Facultative Autotroph Research Articles

Nitrate-dependent [Fe(II)EDTA] 2− oxidation by Paracoccus ferrooxidans sp. nov., isolated from a denitrifying bioreactor

Enrichments with [Fe(II)EDTA] 2− as electron donor and nitrate or nitrite as electron acceptor were established using an inoculum from a bioreactor performing denitrification. A nitrate-reducing, [Fe(II)EDTA] 2− oxidizing strain was isolated and named strain BDN-1. The G+C content of strain BDN-1 was 67%, and the organism was closely affiliated to Paracoccus denitrificans, P. pantotrophus and P. versutus by 16S rRNA sequence comparison. Results from DNA–DNA hybridization, rep-PCR, and whole cell protein analysis gave congruent results confirming the genotypic and phenotypic differences between strain BDN-1 and the other species of Paracoccus. From these results, we considered strain BDN-1 as a novel species for which we propose the name Paracoccus ferrooxidans. Apart from [Fe(II)EDTA] 2−, BDN-1 could also use thiosulfate and thiocyanate as inorganic electron donors. Nitrate, nitrite, N 2O, [Fe(II)EDTA·NO] 2− and oxygen could be used by strain BDN-1 as electron acceptors. Repeated transfer on a culture medium with bicarbonate as the sole carbon source confirmed that strain BDN-1 was a facultative autotroph. [Fe(II)EDTA] 2− oxidation dependent denitrification was also performed by other Paracoccus species, that were closely affiliated to P. ferrooxidans.

Genetics and control of CO 2 assimilation in the chemoautotroph Ralstonia eutropha

The nutritional versatility of facultative autotrophs requires efficient overall control of their metabolism. Most of these organisms are Proteobacteria that assimilate CO(2) via the highly energy-demanding Calvin-Benson-Bassham reductive pentose-phosphate cycle. The enzymes of the cycle are encoded by cbb genes organized in cbb operons differing in size and composition, although conserved features are apparent. Transcription of the operons, which may form regulons, is strictly controlled, being induced during autotrophic but repressed to varying extents during heterotrophic growth of the bacteria. The chemoautotroph Ralstonia eutropha is one of the organisms studied extensively for the mechanisms involved in the expression of cbb gene systems. CbbR is a LysR-type transcriptional regulator and the key activator protein of cbb operons. The cbbR gene is typically located adjacent and in divergent orientation to its cognate operon. The activating function of CbbR seems to be modulated by metabolites signaling the nutritional state of the cell to the cbb system. Phosphoenolpyruvate is such a signal metabolite acting as a negative effector of R. eutropha CbbR, whereas NADPH has been proposed to be a coactivator of the protein in two other chemoautotrophs, Xanthobacter flavus and Hydrogenophilus thermoluteolus. There is evidence for the participation of additional regulators in cbb control. In the photoautotrophs Rhodobacter capsulatus and Rhodobacter sphaeroides, response regulator RegA of the global two-component signal transduction system RegBA serves this function. It is conceivable that specific variants of cbb control systems have evolved to ensure their optimal integration into regulatory networks operating in the diverse autotrophs characterized by different metabolic capabilities.

Dense Community of Hyperthermophilic Sulfur-Dependent Heterotrophs in a Geothermally Heated Shallow Submarine Biotope near Kodakara-Jima Island, Kagoshima, Japan

