Oxidative metabolism of inorganic sulfur compounds by bacteria

The history of the elucidation of the microbiology and biochemistry of the oxidation of inorganic sulfur compounds in chemolithotrophic bacteria is briefly reviewed, and the contribution of Martinus Beijerinck to the study of sulfur-oxidizing bacteria highlighted. Recent developments in the biochemistry, enzymology and molecular biology of sulfur oxidation in obligately and facultatively lithotrophic bacteria are summarized, and the existence of at least two major pathways of thiosulfate (sulfur and sulfide) oxidation confirmed. These are identified as the Paracoccus sulfur oxidation (or PSO) pathway and the S4intermediate (or S4I) pathway respectively. The former occurs in organisms such as Paracoccus (Thiobacillus) versutus and P. denitrificans, and possibly in Thiobacillus novellus and Xanthobacter spp. The latter pathway is characteristic of the obligate chemolithotrophs (e.g. Thiobacillus tepidarius, T. neapolitanus, T. ferrooxidans, T. thiooxidans) and facultative species such as T. acidophilus and T. aquaesulis, all of which can produce or oxidize tetrathionate when grown on thiosulfate. The central problem, as yet incompletely resolved in all cases, is the enzymology of the conversion of sulfane-sulfur (as in the outer [S-] atom of thiosulfate [-S-SO3-]), or sulfur itself, to sulfate, and whether sulfite is involved as a free intermediate in this process in all, or only some, cases. The study of inorganic sulfur compound oxidation for energetic purposes in bacteria (i.e. chemolithotrophy and sulfur photolithotrophy) poses challenges for comparative biochemistry. It also provides evidence of convergent evolution among diverse bacterial groups to achieve the end of energy-yielding sulfur compound oxidation (to drive autotrophic growth on carbon dioxide) but using a variety of enzymological systems, which share some common features. Some new data are presented on the oxidation of 35S-thiosulfate, and on the effect of other anions (selenate, molybdate, tu ngstate, chromate, vanadate) on sulfur compound oxidation, including observations which relate to the roles of polythionates and elemental sulfur as intermediates.     

Biology of budding bacteria

Summary Budding bacteria from aquatic or terrestrial habitats were found to accumulate ferric oxide hydrate (ferric hydroxide) on their cell surfaces. Metal paper clips served as the source of oxidizable iron. Pure cultures deposited ferric hydroxide during growth on sea water medium at a pH of 7.8, but not in a mineral salts medium of normal ionic strength, of pH 7.2, and without NaCl, although some active strains came from fresh water or soil.Ferric iron deposition was found to be initiated at primary active sites on the cell surface; the hyphae and rods eventually become completely encased by the heavy coat.The presence of iron depositing, budding bacteria in fresh water, brackish water or sea water indicates an ubiquitous distribution of these microorganisms.Actively depositing isolates from marine environments are more closely related to Pedomicrobium than to Hyphomicrobium spp. because of their multiple formation of hyphae from rod-shaped swarmer cells. A taxonomic and cultural study of these new forms is in progress.     

Isolation of thermophilic obligately autotrophic hydrogen-oxidizing bacteria,similar to Hydrogenobacter thermophilus,from Icelandic hot springs

Thermophilic obligately autotrophic hydrogen-oxidizing bacteria were isolated from several alkaline hot springs in Iceland. The bacteria were Gram negative rods, 0.4–0.5 m in diameter and 3–4 m long but 6–7 m long cells without septa were often seen. Long and short laments are formed. Spores, flagella or lipid granules were not observed. Strains H1 and H12 grew optimally at 70° C and pH 6.5 under mixture of air plus 0.6 atm H₂ and 0.1 atm CO₂. The cells contained cytochromes and carotenoid-like pigments. They would not grow on agar or silicia gel plates. The cells would not grow heterotrophically on organic substrates and were inhibited by most of these same organic compounds and agar in low concentrations. They were very sensitive to common antibiotics. The role of these bacteria in the hot spring ecosystem is discussed.     

