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.     

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.     

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     

Chemolithotrophic metabolism of the newly-isolated moderately thermophilic,obligately autotrophic Thiobacillus tepidarius

Thiobacillus tepidarius, isolated from the hot springs at Bath, Avon, UK, grew optimally at 43–45°C and pH 6.0–7.5 on thiosulphate or tetrathionate. In batch culture, thiosulphate was oxidized stoichiometrically to tetrathionate, with a rise in pH. The tetrathionate was then oxidized to sulphate, supporting growth and producing a fall in pH to a minimum of ph 4.8. The organism contained high levels of thiosulphate-oxidizing enzyme, rhodanese and ribulose bisphosphate carboxylase. It was obligately chemolithotrophic and autotrophic. In chemostat culture, T. tepidarius grew autotrophically with the following sole energy-substrates: sulphide, thiosulphate, trithionate, tetrathionate, hexathionate or heptathionate. Thiocyanate, dithionate and sulphite were not used as sole substrates, although sulphite enhanced growth yields in the presence of thiosulphate. Maximum specific growth rate on tetrathionate was 0.44 h^-1. True growth yields (Y _max) and maintenance coefficients (m) were calculated for sulphide, thiosulphate, trithionate and tetrathionate and observed yields at a single fixed dilution rate compared with those on hexathionate and heptathionate. Mean values for Y _max, determined from measurements of absorbance, dry wt, total organic carbon and cell protein, were similar for sulphide, thiosulphate and trithionate (10.9 g dry wt/mol substrate) as expected from their equivalent oxygen consumption for oxidation. Y _max for tetrathionate (20.5) and the relative Y _o values (as g dry wt/g atom oxygen consumed) for thiosulphate and all four polythionates indicated that substrate level phosphorylation did not contribute significantly to energy conservation. These Y _max values were 40–70% higher than any of those previously reported for obligately aerobic thiobacilli. Mean values for m were 6.7 mmol substrate oxidized/g dry wt·h for sulphide, thiosulphate and trithionate, and 2.6 for tetrathionate.Abbreviation PIPES Piperazine-N,N-bis(ethane sulphonic acid)     

Oxidation of thiosulfate to tetrathionate by an haloarchaeon isolated from hypersaline habitat

A novel, extremely halophilic, neutrophilic archaeon was isolated from a mixed sediment sample from different hypersaline lakes in Kulunda steppe (Altai, Russia) at 4 M NaCl with acetate and thiosulfate as substrates. The enrichment culture developed in two phases. During the first phase, a rapid growth of heterotrophic, red-colored, polymorphic rods occurred with the concomitant oxidation of thiosulfate to tetrathionate. The latter was subsequently oxidized to sulfate during a second, slower phase by extremely halophilic, chemolithoautotrophic bacteria belonging to the gamma subdivision of the Proteobacteria. The archaeal strain HG 1 was isolated from the first phase of the enrichment culture using acetate as substrate. It was able to oxidize thiosulfate to tetrathionate during heterotrophic growth with acetate—a property not yet demonstrated for any of the known haloarchaea. The presence of tetrathionate synthase, the enzyme responsible for thiosulfate oxidation, was detected in strain HG 1. The activity was associated with membranes and depended specifically on Cl^–, in contrast to the similar activity in extremely halophilic sulfur-oxidizing Gammaproteobacteria from the same enrichment, which was soluble and demanded both Na⁺ and Cl^– . Strain HG 1 was identified as a member of the genus Natronorubrum.     

Thiobacillus strain Q,a chemolithoheterotrophic sulphur bacterium

The physiological properties of an organism isolated from a selective chemostat enrichment using acetate and thiosulphate as the limiting substrates, provisionally called Thiobacillus Q, were investigated. Although the organism made up 85% of the community in the enrichment culture, its expected chemolithotrophic nature was not apparent in batch experiments. The growth yield was not enhanced by the addition of thiosulphate to an acetate containing mineral medium, even though up to 50% of the thiosulphate was oxidized. Under acetate limitation in the chemostat, there was a linear increase in yield with thiosulphate addition up to a concentration of 7 mM. Higher thiosulphate concentrations resulted in loss of thiosulphate oxidizing capacity and a decrease in the biomass to the level obtained with acetate alone. This loss may be due to the presence of inhibitory (50–100 M) levels of sulphite which is probably produced as an intermediate of the biological thiosulphate oxidation. Experiments with sulphide showed that Thiobacillus Q could also use it as an additional energy source. The complete lack of autotrophic growth, both in batch and chemostat experiments, together with the absence of even very low amounts of the key enzymes of the Calvin cycle demonstrated that this organism is a typical chemolithoheterotroph. Although this organism has provisionally been placed in the genus Thiobacillus, standard taxonomic procedures showed a close relationship with Pseudomonas alcaligenes. This study stresses the importance of quantitative chemostat studies in establishing the role of inorganic oxidations in energy metabolism and in the understanding of the role of heterotrophic sulphur oxidation in natural environments.     

