Salt-free Medium Research Articles

Transient electrophoresis of colloidal particles in a salt-free medium

A general theory is developed for the time dependent transient electrophoretic mobility of spherical colloidal particles in a salt-free liquid medium containing only counterions when a step external electric field is suddenly applied to the colloidal suspension. It is found that as in the case of the steady electrophoretic mobility in a salt-free medium, there is a certain critical value of the particle surface charge separating two cases, that is, the low-surface-charge case and the high-surface-charge case. In the latter case the counterion condensation takes place near the particle surface. For the low-surface charge case, the transient electrophoretic mobility agrees with that of a sphere in an electrolyte solution in the limit of very low electrolyte concentrations. For the high-surface-charge case, however, the transient mobility becomes independent of the particle surface charge because of the counterion condensation effects. A simple expression is derived for the ratio of the transient electrophoretic mobility to the steady electrophoretic mobility, which is found to take the same form irrespective of the magnitude of the particle surface charge. Using this equation, it is now possible to predict how the system will approach its final steady state.

Effect of Na, Mg, Ca chloride salts on mineral element, proline and total protein contents in rice (Oryza sativa L.) grown in vitro

In this study, the effects of different types and concentrations of salts on local Siverek rice plant (Oryza sativa L.) grown in vitro were investigated in terms of mineral elements (K, Ca, P, Mg, Na, Fe, Cu, Zn, Mn, Mo, Co), proline, and total protein content. Sterilized seeds were planted in hormone-free and salt-free MS medium. After one week, the seedlings were subjected to different concentrations of NaCl, CaCl2, and MgCl2 salts (0, 30 mM, 90 mM) in order to evaluate the effect of salinity on plant growth and development. In response to salt stress, a decrease in nutrient elements was observed for all three types of salt compared to the control group, which can be attributed to disruptions in ion balance. Changes in element levels generally showed varying levels of increase or decrease depending on both the type and concentration of the salt and these changes were statistically significant. The increase in proline level was found to be directly proportional to the changes in the amounts of Ca, Mg, K, and Na elements. Both total protein and proline content showed the lowest values for all salt concentrations with CaCl2, while the highest values were obtained with NaCl. In conclusion, the changes in the level of mineral elements, total protein, and proline content levels, which decrease or increase in different ratios, depending on the type and concentration rising of the salt, are associated with the varying tolerance of the plant to different types of salts.

Assessment of ultrasonic influence on titanium tanning leather stability

Ultrasound effects on titanium tanning of leather were studied. 30 kHz and 60 kHz ultrasound were applied to cattle skins during titanium tanning. The study included five different treatment conditions, examining effects such as leather shrinkage temperature (Ts), titanium content, and distribution. Heat loading was controlled. Results indicated that 30 kHz ultrasound improved titanium agent penetration and increased shrinkage temperature, while 60 kHz produced minimal improvements. A maximum shrinkage temperature of 107.9 oC was achieved using 30 kHz ultrasound pretreatment of tanning liquor, followed by 30 kHz ultrasound in the tanning mixture in a salt-free medium. Ultrasound was found to enhance titanium tanning and create superior mineral-tanned leather.

Rational design of O/W nanoemulsions based on the surfactant dodecyldiglyceryl ether using the normalized HLD concept and the formulation-composition map

The 1-O-dodecyl diglycerol ether (C12Gly2) is a well-balanced bio-based surfactant whose amphiphilicity and emulsifying property have been studied within the Normalized Hydrophilic-Lipophilic-Deviation (HLDN) framework. Its Hydrophilic-Lipophilic tendency has been measured in saline and salt-free media by two methods. The classic one, is based on the identification of the optimal formulation (Winsor III) in a series of tubes containing a series of C12Gly2/Alkane/Water systems at equilibrium. The alternative method, much faster and more precise, is based on the phase inversion of the same systems under stirring, the HLDN value of which is gradually modified by changing the temperature or the salinity. C12Gly2 is found to be three times less sensitive to temperature and salinity variations than typical ethoxylated surfactants. By stirring C12Gly2/Alkane/Water systems, O/W or W/O emulsions are obtained depending on whether the alkane is long or short. The finest and the least stable emulsions (1 µm) are obtained with n-octane for which HLDN = 0. By systematically varying the Water-to-Oil Ratio (WOR) and the hydrophobicity of the oil, either direct O/W or reverse W/O emulsions are formed and are represented in a Formulation-Composition map. This map is a powerful tool to guide the formulator about which type of emulsion will be obtained depending on the composition of the SOW system and the emulsification protocol used i.e. the pathway in the map. In particular, it is possible to prepare stable and very fine emulsions (≈ 100 nm) by crossing the inversion border of the map favouring the splitting of the droplets and then moving away from it quickly to prevent the coalescence of the droplets.

