POSTOPERATIVE ENDOPHTHALMITIS CAUSED BY BOSEA THIOOXIDANS.

PURPOSE: To report an unusual case of postcataract endophthalmitis secondary to Bosea thiooxidans. METHODS: Case report. RESULTS: An 86-year-old man presented with postoperative endophthalmitis 3 weeks after uncomplicated cataract surgery. He complained of a headache and blurry vision but denied having eye pain. Slit-lamp examination demonstrated leukocytes with a fibrinous membrane in the anterior segment and vitritis. A diagnosis of acute postoperative endophthalmitis was made, and the patient was treated with intravitreal antibiotics. Culture of vitreous tap revealed Bosea thiooxidans, a gram-negative rod found in soil and water systems. CONCLUSION: To our knowledge, this report is the first to describe Bosea thiooxidans endophthalmitis and one of a few reports of human infection with this microbial agent.

[Informative indices of the biocorrosion activity for the determination of the character of the aggression ground].

Underground corrosion is referred to the most difficult types of corrosion in connection with that it is multifactorial and differs in progressive dynamics of the participation of each parameter in the process of destruction of the metal. With the aim of the evaluation of the informativeness of the index of the biocorrosion activity caused by the influence of various factors to determine the character of the soil aggressiveness in the district of pipeline laying there was studied the complex of microbiological and physical-chemical indices). There was determined the amount of sulfur cycle bacteria (autotrophic thiobacteria and sulphate-reducing bacteria), the total concentration of sulfur and iron in the soil samples adjacent to the surface of the underground pipelines in the territory of the Khanty-Mansi Autonomous District of Yugra, and the ratio of these indices with a specific electrical resistance of the soil. There was established the predominance ofsamples with weak aggressiveness of the soil (55.17% of cases), with the criterion ofbiocorrosion soil activity of 2,44 ± 0,19. The results show significant differences in the thiobacteria content and mobile iron in the studied soil-ground samples. There was revealed a direct correlation of the average force of concentrations of identified bacteria and iron content in the soil. There was shown the necessity of the implementation of dynamic control and the development of methods of protection of metal structures to prevent biocorrosion in the design and in the process of the operation of the pipeline.

Thermosulfurimonas dismutans gen. nov., sp. nov., an extremely thermophilic sulfur-disproportionating bacterium from a deep-sea hydrothermal vent.

An extremely thermophilic, anaerobic, chemolithoautotrophic bacterium (strain S95(T)) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Center, Pacific Ocean, at a depth of 1910 m. Cells of strain S95(T) were oval to short Gram-negative rods, 0.5-0.6 µm in diameter and 1.0-1.5 µm in length, growing singly or in pairs. Cells were motile with a single polar flagellum. The temperature range for growth was 50-92 °C, with an optimum at 74 °C. The pH range for growth was 5.5-8.0, with an optimum at pH 7.0. Growth of strain S95(T) was observed at NaCl concentrations ranging from 1.5 to 3.5% (w/v). Strain S95(T) grew anaerobically with elemental sulfur as an energy source and bicarbonate/CO(2) as a carbon source. Elemental sulfur was disproportionated to sulfide and sulfate. Growth was enhanced in the presence of poorly crystalline iron(III) oxide (ferrihydrite) as a sulfide-scavenging agent. Strain S95(T) was also able to grow by disproportionation of thiosulfate and sulfite. Sulfate was not used as an electron acceptor. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to the phylum Thermodesulfobacteria. On the basis of its physiological properties and results of phylogenetic analyses, it is proposed that the isolate represents the sole species of a new genus, Thermosulfurimonas dismutans gen. nov., sp. nov.; S95(T) (=DSM 24515(T)=VKM B-2683(T)) is the type strain of the type species. This is the first description of a thermophilic micro-organism that disproportionates elemental sulfur.

Isolation and characterization of a moderately thermophilic nitrite-oxidizing bacterium from a geothermal spring.