Microbial communities in marine hydrothermal sediments (0 to 30 cm deep) in an inlet of Kodakara-Jima Island, Kagoshima, Japan, were studied with reference to environmental factors, especially the presence of amino acids. The study area was shallow, and the sea floor was covered with sand through which hot volcanic gas bubbled and geothermally heated water seeped out. The total bacterial density increased with depth in the sediments in parallel with a rise in the ambient temperature (80(deg)C at the surface and 104(deg)C at a depth of 30 cm in the sediments). As estimated by most-probable-number studies, hyperthermophilic sulfur-dependent heterotrophs growing at 90(deg)C dominated the microbial community (3 x 10(sup7) cells (middot) g of sediment(sup-1) at a depth of 30 cm in the sediments), followed in abundance by hyperthermophilic sulfur-dependent facultative autotrophs (3.3 x 10(sup2) cells (middot) g of sediment(sup-1)). The cooler sandy or rocky floor surrounding the hot spots was covered with white bacterial mats which consisted of large Beggiatoa-like filaments. Both the total organic carbon content, most of which was particulate (75% in the surface sediments), and the amino acid concentration in void seawater in the sediments decreased with depth. Amino acids, both hydrolyzable and free, constituted approximately 23% of the dissolved organic carbon in the surface sediments. These results indicate that a lower amino acid concentration is probably due to consumption by dense populations of hyperthermophilic sulfur-dependent heterotrophs, which require amino acids for their growth and thus create a gradient of amino acid concentration in the sediments. The role of primary producers, which supply essential amino acids to sustain this microbial community, is also discussed.

Structural and immunological studies on the soluble formate dehydrogenase from Alcaligenes eutrophus.

During growth with formate as the sole energy source the autotrophic bacterium Alcaligenes eutrophus synthesizes a cytoplasmic formate dehydrogenase. The enzyme is a molybdo-iron-sulfur-flavo protein and the major NADH-producing system under these growth conditions, although it was estimated to constitute only 0.65% of the soluble cell protein. An electron microscopic analysis of the purified enzyme revealed that the particle is made up of four nonidentical submasses, corroborating previous structural data. The NH2-terminal amino acid sequences of the enzyme subunits exhibited significant similarities to those of only one other heteromeric formate dehydrogenase, the enzyme from the methane-utilizing bacterium Methylosinus trichosporium. Metal analyses yielded 21.5 g-atom iron, 2.18 g-atom nickel, 0.76 g-atom molybdenum, and 0.59 g-atom zinc per mol of enzyme. Initial electron paramagnetic resonance spectroscopic studies showed at least three distinct signals which appeared upon reduction of the enzyme with NADH or formate. The corresponding spin systems could be attributed to iron-sulfur centers of the enzyme. Comparative immunostaining and activity-staining experiments using cell extracts from various bacteria established immunological similarities between the soluble formate dehydrogenase of A. eutrophus and the soluble enzymes from all tested facultative autotrophs as well as from M. trichosporium.

Transfer and expression of degradative and antibiotic resistance plasmids in acidophilic bacteria

The genetic accessibility of selected acidophilic bacteria was investigated to evaluate their applicability to degrading pollutants in acidic environments. The IncP1 antibiotic resistance plasmids RP4 and pVK101 and the phenol degradation-encoding plasmid pPGH11 were transferred from neutrophilic bacteria into the extreme acidophilic eubacterium Acidiphilium cryptum at frequencies of 1.8 x 10(-2) to 9.8 x 10(-4) transconjugants per recipient cell. The IncQ antibiotic resistance plasmid pSUP106 was mobilizable to A. cryptum by triparental matings at a frequency of 10(-5) transconjugants per recipient cell. In the transconjugants, antibiotic resistances and the ability to degrade phenol were expressed. A. cryptum AC6 (pPGH11) grew with 2.5 mM phenol at a doubling time of 12 h and a yield of 0.52 g (dry cell weight) per g of phenol. A. cryptum harbored five native plasmids of 255 to 6.3 kb in size. Plasmids RP4 and pVK101 were transferred from Escherichia coli into Acidobacterium capsulatum at frequencies of 10(-3) and 2.3 x 10(-4) and to the facultative autotroph Thiobacillus acidophilus at frequencies of 1.1 x 10(-5) and 2.9 x 10(-6) transconjugants per recipient cell, respectively. Plasmid pPGH11 could not be transferred into the latter strains. T. acidophilus wild type contained six so far cryptic plasmids of 220 to 5 kb.