Adaptation of the Acidophilic Fungus <i>Sistotrema brinkmannii</i> to the pH Factor

Abstract—Investigation of the growth rate of Sistotrema brinkmannii at different values of pH values, temperature, and NaCl concentration showed that this fungus was a mesophile, preferred a salt-free medium, and was an obligate acidophile, since it had a pronounced growth optimum at pH 3.0–4.0 and did not grow at pH 7.0. To reveal the protective mechanisms allowing this fungus to develop under acidic conditions, the composition of its osmolytes and lipids was studied. This is the first report on occurrence of a large amount of trehalose (4.0‒6.6% of dry weight) in the mycelium of the fungus during its growth under optimal conditions, confirming the use of osmolytes by acidophiles for adaptation. At the same time, at the borders of the growth range (pH 2.6 and 6.0), the amount of trehalose in the mycelium of the fungus decreased by 2.5 times, which was in agreement with a narrow growth optimum of the fungus in its natural environments (pH 3.0–4.0). The composition of membrane lipids of the fungus was characterized by a high proportion of sphingolipids (up to 60% of the total), which decreased twofold in the course of growth under optimal conditions. The main membrane lipids, apart from sphingolipids, were phosphatidic acids, phosphatidylethanolamines, and sterols; the proportion of these lipids increased with time. The composition of membrane lipids of the fungus at pH 2.6 did not differ much from the optimal conditions, while in the near-neutral region there was a twofold increase in the proportion of sphingolipids, indicating their adaptive value. The simultaneous decrease in the proportion of sphingolipids and the increase in the level of trehalose in the growth dynamics suggest association of these compounds in the protection of cell membranes.

Role of Hfq in glucose utilization, biofilm formation and quorum sensing system in Bacillus subtilis.

Hfq is an RNA-binding protein, its main function is to participate in post-transcriptional regulation of bacteria and regulate small regulatory RNA (sRNA) and messenger RNA (mRNA) stability, but the Hfq function of Bacillus subtilis (B. subtilis) has not been fully explained. In this study, we used the strains of B. subtilis168 (BS168), BS168Δhfq and BS168Δhfq-C to explore the effects of Hfq on the glucose utilization, biofilm formation and quorum sensing (QS) system of B. subtilis. The results showed that the knockout of hfq resulted in growth defects when bacteria were cultured in the Luria-Bertani (LB) medium, but we did not observe the same effects in Nitrogen medium (NM) and Inorganic Salt-free medium (ISM). We further found that the growth of strains under different glucose concentrations was also different, which was related to the expression of CcpA. Interestingly, the hfq mutant showed increased resistance to a high-glucose environment. Furthermore, the biofilm and extracellular poly saccharides (EPS) formation of BS168Δhfq decreased significantly. At the same time, changes were observed in the morphology of the biofilm, such as larger intercellular space of the biofilm and thinner edge. The qRT-PCR results confirmed that the hfq knockout caused significant up-regulation or down-regulation of gene expression in QS system, and down-regulated genes were involved in the positive regulation of biofilm formation. Taken together, we demonstrated that Hfq plays a vital role in glucose utilization, biofilm formation and QS of B. subtilis, which provides a new perspective for subsequent related research.

The Effect of Salinity on Fruit Quality and Yield of Cherry Tomatoes

Hydroponic cultivation of vegetables avoids problems with soil-borne plant pathogens and may allow higher yield. In arid climates and particularly on islands, high concentrations of sodium chloride can be present in the groundwater. For instance, in many sites of Malta, the groundwater contains more than 10 mM sodium chloride. Here we investigated the effects of sodium chloride at levels typically found in Malta on yield, physiology and fruit quality of tomato, the economically most important vegetable. We selected cherry tomatoes since their production is attractive due to their high marketing value. While the yield declined at higher salinity levels tested (17 and 34 mM), the quality increased significantly as indicated by higher total soluble solids and fructose and glucose levels. The type of substrate—coco peat, perlite or Rockwool—had only minor effects. Although the concentration of citric acid and malic acid remained unaffected, the pH dropped by approximately 0.1 unit and the titratable acidity increased slightly. This might be explained by a high uptake of chloride but a lower increase of the sodium content and a reduced potassium level in the fruits, shifting the equilibrium of the organic acids more to their protonated forms. Proline increased significantly, while the level of glutamic acid, which is crucial for the taste, remained unchanged. Our results show that cherry tomatoes can be cultivated in nutrient solutions prepared with salt-containing groundwater, as found in Malta. The yield declined to some extent but the quality of the produced fruits was higher compared to cultivation in salt-free media.