Geothermal environments are a suitable habitat for nitrifying microorganisms. Conventional and molecular techniques indicated that chemolithoautotrophic nitrite-oxidizing bacteria affiliated with the genus Nitrospira are widespread in environments with elevated temperatures up to 55 °C in Asia, Europe, and Australia. However, until now, no thermophilic pure cultures of Nitrospira were available, and the physiology of these bacteria was mostly uncharacterized. Here, we report on the isolation and characterization of a novel thermophilic Nitrospira strain from a microbial mat of the terrestrial geothermal spring Gorjachinsk (pH 8.6; temperature 48 °C) from the Baikal rift zone (Russia). Based on phenotypic properties, chemotaxonomic data, and 16S rRNA gene phylogeny, the isolate was assigned to the genus Nitrospira as a representative of a novel species, for which the name Nitrospira calida is proposed. A highly similar 16S rRNA gene sequence (99.6% similarity) was detected in a Garga spring enrichment grown at 46 °C, whereas three further thermophilic Nitrospira enrichments from the Garga spring and from a Kamchatka Peninsula (Russia) terrestrial hot spring could be clearly distinguished from N. calida (93.6-96.1% 16S rRNA gene sequence similarity). The findings confirmed that Nitrospira drive nitrite oxidation in moderate thermophilic habitats and also indicated an unexpected diversity of heat-adapted Nitrospira in geothermal hot springs.

Sulfurihydrogenibium rodmanii sp. nov., a sulfur-oxidizing chemolithoautotroph from the Uzon Caldera, Kamchatka Peninsula, Russia, and emended description of the genus Sulfurihydrogenibium.

Four thermophilic, sulfur-oxidizing, chemolithoautotrophic strains with >99 % 16S rRNA gene sequence similarity were isolated from terrestrial hot springs in the Geyser Valley and the Uzon Caldera, Kamchatka, Russia. One strain, designated UZ3-5T, was characterized fully. Cells of UZ3-5T were Gram-negative, motile, slightly oval rods (about 0.7 microm wide and 1.0 microm long) with multiple polar flagella. All four strains were obligately microaerophilic chemolithoautotrophs and could use elemental sulfur or thiosulfate as electron donors and oxygen (1-14 %, v/v) as the electron acceptor. Strain UZ3-5T grew at temperatures between 55 and 80 degrees C (optimally at 75 degrees C; 1.1 h doubling time), at pH 5.0-7.2 (optimally at pH 6.0-6.3) and at 0-0.9 % NaCl (optimally in the absence of NaCl). The G+C content of the genomic DNA of strain UZ3-5T was 35 mol%. Phylogenetic analysis revealed that strain UZ3-5T was a member of the genus Sulfurihydrogenibium, its closest relative in culture being Sulfurihydrogenibium azorense Az-Fu1T (98.3 % 16S rRNA gene sequence similarity). On the basis of its physiological and molecular characteristics, strain UZ3-5T represents a novel species of the genus Sulfurihydrogenibium, for which the name Sulfurihydrogenibium rodmanii sp. nov. is proposed. The type strain is UZ3-5T (=OCM 900T =ATCC BAA-1536T =DSM 19533T).

Sulfurihydrogenibium kristjanssonii sp. nov., a hydrogen- and sulfur-oxidizing thermophile isolated from a terrestrial Icelandic hot spring.

Three thermophilic, aerobic, hydrogen- and sulfur-oxidizing bacteria were isolated from an Icelandic hot spring near the town of Hveragerdi and share >99 % 16S rRNA gene sequence similarity. One of these isolates, designated strain I6628T, was selected for further characterization. Strain I6628T is a motile rod, 1.5-2.5 microm long and about 0.5 microm wide. Growth occurred between 40 and 73 degrees C (optimally at 68 degrees C), at pH 5.3-7.8 (optimally at pH 6.6) and at NaCl concentrations between 0 and 0.5 % (w/v). Strain I6628T grew with H2, S0 or S2O3(2-) as an electron donor with O2 (up to 25 %, v/v; optimally at 4-9 %) as the sole electron acceptor. CO2 and succinate were utilized as carbon sources but no organic compounds, including succinate, could be used as an energy source. The G+C content of the genomic DNA was determined to be 28.1 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain I6628T is a member of the genus Sulfurihydrogenibium, the closest cultivated relative being the recently described strain Sulfurihydrogenibium rodmanii UZ3-5T (98.2 % sequence similarity). On the basis of the physiology and phylogeny of this organism, strain I6628T represents a novel species of the genus Sulfurihydrogenibium, for which the name Sulfurihydrogenibium kristjanssonii sp. nov. is proposed. The type strain is I6628T (=DSM 19534T =OCM 901T =ATCC BAA-1535T).

