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.     

Thiobacillus cuprinus sp. nov., a Novel Facultatively Organotrophic Metal-Mobilizing Bacterium

Five strains of mesophilic, facultatively organotrophic, ore-leaching eubacteria were isolated from solfatara fields in Iceland and a uranium mine in the Federal Republic of Germany. The new organisms are aerobic gram-negative rods. They can use sulfidic ores or elemental sulfur as sole energy source, indicating that they belong to the genus Thiobacillus. Alternatively, they grow on organic substrates such as yeast extract, peptone, and pyruvate. In contrast to the other leaching bacteria known so far, the new isolates are unable to oxidize ferrous iron. They consist of extreme and moderate acidophiles growing optimally at pH 3 and 4, respectively. The extreme acidophiles showed leaching characteristics similar to those shown by Thiobacillus ferrooxidans, while the moderate acidophiles exhibited a pronounced preference for copper leaching on some chalcopyrite ores. The G+C content of the DNA is between 66 and 69 mol%, depending on the isolate. In DNA-DNA hybridization experiments, the new strains showed homologies among each other of >70%, indicating that they belong to the same species. No significant DNA homology to Thiobacillus reference strains was detectable. Therefore, the new isolates represent a new species of Thiobacillus, which we name Thiobacillus cuprinus. Isolate Hö5 is designated as the type strain (DSM 5495).     

Thiobacillus sajanensis sp. nov., a new obligately autotrophic sulfur-oxidizing bacterium isolated from Khito-Gol hydrogen-sulfide springs, Buryatia

Four strains of rod-shaped gram-negative sulfur-oxidizing bacteria were isolated from Khoito-Gol hydrogen-sulfide springs in the eastern Sayan Mountains (Buryatia). The cells of the new isolates were motile by means of a single polar flagellum. The strains were obligately chemolithoautotrophic aerobes that oxidized thiosulfate (with the production of sulfur and sulfates) and hydrogen sulfide. They grew in a pH range of 6.8–9.5, with an optimum at pH 9.3 and in a temperature range of 5–39°C, with an optimum at 28–32°C. The cells contained ubiquinone Q-8. The DNA G+C content of the new strains was 62.3–64.2 mol %. According to the results of analysis of their 16S rRNA genes, the isolates belong to the genus Thiobacillus within the subclass Betaproteobacteria. However, the similarity level of nucleotide sequences of the 16S rRNA genes was insufficient to assign the isolates to known species of this genus. The affiliation to the genus Thiobacillus was confirmed by DNA-DNA hybridization of the isolates with the type strain of the type species of the genus Thiobacillus, T. thioparus DSM 505^T (= ATCC 8158^T). Despite the phenotypic similarity, the hybridization level was as low as 21–29%. In addition, considerable differences were revealed in the structure of the genes encoding RuBPC, the key enzyme of autotrophic CO₂ assimilation, between the known Thiobacillus species and the new isolates. Based on molecular-biological features and certain phenotypic distinctions, the new isolates were assigned to a new Thiobacillus species, T. sajanensis sp. nov., with the type strain 4HG^T (= VKM B-2365^T).     

Taxonomic relationships ofThiobacillus halophilus,T. aquaesulis,and other species ofThiobacillus,as determined using 16S rDNA sequencing

Total base sequences of the 16S rRNA genes ofThiobacillus halophilus andThiobacillus aquaesulis show that these bacteria fall into the gamma- and beta-subdivisions, respectively of the Proteobacteria. The closest relative ofT. halophilus isThiobacillus hydrothermalis (with 98.7% similarity), and the closest relative ofT. aquaesulis isThiobacillus thioparus (93.2% similarity). Physiological properties and mol% G+C content of their DNA serve to confirm that these four organisms are all distinct species. It is reiterated that the species currently assigned to the genusThiobacillus are clearly so diverse that they need reclassification into several genera. The type species,T. thioparus, is unequivocally placed in the beta-subdivision of the Proteobacteria, thus requiring that the use of the genus nameThiobacillus be restricted to the chemolithoautotrophic species falling into that group.T. aquaesulis andT. thioparus may thus be regarded as true species ofThiobacillus. The relatively large number of obligately chemolithoautotrophicThiobacillus species falling in the gamma-subdivision of the Proteobacteria need further study in order to assess the case for reclassification into one or more new or different genera.     