The genetic organization of the mau gene cluster of the facultative autotroph Paracoccus denitrificans

The mau gene cluster from Paracoccus denitrificans was cloned. The regions of a cloned fragment carrying genes for the small and the large subunit of the methylamine dehydrogenase were identified and sequenced. Open reading frames for the MADH small subunit gene and the MADH large subunit gene were identified. Three other open reading frames coding polypeptides with unknown function were found in the sequence. The small subunit gene sequence data reveal that the MADH small subunit polypeptide from P. denitrificans has an unusual leader sequence and contains the tryptophan tryptophyl quinone cofactor. The MADH small subunit genes and the parts of the open reading frames found upstream of them in the genome of M. extorquens AM1 and P. denitrificans have considerable similarity. The sequence data have been used for refinement of the X-ray crystallographic structure of the MADH from P. denitrificans, and key conserved residues have been identified.

Metallosphaera sedula gen, and sp. nov. Represents a New Genus of Aerobic, Metal-Mobilizing, Thermoacidophilic Archaebacteria

From a solfataric field in Italy three isolates of spherical thermoacidophilic metal-mobilizing archaebacteria were obtained. They are facultative autotrophs. From sulfidic ores they extract metal ions with very high efficiency. They are also vigorous S∘-oxidizers. Alternatively, they are able to use heterogeneous organic material such as yeast extract. The isolates grow within a temperature range from 50 to 80°C. The GC-content of their DNA is 45 mol %. No significant DNA homology is detectable between the isolates and the type strains of the members of the genera Acidianus and Sulfolobus . The DNA-dependent RNA polymerase of isolate TH2 shows incomplete serological cross-reaction with antibodies against the enzyme of Sulfolobus acidocaldarius . On the basis of the distinct physiological and molecular properties we describe the new strains as members of the new genus Metallosphaera . Type species and type strain is Metallosphaera sedula (TH2, DSM5348).

Isolation and physiological characterisation of Thiobacillus thyasiris sp. nov., a novel marine facultative autotroph and the putative symbiont of Thyasira flexuosa

A novel facultatively chemolithoautotropic Thiobacillus, isolated from the gill tissue of the marine bivalve Thyasira flexuosa, is described. It is believed to be the symbiont from this animal, providing the animal with carbon fixed by the Calvin cycle. The organism grows lithoautotrophically on thiosulphate, tetrathionate and elemental sulphur, which are oxidised to sulphate. It oxidizes sulphide, thiosulphate, trithionate, tetrathionate and hexathionate, but not thiocyanate. Kinetic constants for these substrates are presented. In autotrophic batch culture it produces yields that are among the lowest reported for thiosulphate or tetrathionate as energy substrates (1.25 and 2.5 g cell-carbon per mol substrate, respectively). Autotrophic cultures contain ribulose bisphosphate carboxylase and excreted 20% of their fixed carbon into the medium during growth. Mixotrophic growth on acetate and thiosulphate resulted in partial repression of the carboxylase. The organism is slightly halophilic and markedly halotolerant, showing optimum growth at about pH 7.5 and maximum growth rate at 37° C. It contains ubiquinone Q-10 and its DNA contains 52 mol % G+C. These characteristics distinguish it from any other Thiobacillus or Thiomicrospira species previously described. The organism is formally described and named as Thiobacillus thyasiris.

Simultaneous sulfide and acetate oxidation in a denitrifying fluidized bed reactor—I. Start-up and reactor performance