Venenivibrio stagnispumantis gen. nov., sp. nov., a thermophilic hydrogen-oxidizing bacterium isolated from Champagne Pool, Waiotapu, New Zealand.

A novel thermophilic, hydrogen-oxidizing bacterium, designated strain CP.B2(T), was isolated from a terrestrial hot spring in Waiotapu, New Zealand. Cells were motile, slightly rod-shaped, non-spore-forming and Gram-negative. Isolate CP.B2(T) was an obligate chemolithotroph, growing by utilizing H(2) as electron donor and O(2) as corresponding electron acceptor. Elemental sulfur (S(0)) or thiosulfate ( ) was essential for growth. Microbial growth occurred under microaerophilic conditions in 1.0-10.0 % (v/v) O(2) [optimum 4-8 % (v/v) O(2)], between 45 and 75 degrees C (optimum 70 degrees C) and at pH values of 4.8-5.8 (optimum pH 5.4). The DNA G+C content was 29.3 mol%. 16S rRNA gene sequence analysis demonstrated that strain CP.B2(T) belonged to the order Aquificales, with a close phylogenetic relationship to Sulfurihydrogenibium azorense (94 % sequence similarity to the type strain). However, genotypic and metabolic characteristics differentiated the novel isolate from previously described genera of the Aquificales. Therefore, CP.B2(T) represents a novel species in a new genus, for which the name Venenivibrio stagnispumantis gen. nov., sp. nov. is proposed. The type strain of Venenivibrio stagnispumantis is CP.B2(T) (=JCM 14244(T) =DSM 18763(T)).

Physiological and phylogenetic characterization of a novel lithoautotrophic nitrite-oxidizing bacterium, 'Candidatus Nitrospira bockiana'.

A new isolate of a lithoautotrophic nitrite-oxidizing bacterium was obtained from internal corrosion deposits from a steel pipeline of the Moscow heating system. The organism oxidized nitrite as the sole energy source and fixed carbon dioxide as the only carbon source. The cells were extremely pleomorphic: loosely wound spirals, slightly curved and even straight rods were detected, as well as coccoid cells. The highest rate of nitrite consumption (1.5 mM nitrite as substrate) was measured at 42 degrees C, with a temperature range of 28-44 degrees C. In enrichment cultures with Nocardioides sp. as an accompanying organism, optimal oxidation of 5.8 mM nitrite occurred at 45 degrees C, with a range of 28-48 degrees C. Neither pyruvate nor yeast extract stimulated nitrification. Organotrophic growth was not observed. Phylogenetic analysis of 16S rRNA gene sequences revealed that the novel isolate represents a new sublineage of the genus Nitrospira. On the basis of physiological, chemotaxonomic and molecular characteristics, the name 'Candidatus Nitrospira bockiana' is proposed.

Sulfurihydrogenibium yellowstonense sp. nov., an extremely thermophilic, facultatively heterotrophic, sulfur-oxidizing bacterium from Yellowstone National Park, and emended descriptions of the genus Sulfurihydrogenibium, Sulfurihydrogenibium subterraneum and Sulfurihydrogenibium azorense.

