Sulfite Oxidation Catalyzed by aa 3-Type Cytochrome c Oxidase in Acidithiobacillus ferrooxidans

Sulfite is produced as a toxic intermediate during Acidithiobacillus ferrooxidans sulfur oxidation. A. ferrooxidans D3-2, which posseses the highest copper bioleaching activity, is more resistant to sulfite than other A. ferrooxidans strains, including ATCC 23270. When sulfite oxidase was purified homogeneously from strain D3-2, the oxidized and reduced forms of the purified sulfite oxidase absorption spectra corresponded to those of A. ferrooxidans aa ₃-type cytochrome c oxidase. The confirmed molecular weights of the α-subunit (52.5 kDa), the β-subunit (25 kDa), and the γ-subunit (20 kDa) of the purified sulfite oxidase and the N-terminal amino acid sequences of the γ-subunit of sulfite oxidase (AAKKG) corresponded to those of A. ferrooxidans ATCC 23270 cytochrome c oxidase. The sulfite oxidase activities of the iron- and sulfur-grown A. ferrooxidans D3-2 were much higher than those cytochrome c oxidases purified from A. ferrooxidans strains ATCC 23270, MON-1 and AP19-3. The activities of sulfite oxidase purified from iron- and sulfur-grown strain D3-2 were completely inhibited by an antibody raised against a purified A. ferrooxidans MON-1 aa ₃-type cytochrome c oxidase. This is the first report to indicate that aa ₃-type cytochrome c oxidase catalyzed sulfite oxidation in A. ferrooxidans.     

Isolation and characterization of Acidithiobacillus ferrooxidans strain D3-2 active in copper bioleaching from a copper mine in Chile

Acidithiobacillus ferrooxidans strain D3-2, which has a high copper bioleaching activity, was isolated from a low-grade sulfide ore dump in Chile. The amounts of Cu(2+) solubilized from 1% chalcopyrite (CuFeS(2)) concentrate medium (pH 2.5) by A. ferrooxidans strains D3-2, D3-6, and ATCC 23270 and 33020 were 1360, 1080, 650, and 600 mg x l(-1) x 30 d(-1). The iron oxidase activities of D3-2, D3-6, and ATCC 23270 were 11.7, 13.2, and 27.9 microl O(2) uptake x mg protein(-1) x min(-1). In contrast, the sulfite oxidase activities of strains D3-2, D3-6, and ATCC 23270 were 5.8, 2.9, and 1.0 mul O(2) uptake.mg protein(-1).min(-1). Both of cell growth and Cu-bioleaching activity of strains D3-6 and ATCC 23270, but not, of D3-2, in the chalcopyrite concentrate medium were completely inhibited in the presence of 5 mM sodium bisulfite. The sulfite oxidase of strain D3-2 was much more resistant to sulfite ion than that of strain ATCC 23270. Since sulfite ion is a highly toxic intermediate produced during sulfur oxidation that strongly inhibits iron oxidase activity, these results confirm that strain D3-2, with a unique sulfite resistant-sulfite oxidase, was able to solubilize more copper from chalcopyrite than strain ATCC 23270, with a sulfite-sensitive sulfite oxidase.     

Sulfite oxidation catalyzed by aa(3)-type cytochrome c oxidase in Acidithiobacillus ferrooxidans

Sulfite is produced as a toxic intermediate during Acidithiobacillus ferrooxidans sulfur oxidation. A. ferrooxidans D3-2, which posseses the highest copper bioleaching activity, is more resistant to sulfite than other A. ferrooxidans strains, including ATCC 23270. When sulfite oxidase was purified homogeneously from strain D3-2, the oxidized and reduced forms of the purified sulfite oxidase absorption spectra corresponded to those of A. ferrooxidans aa(3)-type cytochrome c oxidase. The confirmed molecular weights of the α-subunit (52.5 kDa), the β-subunit (25 kDa), and the γ-subunit (20 kDa) of the purified sulfite oxidase and the N-terminal amino acid sequences of the γ-subunit of sulfite oxidase (AAKKG) corresponded to those of A. ferrooxidans ATCC 23270 cytochrome c oxidase. The sulfite oxidase activities of the iron- and sulfur-grown A. ferrooxidans D3-2 were much higher than those cytochrome c oxidases purified from A. ferrooxidans strains ATCC 23270, MON-1 and AP19-3. The activities of sulfite oxidase purified from iron- and sulfur-grown strain D3-2 were completely inhibited by an antibody raised against a purified A. ferrooxidans MON-1 aa(3)-type cytochrome c oxidase. This is the first report to indicate that aa(3)-type cytochrome c oxidase catalyzed sulfite oxidation in A. ferrooxidans.     