Supramolecular assemblies of mucin and lysozyme: Formation and physicochemical characterization

Mucin and lysozyme are the most important components of mucous membranes. The complexes of pig gastric mucin (PGM) and the bacteriolytic enzyme lysozyme (LZ) have been studied using a wide range of physicochemical methods (turbidimetry, light scattering, fluorescence, electron microscopy, chromatography, and electrophoresis). The strongest binding of LZ to PGM was observed at pH 6–7 in a salt–free medium. Complexes between biomolecules were formed due to electrostatic interactions between the positively charged amino groups of LZ and the negatively charged carboxyl groups of the carbohydrate shell of PGM, van der Waals forces, and hydrogen bonds. Supramolecular LZ:PGM assemblies were polydisperse heterogeneous microaggregates with both LZ and PGM molecules located on their surface. The LZ activity in the presence of PGM changed through both the formation of complexes and the fact that PGM caused an increase in the viscosity of the medium and created diffusion restrictions for the enzyme’s access to the cellular substrate. Based on the data obtained, strategies can be developed to regulate antimicrobial properties of lytic enzymes (and their complexes with mucins) for mucosal use.

Obtaining Salt Stress-Tolerant Eggplant Somaclonal Variants from In Vitro Selection.

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208–305–370 µmol min−1 mg−1 FW) and catalase (CAT) (136–211–238 µmol min−1 mg−1 FW) activities compared to control plants (231 and 126 µmol min−1 mg−1 FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants.

Electrophoretic Mobility and Electric Conductivity of Salt-Free Suspensions of Charged Soft Particles

A unit cell model is employed to analyze the electrophoresis and electric conduction in a concentrated suspension of spherical charged soft particles (each is a hard core coated with a porous polyelectrolyte layer) in a salt-free medium. The linearized Poisson–Boltzmann equation applicable to a unit cell is solved for the equilibrium electrostatic potential distribution in the liquid solution containing the counterions only surrounding a soft particle. The counterionic continuity equation and modified Stokes/Brinkman equations are solved for the ionic electrochemical potential energy and fluid velocity distributions, respectively. Closed-form formulas for the electrophoretic mobility of the soft particles and effective electric conductivity of the suspension are derived, and the effect of particle interactions on these transport characteristics is interesting and significant. Same as the case in a suspension containing added electrolytes under the Debye–Hückel approximation, the scaled electrophoretic mobility in a salt-free suspension is an increasing function of the fixed charge density of the soft particles and decreases with increases in the core-to-particle radius ratio, ratio of the particle radius to the permeation length in the porous layer, and particle volume fraction, keeping the other parameters unchanged. The normalized effective electric conductivity of the salt-free suspension also increases with an increase in the fixed charge density and with a decrease in the core-to-particle radius ratio, but is not a monotonic function of the particle volume fraction.

Streptomyces sp. K47 alkaline proteases: partial purification and analysis by zymography

Microbial enzymes are used as organic catalysts in different industrial processes. In this study, we aimed to produce and investigate alkaline proteases from a novel actinobacterium strain isolated from a Black Sea marine sediment. The optimal production conditions for Streptomyces sp. K47 alkaline proteases was 4-days incubation at 28ºC in a salt-free medium buffered with 50 mM Tris-HCl buffer (pH 9.0) and containing glucose (1.0%, w v-1) and yeast extract (0.5%, w v-1). The enzyme solution was partially purified using (NH4)2SO4 precipitation (40-70%). After desalting, it was purified 1-84 fold with a recovery of 19.42%. Zymogram analyses revealed the presence of more than one protease enzyme. The enzyme solution exhibited maximum activity at pH 9.0 and 37ºC, remaining stable after a 2-hour incubation at all tested conditions. Streptomyces sp. K47 has the potential to be used in industrial processes because of its ability to produce multiple protease enzymes displaying stability in a broad pH and temperature range.