A novel thermophilic, sulfur-oxidizing Gram-negative bacterium, designated strain SS-5T, was isolated from the Calcite Hot Springs in Yellowstone National Park, USA. The cells were motile rods (1.2-2.8 microm long and 0.6-0.8 microm wide). The new isolate was a facultative heterotroph capable of using elemental sulfur or thiosulfate as an electron donor and O2 (1-18 %; optimum 6 %, v/v) as an electron acceptor. Hydrogen did not support growth. The isolate grew autotrophically with CO2. In addition, strain SS-5T utilized various organic carbon sources such as yeast extract, tryptone, sugars, amino acids and organic acids. Growth was observed between 55 and 78 degrees C (optimum 70 degrees C; 3.5 h doubling time), pH 6.0 and 8.0 (optimum pH 7.5), and 0 and 0.6 % (w/v) NaCl (optimum 0 %). The G+C content of the genomic DNA was 32 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the isolate was a member of the genus Sulfurihydrogenibium. On the basis of the physiological and molecular characteristics of the new isolate, we propose the name Sulfurihydrogenibium yellowstonense sp. nov. with SS-5T (=JCM 12773T=OCM 840T) as the type strain. In addition, emended descriptions of the genus Sulfurihydrogenibium, Sulfurihydrogenibium subterraneum and Sulfurihydrogenibium azorense are proposed.

Immunological detection of Nitrospira-like bacteria in various soils.

Chemolithotrophic nitrite oxidizers were enriched from five different soils including freshwater marsh, permafrost, garden, agricultural, and desert soils and monitored during the cultivation procedure. Immunoblot analysis was used to identify the nitrite oxidizing organisms with monoclonal antibodies, which recognize the key enzyme of nitrite oxidation in a genus-specific reaction [Bartosch et al. (1999) Appl Environ Microbiol 65:4126-4133]. The morphological characteristics of the enriched nitrite oxidizers were additionally studied using transmission electron microscopy (TEM) and fluorescence microscopy. By means of the antibodies and TEM analysis Nitrospira could be clearly identified in enrichment cultures derived from freshwater marsh and from permafrost soil. Nitrospira cells were enriched simultaneously with cells of the genus Nitrobacter when nitrite concentrations of 0.2 g of NaNO2 L(-1) were used. However, in enrichment cultures containing 2 g of NaNO2 L(-1) Nitrobacter was exclusively detected. During fluorescence microscopic observations of DAPI stained samples microcolonies were found in enrichment cultures from freshwater marsh, permafrost, garden, and agricultural soil. They had a similar morphology to Nitrospira-like microcolonies from activated sludge. In conclusion, Nitrospira seems to be not only a common aquatic but also a usual soil bacterium.

Ammonia-oxidizing bacteria: a model for molecular microbial ecology.

The eutrophication of many ecosystems in recent decades has led to an increased interest in the ecology of nitrogen transformation. Chemolitho-autotrophic ammonia-oxidizing bacteria are responsible for the rate-limiting step of nitrification in a wide variety of environments, making them important in the global cycling of nitrogen. These organisms are unique in their ability to use the conversion of ammonia to nitrite as their sole energy source. Because of the importance of this functional group of bacteria, understanding of their ecology and physiology has become a subject of intense research over recent years. The monophyletic nature of these bacteria in terrestrial environments has facilitated molecular biological approaches in studying their ecology, and progress in this field has been rapid. The ammonia-oxidizing bacteria of the beta-subclass Proteobacteria have become somewhat of a model system within molecular microbial ecology, and this chapter reviews recent progress in our knowledge of their distribution, diversity, and ecology.

Halothiobacillus kellyi sp. nov., a mesophilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium isolated from a shallow-water hydrothermal vent in the Aegean Sea, and emended description of the genus Halothiobacillus.