Part of the post-treatment of an anaerobic wastewater treatment plant described in a recent patent (EPA 0051.888) is a denitrifying fluidized bed reactor in which sulfide and lower fatty acids are removed. In this reactor the sand particles covered with biomass were kept in a fluidized state by the upflowing wastewater. A more detailed insight into the performance and resilience of the reactor under different operating conditions was required to assess the applicability of this type of reactor for a variety of wastewaters. To this goal a laboratory model of this denitrifying, fluidized bed reactor was built. The main objective was to show that sulfide and acetate could be removed from a synthetic wastewater using nitrate as the electron acceptor, and that the laboratory reactor could be used for further study of the mechanisms and performance of the pilot plant reactor. As an initial step, the start-up and overall performance were studied. Sulfide (2–3 kg S m −3d −1), acetate (4–6 kg C m −3 d −1) and nitrate (5 kg N m −3 d −1) were effectively removed. Only after the removal of oxygen from the influent with a pre-treatment column did the occurrence of elemental sulfur as an intermediate of the sulfide oxidation no longer lead to the build up of high sulfur concentrations in the reactor (only 0.3% of the sulfide added was converted to sulfur as long as nitrate was supplied in excess). Bacterial colonization of the sand particles and biomass growth was rapid in the first 4 days despite the high flow (dilution) rates applied. Biomass production was calculated from redox/electron balances in addition to being measured. From the redox balances, it was concluded that biomass production increased with increasing loading rates. Plotting data from the individual days suggested that an average loading rate of 20–40 mequiv electrons 1 − reactor h − would result in roughly no net growth. The redox balances show that net CO 2 fixation may take place when sulfide plus sulfur turnover rates are high relative to the acetate turnover rate. The ratios of sulfide plus sulfur to acetate turnover rates above which CO 2 fixation started agreed well with data from chemostat studies of the facultative autotroph, Thiobacillus versutus. Substrate removal rates and intermediates found in the laboratory system were representative for the behaviour of the pilot plant reactor as described in the above mentioned patent. The results indicate that further studies on the resilience of the reactor to changes in the influent composition and in the operating conditions should be performed. The system is also sufficiently well defined and controllable to allow a study on the physiological behaviour and the microbial selection processes that occur in this system.

CO Metabolism by a Thermophilic Actinomycete, Streptomyces Strain G26

SUMMARY: Streptomyces G26, isolated from compost, is a moderately thermophilic actinomycete and a facultative autotroph capable of aerobic growth on CO or on CO2/H2. Soluble extracts of CO-grown mycelium contained enzymes of the Calvin cycle together with a CO oxidoreductase; the latter was present in heterotrophically grown mycelium at only 1% of the level found in CO-grown cultures. The CO oxidoreductase of Streptomyces G26 was unique in its ability to rapidly reduce low-potential acceptors such as the viologen dyes in addition to acceptors with E o’ values between + 11 mV and +429 mV. Although complete purification of the enzyme proved difficult, evidence is presented that extracts contained only one CO oxidoreductase. The partially purified enzyme had a very low apparent K m for CO, comparable with the CO oxidoreductase from Pseudomonas thermocarboxydovorans. Highest activities were observed at pH 7.2 and 60–65 °C. The enzyme was inactivated by methanol, suggesting that it is a molybdenum hydroxylase like the CO oxidoreductases from other aerobic bacteria.

Lithoautotrophic growth of sulfate-reducing bacteria, and description of Desulfobacterium autotrophicum gen. nov., sp. nov.

The capacity of mesophilic sulfate-reducing bacteria to grow lithoautotrophically with H2, sulfate and CO2 was investigated with enrichment cultures and isolated species. (a) Enrichments in liquid mineral media with H2, sulfate and CO2 consistently yielded mixed cultures of nonautotrophic, acetate-requiring Desulfovibrio species and autotrophic, acetate-producing Acetobacterium species (cell ratio approx. 20:1). (b) By direct dilution of mud samples in agar, various non-sporing sulfate reducers were isolated in pure cultures that did grow autotrophically. Two oval cell types (strains HRM2, HRM4) and one curved cell type (strain HRM6) from marine sediment were studied in detail. The strains grew in mineral medium supplemented only with vitamins (biotin, p-aminobenzoate, nicotinate). Carbon autotrophy was evident (i) from comparative growth experiments with non-autotrophic, acetate-requiring species, (ii) from high cell densities ruling out a cell synthesis from organic impurities in the mineral media, and (iii) by demonstrating that 96–99% of the cell carbon was derived from 14C-labelled CO2. Autotrophic growth occurred with a doubling time of 16–20 h at 24–28°C. Formate, fatty acids up to palmitate, ethanol, lactate, succinate, fumarate, malate and other organic acids were also used and completely oxidized. The three strains possessed cytochromes of the b-and c-type, but no desulfoviridin. Strain HRM2 is described as a new species of a new genus, Desulfobacterium autotrophicum. (c) The capacity for autotrophic growth was also tested with sulfate-reducing bacteria that originally had been isolated on organic substrates. The incompletely oxidizing, non-sporing types such as Desulfovibrio and Desulfobulbus species and Desulfomonas pigra were confirmed to be obligate heterotrophs that required acetate for growth with H2 and sulfate. In contrast, several of the completely oxidizing sulfate reducers were facultative autotrophs, such as Desulfosarcina variabilis, Desulfonema limicola, Desulfococcus niacini, and the newly isolated Desulfobacterium vacuolatum and Desulfobacter hydrogenophilus. The only incompletely oxidizing sulfate reducer that could grow autotrophically was the sporing Desulfotomaculum orientis, which obtained 96% of its cell carbon from 14C-labelled CO2. Desulfovibrio baarsii and Desulfococcus multivorans may also be regarded as types of facultative autotrophs; they could not oxidize H2, but grew on sulfate with formate as the only organic substrate.