Antiquity and evolutionary status of bacterial sulfate reduction: Sulfur isotope evidence

The presently available sedimentary sulfur isotope record for the Precambrian seems to allow the following conclusions: (1) In the Early Archaean, sedimentary ^{3 4} patterns attributable to bacteriogenic sulfate reduction are generally absent. In particular, the ^{3 4} spread observed in the Isua banded iron formation (3.7×10⁹ yr) is extremely narrow and coincides completely with the respective spreads yielded by contemporaneous rocks of assumed mantle derivation. Incipient minor differentiation of the isotope patterns notably of Archaean sulfates may be accounted for by photosynthetic sulfur bacteria rather than by sulfate reducers. (2) Isotopic evidence of dissimilatory sulfate reduction is first observed in the upper Archaean of the Aldan Shield, Siberia (3.0×10⁹ yr) and in the Michipicoten and Woman River banded iron formations of Canada (2.75×10⁹ yr). This narrows down the possible time of appearance of sulfate respirers to the interval 2.8–3.1×10⁹ yr. (3) Various lines of evidence indicate that photosynthesis is older than sulfate respiration, the SO ₄ ^2– utilized by the first sulfate reducers deriving most probably from oxidation of reduced sulfur compounds by photosynthetic sulfur bacteria. Sulfate respiration must, in turn, have antedated oxygen respiration as O₂-respiring multicellular eucaryotes appear late in the Precambrian. (4) With the bulk of sulfate in the Archaean oceans probably produced by photosynthetic sulfur bacteria, the accumulation of SO ₄ ^2– in the ancient seas must have preceded the buildup of appreciable steady state levels of free oxygen. Hence, the occurrence of sulfate evaporites in Archaean sediments does not necessarily provide testimony of oxidation weathering on the ancient continents and, consequently, of the existence of an atmospheric oxygen reservoir.Paper presented at the Fourth College Park Colloquium on Chemical Evolution, Limits of Life, October 18–20, 1978.     

Mathematical simulation of the interactions among cyanobacteria, purple sulfur bacteria and chemotrophic sulfur bacteria in microbial mat communities

Abstract: A deterministic one-dimensional reaction diffusion model was constructed to simulate benthic stratification patterns and population dynamics of cyanobacteria, purple and colorless sulfur bacteria as found in marine microbial mats. The model involves the major biogeochemical processes of the sulfur cycle and includes growth metabolism and their kinetic parameters as described from laboratory experimentation. Hence, the metabolic production and consumption processes are coupled to population growth. The model is used to calculate benthic oxygen, sulfide and light profiles and to infer spatial relationships and interactions among the different populations. Furthermore, the model is used to explore the effect of different abiotic and biotic environmental parameters on the community structure. A strikingly clear pattern emerged of the interaction between purple and colorless sulfur bacteria: either colorless sulfur bacteria dominate or a coexistence is found of colorless and purple sulfur bacteria. The model predicts that purple sulfur bacteria only proliferate when the studied environmental parameters surpass well-defined threshold levels. However, once the appropriate conditions do occur, the purple sulfur bacteria are extremely successful as their biomass outweighs that of colorless sulfur bacteria by a factor of up to 17. The typical stratification pattern predicted closely resembles the often described bilayer communities which comprise a layer of purple sulfur bacteria below a cyanobacterial top-layer; colorless sulfur bacteria are predicted to sandwich in between both layers. The profiles of oxygen and sulfide shift on a diel basis similarly as observed in real systems.     