Isolation and characterization of Thiobacillus hydrothermalis sp. nov., a mesophilic obligately chemolithotrophic bacterium isolated from a deep-sea hydrothermal vent in Fiji Basin

A novel obligately chemolithotrophic Thiobacillus species isolated from a deep-sea hydrothermal vent is described. This organism grows lithoautotrophically on thiosulphate, tetrathionate, sulphide and sulphur which are oxidized to sulphate. The isolate is slightly halophilic and markedly halotolerant, showing optimum growth at pH 7.5 and at 35°C. The G+C content of the DNA is 67.1 mol%. The 16S rRNA sequence is distinct from any other Thiobacilli sequences. Phylogenetic analysis shows the organism to be a representative of the -group of proteobacteria and a specific relative of Thiobacillus neapolitanus. The ubiquinone is ubiquinone-8. These characters distinguish the isolate from any other Thiobacillus or Thiomicrospira species previously reported and is a new species described as Thiobacillus hydrothermalis. The type strain is isolate R3, DSM7121.     

Characterization of a new metal-mobilizing Thiobacillus isolate

A new acidophilic, mineral sulphide oreoxidizing bacterium was isolated from a uranium mine near Salamanca, Spain. Cells were rod-shaped, motile and gram-negative. They were aerobes, could grow on pyrite and use sulphur or thiosulphate as sole energy source, suggesting this new isolate belongs to the genus Thiobacillus. It could grow neither with glucose nor with yeast extract as sole substrates. It could not grow on ferrous sulphate as the only energy source, although it grew in the same medium supplemented with glucose, yeast extract or thiosulphate. It was a mesophilic and extremely acidophilic Thiobacillus, with an optimal pH of 1.5 2. The G+C content of the DNA was 58%. The new isolate could grow in cultures on pyrite where electrophoretic pattern was clearly different from those of other thiobacilli, such as T. ferrooxidans.Abbreviations G+C Guanine + Cytosine     

Desulfosporomusa polytropa gen. nov., sp. nov., a novel sulfate-reducing bacterium from sediments of an oligotrophic lake

Five strains of sulfate-reducing bacteria were isolated from the highest positive dilutions of a most probable number (MPN) series supplemented with lactate and inoculated with sediments from the oligotrophic Lake Stechlin. The isolates were endospore-forming and were motile by means of laterally inserted flagella. They stained Gram-negative and contained b-type cytochromes. CO difference spectra indicated the presence of P582 as a sulfite reductase. Phylogenetic analyses of the 16S rDNA sequences revealed that the isolates were very closely affiliated with the genus Sporomusa. However, sulfate and amorphous Fe(OH)₃, but not sulfite, elemental sulfur, MnO₂, or nitrate were used as terminal electron acceptors. Homoacetogenic growth was found with H₂/CO₂ gas mixture, formate, methanol, ethanol, and methoxylated aromatic compounds. The strains grew autotrophically with H₂ plus CO₂ in the presence or absence of sulfate. Formate, butyrate, several alcohols, organic acids, carbohydrates, some amino acids, choline, and betaine were also utilized as substrates. The growth yield with lactate and sulfate as substrate was 7.0 g dry mass/mol lactate and thus two times higher than in sulfate-free fermenting cultures. All isolates were able to grow in a temperature range of 4–37°C. Physiologically and by the presence of a Gram-negative cell wall, the new isolates resemble known Desulfosporosinus species. However, phylogenetically they are affiliated with the Gram-negative genus Sporomusa belonging to the Selenomonas subgroup of the Firmicutes. Therefore, the new isolates reveal a new phylogenetic lineage of sulfate-reducing bacteria. A new genus and species, Desulfosporomusa polytropa gen. nov., sp. nov. is proposed.Dedicated to Prof. H. G. Schlegel on the occasion of his 80th birthday.     

The first evidence of anaerobic CO oxidation coupled with H<Subscript>2</Subscript> production by a hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent

From 24 samples of hydrothermal venting structures collected at the East Pacific Rise (13°N), 13 enrichments of coccoid cells were obtained which grew on CO, producing H₂ and CO₂ at 80°C. A hyperthermophilic archaeon capable of lithotrophic growth on CO coupled with equimolar production of H₂ was isolated. Based on its 16S rRNA sequence analysis, this organism was affiliated with the genus Thermococcus. Other strains of Thermococcales species (Pyrococcus furiosus, Thermococcus peptonophilus, T. profundus, T. chitonophagus, T. stetteri, T. gorgonarius, T. litoralis, and T. pacificus) were shown to be unable to grow on CO. Searches in sequence databases failed to reveal deposited sequences of genes related to CO metabolism in Thermococcales. Our work provides the first evidence of anaerobic CO oxidation coupled with H₂ production performed by an archaeon as well as the first documented case of lithotrophic growth of a Thermococcales representative.     