Carbon assimilation by the autotrophic thermophilic archaebacterium Thermoproteus neutrophilus

Growth of Thermoproteus neutrophilus at 85°C was studied using an improved mineral medium with CO2, CO2 plus acetate, CO2 plus propionate, or CO2 plus succinate as carbon sources; sulfur reduction with H2 to H2S was the sole source of energy. None of the carbon compounds added was oxidized to CO2. The organism grew autotrophically with a generation time of 9–14 h, up to a cell density of 0.5 g dry weight per liter (2×109 cells/ml). Propionate did not stimulate, succinate slightly stimulated the growth rate. Acetate, even at low concentrations (0.5 mM), stimulated the growth rate, the generation time being shortened to 3–4 h. Acetate provided 70% of the cell carbon, which shows that Thermoproteus neutrophilus is a facultative autotroph. The path of these carbon precursors into cell compounds was studied by 14C long-term labelling and investigation of enzyme activities. Propionate could not be used as a major carbon source and was incorporated only into isoleucine, probably via the citramalate pathway. Acetate was a preferred carbon source which suppressed autotrophic CO2 fixation: acetate grown cells exhibited an incomplete citric acid cycle in which 2-oxoglutarate dehydrogenase was present, but fumarate reductase was “repressed”. The succinate incorporation pattern and enzyme pattern indicated that autotrophic CO2 fixation proceeded via a yet to be defined reductive citric acid cycle.

Hydrogenobacter thermophilus gen. nov., sp. nov., an Extremely Thermophilic, Aerobic, Hydrogen-Oxidizing Bacterium

Six strains of strictly thermophilic, obligately chemolithotrophic, hydrogen-oxidizing bacteria were isolated from hot springs located in Izu and Kyushu, Japan. The bacterial strains which we tested were gram negative, nonmotile, nonsporeforming, long, straight, and rod shaped. The cell size was 0.3 to 0.5 by 2.0 to 3.0 μm. The deoxyribonucleic acid guanine-plus-cytosine contents of the six strains were between 43.5 and 43.9 mol%. The optimal temperature for autotrophic growth on H2-O2-CO2 was between 70 and 75°C. None of the strains grew at 37 or 80°C. The neutral pH range was suitable for growth. No strain showed heterotrophic growth at the expense of 48 organic compounds or on complex media, in contrast to all other known aerobic hydrogen-oxidizing bacteria which are facultative autotrophs. The major cellular fatty acids were a straight-chain saturated C18:0 acid and a straight-chain unsaturated C20:1 acid with one double bond. C16:0 and C18:1 fatty acids and a C21:0 cyclopropane acid were minor components. Cytochromes b and c were found in all of the strains. The polyacrylamide gel electrophoretic patterns of the total soluble proteins of all of the strains were essentially the same. The name Hydrogenobacter thermophilus gen. nov., sp. nov., is proposed for the six new isolates, and type strain TK-6 has been deposited with the culture collection of the Institute of Applied Microbiology, University of Tokyo, as strain IAM 12695.