Acidobacterium capsulatum gen. nov., sp. nov.: An acidophilic chemoorganotrophic bacterium containing menaquinone from acidic mineral environment

Acidobacterium is proposed as a new genus for the acidophilic, chemoorganotrophic bacteria containing menaquinone isolated from acidic mineral environments.Acidobacterium capsulatum is proposed for the singleAcidobacterium species which consists of eight strains (Biogroup 5). The members of this species are gram-negative, aerobic, mesophilic, non-spore-forming, capsulated, saccharolytic, and rod-shaped bacteria. They are motile by peritrichous flagella. They can grow between pH 3.0 and 6.0, but not at pH 6.5. They give positive results in tests for esculin hydrolysis, catalase, and -galactosidase. Oxidase and urease are negative. They can use glucose, cellobiose, starch, maltose, or -gentiobiose as a sole carbon source, but cannot use elemental sulfur and ferrous iron as an energy source. The DNA base composition is 59.7–60.8 guanine plus cytosine (G+C) mol%. The major isoprenoid quinone is menaquinone with eight isoprene units (MK-8). The major fatty acid is 13-methyltetradecanoic acid. DNA relatedness between this species and the species ofAcidiphilium, Acidomonas, andDeinobacter was 18 to 2%. From phenotypic and chemotaxonomic characters, these member do not belong to any known taxa of gram-negative bacteria. A culture of the type strain (strain 161) has been deposited in the Japan Collection of Microorganisms as JCM 7670.     

Thiobacillus prosperus sp. nov., represents a new group of halotolerant metal-mobilizing bacteria isolated from a marine geothermal field

From the shallow geothermally heated seafloor at the beach of Porto di Levante (Vulcano, Italy) 8 strains of long, tiny rods were isolated, which represent the first marine metal-mobilizing bacteria. Cells are Gram negative. They grow in a temperature range between 23 and 41°C with an optimum around 37°C at a salt concentration of up to 6.0% NaCl. The isolates are obligately chemolithotrophic, acidophilic aerobes which use sulfidic ores, elemental sulfur or ferrous iron as energy sources and procedure sulfuric acid. They show an upper pH-limit of growth at around 4.5. The G+C content of their DNA is around 64 mol%. Based on the results of the DNA-DNA hybridization they represent a new group within the genus Thiobacillus. Isolate LM3 is described as the type strain of the new species Thiobacillus prosperus.     

Rhodopseudomonas sulfidophila,nov. spec., a new species of the purple nonsulfur bacteria

Summary From marine mud flats a new type of photosynthetic purple bacterium was isolated. This type is described as a new species of the Rhodospirillaceae and is named Rhodopseudomonas sulfidophila. The cells are rod-shaped, 0.6 to 0.9 wide and 0.9 to 2.0 long, and motile by means of polar flagella. Cell division occurs by binary fission. The photosynthetic membrane system is of the vesicular type. The pigments consist of bacteriochlorophyll a and of carotenoids, most probably of the spheroidene group. A wide range of organic compounds can be utilized anaerobically in the light. Growth on organic compounds aerobically in the dark is also possible. Niacin, thiamin, biotin and p-aminobenzoic acid are required as growth factors. The new species needs 2.5% (w/v) sodium chloride for optimal growth. All strains show excellent photolithotrophic growth on hydrogen, hydrogen sulfide, and thiosulfate. They show a remarkably high sulfide tolerance. Sulfide and thiosulfate are oxidized to sulfate without an intermediate accumulation of elemental sulfur. The new species seems to be one of the most versatile types of photosynthetic bacteria isolated thus far.     

The relative abundance and seawater requirements of gram-positive bacteria in near-shore tropical marine samples

The relative abundance of gram-positive bacteria in a variety of near-shore marine samples was determined using the KOH method. Gram-positive bacteria accounted for 14%, 25%, 31 %, and 12%, respectively, of the colony-forming bacteria obtained from seawater, sediments, and the surfaces of algae and invertebrates. A total of 481 gram-positive strains were isolated representing a wide range of morphological groups including regular and irregular rods, cocci, and actinomycetes. Seventy-seven percent of the strains characterized did not form spores and were aerobic, catalase-positive rods with regular to irregular cell morphologies. Eighty-two percent of the strains tested showed an obligate requirement of seawater for growth. None of the cocci tested required seawater or sodium for growth. This is the first report documenting that gram-positive bacteria can compose a large percentage of the culturable, heterotrophic bacteria associated with the surfaces of tropical marine algae. Correspondence to: P.R. Jensen     