Reduction of Hg2+ with Reduced Mammalian Cytochrome c by Cytochrome c Oxidase Purified from a Mercury-Resistant Acidithiobacillus ferrooxidans Strain,MON-1

Acidithiobacillus ferrooxidans AP19-3, ATCC 23270, and MON-1 are mercury-sensitive, moderately mercury-resistant, and highly mercury-resistant strains respectively. It is known that 2,3,5,6-tetramethyl-p-phenylendiamine (TMPD) and reduced cytochrome c are used as electron donors specific for cytochrome c oxidase. Resting cells of strain MON-1 had TMPD oxidase activity and volatilized metal mercury with TMPD as an electron donor. Cytochrome c oxidase purified from strain MON-1 reduced mercuric ions to metalic mercury with reduced mammalian cytochrome c as well as TMPD. These mercury volatilization activities with reduced cytochrome c and TMPD were completely inhibited by 1 mM NaCN. These results indicate that cytochrome c oxidase is involved in mercury reduction in A. ferrooxidans cells. The cytochrome c oxidase activities of strains AP19-3 and ATCC 23270 were completely inhibited by 1 μM and 5 μM of mercuric chloride respectively. In contrast, the activity of strain MON-1 was inhibited 33% by 5 μM, and 70% by 10 μM of mercuric chloride, suggesting that the levels of mercury resistance in A. ferrooxidans strains correspond well with the levels of mercury resistance of cytochrome c oxidase.     

A genomic island provides <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> ATCC 53993 additional copper resistance: a possible competitive advantage

There is great interest in understanding how extremophilic biomining bacteria adapt to exceptionally high copper concentrations in their environment. Acidithiobacillus ferrooxidans ATCC 53993 genome possesses the same copper resistance determinants as strain ATCC 23270. However, the former strain contains in its genome a 160-kb genomic island (GI), which is absent in ATCC 23270. This GI contains, amongst other genes, several genes coding for an additional putative copper ATPase and a Cus system. A. ferrooxidans ATCC 53993 showed a much higher resistance to CuSO₄ (>100 mM) than that of strain ATCC 23270 (<25 mM). When a similar number of bacteria from each strain were mixed and allowed to grow in the absence of copper, their respective final numbers remained approximately equal. However, in the presence of copper, there was a clear overgrowth of strain ATCC 53993 compared to ATCC 23270. This behavior is most likely explained by the presence of the additional copper-resistance genes in the GI of strain ATCC 53993. As determined by qRT-PCR, it was demonstrated that these genes are upregulated when A. ferrooxidans ATCC 53993 is grown in the presence of copper and were shown to be functional when expressed in copper-sensitive Escherichia coli mutants. Thus, the reason for resistance to copper of two strains of the same acidophilic microorganism could be determined by slight differences in their genomes, which may not only lead to changes in their capacities to adapt to their environment, but may also help to select the more fit microorganisms for industrial biomining operations.     

Inhibition of Sulfur Use by Sulfite Ion in Thiobacillus ferrooxidans

In Thiobacillus ferrooxidans AP19-3, elemental sulfur is oxidized by the cooperation of three enzymes, namely, hydrogen sulfide: ferric ion oxidoreductase (SFORase), sulfite: ferric ion oxidoreductase, and iron oxidase. Sulfite ions are one of the products when elemental sulfur is oxidized by SFORase. Under the conditions in which sulfite ions are accumulated in the cells, use of sulfur as an energy source by this strain was strongly inhibited. So the mechanism of inhibition by sulfite ions in T. ferrooxidans AP19-3 was studied. The activities of SFORase and iron oxidase were completely inhibited by 0.8 mm and 1.5 mm NaHSO₃, respectively. ¹⁴CO₂ uptake into washed intact cells was also completely inhibited by 1mm NaHSO₃ when ferrous ion or elemental sulfur was used as an energy source. However, the activities of ribulose-1,5-bisphosphate carboxylase, phosphoribulokinase, and ribosephosphate isomerase measured with a cell-free extract were not inhibited by NaHSO₃ at 1 mm, indicating that sulfite ions didn’t inhibit key enzymes of the Calvin cycle. Since the activity of CO₂ uptake into washed intact cells was absolutely dependent on Fe^{2 +} - or S0-oxidation, mechanism of inhibition of sulfur use by sulfite ions is proposed as follows: sulfite ions inhibit SFORase and iron oxidase, as a result T. ferrooxidans AP19-3 can not obtain a carbon source for CO₂ fixation and stops cell growth on sulfur-salts medium.     