Taxonomic Characterization of New Alkaliphilic and Alkalitolerant Methanotrophs from Soda Lakes of the Southeastern Transbaikal Region and description of Methylomicrobium buryatense sp.nov.

Five strains of obligate methanotrophic bacteria (4G, 5G, 6G, 7G and 5B) isolated from bottom sediments of Southeastern Transbaikal soda lakes (pH 9.5–10.5) are taxonomically described. These bacteria are aerobic, Gram-negative monotrichous rods having tightly packed cup-shaped structures on the outer cell wall surface (S-layers) and Type I intracytoplasmic membranes. All the isolates possess particulate methane monooxygenase (pMMO) and one strain (5G) also contains soluble methane monooxygenase (sMMO). They assimilate methane and methanol via the ribulose monophosphate pathway (RuMP). The isolates are alkalitolerant or facultatively alkaliphilic, able to grow at pH 10.5–11.0 and optimally at pH 8.5–9.5. These organisms are obligately dependent on the presence of sodium ions in the growth medium and tolerate up to 0.9–1.4 M NaCl or 1 M NaHCO₃. Although being mesophilic, all the isolates are resistant to heating (80 °C, 20 min), freezing and drying. Their cellular fatty acids profiles primarily consist of C_16:1. The major phospholipids are phosphatidylethanolamine and phosphatidylglycerol. The main quinone is Q-8. The DNA G+C content ranges from 49.2–51.5 mol%. Comparative 16S rDNA sequencing showed that the newly isolated methanotrophs are related to membres of the Methylomicrobium genus. However, they differ from the known members of this genus by DNA-DNA relatedness. Based on pheno- and genotypic characteristics, we propose a new species of the genus Methylomicrobium - Methylomicrobium buryatense sp. nov.     

Isolation and characterization of Methanocorpusculum parvum,gen. nov., spec. nov., a new tungsten requiring,coccoid methanogen

A new mesophilic, monotrichously flagellated methane-producing coccus of 1m in diameter was isolated from an anaerobic sour whey digester, originally inoculated with sewage sludge. Growth and methane production were observed with H₂/CO₂, formate and — less effectively — with 2-propanol/CO₂. The isolate grew at temperatures between 15° C and 45° C with the optimum at around 37° C. Acetate, yeast extract and tungstate were required in the medium. Clarified rumen fluid stimulated growth.The DNA of the new methanogen has a G+C content of 48.5 mol%. Comparative 16 S rRNA oligonucleotide cataloguing allows to define the new isolate as a member of a new genus of the order Methanomicrobiales. Further evidence for this is provided by the antigenic crossreactivity with anti-S probes and by metabolic features.Because of its small size the new methanogen is named Methanocorpusculum parvum.This work was supported by a grant of the Deutsche Forschungsgemeinschaft DFG to J. W. and E. S. Immunologic studies were supported in part by grants No. DE-FGO2-84 R 13197 from the U.S. Department of Energy, and No. 261.81/82 from the North Atlantic Treaty Organization (NATO)     

Novel Aerobic Methylotrophic Isolates from the Soda Lakes of the Southern Transbaikal Region

