Extreme Acidic Conditions Research Articles

Río tinto: a geochemical and mineralogical terrestrial analogue of Mars.

The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic heavy metals), but also in maintaining the high level of microbial diversity detected in the basin. It has been proven that the extreme acidic conditions of Río Tinto basin are not the product of 5000 years of mining activity in the area, but the consequence of an active underground bioreactor that obtains its energy from the massive sulfidic minerals existing in the Iberian Pyrite Belt. Two drilling projects, MARTE (Mars Astrobiology Research and Technology Experiment) (2003–2006) and IPBSL (Iberian Pyrite Belt Subsurface Life Detection) (2011–2015), were developed and carried out to provide evidence of subsurface microbial activity and the potential resources that support these activities. The reduced substrates and the oxidants that drive the system appear to come from the rock matrix. These resources need only groundwater to launch diverse microbial metabolisms. The similarities between the vast sulfate and iron oxide deposits on Mars and the main sulfide bioleaching products found in the Tinto basin have given Río Tinto the status of a geochemical and mineralogical Mars terrestrial analogue.

Chemistry and photochemistry of 2,6-bis(2-hydroxybenzilidene)cyclohexanone. An example of a compound following the anthocyanins network of chemical reactions.

The kinetics and thermodynamics of the 2,6-bis(2-hydroxybenzilidene)cyclohexanone chemical reactions network was studied at different pH values using NMR, UV-vis, continuous irradiation, and flash photolysis. The chemical behavior of the system partially resembles anthocyanins and their analogue compounds. 2,6-Bis(2-hydroxybenzilidene)cyclohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 × 10(-5) s(-1)) is pH independent and controlled by the cis-trans isomerization barrier. However, the interesting feature is the appearance of the colorless compound, 7,8-dihydro-6H-chromeno[3,2-d]xanthene, isolated from solutions of acid to neutral range, characterized by (1)H NMR and single crystal X-ray diffraction. Light absorption by 2,6-bis(2-hydroxybenzilidene)cyclohexanone solutions immediately after preparation exclusively results in cis-isomer as photoproduct, which via hemiketal formation yields (i) red styrylflavylium by dehydration under extremely acidic solutions (pH < 1) and (ii) colorless 7,8-dihydro-6H-chromeno[3,2-d]xanthene by cyclization in solutions of acid to neutral range.

Microbial mediated formation of Fe-carbonate minerals under extreme acidic conditions

Discovery of Fe-carbonate precipitation in Rio Tinto, a shallow river with very acidic waters, situated in Huelva, South-western Spain, adds a new dimension to our understanding of carbonate formation. Sediment samples from this low-pH system indicate that carbonates are formed in physico-chemical conditions ranging from acid to neutral pH. Evidence for microbial mediation is observed in secondary electron images (Fig. 1), which reveal rod-shaped bacteria embedded in the surface of siderite nanocrystals. The formation of carbonates in Rio Tinto is related to the microbial reduction of ferric iron coupled to the oxidation of organic compounds. Herein, we demonstrate for the first time, that Acidiphilium sp. PM, an iron-reducing bacterium isolated from Rio Tinto, mediates the precipitation of siderite (FeCO3) under acidic conditions and at a low temperature (30°C). We describe nucleation of siderite on nanoglobules in intimate association with the bacteria cell surface. This study has major implications for understanding carbonate formation on the ancient Earth or extraterrestrial planets.

The influence of pH on organovermiculite structure stability

There is a large amount of research and application studies in the topic of organically modified vermiculites and their properties. In this work, the stability of two organovermiculites, one modified with hexadecyltrimethylammonium (HDTMA+) and the other modified with hexadecylpyridinium (HDP+) ions, was investigated at pH values from 1 to 14 at laboratory temperature. The organovermiculites in the pH range of 4–10 were stable. In addition, the HDTMA+-vermiculite was stable in strong alkaline media and under extreme acidic conditions as well. However, HDP+-vermiculite underwent significant decomposition when exposed to strong acidic or alkaline conditions (pH 1, 2 and 12, 14). The prepared and tested materials were investigated using X-ray diffraction (XRD) method, Fourier transform infrared (FTIR) spectrometry, total organic carbon content (TOC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The leaching of structural cations was determined as well.