Reduction of Soluble Iron and Reductive Dissolution of Ferric Iron-Containing Minerals by Moderately Thermophilic Iron-Oxidizing Bacteria

Five moderately thermophilic iron-oxidizing bacteria, including representative strains of the three classified species (Sulfobacillus thermosulfidooxidans, Sulfobacillus acidophilus, and Acidimicrobium ferrooxidans), were shown to be capable of reducing ferric iron to ferrous iron when they were grown under oxygen limitation conditions. Iron reduction was most readily observed when the isolates were grown as mixotrophs or heterotrophs with glycerol as an electron donor; in addition, some strains were able to couple the oxidation of tetrathionate to the reduction of ferric iron. Cycling of iron between the ferrous and ferric states was observed during batch culture growth in unshaken flasks incubated under aerobic conditions, although the patterns of oxidoreduction of iron varied in different species of iron-oxidizing moderate thermophiles and in strains of a single species (S. acidophilus). All three bacterial species were able to grow anaerobically with ferric iron as a sole electron acceptor; the growth yields correlated with the amount of ferric iron reduced when the isolates were grown in the absence of oxygen. One of the moderate thermophiles (identified as a strain of S. acidophilus) was able to bring about the reductive dissolution of three ferric iron-containing minerals (ferric hydroxide, jarosite, and goethite) when it was grown under restricted aeration conditions with glycerol as a carbon and energy source. The significance of iron reduction by moderately thermophilic iron oxidizers in both environmental and applied contexts is discussed.Moderately thermophilic acidophilic bacteria that catalyze the dissimilatory oxidation of ferrous iron are distinct both phylogenetically and in aspects of their physiology. They differ from the known acidophilic mesophilic iron oxidizers (gram-negative, nonsporulating chemolithotrophic bacteria) and the extremely thermophilic iron oxidizers (certain archaea) in several fundamental ways, including cellular morphology (they are gram-positive rods that often form endospores) and growth temperature optima, which are typically 45 to 55°C (15). In addition, the moderately thermophilic iron-oxidizing acidophiles characteristically have a highly versatile metabolism (18) and may grow as autotrophs (e.g., in media containing ferrous iron or reduced sulfur), heterotrophs (e.g., on yeast extract), mixotrophs (e.g., in media containing both ferrous iron and glucose, in which both CO₂ and glucose are used as carbon sources), or chemolithoheterotrophs (e.g., in ferrous iron-yeast extract medium, in which iron acts as the energy source and yeast extract is the carbon source). Isolates have been obtained from a range of thermal acidic environments, such as geothermal areas, self-heating mine waste spoils, and commercial mineral-processing operations (2a, 5, 14). There are currently two recognized genera of these bacteria. All but one Sulfobacillus species are iron- and sulfur-oxidizing, gram-positive, sporulating rods. Two such species have been described, Sulfobacillus thermosulfidooxidans and Sulfobacillus acidophilus, which may be distinguished by their different chromosomal DNA base compositions and by their abilities to grow autotrophically on reduced sulfur (16). The genus Acidimicrobium currently contains a single species, Acidimicrobium ferrooxidans. This organism differs from Sulfobacillus spp. by its greater capacity to fix CO₂, by its lower tolerance of ferric iron, by its apparent lack of spore formation (although it is also gram positive), and by its chromosomal DNA base composition (4). Analysis of 16S rRNA sequences has also differentiated this moderate thermophile from Sulfobacillus spp. (9).The small amount of energy associated with the oxidation of ferrous iron (−30 kJ mol⁻¹ at pH 2) can serve as the exclusive source of energy for moderately thermophilic iron-oxidizing acidophiles when they are growing autotrophically with oxygen as the terminal electron acceptor. Under limited aeration conditions, ferric iron, which is often abundant and present in a soluble form in extremely acidic environments, is a thermodynamically attractive alternative electron sink (electrode potential [E′], +780 mV). Ferric iron reduction by mesophilic chemolithotrophic and heterotrophic acidophiles has been observed previously (5, 7, 17). Some moderately thermophilic, acidophilic, heterotrophic bacteria (Alicyclobacillus-like isolates) (5a) and the extremely thermophilic archaeon Sulfolobus acidocaldarius (3) can also reduce iron. While many neutrophilic microorganisms are also able to reduce ferric iron, the ability to conserve energy to support growth by coupling organic matter oxidation exclusively to ferric iron reduction appears to be more restricted among neutrophilic bacteria (11).In this paper, we describe the dissimilatory reduction of ferric iron by representative isolates of different species of iron-oxidizing moderate thermophiles with both an organic electron donor (glycerol) and an inorganic electron donor (tetrathionate), and we also describe the reductive dissolution of ferric iron-containing minerals by a Sulfobacillus isolate.     

