Studies on isocitrate lyase from the facultative autotroph Thiobacillus novellus

Isocitrate lyase from Thiobacillus novellus was purified about eightfold from crude extracts of acetate-grown cells. Polyacrylamide gel "disc" electrophoresis revealed that the partly purified material contained one major and two minor peaks. The optimum pH for activity in the forward direction with glycylglycine buffer and the reverse direction with either glycylglycine or potassium phosphate was around pH 8.0. Plots of v vs. s gave Michaelis–Menten kinetics with an apparent Km of 4.3 × 10−5 M for isocitrate and 2.3 × 10−4 M for succinate. However, for glyoxylate, v vs. s plots were sigmoidal. Hill plots gave an n value of 2.6 and a k value of about 7.76 × 10−5 M. Since biosynthetic enzymes usually have sigmoidal kinetics, it follows that isocitrate lyase may be important in the synthesis of isocitrate. Also of interest was the finding that the enzyme did not show an absolute requirement for a divalent cation, but in the presence of 0.3 mM Mg2+ activity was stimulated about threefold over that observed in the absence of metal. Km for Mg2+ was 7.0 × 10−4 M. Complete loss of activity found on addition of 0.03 mM HgCl2 or CuSO4 to the enzyme in the absence of Mg2+, as well as the restoration of activity lost during storage by the addition of cysteine or glutathione supports the idea that sulfhydryl groups are required for activity. The effect of adenine nucleotides on activity revealed in decreasing order of inhibition that ATP > ADP > AMP. Adenosine or pyrophosphate were not inhibitory at any concentration.

Effect of supplementary aeration on the growth of Thiobacillus thiooxidans in shaken cultures

The growth rate of shaken cultures of the strict autotroph, Thiobacillus thiooxidans, usually very slow, has been increased about threefold by increasing the level of aeration. The cell yield has also been improved somewhat by this procedure. CO2 enriched air does not enhance growth further.

Oxidation of copper (II) selenide by Thiobacillus ferrooxidans

Thiobacillus ferrooxidans can derive its energy from the oxidation of copper selenide. In this metabolic oxidation process, copper goes into solution and elemental selenium is deposited.

Effect of cultural conditions on the fatty acid composition of Thiobacillus novellus

The fatty acid content of Thiobacillus novellus was determined under various cultural conditions. Four fatty acids, C(16:0), C(18:0), C(18:1), and a C(19) cyclopropane acid (C(19:cyc)), generally accounted for 90 to 99% of the total acids. Phosphate concentration, temperature, culture agitation, and the presence of branch-chain precursors had no significant effect on cellular fatty acids. Autotrophically grown cells contained more saturated C(16) and C(18) acids than did heterotrophic ones, and the sum of the percentages of the C(18:1) and the C(19:cyc) acids was consistently higher in the heterotrophs. When the inorganic medium was supplemented with biotin, autotrophic cells produced more C(19:cyc) and much less C(18:1) than did autotrophs in unsupplemented medium. Heterotrophic cells grown with biotin also showed a marked reduction of the unsaturated acid and an increase in the cyclopropane acid, except when glutamatecitrate medium was employed, in which case the opposite effect was noted. Two different biotin-supplemented media yielded cells with 75 to 77% of the total fatty acids being the C(19) cyclopropane acid, one of the highest reported values for this class of acid.

Comparison of the kinetics of thiosulfate oxidation by three iron-sulfur oxidizers

The sulfur metabolism of Thiobacillus ferrooxidans, Ferrobacillus ferrooxidans, and Ferrobacillus sulfooxidans was found to differ in the rate of utilization of thiosulfate and tetrathionate, with tetrathionate showing the most significant difference between the three organisms. The apparent Km values of the three organisms ranged from 2–5 × 10−2 M for T. ferrooxidans and F. sulfooxidans to 5–7 × 10−3 M for F. ferrooxidans. Increasing the temperature caused a greater effect on thiosulfate oxidation by F. ferrooxidans than with the other two as shown by the apparent Ea values (Ea′ for F. ferrooxidans, 18 000; F. sulfooxidans, 11 400; T. ferrooxidans, 11 000).The initial pH of the medium determined the rate of thiosulfate oxidation. If the initial pH was 4.0–4.5, a sharp break in oxygen uptake was shown by T. ferrooxidans and F. sulfooxidans after 20–30 min, but not with F. ferrooxidans.When the disappearance of thiosulfate and tetrathionate from the medium was used as an indicator of the affinity of the three test organisms for the sulfur compounds, F. ferrooxidans demonstrated the highest net loss of both compounds from the medium.