PH-induced structural changes of ovalbumin studied by 2D correlation IR spectroscopy

The secondary structural changes of pH-induced ovalbumin during the transition from native state into intermediate state were studied with the use of 2D correlation spectroscopy and principal component analysis. 2D correlation spectra constructed from the pH-dependent IR spectra of ovalbumin solution revealed the following scenario of the intensity changes with pH decrease. When pH decreased from 5.5 and 3.6 intensity of components attributed to the β-turns, the α-helical elements, and native β-sheets increased. It was caused by protonation induced changes in environment of these elements. When the protonation of the acidic groups were finalized the system adopted the intermediate structure. It was accompanied by weak structural changes that mainly included the β-turns and the α-helices. In extreme acidic conditions at pH below pH 2 the intermediate structure was no longer stable and oligomers rich in the β-sheet structure were formed.

Characterization of Extreme Acidophile Bacteria (Acidithiobacillus ferrooxidans) Bioleaching Copper from Flexible PCB by ICP-AES

In order to improve copper leaching efficiency from the flexible printed circuit board (PCB) byAcidithiobacillus ferrooxidans, it is necessary to quantitatively measure the bacteria bioleaching copper under extreme acidic condition from flexible PCB. The inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is a very accurate way to analyze metals in solution; this paper investigated the optimal conditions for copper bioleaching byAcidithiobacillus ferrooxidansfrom flexible PCB through ICP-AES. The conditions included particle size of flexible PCB powder, quantity of flexible PCB powder, initial pH of culture medium, bacteria inoculation, bacteria activation time, and quantity of FeSO4·7H2O. Prior to ICP-AES measurement, culture solution was digested by aqua regia. The experimental results demonstrated that flexible PCB contained one main metal (copper); this was associated with the structure of flexible PCB. The optimization conditions were in 50 mL medium, flexible PCB 10 g/L, particle size of flexible PCB 0.42~0.84 mm, culture medium initial pH 2.5, bacteria inoculation 5%, bacteria activation time 5 d, and quantity of FeSO4·7H2O 30 g/L. Under the optimization condition, the leaching rate of copper was 90.10%, which was 42.4% higher than the blank group. For the ICP-AES determination, it reached a conclusion that the best corresponding wavelength (nm) of copper will be 224.7 (nm).

Cation exchange, solvent free synthesis and packing patterns of quinolinium nickel(II) dipicolinates

Nickel dipicolinate complexes (HQ)2[NiL2]·5H2O (1) and (H5AQ)2[NiL2]·4H2O (2) (where L=pyridine-2,6-dicarboxylate anion, Q=quinoline, 5AQ=5-aminoquinoline) are synthesized in solution and also through solvent free cation exchange reactions of H2[NiL2]·3H2O. The crystal structures of the complexes 1 and 2 are determined. The strong π–π interactions between the quinolinium cations disrupt the conventional π-stacking interactions of the nickel–dipicolinate anions. The quinolinium cations of these complexes exchanges with alkali metal cations in basic medium and only at an extreme acidic condition the pyridine-2,6-dicarboxylate can be replaced from these complexes by halide ions.

Biomaterials Availability: Potential for Bioethanol Production

Over the last decade, there has been increasing research interest in the value of biosourced materials from lignocellulosic biomass. Abundant sources of lignocellulosic biomass such as palm,napiergrass,luceanatree, urban waste, municipal solid waste, agricultural waste and other waste have the potential to become a sustainable source of biofuel. In Malaysia, dissolution of cellulose from palm biomass to produce ethanol as future biofuels is very promising since palm residues from palm industry are highly abundant. In addition, cellulose contents in palm wastes or residues are relatively high for instance from empty fruit bunch or palm trunk. An efficient pretreatment is highly required prior to processes which convert the lignocellulosic palm biomass to bioethanol. The kinds of processes needed nowadays are called as green technology based techniques which are environmental friendly. Various solvents have been applied to dissolve cellulose including various types of ionic liquid as well. Previously, other method such as acid hydrolysis pretreatment process cause many drawbacks due to their low rates of hydrolysis and extreme acidic conditions. The dissolution process of the lignocellulosic biomass with ionic liquids is at its better advantage due to better dissolution as compared to by using organic or inorganic solvents. Therefore, at the moment, ionic liquid is becoming more preferable in dissolving the lignocellulosic biomass or any palm residues for instance.