Salinity Effects on Gene Expression, Morphological, and Physio-Biochemical Responses of Stevia rebaudiana Bertoni In Vitro.

Stevia rebaudiana Bertoni is a little bush, which is cultivated on a large scale in many countries for medicinal purposes and used as a natural sweetener in food products. The present work aims to conduct a protocol for stevia propagation in vitro to produce and introduce Stevia rebaudiana plants as a new sweetener crop to Egyptian agriculture. To efficiently maximize its propagation, it is important to study the influence of stress factors on the growth and development of Stevia rebaudiana grown in vitro. Two stevia varieties were investigated (Sugar High A3 and Spanti) against salt stress. Leaves were used as the source of explants for callus initiation, regeneration, multiplication and rooting. Some stress-related traits, i.e., photosynthetic pigments, proline contents, and enzyme activity for peroxidase (POD), polyphenol oxidase (PPO), and malate dehydrogenase (MDH) were studied. Murashig and Skoog (MS) medium was supplemented with four NaCl concentrations: 500, 1000, 2000, and 3000 mgL−1, while a salt-free medium was used as the control. The data revealed that salinity negatively affected all studied characters: the number of surviving calli, regeneration%, shoot length, the number of multiple shoots, number of leaf plantlets−1, number of root plantlets−1, and root length. The data also revealed that Sugar High A3 is more tolerant than Spanti. The total chlorophyll content decreased gradually with increasing NaCl concentration. However, the opposite was true for proline content. Isozyme’s fractionation exhibited high levels of variability among the two varieties. Various biochemical parameters associated with salt tolerance were detected in POD. Namely, POD4, POD6, POD 9 at an Rf of 0.34, 0.57, and 0.91 in the Sugar High A3 variety under high salt concentration conditions, as well as POD 10 at an Rf of 0.98 in both varieties under high salt concentrations. In addition, the overexpression of POD 5 and POD 10 at Rf 0.52 and 0.83 was found in both varieties at high NaCl concentrations. Biochemical parameters associated with salt tolerance were detected in PPO (PPO1, PPO2 and PPO4 at an Rf of 0.38, 0.42 and 0.62 in the Sugar High A3 variety under high salt concentrations) and MDH (MDH 3 at an Rf of 0.40 in both varieties at high salt concentrations). Therefore, these could be considered as important biochemical markers associated with salt tolerance and could be applied in stevia breeding programs (marker-assisted selection). This investigation recommends stevia variety Sugar High A3 to be cultivated under salt conditions.

Polylysine effect on thylakoid membranes

Thylakoid membranes of photosynthetic plant chloroplasts are involved in a wide range of energy producing pathways. Their stacking can be employed in order to provide increased surface area for biocatalytic purposes. Here we probe the aggregate formation of higher plants' thylakoids using low-molecular poly-l-lysine as an electrostatic polymer linker in low ionic strength media. Microelectrophoresis, actinic light scattering, millisecond-delayed fluorescence and free radical production of thylakoid membranes are measured and analyzed in the presence of the cationic polypeptide to track its influence on the surface electrical properties, the electron-transport processes and the proton gradient accumulation across membranes. Enhanced proton gradient in polylysine-treated thylakoids is obtained upon illumination due to alterations of the proton intake across the membrane resulting from the non-specific electrostatic interactions of the cationic polypeptide with thylakoids. We report lower rates of lipid peroxidation in polylysine-treated thylakoids measured both in the dark and under illumination in salt-free medium. The gained insight on the effect of polycations on photosynthetic membranes may be used in future developments of thylakoid-based approaches for energy transfer applications.

