUTHOR]

Acidithiobacillus ferrooxidansis a commonly used bacterial species for leaching gold ores to recover gold. The pH ofA. ferrooxidansbioleachates drastically changes from around 2.0 during bioleaching to about pH 8.0 as the cells are discharged together with the mine tailings containing high levels of Hg. It is not known how such a large pH shock would affect the properties of bacterial extracellular polymeric substances (EPS) and the transport of Hg in the mine tailings. In this study, the biochemical composition, molecular distribution, fluorescence properties and Hg(II) complexation by EPS ofA. ferrooxidanscultured at pH 2 and 8 were investigated. It was found that pH shock significantly altered the composition of EPS.A. ferrooxidansyielded more EPS under acid conditions than basic conditions. The acidic EPS contained more macromolecular proteins but less polysaccharide in comparison with the basic EPS. Phosphodiester functional groups in phospholipids and polysaccharides were found in the acidic EPS but not in the basic EPS. One tryptophan protein-like peak and one aromatic protein-like peak were identified in fluorescence spectra of the acidic EPS. Two aromatic protein-like peaks were identified from the fluorescence spectra of the basic EPS. The tryptophan protein-like substances in the acidic EPS interacted with Hg(II) and formed relatively stable complexes but with weak binding ability whereas the fluorescent aromatic protein-like substances in the acidic EPS did not bind Hg(II). However the aromatic protein-like substances in the basic EPS had a strong binding ability for Hg(II). The significant differences in composition and Hg complexation ability between EPS from acidic and basic environments indicate that a large pH shock during leaching of gold may exert a considerable impact on the behavior and fate of Hg in the mining areas. [ABSTRACT FROM AUTHOR]

Groundwater in many parts of the world is contaminated with arsenic and nitrate. To date no technology is available that canin situremediate arsenic and nitrate pollution of groundwater using one single bacterial species. In this study, a novel anaerobic nitrate-dependent Fe(II)-oxidizing bacterium,Clostridiumsp. strain PXL2, was isolated from anoxic activated sludge. The strain PXL2 could efficiently oxidize Fe(II) associated with the reduction of nitrate. Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FTIR) analysis showed that strain PXL2 formed nanosize and poorly crystalline Fe(III) oxides which encrusted the cells, with the viability and function of the cells might being inhibited by the encrustation of Fe(III) oxides. It was found that strain PXL2 was an excellent candidate microbe for bioremediation of nitrate and arsenic pollution. It could effectively and simultaneously remove As(III) and nitrate from water due to its Fe(II) oxidation and denitrtification activity. 40.6–100% of NO3−was removed from an initial concentration of 12.3 mM. High concentrations of As(III) decreased nitrate removal. With initial concentrations of 10 μM, 65 μM and 125 μM As(III), 100% of As(III) was removed in a 20 d treatment. Arsenic was removed by adsorption to the biogenic Fe(III) oxides but not by adsorption to the cells. Strain PXL2 was also able to oxidize As(III) to less mobile and less toxic As(V) and this may significantly enhance the performance of bioremediation of arsenic pollution. Anaerobic nitrate-dependent Fe(II)-oxidizing species, such as strain PXL2, has great application potential forin situremediation of nitrate and metal(loid)s polluted groundwater with advantages of high efficiency and low cost. [ABSTRACT FROM AUTHOR]

Bioreduction of Cr(VI) to less toxic Cr(III) by chromate-reducing bacteria has offered an ecological and economical option for chromate detoxification. The present study reports isolation of chromate-resistant bacterial strain Cr8 from chromium slag, identified asPseudomonas stutzeri, based on 16S rRNA gene sequencing and their potential use in Cr(VI) reduction. The reduced product associated with bacterial cell was characterized by scanning electron microscopy–energy-dispersive x-ray spectroscopy (SEM-EDS) and x-ray diffraction (XRD) analyses. At initial concentrations of 100 and 200 mg L−1Cr(VI),P. stutzeriCr8 reduced Cr(VI) completely within 24 h, whereas it reduced almost 1000 mg L−1Cr(VI) at the end of 120 h. Further, soil column leaching experiments were performed and found that bacterial cells reduced Cr(VI) leachate at faster rate that almost disappeared at the end of 168 h. The leachate precipitates also revealed efficient chromate bioreduction. The remediation process utilizingP. stutzericould be considered as a viable alternative to reduce Cr(VI) contamination, especially emanating from the overburden dumps of chromite ores and mine drainage. [ABSTRACT FROM PUBLISHER]