Membrane Reactors for in Situ Water Removal: A Review of Applications

This paper reviews the investigated applications of membrane reactors for in situ water removal during catalytic reactions in the food, pharmaceutical, cosmetics, and petrochemical sectors. The global target in the works reported herein was the design of a compact and more efficient catalytic reactor (process intensification). By applying in situ water removal, two objectives have been pursued: i) overcoming the thermodynamic limitations of the reaction and ii) avoiding catalyst poisoning. Different solution strategies proposed to overcome the difficulties in operating a membrane reactor in extreme acidic or temperature conditions are addressed covering various aspects ranging from membrane materials to reactor configuration design using pervaporation or vapor permeation techniques. As a general remark, membrane materials (polymeric and inorganic) still lack the required characteristics or reproducibility necessary for industrial application in the sectors under study. Further investigation is required to accomplish this task.

An Arginine-Agmatine Antiporter Optimized for Extreme Acid Resistance in Enteric Bacteria

Enteric bacteria such as E. coli and Salmonella species can maintain cytoplasmic pH in the extremely acidic gastric environments by consuming intracellular protons for arginine decarboxylation. This reaction is kept energetically favorable by an APC (amino-acid-polyamine-organocation) family antiporter AdiC, which imports arginine while pumping out the decarboxylated product agmatine in a 1:1 exchange stoichiometry. To characterize AdiC's transport behavior in extreme acid conditions, we developed an oriented reconstituted liposome system able to hold a 3-unit transmembrane pH gradient. Our work reveals two unique functional properties by which AdiC maximizes its effectiveness in conferring acid resistance. First, AdiC possesses a pH-sensing mechanism that permits maximal transport activity only under intra- and extracellular pH conditions of bacteria experiencing strong acid stress (i.e., outside pH 2-3; inside pH 4.5-5.5). Second, we demonstrate that AdiC mainly catalyzes electropositive exchange between extracellular arginine (50% Arg+, 50% Arg2+, pH2.2) and cytoplasmic agmatine (Agm2+, pH5.5) - the exchange is strongly inhibited by the imposition of negative membrane potentials. Thus, at gastric pH, AdiC selectively imports the less common Arg+ against the useless α-carboxyl protonated Arg2+, whose deprotonation upon entry into the cytosol would cancel out the proton-removing effect of arginine decarboxylation. We are currently investigating the underlying mechanisms for this second feature of AdiC. Preliminary results from testing various arginine analogues suggest that AdiC differentiates Arg+ and Arg2+ based on their difference in valence number rather than the protonation status in the α-carboxyl.

Oxidation of hydrogen sulfide in biogas using dissolved oxygen in the extreme acidic biofiltration operation

This work aimed to investigate the interactive effects of empty bed retention time (EBRT), specific hydraulic loading rate (q) and initial pH (pHi) of the aerated recirculating liquid to remove H2S in extreme acidic biofiltration. Biogas containing H2S 6395±2309ppm and CH4 79.8±2.5% was fed to the biofilter as pH of the high dissolved oxygen recirculating liquid swung between pHi to 0.5. Response surface methodology was employed that gave the H2S removal relationship model with R2 0.882. The predicted highest H2S removal within the studied parameter ranges was 94.7% at EBRT 180.0s, q 4.0m3/m2/h and pHi 3.99. Results from separate runs at a random condition were not statistically different from the model prediction, signifying a validity of the model. Additionally, CH4 content in the exit biogas increased by 4.7±0.4%. Acidithiobacullus sp. predominance in the consortia of this extreme acidic condition was confirmed by DGGE.