A New Enzyme Species of p-Hydroxybenzoate Hydroxylase during Oxygenating Process Observed by the Stopped-flow Method

Sulfite ion (HSO₃ ^-) is one of the products when elemental sulfur is oxidized by the hydrogen sulfide:ferric ion oxidoreductase of Thiobacillus ferrooxidans AP19-3. Under the conditions in which HSO₃ ^- is accumulated in the cells, the iron oxidase of this bacterium was strongly inhibited by HSO₃ ^-. Since cytochrome c oxidase is one of the most important components of the iron oxidase enzyme system in T. ferrooxidans, effects of HSO₃ ^- on cytochrome c oxidase activity were studied with the plasma membranes of HSO₃ ^--resistant and -sensitive strains of T. ferrooxidans, OK1-50 and AP19-3. The enzyme activity of AP19-3 compared with OK1-50 was strongly inhibited by HSO₃ ^-. To investigate the inhibition mechanism of HSO₃ ^- in T. ferrooxidans, cytochrome c oxidases were purified from both strains to an electrophoretically homogeneous state. Cytochrome c oxidase activity of a purified OK1-50 enzyme was not inhibited by 5 mM HSO₃ ^-. In contrast, the same concentration of HSO₃ ^- inhibited the enzyme activity of AP19-3 50%, indicating that the cytochrome c oxidase of OK1-50 was more resistant to HSO₃ ^- than that of AP19-3. Cytochrome c oxidases purified from both strains were composed of three subunits. However, the molecular weight of the largest subunit differed between OK1-50 and AP19-3. Apparent molecular weights of the three subunits of cytochrome c oxidases were 53,000, 24,000, and 19,000 for strain AP19-3 and 55,000, 24,000, and 19,000 for strain OK1-50, respectively.     

Reconstitution of Iron Oxidase from Sulfur-Grown Acidithiobacillus ferrooxidans

The iron oxidation system from sulfur-grown Acidithiobacillus ferrooxidans ATCC 23270 cells was reconstituted in vitro. Purified rusticyanin, cytochrome c, and aa₃-type cytochrome oxidase were essential for reconstitution. The iron-oxidizing activity of the reconstituted system was 3.3-fold higher than that of the cell extract from which these components were purified.     

Plasmid Profiles of Acidithiobacillus ferrooxidans Strains Adapted to Different Oxidation Substrates

Plasmid profiles were studied in five Acidithiobacillus ferrooxidans strains of various origin cultivated on a medium with Fe²⁺, as well as adapted to such oxidation substrates as S⁰, FeS₂, and sulfide concentrate. The method used revealed plasmids in all A. ferrooxidans strains grown on a medium with Fe²⁺. One plasmid was found in strain TFL-2; two plasmids, in strains TFO, TFBk, and TFV-1; and three plasmids were detected in strain TFN-d. The adaptation of strain TFN-d to sulfide concentrate and the adaptation of strain TFV-1 to S⁰, FeS₂, or sulfide concentrate resulted in a change in the number of plasmids occurring in cells. In cells of strain TFN-d adapted to sulfide concentrate, the number of plasmids decreased from three to two. The number of plasmids in cells of strain TFV-1 adapted to different substrates varied from three to six depending on the energy source present in the medium: three plasmids were found after growth on FeS₂, four after growth on S⁰, and six after growth on sulfide concentrate. The possible role of plasmids in the adaptation of A. ferrooxidans to new energy substrates and in the regulation of the intensity of their oxidation is discussed.     

Existence of a Hydrogen Sulfide:Ferric Ion Oxidoreductase in Iron-Oxidizing Bacteria

The existence of a hydrogen sulfide:ferric ion oxidoreductase, which catalyzes the oxidation of elemental sulfur with ferric ions as an electron acceptor to produce ferrous and sulfite ions, was assayed with washed intact cells and cell extracts of various kinds of iron-oxidizing bacteria, such as Thiobacillus ferrooxidans 13598, 13661, 14119, 19859, 21834, 23270, and 33020 from the American Type Culture Collection, Leptospirillum ferrooxidans 2705 and 2391 from the Deutsche Sammlung von Mikroorganismen, L. ferrooxidans BKM-6-1339 and P3A, and moderately thermophilic iron-oxidizing bacterial strains BC1, TH3, and Alv. It was found that hydrogen sulfide:ferric ion oxidoreductase activity comparable to that of T. ferrooxidans AP19-3 was present in all iron-oxidizing bacteria tested, suggesting a wide distribution of this enzyme in iron-oxidizing bacteria.     