A new mesophilic, chemolithoautotrophic, sulfur-oxidizing bacterium, strain Milos-BII1T, was isolated from a sediment sample taken from a shallow-water hydrothermal vent in the Aegean Sea with thiosulfate as electron donor and CO2 as carbon source. Based on the almost complete sequence of the 16S rRNA gene, strain Milos-BII1T forms a phylogenetic cluster with Thiobacillus hydrothermalis, Thiobacillus neapolitanus, Thiobacillus halophilus and Thiobacillus sp. W5, all of which are obligately chemolithoautotrophic bacteria. Because of their phylogenetic relatedness and their physiological similarities it is proposed to transfer these organisms to a newly established genus within the gamma-subclass of the Proteobacteria, Halothiobacillus gen. nov. (Kelly and Wood 2000). Strain Milos-BII1T represents a new species of this genus, named Halothiobacillus kellyi. Cells were Gram-negative rods and highly motile. The organism was obligately autotrophic and strictly aerobic. Nitrate was not used as electron acceptor. Chemolithoautotrophic growth was observed with thiosulfate, tetrathionate, sulfur and sulfide. Growth was observed between pH values of 3.5 and 8.5, with an optimum at pH 6.5. The temperature limits for growth were 3.5 and 49 degrees C, with an optimum between 37 and 42 degrees C. Growth occurred between 0 and 2 M NaCl, with an optimum NaCl concentration between 400 and 500 mM. The mean maximum specific growth rate on thiosulfate was 0.45 h(-1).

A new chemolithoautotrophic arsenite-oxidizing bacterium isolated from a gold mine: phylogenetic, physiological, and preliminary biochemical studies.

A previously unknown chemolithoautotrophic arsenite-oxidizing bacterium has been isolated from a gold mine in the Northern Territory of Australia. The organism, designated NT-26, was found to be a gram-negative motile rod with two subterminal flagella. In a minimal medium containing only arsenite as the electron donor (5 mM), oxygen as the electron acceptor, and carbon dioxide-bicarbonate as the carbon source, the doubling time for chemolithoautotrophic growth was 7.6 h. Arsenite oxidation was found to be catalyzed by a periplasmic arsenite oxidase (optimum pH, 5.5). Based upon 16S rDNA phylogenetic sequence analysis, NT-26 belongs to the Agrobacterium/Rhizobium branch of the alpha-Proteobacteria and may represent a new species. This recently discovered organism is the most rapidly growing chemolithoautotrophic arsenite oxidizer known.

Distribution and diversity of sulfur-oxidizing Thiomicrospira spp. at a shallow-water hydrothermal vent in the Aegean Sea (Milos, Greece).

A shallow-water hydrothermal vent system in the Aegean Sea close to the island of Milos (Greece) was chosen to study the diversity and distribution of the chemolithoautotrophic sulfur-oxidizing bacterium Thiomicrospira. Cell numbers in samples from different regions around a solitary vent decreased toward the center of the vent (horizontal distribution), as well as with depth (vertical distribution), corresponding to an increase in temperature (from ca. 25 to 60 degrees C) and a decrease in pH (from ca. pH 7 to 5). Thiomicrospira was one of the most abundant culturable sulfur oxidizers and was even dominant in one region. Phylogenetic analysis of Thiomicrospira spp. present in the highest most-probable-number (MPN) dilutions revealed that most of the obtained sequences grouped in two new closely related clusters within the Thiomicrospira branch. Two different new isolates, i.e., Milos-T1 and Milos-T2, were obtained from high-dilution (10(-5)) enrichments. Phylogenetic analysis indicated that isolate Milos-T1 is related to the recently described Thiomicrospira kuenenii and Hydrogenovibrio marinus, whereas isolate Milos-T2 grouped with the MPN sequences of cluster 2. The predominance of strain Milos-T2 was indicated by its identification in several environmental samples by hybridization analysis of denaturing gradient gel electrophoresis (DGGE) patterns and by sequencing of one of the corresponding bands, i.e., ML-1, from the DGGE gel. The results shown in this paper support earlier indications that Thiomicrospira species are important members of hydrothermal vent communities.

Nitrification and autotrophic nitrifying bacteria in a hydrocarbon-polluted soil.