Ectothiorhodospira marismortui sp. nov., an obligately anaerobic,moderately halophilic purple sulfur bacterium from a hypersaline sulfur spring on the shore of the Dead Sea

A novel type of purple sulfur bacterium was isolated from a hypersaline sulfur spring on the shore of the Dead Sea. The cells of the isolate are irregularly rod-shaped or curved, and motile by means of a tuft of polar flagella. The photosynthetic system, containing bacteriochlorophyll a and carotenoids of the spirilloxanthin series, is located on stacks of lamellar membranes in the cell cytoplasm. The organism can grow either photoautotrophically with sulfide as electron donor, which is oxidized via extracellular sulfur to sulfate, or photoheterotrophically, using acetate, succinate, fumarate, malate or pyruvate as carbon sources. The bacterium is obligately anaerobic, and requires a source of reduced sulfur for growth. The isolate is moderately halophilic, and grows optimally at NaCl concentrations between 3 and 8%, temperatures between 30 and 45°C, and neutral pH. 16S ribosomal RNA oligonucleotide cataloging suggests a close relationship to purple sulfur bacteria of the genus Ectothiorhodospira. As the isolate differs greatly from the described members of the genus Ectothiorhodospira, we describe the isolate as a new species, and propose the name Ectothiorhodospira marismortui sp. nov.     

Rhodospirillum sodomense,sp. nov., a Dead Sea rhodospirillum species

A new species of halophilic anoxygenic purple bacteria of the genus Rhodospirillum is described. The new organism, isolated from water/sediment of the Dead Sea, was vibrio-shaped and an obligate halophile. Growth was best at 12% NaCl, with only weak growth occurring at 6% or 21% NaCl. Growth occurred at Mg²⁺ concentrations up to 1 M but optimal growth was obtained at 0.05–0.1 M Mg²⁺. Bromide was well tolerated as an alternative anion to chloride. The new organism is an obligate phototroph, growing photoheterotrophically in media containing yeast extract and acetate or a few other organic compounds. Growth of the Dead Sea Rhodospirillum species under optimal culture conditions was slow (minimum t_d 20 h). Cells contained bacteriochlorophyll a and carotenoids of the spirilloxanthin series and mass cultures were pink in color. Absorption spectra revealed the presence of a B875 (light-harvesting I) but no B800/B850 (light-harvesting II) photopigment complex. The new organism shares a number of properties with the previously described halophilic phototrophic bacterium Rhodospirillum salinarum and was shown to be related to this phototroph by 16S rRNA sequencing. However, because of its salinity requirements, photosynthetic properties, and isolation from the Dead Sea, the new phototroph is proposed as a new species of the genus Rhodospirillum, R. sodomense.     

Rhodospirillum salinarum sp. nov., a halophilic photosynthetic bacterium isolated from a Portuguese saltern

A new species of halophilic photosynthetic bacteria, Rhodospirillum salinarum, has been isolated and described. Its natural habitat are the terminal crystallization ponds of solar salt production plants. R. salinarum grows optimally at 42°C in the presence of 6–18% NaCl (w/v). Growth requirements are complex, yeast extract and peptone being required both for aerobic heterotrophic and for anaerobic phototrophic growth. Increasing concentrations of NaCl in the growth media did not give rise to any corresponding increase in intracellular concentrations of K⁺, Na⁺, polyalcohols or amino acids. Malate dehydrogenase from R. salinarum is not halophilic, being inhibited even at low concentrations of Na⁺ or K⁺. The GC mol % of DNA from R. salinarum is markedly higher than that for DNA from R. salexigens, the only previously described halophilic species of the genus Rhodospirillum.     

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.     

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.     

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     

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.     

<Emphasis Type="Italic">Desulfonatronovibrio halophilus</Emphasis> sp. nov., a novel moderately halophilic sulfate-reducing bacterium from hypersaline chloride–sulfate lakes in Central Asia

Four strains of lithotrophic sulfate-reducing bacteria (SRB) have been enriched and isolated from anoxic sediments of hypersaline chloride–sulfate lakes in the Kulunda Steppe (Altai, Russia) at 2 M NaCl and pH 7.5. According to the 16S rRNA gene sequence analysis, the isolates were closely related to each other and belonged to the genus Desulfonatronovibrio, which, so far, included only obligately alkaliphilic members found exclusively in soda lakes. The isolates utilized formate, H₂ and pyruvate as electron donors and sulfate, sulfite and thiosulfate as electron acceptors. In contrast to the described species of the genus Desulfonatronovibrio, the salt lake isolates could only tolerate high pH (up to pH 9.4), while they grow optimally at a neutral pH. They belonged to the moderate halophiles growing between 0.2 and 2 M NaCl with an optimum at 0.5 M. On the basis of their distinct phenotype and phylogeny, the described halophilic SRB are proposed to form a novel species within the genus Desulfonatronovibrio, D. halophilus (type strain HTR1^T = DSM24312^T = UNIQEM U802^T).     