Cooperation of Three Denitrifying Bacteria in Nitrate Removal of Acidic Nitrate- and Uranium-Contaminated Groundwater

In uranium-contaminated aquifers co-contaminated with nitrate, denitrifiers play a critical role in bioremediation. Six strains of denitrifying bacteria belonging to Rhizobium, Pseudomonas, and Castellaniella were isolated from the Oak Ridge Integrated Field Research Challenge Site (OR-IFRC), where biostimulation of acidic (pH 3.5–6.5), nitrate-contaminated (up to 140 mM) groundwater occurred. Three isolates were characterized in regards to nitrite tolerance, denitrification kinetic parameters, and growth on different denitrification intermediates. Kinetic and growth experiments showed that Pseudomonas str. GN33#1 reduced NO^? ₃ most rapidly (V_max = 15.8 μmol e^?·min^?1·mg protein^?1) and had the fastest generation time (gt) on NO^? ₃ (2.6 h). Castellaniella str. 4.5A2 was the most low pH and NO^? ₂ tolerant and grew rapidly on NO^? ₂ (gt = 4.0 h). Rhizobium str. GN32#2 was also tolerant of low pH values and reduced NO^? ₂ rapidly (V_max = 10.6 μmol e^?·min^?1·mg protein^?1) but was far less NO^? ₂ tolerant than Castellaniella str. 4.5A2. Growth of and denitrification by these three strains incubated together and individually were measured in OR-IFRC groundwater at pHs 5 and 7 to determine whether they cooperate or compete during denitrification. Mixed assemblages reduced NO^? ₃ more rapidly and more completely than any individual isolate over the course of the experiment. The results described in this article demonstrate 1) that this synthetic assemblage comprised of three physiologically distinct denitrifying bacterial isolates cooperate to achieve more complete levels of denitrification and 2) the importance of pH- and nitrite-tolerant bacteria such as Castellaniella str. 4.5A2 in minimizing NO^? ₂ accumulation in high-NO^? ₃ groundwater during bioremediation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.     

Cytoplasmic membrane response to copper and nickel in Acidithiobacillus ferrooxidans

Metal tolerance has been found to vary among Acidithiobacillus ferrooxidans strains and this can impact the efficiency of biomining practices. To explain observed strain variability for differences in metal tolerance we examined the effects of Cu²⁺ and Ni²⁺ concentrations (1-200 mM) on cytoplasmic membrane properties of two A. ferrooxidans type strains (ATCC 23270 and 19859) and four strains isolated from AMD water around Sudbury, Ontario, Canada. Growth rate, membrane fluidity and phase, determined from the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), and fatty acid profiles indicated that three different modes of adaptation were present and could separate between strains showing moderate, or high metal tolerance from more sensitive strains. To compensate for the membrane ordering effects of the metals, significant remodelling of the membrane was used to either maintain homeoviscous adaptation in the moderately tolerant strains or to increase membrane fluidity in the sensitive strains. Shifts in the gel-to-liquid crystalline transition temperature in the moderately tolerant strains led to multiple phase transitions, increasing the potential for phase separation and compromised membrane integrity. The metal-tolerant strain however, was able to tolerate increases in membrane order without significant compensation via fatty acid composition. Our multivariate analyses show a common adaptive response which involves changes in the abundant 16:0 and 18:1 fatty acids. However, fatty acid composition and membrane properties showed no difference in response to either copper or nickel suggesting that adaptive response was non-specific and tolerance dependent. We demonstrate that strain variation can be evaluated using differences in membrane properties as intrinsic determinants of metal susceptibility.     