In vitro ammonia-oxidizing bacteria are capable of oxidizing hydrocarbons incompletely. This transformation is accompanied by competitive inhibition of ammonia monooxygenase, the first key enzyme in nitrification. The effect of hydrocarbon pollution on soil nitrification was examined in situ. In a microcosm study, adding diesel fuel hydrocarbon to an uncontaminated soil (agricultural unfertilized soil) treated with ammonium sulfate dramatically reduced the amount of KCl-extractable nitrate but stimulated ammonium consumption. In a soil with long history of pollution that was treated with ammonium sulfate, 90% of the ammonium was transformed into nitrate after 3 weeks of incubation. Nitrate production was twofold higher in the contaminated soil than in the agricultural soil to which hydrocarbon was not added. To assess if ammonia-oxidizing bacteria acquired resistance to inhibition by hydrocarbon, the contaminated soil was reexposed to diesel fuel. Ammonium consumption was not affected, but nitrate production was 30% lower than nitrate production in the absence of hydrocarbon. The apparent reduction in nitrification resulted from immobilization of ammonium by hydrocarbon-stimulated microbial activity. These results indicated that the hydrocarbon inhibited nitrification in the noncontaminated soil (agricultural soil) and that ammonia-oxidizing bacteria in the polluted soil acquired resistance to inhibition by the hydrocarbon, possibly by increasing the affinity of nitrifying bacteria for ammonium in the soil.

Identification of nitrite-oxidizing bacteria with monoclonal antibodies recognizing the nitrite oxidoreductase.

Immunoblot analyses performed with three monoclonal antibodies (MAbs) that recognized the nitrite oxidoreductase (NOR) of the genus Nitrobacter were used for taxonomic investigations of nitrite oxidizers. We found that these MAbs were able to detect the nitrite-oxidizing systems (NOS) of the genera Nitrospira, Nitrococcus, and Nitrospina. The MAb designated Hyb 153-2, which recognized the alpha subunit of the NOR (alpha-NOR), was specific for species belonging to the genus Nitrobacter. In contrast, Hyb 153-3, which recognized the beta-NOR, reacted with nitrite oxidizers of the four genera. Hyb 153-1, which also recognized the beta-NOR, bound to members of the genera Nitrobacter and Nitrococcus. The molecular masses of the beta-NOR of the genus Nitrobacter and the beta subunit of the NOS (beta-NOS) of the genus Nitrococcus were identical (65 kDa). In contrast, the molecular masses of the beta-NOS of the genera Nitrospina and Nitrospira were different (48 and 46 kDa). When the genus-specific reactions of the MAbs were correlated with 16S rRNA sequences, they reflected the phylogenetic relationships among the nitrite oxidizers. The specific reactions of the MAbs allowed us to classify novel isolates and nitrite oxidizers in enrichment cultures at the genus level. In ecological studies the immunoblot analyses demonstrated that Nitrobacter or Nitrospira cells could be enriched from activated sludge by using various substrate concentrations. Fluorescence in situ hybridization and electron microscopic analyses confirmed these results. Permeated cells of pure cultures of members of the four genera were suitable for immunofluorescence labeling; these cells exhibited fluorescence signals that were consistent with the location of the NOS.

Comparative diversity of ammonia oxidizer 16S rRNA gene sequences in native, tilled, and successional soils.

Autotrophic ammonia oxidizer (AAO) populations in soils from native, tilled, and successional treatments at the Kellogg Biological Station Long-Term Ecological Research site in southwestern Michigan were compared to assess effects of disturbance on these bacteria. N fertilization effects on AAO populations were also evaluated with soils from fertilized microplots within the successional treatments. Population structures were characterized by PCR amplification of microbial community DNA with group-specific 16S rRNA gene (rDNA) primers, cloning of PCR products and clone hybridizations with group-specific probes, phylogenetic analysis of partial 16S rDNA sequences, and denaturing gradient gel electrophoresis (DGGE) analysis. Population sizes were estimated by using most-probable-number (MPN) media containing varied concentrations of ammonium sulfate. Tilled soils contained higher numbers than did native soils of culturable AAOs that were less sensitive to different ammonium concentrations in MPN media. Compared to sequences from native soils, partial 16S rDNA sequences from tilled soils were less diverse and grouped exclusively within Nitrosospira cluster 3. Native soils yielded sequences representing three different AAO clusters. Probes for Nitrosospira cluster 3 hybridized with DGGE blots from tilled and fertilized successional soils but not with blots from native or unfertilized successional soils. Hybridization results thus suggested a positive association between the Nitrosospira cluster 3 subgroup and soils amended with inorganic N. DGGE patterns for soils sampled from replicated plots of each treatment were nearly identical for tilled and native soils in both sampling years, indicating spatial and temporal reproducibility based on treatment.