Ribulose diphosphate carboxylase from autotrophic microorganisms

Thiobacillus denitrificans was grown anaerobically with nitrate as an acceptor in both sterile and nonsterile media. Ribulose diphosphate carboxylase was stable throughout the exponential growth phase and declined slowly only after cells reached the stationary phase. Reversible inactivation of the carboxylase occurred in extracts as a result of bicarbonate omission. The enzyme was purified 32-fold with excellent recovery of a preparation which was 50 to 60% pure by the criterion of polyacrylamide gel electrophoresis. This purified preparation catalyzed the fixation of 1.25 mumoles of CO(2) per min per mg of protein at pH 8.1 and 30 C, and the molecular weight of ribulose diphosphate carboxylase was approximately 350,000 daltons. A striking biphasic time course of CO(2) fixation that was independent of protein and ribulose diphosphate concentration was observed. The optimal pH of the enzyme assay was fairly broad, ranging from 7 to 8.2. Kinetic dependence upon bicarbonate, ribulose diphosphate, and Mg(2+) was characterized and indicated that bicarbonate and Mg(2+) must combine with enzyme prior to addition of ribulose diphosphate. Antiserum to ribulose diphosphate carboxylase from Hydrogenomonas eutropha was only slightly inhibitory when added to the enzyme from T. denitrificans, and the mixture did not precipitate. Cyanide (4 x 10(-5)m) gave 61% inhibition of the enzyme from T. denitrificans. Ribulose diphosphate carboxylase in extracts of H. eutropha, H. facilis, Chromatium D, Rhodospirillum rubrum, and Chlorella pyrenoidosa were also inhibited to varying extents by cyanide and antiserum to the H. eutropha enzyme.

Growth of obligate autotrophic bacteria on glucose in a continuous flow-through apparatus

Nitrosomonas europaea, Nitrobacter agilis, Thiobacillus denitrificans, T. neapolitanus, and T. thioparus (all obligate autotrophic bacteria) have been grown in dialysis culture, on glucose salts media, in the absence of their specific inorganic energy source. Metabolic products for N. agilis grown on nitrite salts medium were identified as keto acids. Pyruvic acid inhibited this organism at 5 x 10(-5)m. Keto acids were not inhibitory for the thiobacilli grown on thiosulfate medium. However, when T. denitrificans was grown on glucose with dialysis, addition of 5 x 10(-4)m pyruvate inhibited growth. Thus, it appears pyruvate may be inhibitory for other autotrophs, as has been reported for T. thiooxidans.

Heterotrophic metabolism of the chemolithotroph Thiobacillus ferrooxidans

Glucose-6-phosphate dehydrogenase and the enzymes of the Entner-Doudoroff pathway, 6-phosphogluconate dehydrase and 2-keto-3-deoxy-6-phosphogluconate aldolase (assayed together), are induced during heterotrophic growth of Thiobacillus ferrooxidans on an iron-glucose-supplemented medium or on glucose alone. By contrast, autotrophic cells (iron-grown) contain low levels of these enzymes. Fructose 1, 6-diphosphate aldolase, an enzyme of the Embden-Meyerhof pathway, is present at low levels irrespective of the growth medium, suggesting that this enzyme is not involved in energy-yielding reactions but merely provides intermediates for biosynthesis. The Entner-Doudoroff and pentose-phosphate pathways are the principle means through which glucose is dissimilated and is presumed to be concerned with energy production. Isotopic studies showed that a high rate of CO(2) formation from specifically labeled glucose came from carbon atoms 1 and 4. An unexpectedly high rate of evolution of CO(2) also came from carbon 6, suggesting that the triose phosphate formed during glucose breakdown and specifically as a result of 2-keto-3-deoxy-6-phosphogluconate aldolase activity, was metabolized via some unorthodox metabolic route. Cells grown in the iron-supplemented and glucose-salts media have a complete tricarboxylic acid cycle, whereas autotrophically grown T. ferrooxidans lacked both alpha-ketoglutarate dehydrogenase and reduced nicotinamide adenine dinucleotide oxidase. Two isocitrate dehydrogenases [nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP) specific] were present. NAD-linked enzyme was constitutive, whereas the NADP-linked enzyme was induced upon adaptation of autotrophic cells to heterotrophic growth.

Glucose-6-phosphate dehydrogenase from the chemolithotroph Thiobacillus ferrooxidans

Glucose-6-phosphate dehydrogenase was partially purified from both glucose-grown and iron-glucose-grown Thiobacillus ferrooxidans. The enzyme possesses a dual nucleotide specificity for either nicotinamide adenine dinucleotide phosphate (NADP) or nicotinamide adenine dinucleotide (NAD) and has a molecular weight of 110,000 as determined by gel electrophoresis. Evidence is presented that T. ferrooxidans glucose-6-phosphate dehydrogenase is identical when isolated from cells grown mixotrophically (iron-glucose grown) or cells grown heterotrophically (glucose-grown cells). The enzyme is activated by Mg(2+), and to a lesser extent by low concentrations of Mn(2+). Reduced NAD inhibits the enzyme from T. ferrooxidans. No deviation from normal Michaelis-Menten kinetics was observed in velocity versus substrate concentration experiments. Adenosine triphosphate exerted a profound inhibition of the enzyme; the effect was 10 times more pronounced in the presence of NAD as compared to NADP. The physiological significance of this inhibition is discussed.