Reduction of Hg2+ with reduced mammalian cytochrome c by cytochrome c oxidase purified from a mercury-resistant acidithiobacillus ferrooxidans strain, MON-1

Acidithiobacillus ferrooxidans AP19-3, ATCC 23270, and MON-1 are mercury-sensitive, moderately mercury-resistant, and highly mercury-resistant strains respectively. It is known that 2,3,5,6-tetramethyl-p-phenylendiamine (TMPD) and reduced cytochrome c are used as electron donors specific for cytochrome c oxidase. Resting cells of strain MON-1 had TMPD oxidase activity and volatilized metal mercury with TMPD as an electron donor. Cytochrome c oxidase purified from strain MON-1 reduced mercuric ions to metalic mercury with reduced mammalian cytochrome c as well as TMPD. These mercury volatilization activities with reduced cytochrome c and TMPD were completely inhibited by 1 mM NaCN. These results indicate that cytochrome c oxidase is involved in mercury reduction in A. ferrooxidans cells. The cytochrome c oxidase activities of strains AP19-3 and ATCC 23270 were completely inhibited by 1 muM and 5 muM of mercuric chloride respectively. In contrast, the activity of strain MON-1 was inhibited 33% by 5 muM, and 70% by 10 muM of mercuric chloride, suggesting that the levels of mercury resistance in A. ferrooxidans strains correspond well with the levels of mercury resistance of cytochrome c oxidase.     

Identification of IS elements in <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> strains grown in a medium with ferrous iron or adapted to elemental sulfur

IS elements were identified in the genomes of five Acidithiobacillus ferrooxidans strains isolated from various media. IST2 elements were revealed in all the strains grown in a medium with ferrous iron, ISAfe1 elements were detected in four strains (TFBk, TFL-2, TFV-1 and TFO). Three strains (TFV-1, TFN-d and TFO) were found to contain IS elements, ~600 bp long. These were named preliminary as ISAfe600. Partial sequencing of the 5′- and 3′-terminal nucleotide stretches of an ISAfe1 element in TFBk and TFL-2 strains and complete sequencing of the ISAfe1 element in the TFBk strain has revealed nucleotide substitutions as compared to the prototype, i.e., the ISAfe1 element of an ATCC 19859 strain. Partial sequencing of the 5′- and 3′-terminal nucleotide stretches of the IST2 elements in TFO, TFBk and TFL-2 strains has shown numerous nucleotide substitutions when compared to the IST2 element of an ATCC 19859 strain. Complete sequencing of the IST2 element in the TFBk strain has revealed: the divergence between the IST2 elements in the TFBk strain and the prototype was 21.2%. Southern hybridization of EcoRI fragments of the chromosomal DNA from five A. ferrooxidans strains grown in a medium with ferrous iron using an internal region of ISAfe1, a full-length ISAfe1 or a full-length IST2 as probes has shown them to differ in the number of copies of IS elements and their localization on the chromosomes. Adaptation to elemental sulfur in A. ferrooxidans strains caused changes in the number, intensity and localization of hybridization bands. The authors discuss the role of IS elements in the adaptation of A. ferrooxidans to the new energy substrate. The nucleotide sequence data reported in this paper were deposited in GenBank under accession numbers: AY823401, the ISAfe1 from A. ferrooxidans TFBk; AY825254, the IST2 from TFBk; DQ002894, the 5′-terminal nucleotide sequence of ISAfe1 from TFL-2; DQ002895, the 3′-terminal nucleotide sequence of ISAfe1 from TFL-2; DQ005952, the 5′-terminal nucleotide sequence of IST2 from TFV-1; DQ005953, the 3′-terminal nucleotide sequence of IST2 from TFV-1.     

The Effect of the Facultative Chemolithotrophic Bacterium Thiobacillus acidophilus on the Leaching of Low-Grade Cu-Ni Sulfide Ore by Thiobacillus ferrooxidans

The purpose of this investigation was to determine the effect of Thiobacillus acidophilus on the leaching of a low-grade Cu-Ni sulfide ore by Thiobacillus ferrooxidans. A sample of low-grade Cu-Ni sulfide ore containing 0.36% Cu, 0.48% Ni, and 7.87% Fe was pulverized and initially leached for a 21-day period using two different pure cultures of T. ferrooxidans, an environmental strain (F2) and a strain from the American Type Culture Collection (ATCC 23270). Samples of the ore slurries were drawn and the pH was monitored over the course of the leaching period. The concentrations of Cu and Ni leached by each strain were determined and compared. No significant differences were observed in the concentrations of Cu and Ni leached by the two pure cultures of T. ferrooxidans. Subsequently, the ore was leached with mixed cultures of T. ferrooxidans and T. acidophilus to determine the effect of the latter on the concentrations of Cu and Ni leached from the ore. The environmental strain F2 of T. ferrooxidans was used in combination with both a type strain (ATCC 27807) and an environmental strain (64) of T. acidophilus. After 21 days, the mixed cultures of T. ferrooxidans and T. acidophilus leached significantly greater amounts of copper than the pure strain alone, but no such difference was observed for the leaching of nickel.     