Osmolytes and membrane lipids in the adaptation of micromycete Emericellopsis alkalina to ambient pH and sodium chloride

The accumulation of low molecular weight cytoprotective compounds (osmolytes) and changes in the membrane lipids composition are of key importance for the adaptation to stress impacts. However, the reason behind the wide variety of osmolytes present in the cell remains unclear. We suggest that specific functions of osmolytes can be revealed by studying the adaptation mechanisms of the mycelial fungus Emericellopsis alkalina (Hypocreales, Ascomycota) that is resistant to both alkaline pH values and high sodium chloride concentrations. It has been established that the fungus uses different osmolytes to adapt to ambient pH and NaCl concentration. Arabitol was predominant osmolyte in alkaline conditions, while mannitol prevailed in acidic conditions. On the salt-free medium mannitol was the main osmolyte; under optimal conditions (pH 10.2; 0.4 M NaCl) arabitol and mannitol were both predominant. Higher NaCl concentrations (1.0–1.5 M) resulted in the accumulation of low molecular weight polyol - erythritol, which amounted up to 12–14%, w/w. On the contrary, changes in the composition of membrane lipids were limited under pH and NaCl impacts; only higher NaCl concentrations led to the increase in the degree of unsaturation of membrane lipids. Results obtained indicated the key role of the osmolytes in the adaptation to the ambient pH and osmotic impacts.

Electrostatically PEGylated DNA enables salt-free hybridization in water.

Chemically modified nucleic acids have long served as a very important class of bio-hybrid structures. In particular, the modification with PEG has advanced the scope and performance of oligonucleotides in materials science, catalysis and therapeutics. Most of the applications involving pristine or modified DNA rely on the potential of DNA to form a double-stranded structure. However, a substantial requirement for metal-cations to achieve hybridization has restricted the range of applications. To extend the applicability of DNA in salt-free or low ionic strength aqueous medium, we introduce noncovalent DNA-PEG constructs that allow canonical base-pairing between individually PEGylated complementary strands resulting in a double-stranded structure in salt-free aqueous medium. This method relies on grafting of amino-terminated PEG polymers electrostatically onto the backbone of DNA, which results in the formation of a PEG-envelope. The specific charge interaction of PEG molecules with DNA, absolute absence of metal ions within the PEGylated DNA molecules and formation of a double helix that is significantly more stable than the duplex in an ionic buffer have been unequivocally demonstrated using multiple independent characterization techniques.

Mutant citrus rootstocks tolerant to salinity: in vitro assessment of the growth changes produced by salt

Salinity is one of the main environmental stresses affecting citrus production and may be partially overcome through the combined use of mutagenesis and tissue culture to select salinity-tolerant rootstocks. This study evaluated the effect of saline medium on explants from mutant lines obtained by irradiation of Alemow (Citrus macrophylla) seeds and in vitro selection. Explants from mutant clones (MM1A, MM3A, MM1B, MM3B, MM4B and MM5B) and explants from Alemow (control) were cultured in vitro in a proliferation medium with different concentrations of NaCl depending on the mutant: 0 and 60 mM NaCl (MM1B, MM3B, MM4B and MM5B); 0 and 80 mM NaCl (MM1A and MM3A); 0, 60 and 80 mM NaCl (explants from Alemow control). The mutant explants showed better growth than control explants in the saline medium. MM1B productivity was similar in both 0 and 60 mM NaCl. In the case of MM3B and MM4B, productivity in the salt medium was only 9% lower than in the 0 mM NaCl medium; however, MM5B productivity was 17% lower in the saline medium than in the unsalted medium, being similar to the control in these conditions. In MM1A and MM3A, productivity decreased by only 10% in saline medium (80 mM NaCl) compared to the salt-free medium; however, in the control this decrease was 27%. The number of damaged leaves was lower in MM1B, MM4B and MM5B explants than in control explants in the saline medium, but no significant differences from the control were observed for MM3B, MM1A or MM3A. The salinity tolerance of these mutants is currently being tested in ex vitro conditions.

A Proteolytic Complex Targets Multiple Cell Wall Hydrolases in Pseudomonas aeruginosa.

ABSTRACTCarboxy-terminal processing proteases (CTPs) occur in all three domains of life. In bacteria, some of them have been associated with virulence. However, the precise roles of bacterial CTPs are poorly understood, and few direct proteolytic substrates have been identified. One bacterial CTP is the CtpA protease of Pseudomonas aeruginosa, which is required for type III secretion system (T3SS) function and for virulence in a mouse model of acute pneumonia. Here, we have investigated the function of CtpA in P. aeruginosa and identified some of the proteins it cleaves. We discovered that CtpA forms a complex with a previously uncharacterized protein, which we have named LbcA (lipoprotein binding partner of CtpA). LbcA is required for CtpA activity in vivo and promotes its activity in vitro. We have also identified four proteolytic substrates of CtpA, all of which are uncharacterized proteins predicted to cleave the peptide cross-links within peptidoglycan. Consistent with this, a ctpA null mutant was found to have fewer peptidoglycan cross-links than the wild type and grew slowly in salt-free medium. Intriguingly, the accumulation of just one of the CtpA substrates was required for some ΔctpA mutant phenotypes, including the defective T3SS. We propose that LbcA-CtpA is a proteolytic complex in the P. aeruginosa cell envelope, which controls the activity of several peptidoglycan cross-link hydrolases by degrading them. Furthermore, based on these and other findings, we suggest that many bacterial CTPs might be similarly controlled by partner proteins as part of a widespread mechanism to control peptidoglycan hydrolase activity.