Patents Review on Lignocellulosic Biomass Processing Using Ionic Liquids

With the depletion of resources, biomass becomes a promising source of chemicals and fuels, currently obtained from petroleum. Cellulose is the most abundant material produced in earth, but it is difficult to dissolve which makes its transformation limited. Dissolution of cellulose requires severe temperature, non-conventional solvents and/or extreme acid or basic conditions. Thus, its processing is very pollutant. Ionic liquids are presented as clean solvents for cellulose. These are substances composed entirely of ions that are liquid at room temperature. Among other interesting properties, ionic liquids are non volatile and they are good solvents for a number of substances. Processes for cellulose processing in ionic liquids have been patented for several applications, the most important being: pre-treatment for biomass prior to fermentation for bio-ethanol production, hydrolysis for obtaining chemicals from biomass and substitution reaction for obtaining derivatives of cellulose and other natural polymers.

Mineral respiration under extreme acidic conditions: from a supramolecular organization to a molecular adaptation in Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotrophic Gram-negative bacterium that can derive energy from the oxidation of ferrous iron at pH 2 using oxygen as electron acceptor. The study of this bacterium has economic and fundamental biological interest because of its use in the industrial extraction of copper and uranium from ores. For this reason, its respiratory chain has been analysed in detail in recent years. Studies have shown the presence of a functional supercomplex that spans the outer and the inner membranes and allows a direct electron transfer from the extracellular Fe2+ ions to the inner membrane cytochrome c oxidase. Iron induces the expression of two operons encoding proteins implicated in this complex as well as in the regeneration of the reducing power. Most of these are metalloproteins that have been characterized biochemically, structurally and biophysically. For some of them, the molecular basis of their adaptation to the periplasmic acidic environment has been described. Modifications in the metal surroundings have been highlighted for cytochrome c and rusticyanin, whereas, for the cytochrome c oxidase, an additional partner that maintains its stability and activity has been demonstrated recently.

Effect of pH and Reaction Time on the Structures of Early Lanthanide(III) Borate Perchlorates

Reactions of LnCl(3)·6H(2)O (Ln = La-Nd, Sm, Eu), concentrated (11 M) perchloric acid, and molten boric acid result in the formation of four different compounds. These compounds are Ln[B(8)O(10)(OH)(6)(H(2)O)(ClO(4))]·0.5H(2)O (Ln = La-Nd, Sm), Pr[B(8)O(11)(OH)(4)(H(2)O)(ClO(4))], Ln[B(7)O(11)(OH)(H(2)O)(2)(ClO(4))] (Ln = Pr, Nd, Sm, and Eu), and Ce[B(8)O(11)(OH)(4)(H(2)O)(ClO(4))]. All Ln(III) cations are ten-coordinate with a capped triangular cupola geometry and contain an inner-sphere, monodentate perchlorate moiety. This geometry is obtained because of the coordination of the oxygen donors within the polyborate sheet which create triangular holes and provide residence for the lanthanide metal centers. Aside from Ln[B(8)O(10)(OH)(6)(H(2)O)(ClO(4))]·0.5H(2)O (Ln = La-Nd, Sm), which are two-dimensional sheet structures, all other compounds are three-dimensional frameworks in which the layers are tethered together by BO(3) units found roughly perpendicular to the sheets. Furthermore, a change in product is observed depending on the reaction duration while holding all other synthetic variables constant. This report also demonstrates that lanthanide borates can be prepared in extreme acidic conditions.

Enhancement of acid resistance of Scenedesmus dimorphus by acid adaptation

When using flue gas as carbon source for microalgae cultivation, the resulting acidic environment caused by SO (X) and NO (X) can inhibit microalgal growth. In this study, Scenedesmus dimorphus acquired increased acid resistance by prior exposure to sublethal acid stress; a process defined as acid adaptation. Among the five algal species tested, S. dimorphus showed the highest level of acid tolerance to extreme acid challenge (exposure to pH 3.0). Non-adapted and acid-adapted exponential algal cells were used as inocula for tubular photobioreactors aerated with 2 % CO2. Previously adapted at pH 4.0 for 1 h, S. dimorphus developed highest growth rate under extreme acidic condition, and the maximum biomass concentration and specific growth rate at pH 3.0 (3.638 +/- 0.074 g L-1 and 1.037 +/- 0.008 d(-1), respectively) were respectively 14.22 and 10.79 % higher than those of non-adapted cells. Moreover, acid-adapted cells could tolerate lower pH of 2.5, at which the growth of non-adapted cells was totally inhibited. All the results indicated that acid adaptation was an effective approach for the acid resistance enhancement of microalgae.