Oxygen Consumption by Desulfovibrio Strains with and without Polyglucose

The kinetics of oxygen reduction by Desulfovibrio salexigens Mast1 and the role of polyglucose in this activity were examined and compared with those of strains of D. desulfuricans and D. gigas. Oxidation rates were highest at air saturation (up to 40 nmol of O₂ min⁻¹ mg of protein⁻¹) and declined with decreasing oxygen concentrations. Studies with cell extracts (CE) indicated that NADH oxidase was entirely responsible for the oxygen reduction in strain Mast1. In D. desulfuricans CSN, at least three independent systems appeared to reduce oxygen. Two were active at all oxygen concentrations (NADH oxidase and NADPH oxidase), and one was maximally active at less than 10 μM oxygen. In contrast to D. gigas and D. salexigens strains, the D. desulfuricans strains also contained NADH peroxidase and NADPH peroxidase activities and did not accumulate polyglucose under nonlimiting growth conditions. At air saturation, initial activities of the oxidases and peroxidases of cells harvested at the end of the log phase were on the order of 20 to 140 nmol of O₂ min⁻¹ mg of protein⁻¹. In all strains, these enzymes were relatively stable but were susceptible to inactivation as soon as substrates were added to the assay mixture. Under those conditions, all oxidation activity disappeared after ca. 1 h of incubation. The same finding was observed with whole cells of D. desulfuricans CSN and D. desulfuricans ATCC 27774, but inactivation was less pronounced with cells of D. salexigens Mast1. It appeared that the presence of polyglucose in the whole cells retarded the process of inactivation of NADH oxidase, but this property was lost in crude CE. In spite of the effect of polyglucose on the oxidative potential, oxygen-dependent growth of D. salexigens Mast1 could be demonstrated neither in batch nor in continuous culture.     

Toxin-Antitoxin Systems in the Mobile Genome of Acidithiobacillus ferrooxidans

Toxin-antitoxin (TA) systems are genetic modules composed of a pair of genes encoding a stable toxin and an unstable antitoxin that inhibits toxin activity. They are widespread among plasmids and chromosomes of bacteria and archaea. TA systems are known to be involved in the stabilization of plasmids but there is no consensus about the function of chromosomal TA systems. To shed light on the role of chromosomally encoded TA systems we analyzed the distribution and functionality of type II TA systems in the chromosome of two strains from Acidithiobacillus ferrooxidans (ATCC 23270 and 53993), a Gram-negative, acidophilic, environmental bacterium that participates in the bioleaching of minerals. As in other environmental microorganisms, A. ferrooxidans has a high content of TA systems (28-29) and in twenty of them the toxin is a putative ribonuclease. According to the genetic context, some of these systems are encoded near or within mobile genetic elements. Although most TA systems are shared by both strains, four of them, which are encoded in the active mobile element ICEAfe1, are exclusive to the type strain ATCC 23270. We demostrated that two TA systems from ICEAfe1 are functional in E. coli cells, since the toxins inhibit growth and the antitoxins counteract the effect of their cognate toxins. All the toxins from ICEAfe1, including a novel toxin, are RNases with different ion requirements. The data indicate that some of the chromosomally encoded TA systems are actually part of the A. ferrooxidans mobile genome and we propose that could be involved in the maintenance of these integrated mobile genetic elements.     

Attachment of Acidithiobacillus ferrooxidans onto different solid substrates and fitting through Langmuir and Freundlich equations

Attachments of Acidithiobacillus ferrooxidans ATCC 23270 onto elemental sulfur, quartz and complex chalcopyrite were investigated by analysis of its extracellular polymeric substances as well as applying Langmuir and Freundlich equations. The two equations fitted the adsorption equilibrium data with significant correlation coefficient over 0.9. This indicated that bacterial attachment is complicated and involves Langmuir and Freundlich characterizations. Sulfur-grown cells showed the highest affinity for the three solid substrates. The investigated complex chalcopyrite possessed a higher maximum adsorption capacity for A. ferrooxidans than elemental sulfur or quartz. The Freundlich fitting parameters suggested that quartz had a weaker adsorption capacity and smaller adsorption areas than elemental sulfur or the complex chalcopyrite. It is not the content of total carbohydrates or proteins in EPS but their ratios that determine the affinity differences between cells and substrates.