Twenty-one bacterial associations isolated from the soda lakes of the southern Transbaikal region were found to be able to actively grow at pH 9–10 on methanol as the source of carbon and energy. Two alkalitolerant facultatively methylotrophic strains, Bur 3 and Bur 5, were obtained in pure cultures. Both strains represent gram-negative, nonmotile, bean-shaped, encapsulated cells that reproduce by binary fission. The strains are able to grow at temperatures ranging from 6 to 42°C, with an optimum growth temperature of 25–29°C (strain Bur 3) and 35–37°C (strain Bur 5) and at pH between 6.5 and 9.5, with an optimum pH value of 8.0–8.5. At pH 9.0, strain Bur 3 exhibits an increased content of phosphatidylglycerol and a decreased content of phosphatidylethanolamine. Strains Bur 3 and Bur 5 are similar in the G+C content of their DNAs (66.2 and 65.5 mol %, respectively) and in the type of the dominant ubiquinone (Q ₁₀). Unlike Bur 5, strain Bur 3 is able to grow autotrophically in an atmosphere of CO₂+ O₂+ H₂. The strains oxidize, by the respective dehydrogenases, methanol to CO₂, which is assimilated by the ribulose bisphosphate pathway. Ammonium ions are assimilated in the glutamate cycle and by the reductive amination of -ketoglutarate. The strains are highly homologous to each other (92%) and are much less homologous (at a level of 28–35%) to representatives of the genus Ancylobacter, A. aquaticusATCC 25396^Tand A. vacuolatumDSM 1277. Based on the results obtained, both strains are assigned to a new species, Ancylobacter natronumsp. nov.     

Thermotolerant poly(3-hydroxybutyrate)-degrading bacteria from hot compost and characterization of the PHB depolymerase of Schlegelella sp. KB1a

Eighteen gram-negative thermotolerant poly(3-hydroxybutyrate) (PHB)-degrading bacterial isolates (T _max60°C) were obtained from compost. Isolates produced clearing zones on opaque PHB agar, indicating the presence of extracellular PHB depolymerases. Comparison of physiological characteristics and determination of 16S rRNA gene sequences of four selected isolates revealed a close relatedness of three isolates (SA8, SA1, and KA1) to each other and to Schlegelella thermodepolymerans and Caenibacterium thermophilum. The fourth strain, isolate KB1a, showed reduced similarities to the above-mentioned isolates and species and might represent a new species of Schlegelella. Evidence is provided that S. thermodepolymerans and C. thermophilum are only one species. The PHB depolymerase gene, phaZ, of isolate KB1a was cloned and functionally expressed in Escherichia coli. Purified PHB depolymerase was most active around pH 10 and 76°C. The DNA-deduced amino acid sequence of the mature protein (49.4 kDa) shared significant homologies to other extracellular PHB depolymerases with a domain substructure: catalytic domain type 2—linker domain fibronectin type 3—substrate-binding domain type 1. A catalytic triad consisting of S₂₀, D₁₀₄, and H₁₃₈ and a pentapeptide sequence (GLS₂₀AG) characteristic for PHB depolymerases (PHB depolymerase box, GLSXG) and for other serine hydrolases (lipase box, GXSXG) were identified.This contribution is dedicated to Hans G. Schlegel in honor of his 80th birthday.Fabian Romen and Simone Reinhardt share first authorship.     

Heliobacterium modesticaldum,sp. nov., a thermophilic heliobacterium of hot springs and volcanic soils

Enrichment cultures for heliobacteria at 50°C yielded several strains of a thermophilic heliobacterium species from Yellowstone hot spring microbial mats and volcanic soils from Iceland. The novel organisms grew optimally above 50°C, contained bacteriochlorophyll g, and lacked intracytoplasmic membranes. All isolates were strict anaerobes and grew best as photoheterotrophs, although chemotrophic dark growth on pyruvate was also possible. These thermophilic heliobacteria were diazotrophic and fixed N₂ up to their growth temperature limit of 56°C. Phylogenetic studies showed the new isolates to be specific relatives of Heliobacterium gestii and, as has been found in H. gestii, they produce heat-resistant endospores. The unique assemblage of properties found in these thermophilic heliobacteria implicate them as a new species of this group, and we describe them herein as a new species of the genus Heliobacterium, Heliobacterium modesticaldum.     

Isolation and characterisation of Thiobacillus halophilus sp. nov., a sulphur-oxidising autotrophic eubacterium from a Western Australian hypersaline lake

The isolation of a novel obligately chemolithotrophic, halophilic and extremely halotolerant Thiobacillus from a hypersaline lake is described. Attempts to demonstrate sulphur- and ferrous iron-oxidizing chemolithotrophs in neighbouring hypersaline lakes were unsuccessful. The organism isolated differs from any other Thiobacillus species previously described and is formally named as Thiobacillus halophilus. It possesses ribulose bisphosphate carboxylase and grows chemolithoautotrophically on thiosulphate, tetrathionate and sulphur, oxidising them to sulphate. Kinetic constants for oxidation of sulphide, thiosulphate, trithionate and tetrathionate are presented. The organism is obligately halophilic, growing best with 0.8–1.0 M NaCl, and tolerating up to 4 M NaCl. Optimum growth was obtained at about 30° C and pH 7.0–7.3. It contains ubiquinone Q-8 and its DNA contains 45 mol % G+C. Organisms of this type might contribute significantly to the autotrophic fixation of carbon dioxide in some hypersaline extreme environments of the kind described.     