Anaerobic Fe(II) Oxidizing Denitrifiers (AFODN), a type of newly found Fe(II)-oxidizing bacteria, play an important role in iron and nitrogen cycling. In the present study, a novel AFODN strain PXL1 was isolated from anaerobic activated sludge. Phylogenetic analysis of 16S rRNA gene sequence revealed similarity between this strain andCitrobactor freundii. The strain reduced 30% of nitrate and oxidized 85% of Fe(II) over 72 h with an initial Fe(II) concentration of 3.4 mM and nitrate concentration of 9.5 mM. Oxidation of iron was dependent on the reduction of nitrate to nitrite in the absence of other electron donors or acceptors. Nitrate reduction and Fe(II) oxidation followed first-order reaction kinetics. Iron oxides accumulated in the culture were analyzed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The strain recovered deposited oxidized Fe in the form of amorphous Fe oxides. [ABSTRACT FROM AUTHOR]

Cd(II) adsorption of root exudates from sunflower (Helianthus annuusL.) seedling was investigated by Cd ion-selective electrode, Fourier Transform Infrared spectroscopy, and fluorescence spectroscopy. Root exudates fromHelianthus annuusL. had strong adsorption ability toward Cd(II). The adsorption process was pH-dependent and the maximum adsorption capacity, 150.8 mg g−1, was observed at pH 7.0. Root exudates hadpKa1at 4.7 for carboxyl andpKa2at 9.2 for phenolic, and amino groups. The aliphatic and aromatic (C−H) groups, amide III group, and the C (=O)−O and sulfonate groups were responsible for Cd(II) adsorption. The excitation emission matrix fluorescence spectroscopy showed protein-like substances participated in Cd adsorption and formed strong complexes, with conditional stability constants of 4.70 and 4.32, which is a little lower than that determined by potentiometric methods, 5.13. The strong Cd complexing ability of root exudates implies that root exudates may significantly affect mobility, toxicity, and phytoavailability of Cd. Cd binding of root exudates may be attributed to its interaction with the proteins, polysaccharides, and phenolic compounds in root exudates. [ABSTRACT FROM PUBLISHER]

Hydrolytic enzymes released by the microorganisms in activated sludge are responsible for the organic matter degradation there; however, the optimal extraction procedure of this valuable resource has not been well established until now. In this study protease and lipase were extracted from activated sludge using ultrasound disintegration combined with a nonionic detergent (Triton X-100) and cation-exchange resin (CER) in combination for the extraction of protease and lipase. It was observed that the concentration of 0.1% and 1% Triton X-100 has a strong influence for the extraction of lipase and protease respectively. Closer study of the enzyme extraction process is essential for different enzymes from activated sludge process. [ABSTRACT FROM PUBLISHER]

Root exudates are considered to have an important role in mobility and bioavailability of heavy metals. High molecular weight (HMW) substances are the main components of root exudates, however, knowledge about their interactions with heavy metals is lacking. In the present study, Pb(II) complexation of the HMW fluorescent fractions in root exudates from Salicornia europaea L. was investigated using excitation emission matrix (EEM) fluorescence spectroscopy. Two protein-like fluorescence peaks were identified in the EEM spectrum of root exudates. The fluorescence of both peaks was clearly quenched by Pb(II). The values of conditional stability constants, log Ka, for these two protein-like fluorescence peaks were 4.14 and 3.79. This indicates that the fluorescent substances are strong Pb(II) complexing organic ligands. [ABSTRACT FROM AUTHOR]