Autotrophic growth and inorganic sulphur compound oxidation by Sulfolobus sp. in chemostat culture

Sulfolobus strain LM was grown in tetrathionate and thiosulphate-limited continuous culture. CO₂ limitation resulted in a decrease of the steady-state biomass and an increase in the specific rate of thiosulphate oxidation so that substrate did not accumulate in the medium. The initial step in thiosulphate utilization appeared to be its conversion to tetrathionate. The affinity for tetrathionate oxidation appeared to increase with prolonged continuous culture giving an apparent K _m of about 6 M tetrathionate, a higher affinity than for thiosulphate oxidation and in the same range as values observed with acidophilic, sulphur-oxidizing eubacteria.     

Tetrathionate Disproportionation by Thiomonas intermedia K12

Thiomonas intermedia K12, a moderately acidophilic bacterium, which oxidises sulphur compounds, – exhibited the capability to use tetrathionate under oxic and anoxic conditions. Whereas under oxic conditions, the reduced sulphur tetrathionate compound was oxidised, under anoxic conditions, the organism disproportionated the compound. In both cases, trithionate and sulphate were produced but in different amounts. The results of the tetrathionate degradation experiments under oxic conditions pointed towards a cyclic degradation process with a transient formation of trithionate and sulphate as the final products, similar to the mechanism described for acidophilic sulphur compound oxidising bacteria. The results of the tetrathionate degradation experiments under anoxic conditions hinted to a partial reduction of tetrathionate to thiosulphate and a fractional oxidation to trithionate and sulphate. 4 M tetrathionate were converted to 6 M thiosulphate, 1 M trithionate, 1 M sulphate, and 8 M protons. The ΔG₀' of this reaction was found to be –16.1 kJ per mol tetrathionate degraded. Additionally, Thiomonas intermedia K12 grew under anoxic conditions with tetrathionate as the sole energy source. The cell numbers increased from 10⁵ as the start value to 10⁷/mL at the end. Organic compounds, excluding traces of yeast extract, did not enhance growth. Therefore, it is proposed that tetrathionate disproportionation is a novel lithotrophic metabolism, which allowed Thiomonas intermedia K12 to survive changing conditions of oxygen supply in sulphur‐compound‐rich environments and even to grow during this reaction. The extensive sulphur compound analysis was carried out by ion‐pair chromatography.     

Salinicoccus salitudinis sp. nov., a new moderately halophilic bacterium isolated from a saline soil sample

A novel pale-yellow-pigmented, moderately halophilic, facultatively alkaliphilic, non-motile, non-spore-forming, catalase- and oxidase-positive, obligately aerobic Gram-positive coccus, strain YIM-C678^T was isolated from a saline soil sample collected from a hypersaline habitat in the Qaidam basin, northwest China. The organism grew at 4–37°C and pH 6.0–11.0, with optimum growth at 25°C and pH 8.0. Strain YIM-C678^T grew optimally in the presence of 10–12% (w/v) NaCl and growth was observed in 1–25% (w/v) NaCl. The cell wall murein type was l-Lys-Gly₅. Major cellular fatty acids were anteiso-C_15:0, iso-C_15:0, iso-C_16:0 and C_16:0. Menaquinone 6 (MK-6) was the major respiratory quinone. The DNA G + C content was 46.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain YIM-C678^T belonged to the family Staphylococcaceae and was most closely related to the eight described species of the genus Salinicoccus with sequence similarities from 92.2 (S. luteus YIM 70202^T) to 97.5% (S. kunmingensis YIM Y15^T). The DNA–DNA relatedness between strain YIM-C678^T and S. kunmingensis YIM Y15^T was 35.4%. Chemotaxonomic data and 16S rRNA gene sequence analysis supported the affiliation of strain YIM-C678^T with the genus Salinicoccus. The combination of phylogenetic analysis, phenotypic characteristics, chemotaxonomic differences and DNA–DNA hybridization data supported the view that the bacterium represents a novel species of the genus Salinicoccus, for which the name Salinicoccus salitudinis sp. nov. is proposed, with YIM-C678^T (=DSM 17846 = CGMCC 1.6299) as the type strain.     