Purification and characterization of a periplasmic thiosulfate dehydrogenase from the obligately autotrophicThiobacillus sp. W5

A periplasmic thiosulfate dehydrogenase (EC 1.8.2.2) was purified to homogeneity from the neutrophilic, obligately chemolithoautotrophicThiobacillus sp. W5. A five-step procedure resulted in an approximately 2,300-fold purification. The purified protein had a molecular mass of 120±3 kDa, as determined by gel filtration. It is probably a tetramer containing two different subunits with molecular masses of 33±1 kDa and 27±0.5 kDa, as determined by SDS-PAGE. UV/visible spectroscopy revealed that the enzyme contained haemc; haem staining showed that both subunits contained haemc. A haemc content of 4 mol per mol of enzyme was calculated using the pyridine haemochrome test. The pH optimum of the enzyme was 5.5 At pH 7.5, the K_m and V_max were 120±10 M and 1,160±30 U mg^-1, respectively. The absence of 2-heptyl-4-hydroquinoline-N-oxide (HQNO) inhibition for the oxidation of thiosulfate by whole cells suggested that the electrons enter the respiratory chain at the level of cytochromec. Comparison with thiosulfate dehydrogenases from otherThiobacillus species showed that the enzyme was structurally similar to the thiosulfate dehydrogenase of the acidophilic, facultatively chemolithoautotrophicThiobacillus acidophilus, but not to the thiosulfate dehydrogenases published for the obligately chemolithoautotrophicThiobacillus tepidarius andThiobacillus thioparus.Abbreviations BV Benzyl viologen - DCPIP 2,6-Dichloroindophenol - HQNO 2-Heptyl-4-hydroquinoline-N-oxide - NEM N-ethylmaleimide - PES Phenazine ethosulfate - PMS Phenazine methosulfate     

A new isolate of Hydrogenobacter,an obligately chemolithoautotrophic,thermophilic, halophilic and aerobic hydrogen-oxidizing bacterium from seaside saline hot spring

An obligately chemolithoautotrophic and aerobic hydrogen-oxidizing bacterium was isolated from a seaside saline hot spring in Izu Peninsula, Japan. The isolate was a Gram-negative, non-motile, non-spore-forming rod cell measuring 0.3 to 0.5 by 1.0 to 2.5 m. The optimal temperature for growth was around 70°C, and no growth was observed at 40°C or 80°C. Elemental sulfur or thiosulfate could be an alternative to molecular hydrogen as the sole energy source. The DNA base composition of the isolate was 46.0 mol% G+C. 2-Methylthio-3-VI,VII-tetrahydromultiprenyl⁷-1,4-naphthoquinone (methionaquinone) was the major component of the quinone system. C_18:0, C_18:1 and C_20:1 were the major components of the cellular fatty acids. These properties clearly indicate that the isolate belongs to genus Hydrogenobacter, but differed from H. thermophilus in some respects. Specifically, the isolate was a halophile which grew optimally at around 0.3–0.5 M NaCl, while H. thermophilus could not grow at such NaCl concentration levels. A new species name H. halophilus is proposed for this new halophilic isolate.     

Isolation and physiological characterisation of Thiobacillus aquaesulis sp. nov., a novel facultatively autotrophic moderate thermophile

A moderately thermophilic, facultatively chemolithoautotrophic thiobacillus isolated from a thermal sulphur spring is described. It differs from all other species currently known to be in culture. It grows lithoautotrophically on thiosulphate, trithionate or tetrathionate, which are oxidized to sulphate. Batch cultures on thiosulphate do not produce tetrathionate, but do precipitate elemental sulphur during growth. In autotrophic chemostat cultures the organism produces yields on thiosulphate, trithionate and tetrathionate that are among the highest observed for a Thiobacillus. Autotrophic cultures contain ribulose bisphosphate carboxylase. Heterotrophic growth has been observed only on complex media such as yeast extract and nutrient broth. It is capable of autotrophic growth and denitrification under anaerobic conditions with thiosulphate and nitrate. It grows between 30 to 55° C, and pH 7 to 9, with best growth at about 43°C and pH 7.6. It contains ubiquinone Q-8, and its DNA contains 65.7 mol% G+C. The organism is formally described and named as Thiobacillus aquaesulis.Now the Department of Biological Sciences     