Morphology of bacterial leaching patterns by Thiobacillus ferrooxidans on synthetic pyrite

Thiobacillus ferrooxidans has been cultivated on synthetic pyrite (FeS₂) single crystals as the only energy source and the pyrite interface investigated with respect to characteristic morphological changes using scanning electron microscopy. Corrosion patterns of bacterial size were identified in different stages of development and correlated with bacterial activity. It appears that bacterial attack of the sulfide interface starts by secretion of organic substances around the contact area between the bacterial cell and the sulfide energy source. They might either be part of a pseudo capsule which shields the contact area or may form a sulfur absorbing and transporting organic film. Degradation of the sulfide occurs in the contact area below the bacterial cell leading to a corrosion pit which the bacterium may abandon after it has reached a depth of bacterial dimension. Electron spectroscopic (XPS) and X-ray fluorescence studies indicate a layer of organic substances covering the sulfide surface under bacterial leaching conditions, which is sufficiently thick for consideration in interfacial chemical mechanisms.     

Photoproduction of H2 from acetate by syntrophic cocultures of green sulfur bacteria and sulfur-reducing bacteria

The marine green sulfur bacterium Chlorobium vibrioforme strain 1930 produced H₂ and elemental sulfur from sulfide or thiosulfate under N limitation in the light. H₂ production depended on nitrogenase and occurred only in the absence of ammonia. Methionine sulfoximine, an inhibitor of glutamine synthetase, prevented the switch-off by ammonia. In defined syntrophic cocultures of the acetate-oxidizing, sulfur-reducing bacterium Desulfuromonas acetoxidans with green sulfur bacteria, H₂ was produced from acetate via a light-driven sulfur cycle. The sulfur-reducing bacterium could not be replaced by sulfate-reducing bacteria in these experiments. In a coculture of the marine Chlorobium vibrioforme strain 1930 and the sulfur-reducing bacterium Desulfuromonas acetoxidans strain 5071, optimum long-term H₂ production from acetate was obtained with molecular nitrogen as N source, at low light intensity (110 mol · m^-2 · s^-1), in sulfide-reduced mineral medium (2 mM Na₂S) at pH 6.8. Traces of sulfide (10 M) were sufficient to keep the sulfur cycle running. The coculture formed no poly--hydroxyalkanoates (PHA), but 20%–40% polysaccharide per cell dry mass. Per mol acetate added, the coculture formed 3.1 mol of H₂ (78% of the theoretical maximum). Only 8% of the reducing equivalents was incorporated into biomass. The maximum rate of H₂ production was 1300 ml H₂ per day and g cell dry mass.Non-standard abbrevations MOPS 2-(N-morpholino) propane sulfonic acid - MSX Methionine sulfoximine - PHA poly--hydroxyalkanoates     