Utilization of glucose and the effect of organic compounds on the chemolithotroph Thiobacillus ferrooxidans

The utilization of glucose by the chemolithotroph Thiobacillus ferrooxidans results in a repression of the ability to oxidize iron, the substrate for autotrophic growth. An assay with resting cells was used to measure iron oxidation rates. Concomitant with the decreased iron oxidation rates, the enzyme responsible for carbon dioxide fixation, ribulose diphosphate (RuDP) carboxylase, was also repressed. Maximum iron oxidation rates precede peak RuDP carboxylase levels, consistent with the role of these processes in autotrophic metabolism in nonrepressed cells. The degree of iron oxidation repression depends on the organic substrate supplied, as does the level of RuDP carboxylase. The uptake of glucose parallels an increase in synthesis of glucose-6-phosphate dehydrogenase and the accumulation in cells of poly-beta-hydroxybutyrate. The organism is also capable of growing on glucose and other organic supplements in the absence of its inorganic energy source; growth rates depend on the organic substrate supplied.

The sulfite oxidase of Thiobacillus ferrooxidans (Ferrobacillus ferrooxidans)

The sulfite oxidase (sulfite: cytochrome c oxidoreductase) from sulfur-grown Thiobacillus ferrooxidans was isolated and partially purified, and its properties were studied. The enzyme was purified 7.3-fold and was 75–85% of the protein present. Sulfite oxidase required SO32− for activity, and could use horse heart cytochrome c and ferricyanide as electron acceptors. The molecular weight was 41 500. The enzyme had a Km for sulfite of 0.58 mM with either ferricyanide or cytochrome c as the electron acceptor. The Km for ferricyanide was 0.25 mM. 5′-AMP did not stimulate enzyme activity. Other properties of the enzyme were similar to the enzyme from Thiobacillus thioparus and Thiobacillus novellus. A metabolic scheme of sulfur utilization for energy production in Thiobacillus ferrooxidans is presented.

Enzymes of carbohydrate metabolism in Thiobacillus species

A study was made of enzymes of carbohydrate metabolism in representative thiobacilli grown with and without glucose. The data show that Thiobacillus perometabolis possesses an inducible Entner-Doudoroff pathway and is thus similar to T. intermedius and T. ferrooxidans. T. novellus lacks this pathway. Instead, a non-cyclic pentose phosphate pathway along with the Krebs cycle is apparently the major route of glucose dissimilation in this organism. Glucose does not support or stimulate the growth of strains of T. neapolitanus, T. thioparus, and T. thiooxidans examined, nor does its presence in the growth medium greatly influence their enzymatic constitution. These obligately chemolithotrophic thiobacilli do not possess the Entner-Doudoroff pathway. Their nicotinamide adenine dinucleotide (NAD)-linked isocitrate dehydrogenase activity predominates over their nicotinamide adenine dinucleotide phosphate (NADP)-linked activity; the converse is true for the other thiobacilli. The data suggest that NAD-linked isocitrate dehydrogenase activity in thiobacilli is involved in biosynthetic reactions.

Effect of growth substrate on enzymes of the citric and glyoxylic acid cycles in Thiobacillus novellus

A quantitative study was conducted of enzymes involved in the citric acid cycle and associated systems of the facultative autotroph Thiobacillus novellus grown on five different substrates. Irrespective of the growth substrate the organism possessed complete citric and glyoxylic acid cycles and the specific activity of α-ketoglutarate dehydrogenase was always quite low. Also, the activities of the enzymes of both cycles were usually lowest in extracts from autotrophic cells, and highest in extracts from acetate-grown cells. The three remaining extracts had activities that were between the two extremes with those from glucose-grown cells generally lower than those from pyruvate and succinate. Several exceptions should be noted among these generalizations. For example, the activity of aconitate hydratase and malic dehydrogenase was lowest in extracts from glucose-grown cells while that of isocitric dehydrogenase was lowest in extracts from pyruvate-grown cells. Transhydrogenase activity was virtually absent from extracts of pyruvate- and succinate-grown cells while NADH oxidase, which was identical in these two extracts, was also relatively low. Of interest is the large amount of cytochrome c found in high-speed supernatants. In extracts from autotrophic cells this was about 2.3% of the soluble protein and is suggestive of a significant role being played by the electron-transport system during growth of the organism.

Utilization of glucose in heterotrophic media by Thiobacillus intermedius

The growth yield of Thiobacillus intermedius is greater in glucose-yeast extract or glucose-casein hydrolysate broth than in comparable media without glucose. The quantity of glucose utilized in the glucose-supplemented media is much greater than the increase in cell yield observed relative to the unsupplemented media. Addition of glucose to cell-free extracts of glucose-yeast extract or glucose-casein hydrolysate grown cells results in the reduction of endogenous cytochrome c. Thus, in these media, glucose serves as a source of energy. This is in contrast to thiosulfate-glucose broth in which glucose provides only cell carbon. The presence of thiosulfate in glucose-casein hydrolysate broth results in a marked decrease in glucose consumption. Cytochrome c in extracts of cells grown in this medium is not reduced by glucose addition. The data suggest that thiosulfate prevents the utilization of glucose for energy generation. The final growth yield in glucose-casein hydrolysate broth is directly proportional to the initial glucose concentration, although not all the glucose was utilized even at the lowest concentration tested. This effect may be due to an inefficient glucose transport in this organism.