The inner membrane protein, YhiM, is necessary for Escherichia coli (E. coli) survival in acidic conditions

Escherichia coli must be able to survive extreme acidic conditions. We were interested in determining the role of the inner membrane protein YhiM in survival in acidic conditions. Previous data demonstrated that the yhiM gene was upregulated in acidic conditions (Tucker et al. in J Bacteriol. 184:6551-6558, 2002). We therefore tested tn10 insertions into the yhiM gene for their ability to survive at low pH (pH 2.5). We show that YhiM was required for survival at pH 2.5. We also tested the YhiM dependence of the different acid resistance pathways. YhiM was required for the RpoS, glutamine and lysine-dependent acid resistance pathways. In contrast, YhiM was not required for the arginine-dependent acid resistance pathway.

Salmonella spp. survival strategies within the host gastrointestinal tract

Human salmonellosis infections are usually acquired via the food chain as a result of the ability of Salmonella serovars to colonize and persist within the gastrointestinal tract of their hosts. In addition, after food ingestion and in order to cause foodborne disease in humans, Salmonella must be able to resist several deleterious stress conditions which are part of the host defence against infections. This review gives an overview of the main defensive mechanisms involved in the Salmonella response to the extreme acid conditions of the stomach, and the elevated concentrations of bile salts, osmolytes and commensal bacterial metabolites, and the low oxygen tension conditions of the mammalian and avian gastrointestinal tracts.

Robust and responsive silk ionomer microcapsules.

We demonstrate the assembly of extremely robust and pH-responsive thin shell LbL microcapsules from silk fibroin counterparts modified with poly(lysine) and poly(glutamic) acid, which are based on biocompatible silk ionomer materials in contrast with usually exploited synthetic polyelectrolytes. The microcapsules are extremely stable in an unusually wide pH range from 1.5 to 12.0 and show a remarkable degree of reversible swelling/deswelling response in dimensions, as exposed to extreme acidic and basic conditions. These changes are accompanied by reversible variations in shell permeability that can be utilized for pH-controlled loading and unloading of large macromolecules. Finally, we confirmed that these shells can be utilized to encapsulate yeast cells with a viability rate much higher than that for traditional synthetic polyelectrolytes.

Contribution of the Lipopolysaccharide to Resistance of Shigella flexneri 2a to Extreme Acidity

Shigella flexneri is endemic in most underdeveloped countries, causing diarrheal disease and dysentery among young children. In order to reach its target site, the colon, Shigella must overcome the acid environment of the stomach. Shigella is able to persist in this stressful environment and, because of this ability it can initiate infection following the ingestion of very small inocula. Thus, acid resistance is considered an important virulence trait of this bacterium. It has been reported that moderate acid conditions regulate the expression of numerous components of the bacterial envelope. Because the lipopolysaccharide (LPS) is the major component of the bacterial surface, here we have addressed the role of LPS in acid resistance of S. flexneri 2a. Defined deletion mutants in genes encoding proteins involved in the synthesis, assembly and length regulation of the LPS O antigen were constructed and assayed for resistance to pH 2.5 after adaptation to pH 5.5. The results showed that a mutant lacking O antigen was significantly more sensitive to extreme acid conditions than the wild type. Not only the presence of polymerized O antigen, but also a particular polymer length (S-OAg) was required for acid resistance. Glucosylation of the O antigen also contributed to this property. In addition, a moderate acidic pH induced changes in the composition of the lipid A domain of LPS. The main modification was the addition of phosphoethanolamine to the 1′ phosphate of lipid A. This modification increased resistance of S. flexneri to extreme acid conditions, provide that O antigen was produced. Overall, the results of this work point out to an important role of LPS in resistance of Shigella flexneri to acid stress.

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1–1.3

The extreme acid conditions required for scorodite (FeAsO4·2H2O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO2 in air were added as sole energy and carbon source. The highest growth rate (0.066 h−1) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO2 concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h−1, with ferrous iron oxidation rates of 1.5 g L−1 d−1. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L−1 caused instability of Fe2+ oxidation, probably due to product (Fe3+) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-011-3460-7) contains supplementary material, which is available to authorized users.