Thiosphaera pantotropha gen. nov. sp. nov., a Facultatively Anaerobic, Facultatively Autotrophic Sulphur Bacterium

During studies on a desulphurizing, denitrifying effluent-treatment system, an organism which is able to grow aerobically and anaerobically on reduced sulphur compounds and hydrogen, while fixing carbon dioxide, was isolated. The new isolate is also capable of mixotrophic and heterotrophic growth on a wide range of substrates, and is therefore a facultatively aerobic, facultative autotroph. Comparisons with two similar species, Thiobacillus A2 and Paracoccus denitrificans, showed that the new isolate is significantly different from the other two, and merits separate classification. In view of its ability to oxidize reduced sulphur compounds, and because it is a chain-forming coccus rather than a rod, the new isolate has been given the generic name of Thiosphaera, and the species name pantotropha in recognition of its wide range of possible substrates.

Genomic and Physiological Comparisons Between Heterotrophic Thiobacilli and Acidiphilium cryptum, Thiobacillus versutus sp. nov., and Thiobacillus acidophilus nom. rev.

Acidiphilium cryptum grows in yeast extract media with or without elemental sulfur. The growth rate and the cell yield are not changed by the presence of sulfur, but the pH of the medium drops slightly when sulfur is present, presumably because of gratuitous sulfur oxidation. No growth occurs with sulfur alone. A. cryptum is an obligate chemoorganotroph. Thiobacillus acidophilus grows equally well with either elemental sulfur or glucose as a sole energy source; this organism is a facultative autotroph. Since the name T. acidophilus does not appear on the Approved Lists of Bacterial Names, it is revived here, and strain ATCC 27807 is designated the type strain. Thiobacillus perometabolis is considered a subspecies of Thiobacillus intermedius on the basis of close phenotypic similarity and deoxyribonucleic acid homology. Thiobacillus sp. strain A2 is a distinctive mixotroph that shows little deoxyribonucleic acid homology with other species of Thiobacillus. This organism is named Thiobacillus versutus, and strain ATCC 25364 is designated the type strain.

The Methanol: Cytochrome c Oxidoreductase Activity of Methylotrophs

Both the soluble cytochromes c of the obligate methylotroph Methylophilus methylotrophus were rapidly autoreducible at high pH. The intramolecular autoreduction mechanism was also involved in the reduction of the cytochrome c L by methanol dehydrogenase which occurred in the absence of methanol. Pure soluble methanol dehydrogenase was shown to be able to catalyse the methanol-dependent reduction of pure cytochrome c from M. methylotrophus and from the facultative methylotroph Pseudomonas AM1 by coupling oxidation of the bacterial cytochrome to the reduction of a large excess of mammalian cytochrome c. Only one of the two cytochromes c (cytochrome c L of each organism) could react with methanol dehydrogenase to give methanol:cytochrome c oxidoreductase activity. This activity, using proteins from M. methylotrophus, was independent of pH between pH 7·0 and 9·0 and ammonia was not required. By contrast, the pH optimum for the system from Pseudomonas AM1 was 9.0 and activity was stimulated about fourfold by NH4Cl. The product of methanol oxidation was formaldehyde, which was also a substrate for the oxidoreductase system. During formaldehyde oxidation two molecules of cytochrome c were reduced for every molecule of formaldehyde oxidized. In a survey of methanol dehydrogenases and cytochromes c from Pseudomonas AM1, M. methylotrophus and the facultative autotroph Paracoccus denitrificans, it was shown that, of the two soluble cytochromes c found in each methylotroph only one was able to react with methanol dehydrogenase. The cytochrome c L from M. methylotrophus and the cytochrome c(2) of Pa. denitrificans were specific, only reacting with methanol dehydrogenase from the same organism, whereas the cytochrome c L of Pseudomonas AM1 reacted with all three methanol dehydrogenases tested.