Classification of secondary alcohol-utilizing methanogens including a new thermophilic isolate

A thermophilic coccoid methanogenic bacterium, strain TCI, that grew optimally around 55° C was isolated with 2-propanol as hydrogen donor for methanogenesis from CO₂. H₂, formate or 2-butanol were used in addition. Each secondary alcohol was oxidized to its ketone. Growth occurred in defined freshwater as well as salt (2% NaCl, w/v) medium. Acetate was required as carbon source, and 4-aminobenzoate and biotin as growth factors. A need for molybdate or alternatively tungstate was shown.Strain TCI was further characterized together with two formerly isolated mesophilic secondary alcohol-utilizing methanogens, the coccoid strain CV and the spirilloid strain SK. The guanine plus cytosine content of the DNA of the three strains was 55,47, and 39 mol%, respectively. Determination of the molecular weights of the methylreductase subunits and sequencing of ribosomal 16S RNA of strains TCI and CV revealed close relationships to the genus Methanogenium. The new isolate TCI is classified as a strain of the existing species, Methanogenium thermophilum (thermophilicum). For strain CV, that uses ethanol or 1-propanol in addition, a classification as new species, Methanogenium organophilum, is proposed. Strain SK is affiliated with the existing species, Methanospirillum hungatei. The ability to use secondary alcohols was also tested with described species of methanogens. Growth with secondary alcohols was observed with Methanogenium marisnigri, Methanospirillum hungatei strain GP1 and Methanobacterium bryantii, but not with Methanospirillum strains JF1 and M1h, Methanosarcina barkeri, Methanococcus species or thermophilic strains or species other than the new isolate TCI.     

Geobacillus uralicus,a New Species of Thermophilic Bacteria

The K^T ₂ strain of thermophilic spore-forming bacteria was isolated from a biofilm on the surface of a corroded pipeline in an extremely deep well (4680 m, 40–72°C) in the Urals. The cells are rod-shaped, motile, gram-variable. They grow on a complex medium with tryptone and yeast extract and on a synthetic medium with glucose and mineral salts without additional growth factors. The cells use a wide range of organic substances as carbon and energy sources. They exhibit a respiratory metabolism but are also capable of anaerobic growth on a nitrate-containing medium. Growth occurs within the 40–75°C temperature range (with an optimum of 65°C) and at pH 5–9. The minimum generation time (15 min) was observed at pH 7.5. Ammonium salts, nitrates, and arginine are used as nitrogen sources. The G+C content of the DNA is 54.5 mol %. From the morphological, physiological, and biochemical properties and the nucleotide sequence of the 16S rRNA gene, it was concluded that the isolate K^T ₂ represents a new species of the genus Geobacillus, Geobacillus uralicus.     

Spirochaeta caldaria sp. nov., a thermophilic bacterium that enhances cellulose degradation by Clostridium thermocellum

Two strains of obligately anaerobic, thermophilic spirochetes were isolated from cyanobacterial mat samples collected at freshwater hot springs in Oregon and Utah, USA. The isolates grew optimally between 48° and 52°C, and did not grow at 25° or 60°C. Both strains fermented various pentoses, hexoses, and disaccharides. Amino acids or cellulose did not serve as fermentable substrates for growth. H₂, CO₂, acetate, and lactate were end products of d-glucose fermentation. On the basis of physiological characteristics, guanine + cytosine content of DNA, and comparisons of 16S ribosomal RNA sequences, it was concluded that the two isolates were representatives of a novel species of Spirochaeta for which the name Spirochaeta caldaria is proposed. One of the two strains was grown in coculture with a thermophilic cellulolytic bacterium (Clostridium thermocellum) in a medium containing cellulose as the only fermentable substrate. In the coculture cellulose was broken down at a faster rate than in the clostridial monoculture. The results are consistent with the suggestion that interactions between cellulolytic bacteria and non-cellulolytic spirochetes enhance cellulose breakdown in natural environments in which cellulose-containing plant material is biodegraded.