Gas vacuolate bacteria obtained from marine waters of Antarctica

Several strains of heterotrophic, gas vacuolate bacteria were isolated from marine waters of Antarctica. To our knowledge these are the first marine forms of gas vacuolate bacteria to be reported. Current isolates are all Gram-negative rods. All isolates are psychrophiles that grow at temperatures between –1.5°C and 7°C, with none growing at temperatures higher than 14°C. All can grow at salt concentrations of sea water, although some can grow at 1/16th that concentration. Two of the strains produce orange colored pigments, whereas all heterotrophic gas vacuolate bacteria known to date are nonpigmented. The two pigmented filamentous strains grow well at 5.0% NaCl and have a specific sodium ion requirement. Isolates differ in the substrates they use for growth. Organic acids, amino acids, and sugars are used depending upon the strain. All isolates appear to be microaerophilic and oxidase and catalase positive. All grow well at pH 7.0. The mol% G+C of the pigmented strains is 31 and that of the non-pigmented strains, 52–57.     

Archaea S‐layer nanotube from a “black smoker” in complex with cyclo‐octasulfur (S8) rings

Elemental sulfur exists primarily as an ring and serves as terminal electron acceptor for a variety of sulfur‐fermenting bacteria. Hyperthermophilic archaea from black smoker vents are an exciting research tool to advance our knowledge of sulfur respiration under extreme conditions. Here, we use a hybrid method approach to demonstrate that the proteinaceous cavities of the S‐layer nanotube of the hyperthermophilic archaeon Staphylothermus marinus act as a storage reservoir for cyclo‐octasulfur . Fully atomistic molecular dynamics (MD) simulations were performed and the method of multiconfigurational thermodynamic integration was employed to compute the absolute free energy for transferring a ring of elemental sulfur from an aqueous bath into the largest hydrophobic cavity of a fragment of archaeal tetrabrachion. Comparisons with earlier MD studies of the free energy of hydration as a function of water occupancy in the same cavity of archaeal tetrabrachion show that the sulfur ring is energetically favored over water.     

Assimilatory sulfur metabolism in marine microorganisms: Sulfur metabolism,growth, and protein synthesis of Pseudomonas halodurans and Alteromonas luteo-violaceus during sulfate limitation

Sulfate concentration in the growth medium exerted a strong influence on the sulfur content of protein in two marine bacteria, Pseudomonas halodurans and Alteromonasluteo-violaceus, but the distribution of sulfur in major biochemical fractions was not affected. 90% of the total cellular sulfur was contained in low molecular weight organic compounds and protein; inorganic sulfate was not an important component. The sulfur content of isolated protein and total cellular sulfur increased in proportion to the external sulfate concentration for both bacteria, reaching a maximum at about 100–250 M. The growth rate of P. halodurans only was dependent on the sulfate concentration.Sulfur starvation of cells labeled to equilibrium with ³⁵S-sulfate resulted in a rapid decrease in low molecular weight organic S with a concommitant increase in alcohol soluble (P. halodurans) or residue protein (A. luteo-violaceus). Although cell division was prevented, total protein increased in both bacteria, resulting in synthesis of sulfur-deficient protein. This effect was most pronounced in P. halodurans.Addition of ³⁵S-sulfate to sulfur-starved A. luteo-violaceus further demonstrated that sulfur metabolism was restricted primarily to the synthesis and utilization of sulfurcontaining protein precursors. The low molecular weight organic S pool was replenished rapidly, and the pool size per cell reached twice the normal value before cell division resumed. Incorporation into protein was very rapid.Abbreviations L.M.W. low molecular weight - TCA trichloroacetic acid     

Macromolecular synthesis and cell division during morphogenesis of Arthrobacter crystallopoietes