Floridosides in unicellular hot spring algae

Cyanidium caldarium strains RK-1, KS-1 and 001 are probably obligate autotrophs, while Chroococcidiopsis sp. strains M-8 and 002 (formerly named Cyanidium caldarium) are facultative autotrophs. The Cyanidium strains contain floridoside (2- O-glycerol-α- d-galactopyranoside) and a small amount of iso-floridoside (1- O-glycerol-α- d-galactopyranoside), both of which are known to be distributed in Rhodophyta. The Chroococcidiopsis strains also contain floridoside, but no iso-floridoside, under various culture conditions. These results indicate that Cyanidium is clearly distinguishable from Chroococcidiopsis in iso-floridoside content and nutritional properties, and suggest that all strains tested may be closely related to Rhodophyta.

Thiobacillus acidophilus: a study of its presence in Thiobacillus ferrooxidans cultures

A study has been undertaken to account for the presence of Thiobacillus acidophilus in iron-grown cultures of Thiobacillus ferrooxidans. Attempts to adapt T. acidophilus to ferrous iron were not successful but the facultative autotroph grew to a limited extent in the spent medium of T. ferrooxidans and was able to grow oligotrophically. Possible oligotrophic substrates were methanol, ethanol, and sulphide. Thiobacillus ferrooxidans may benefit from the presence of T. acidophilus because in mixed cultures some inhibiting organic compounds such as alcohols, organic acids, and amino acids were utilized by T. acidophilus. The number of T. acidophilus cells in heterogeneous cultures with T. ferrooxidans was of the same order of magnitude as the number of T. ferrooxidans cells as revealed by fluorescent-labelled antibodies.

Competition in the Chemostat between an Obligately and a Facultatively Chemolithotrophic Thiobacillus

The outcome of competition in thiosulphate-limited chemostat culture between the obligate chemolithotroph Thiobacillus neapolitanus and the versatile facultative autotroph Thiobacillus A2 was in part a function of pH. In pure culture T. neapolitanus grew faster than Thiobacillus A2 at pH values up to pH 7·6, but in competition Thiobacillus A2 dominated at pH 7·35 and 7·6. At pH 7·1, T. neapolitanus dominated, although a significant steady state population of Thiobacillus A2 persisted, apparently growing on organic nutrients excreted by T. neapolitanus. Coexistence of both organisms occurred under all chemolithotrophic growth conditions tested with the dominant organism comprising 85 to 99% of the population, indicating that competition was not the sole interaction between the species. At pH 7·1, the inclusion of glucose in the thiosulphate medium resulted in rapid domination of the culture by Thiobacillus A2, with the virtual elimination of T. neapolitanus. It is concluded that the capacity for mixotrophy is a selective advantage to a facultative thiobacillus in competition with an obligately chemolithotrophic species.

Thiobacillus acidophilus sp. nov.; isolation and some physiological characteristics

After a brief exposition to glucose, Thiobacillus acidophilus was isolated from a culture of iron-grown T. ferrooxidans. Physicochemical analysis of its DNA showed a G+C content of 62.9-63.2%. The new isolate grows best at 25-30 degrees C and at pH 3.0. Growth is possible between pH 1.5 and 6.0. Thiobacillus acidophilus is apparently strictly aerobic. Ammonium salts are the only suitable source of nitrogen. The bacterium is a facultative autotroph. In addition to elemental sulfur, it obtains energy from organic compounds such as D-glucose, D-galactose, D-fructose, D-mannitol, D-xylose, D-ribose, D-arabinose, L-arabinose, sucrose, sodium citrate, malic acid,dl-aspartic acid, and dl-glutamic acid. Thiobacillus acidophilus possesses the key enzymes of the tricarboxylic acid (TCA) cycle including NAD-and NADP-linked isocitric dehydrogenase and alpha-ketoglutarate dehydrogenase, and the key enzymes of the hexose monophosphate pathway (glucose-6-phosphate and 6-phosphogluconate dehydrogenase, and fructose 1,6-diphosphate aldolase). NADH oxidase has been found in particulate fraction of extracts. Rhodanese and thiosulfate oxidase have also been detected.