<Emphasis Type="Italic">Halobacillus locisalis</Emphasis> sp. nov., a halophilic bacterium isolated from a marine solar saltern of the Yellow Sea in Korea

A Gram-positive, motile, endospore-forming and rod-shaped halophilic bacterial strain MSS-155 (KCTC 3788 and KCCM 41687) was isolated from a marine solar saltern of the Yellow Sea in Korea and was subjected to a polyphasic taxonomic study. This organism grew at temperature of 10.0–42.0°C with an optimum of 35°C. Strain MSS-155 grew optimally in the presence of 10% NaCl and did not grow in the absence of NaCl. The cell wall peptidoglycan type of strain MSS-155 was A4 based on l-Orn-d-Asp. Strain MSS-155 was also characterized chemotaxonomically by having menaquinone-7 (MK-7) as the predominant isoprenoid quinone and anteiso-C_15:0 as the major fatty acid. The DNA G+C content was 44.0 mol%. Phylogenetic analysis based on 16S rDNA sequences showed that strain MSS-155 falls within the radiation of the cluster comprising Halobacillus species. Levels of 16S rDNA sequence similarity between strain MSS-155 and the type strains of four Halobacillus species were in the range 97.6–98.8%. Strain MSS-155 exhibited levels of DNA-DNA relatedness of 6.2–11.2% to the type strains of Halobacillus species described previously. On the basis of phenotypic properties, phylogeny, and genomic data, strain MSS-155 should be placed in the genus Halobacillus as a member of a novel species, for which we propose the name Halobacillus locisalis sp. nov.Communicated by W.D. Grant     

Halonatronum saccharophilum gen. nov. sp. nov.: A New Haloalkaliphilic Bacterium of the Order Haloanaerobiales from Lake Magadi

A new alkaliphilic and moderately halophilic chemoorganotrophic anaerobic bacterium (strain Z-7986), which is spore-forming, rod-shaped, and has a gram-negative cell wall pattern, was isolated from the coastal lagoon mud of the highly mineralized Lake Magadi (Kenya). The organism is an obligatorily carbonate- and sodium chloride-dependent motile peritrichously flagellated rod that grows within a 3–17% NaCl concentration range (with an optimum at 7–12% NaCl) and within a pH range of 7.7–10.3 (with an optimum at pH values of 8–8.5). It is a moderate thermophile with a broad temperature optimum at 36–55°C; maximum growth temperature is 60°C. The bacterium catabolizes glucose, fructose, sucrose, maltose, starch, glycogen, N-acetyl-D-glucosamine, and, to a slight degree, peptone and yeast extract. Its anabolism requires yeast extract or casamino acids. Glucose fermentation yields formate, acetate, ethanol, H₂, and CO₂. The bacterium is sulfide-tolerant and capable of the nonspecific reduction of S⁰ to H₂S. The G+C content of the DNA is 34.4 mol %. The analysis of the 16S rRNA sequence revealed that strain Z-7986 belongs to the order Haloanaerobiales and represents a new genus in the family Halobacteroidaceae. We suggest the name Halonatronum saccharophilum gen. nov. sp. nov. The type strain of this species is Z-7986^T (= DSM13868, = Uniqem*211).     

Biodegradation of crude oil and pure hydrocarbons by extreme halophilic archaea from hypersaline coasts of the Arabian Gulf

Two extreme halophilic Haloferax strains and one strain each of Halobacterium and Halococcus were isolated from a hypersaline coastal area of the Arabian Gulf on a mineral salt medium with crude oil vapor as a sole source of carbon and energy. These archaea needed at least 1 M NaCl for growth in culture, and grew best in the presence of 4 M NaCl or more. Optimum growth temperatures lied between 40 and 45oC. The four archaea were resistant to the antibiotics chloramphenicol, cycloheximide, nalidixic acid, penicillin, streptomycin and tetracycline. The strains could grow on a wide scope of aliphatic and aromatic (both mono-and polynuclear) hydrocarbons, as sole sources of carbon and energy. Quantitative measurements revealed that these extreme halophilic prokaryotes could biodegrade crude oil (13–47%, depending on the strain and medium salinity), n-octadecane (28–67%) and phenanthrene (13–30%) in culture after 3 weeks of incubation. The rates of biodegradation by all strains were enhanced with increasing NaCl concentration in the medium. Optimal concentration was 3 M NaCl, but even with 4 M NaCl the hydrocarbon-biodegradation rates were higher than with 1 and 2 M NaCl. It was concluded that these archaea could contribute to self-cleaning and bioremediation of oil-polluted hypersaline environments.