Ion size effect on counterion condensation around a spherical colloidal particle in a salt-free medium containing only counterions

A theory of counterion condensation around a spherical colloidal particle in a salt-free medium containing only counterions developed by Imai and Oosawa as reported by Busseiron Kenkyu 52:42, 1952 ibid. 59:99, 1953) and later by Ohshima (J Colloid Interface Sci 247:18, 2002) is extended to incorporate the ion size effect on the basis of the modified Poisson-Boltzmann equation using the Carnahan-Starling activity coefficient of counterions. The potential distribution depends on the particle surface charge, the particle volume fraction, and the average counterion volume fraction. It is shown that for a dilute particle suspension, the counterion condensation occurs, leading to a decrease in the particle surface potential when the following two conditions are both satisfied: (i) the scaled particle surface charge is greater than the logarithm of the inverse of the particle volume fraction and (ii) the average counterion volume fraction is much smaller than the particle volume fraction.

Salt Stress-Induced Loss of Iron Oxidoreduction Activities and Reacquisition of That Phenotype Depend on rus Operon Transcription in Acidithiobacillus ferridurans.

The type strain of the mineral-oxidizing acidophilic bacterium Acidithiobacillus ferridurans was grown in liquid medium containing elevated concentrations of sodium chloride with hydrogen as electron donor. While it became more tolerant to chloride, after about 1 year, the salt-stressed acidophile was found to have lost its ability to oxidize iron, though not sulfur or hydrogen. Detailed molecular examination revealed that this was due to an insertion sequence, ISAfd1, which belongs to the ISPepr1 subgroup of the IS4 family, having been inserted downstream of the two promoters PI and PII of the rus operon (which codes for the iron oxidation pathway in this acidophile), thereby preventing its transcription. The ability to oxidize iron was regained on protracted incubation of the culture inoculated onto salt-free solid medium containing ferrous iron and incubated under hydrogen. Two revertant strains were obtained. In one, the insertion sequence ISAfd1 had been excised, leaving an 11-bp signature, while in the other an ∼2,500-bp insertion sequence (belonging to the IS66 family) was detected in the downstream inverted repeat of ISAfd1 The transcriptional start site of the rus operon in the second revertant strain was downstream of the two ISs, due to the creation of a new "hybrid" promoter. The loss and subsequent regaining of the ability of A. ferriduransT to reduce ferric iron were concurrent with those observed for ferrous iron oxidation, suggesting that these two traits are closely linked in this acidophile.IMPORTANCE Iron-oxidizing acidophilic bacteria have primary roles in the oxidative dissolution of sulfide minerals, a process that underpins commercial mineral-processing biotechnologies ("biomining"). Most of these prokaryotes have relatively low tolerance to chloride, which limits their activities when only saline or brackish waters are available. The study showed that it was possible to adapt a typical iron-oxidizing acidophile to grow in the presence of salt concentrations similar to those in seawater, but in so doing they lost their ability to oxidize iron, though not sulfur or hydrogen. The bacterium regained its capacity for oxidizing iron when the salt stress was removed but simultaneously reverted to tolerating lower concentrations of salt. These results suggest that the bacteria that have the main roles in biomining operations could survive but become ineffective in cases where saline or brackish waters are used for irrigation.

Effect of dielectric discontinuity on a spherical polyelectrolyte brush.

In this paper we perform molecular dynamics simulations of a spherical polyelectrolyte brush and counterions in a salt-free medium. The dielectric discontinuity on the grafted nanoparticle surface is taken into account by the method of image charges. Properties of the polyelectrolyte brush are obtained for different parameters, including valency of the counterions, radius of the nanoparticle, and the brush total charge. The monovalent counterions density profiles are obtained and compared with a simple mean-field theoretical approach. The theory allows us to obtain osmotic properties of the system.