The sphere-rod-sphere morphology cycle of Arthrobacter crystallopoietes was accompanied by changes in the rate of growth and the rates of DNA, RNA and protein synthesis. The patterns of macromolecule synthesis resembled those found in other bacteria during a step-up followed by a step-down in growth rate. During the step-up in growth spherical cells grew into rods and macromolecules were synthesized in the absence of cell division. During stepdown, successive rounds of septation produced progressively smaller cells which did not separate and remained in chains. The morphology of the cells was dependent on the growth rate and could be altered by changing the dilution rate in a malate-limited chemostat. Gradual transitions in morphology and gradual increases in macromolecule content of the cells occurred as the growth rate was increased in the chemostat. Sphere to rod morphogenesis occurred when DNA synthesis was inhibited by treatment with mitomycin C or by thymine starvation. The DNA-deficient rods did not divide and eventually lysed. DNA, RNA and protein synthesis were continuously required for the reductive division of rods to spheres.Abbreviations MS mineral salts - GS mineral salts plus glucose - CA casamino acids - GSCA mineral salts plus glucose plus casamino acids - cAMP cyclic adenosine-3,5-monophosphate - RNA ribonucleic acid - DNA deoxyribonucleic acid     

Na+-dependent accumulation of sulfate and thiosulfate in marine sulfate-reducing bacteria

Uptake of ³⁵S-labelled sulfate and thiosulfate was studied in twenty sulfate-reducing bacteria. Micromolar additions of these substrates were highly accumulated by washed cells of freshwater and marine strains. In marine strains accumulation required Na⁺. Generally, the uptake capacity was increased after sulfate limitation during growth. With two marine species, Desulfovibrio salexigens and Desulfobacterium autotrophicum, the effects of various ionophores and inhibitors affecting the transmembrane pH or Na⁺ gradient or the membrane potential were studied. In both strains transport was reversible. There was no discrimination between sulfate and thiosulfate. With increasing additions the amount taken up increased, while the accumulation factor (C_in/C_out) decreased. Uptake was not directly correlated with the ATP level inside the cells. From these results and the action patterns of the inhibitors tested it is concluded that marine sulfate-reducing bacteria accumulate sulfate and thiosulfate electrogenically in symport with Na⁺ ions, while in freshwater strains protons are symported. The high-accumulating systems are induced only at low sulfate concentration, while low-accumulating systems are active at sulfate-sufficient conditions.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - DCCD dicyclohexylcarbodiimide - ETH 157 N, N-dibenzyl-N,N-diphenyl-1,2-diphenylendioxydiacetamide - TCS 3,3,4,5-tetrachlorosalicylanilide     

Sulfur metabolism in bacteria associated with cheese

Metabolism of sulfur in bacteria associated with cheese has long been a topic of interest. Volatile sulfur compounds, specifically methanethiol, are correlated to desirable flavor in Cheddar cheese, but their definitive role remains elusive. Only recently have enzymes been found that produce this compound in bacteria associated with cheese making. Cystathionine - and -lyase are found in lactic acid bacteria and are capable of producing methanethiol from methionine. Their primary function is in the metabolism of cysteine. Methionine -lyase produces methanethiol from methionine at a higher efficiency than the cystathionine enzymes. This enzyme is found in brevibacteria, bacilli, and pseudomonads. Addition of brevibacteria containing this enzyme improves Cheddar cheese flavor. Despite recent progress in sulfur metabolism more information is needed before cheese flavor associated with sulfur can be predicted or controlled.     

Comparison of membrane ATPases from extreme halophiles isolated from ancient salt deposits

Halophilic microorganisms were isolated from Triassic and Permian salt deposits. Two were rods and grew as red colonies; another was a coccus and produced pink colonies. The rods lysed in solutions that lacked added sodium chloride. Growth of all isolates was inhibited by aphidicolin and their bulk proteins were acidic as judged from isoelectric focusing. Therefore, these organisms were tentatively identified as extreme halophiles. Whole cell proteins patterns of the isolates following gel electrophoresis were distinct and differed from those of representative type strains of halophilic bacteria. The membrane ATPases from the rods were similar to the enzyme fromHalobacterium saccharovorum with respect to subunit composition, enzymatic properties and immunological cross-reaction, but differed slightly in amino acid composition. If the age of the microbial isolated is similar to that of the salt deposits, they can be considered repositories of molecular information of great evolutionary interest.Presented at the Session Water in the Solar System and Its Role in Exobiology during the 26th General Assembly of the European Geophysical Society, 22–26 April 1991 in Wiesbaden, Germany.