Nitrous oxide production and methane oxidation by different ammonia-oxidizing bacteria.

Ammonia-oxidizing bacteria (AOB) are thought to contribute significantly to N2O production and methane oxidation in soils. Most of our knowledge derives from experiments with Nitrosomonas europaea, which appears to be of minor importance in most soils compared to Nitrosospira spp. We have conducted a comparative study of levels of aerobic N2O production in six phylogenetically different Nitrosospira strains newly isolated from soils and in two N. europaea and Nitrosospira multiformis type strains. The fraction of oxidized ammonium released as N2O during aerobic growth was remarkably constant (0.07 to 0.1%) for all the Nitrosospira strains, irrespective of the substrate supply (urea versus ammonium), the pH, or substrate limitation. N. europaea and Nitrosospira multiformis released similar fractions of N2O when they were supplied with ample amounts of substrates, but the fractions rose sharply (to 1 to 5%) when they were restricted by a low pH or substrate limitation. Phosphate buffer (versus HEPES) doubled the N2O release for all types of AOB. No detectable oxidation of atmospheric methane was detected. Calculations based on detection limits as well as data in the literature on CH4 oxidation by AOB bacteria prove that none of the tested strains contribute significantly to the oxidation of atmospheric CH4 in soils.

Thiomicrospira kuenenii sp. nov. and Thiomicrospira frisia sp. nov., two mesophilic obligately chemolithoautotrophic sulfur-oxidizing bacteria isolated from an intertidal mud flat.

Two new members of the genus Thiomicrospira were isolated from an intertidal mud flat sample with thiosulfate as the electron donor and CO2 as carbon source. On the basis of differences in genotypic and phenotypic characteristics, it is proposed that strain JB-A1T (= DSM 12350T) and strain JB-A2T (= DSM 12351T) are members of two new species, Thiomicrospira kuenenii and Thiomicrospira frisia, respectively. The cells were Gram-negative vibrios or slightly bent rods. Strain JB-A1T was highly motile, whereas strain JB-A2T showed a much lower degree of motility combined with a strong tendency to form aggregates. Both organisms were obligately autotrophic and strictly aerobic. Nitrate was not used as electron acceptor. Chemolithoautotrophic growth was observed with thiosulfate, tetrathionate, sulfur and sulfide. Neither isolate was able to grow heterotrophically. For strain JB-A1T, growth was observed between pH values of 4.0 and 7.5 with an optimum at pH 6.0, whereas for strain JB-A2T, growth was observed between pH 4.2 and 8.5 with an optimum at pH 6.5. The temperature limits for growth were between 3.5 and 42 degrees C and 3.5 and 39 degrees C, respectively. The optimum growth temperature for strain JB-A1T was between 29 and 33.5 degrees C, whereas strain JB-A2T showed optimal growth between 32 and 35 degrees C. The mean maximum growth rate on thiosulfate was 0.35 h-1 for strain JB-A1T and 0.45 h-1 for strain JB-A2T.

Thiomicrospira chilensis sp. nov., a mesophilic obligately chemolithoautotrophic sulfuroxidizing bacterium isolated from a Thioploca mat.

A new member of the genus Thiomicrospira, which utilizes thiosulfate as the electron donor and CO2 as the carbon source, was isolated from a sediment sample dominated by the filamentous sulfur bacterium Thioploca. Although the physiological properties investigated are nearly identical to other described species of the genus, it is proposed that strain Ch-1T is a member of a new species, Thiomicrospira chilensis sp. nov., on the basis of differences in genotypic characteristics (16S rRNA sequence, DNA homology, G + C content). Strain Ch-1T was highly motile with a slight tendency to form aggregates in the stationary growth phase. The organism was obligately autotrophic and strictly aerobic. Nitrate was not used as an electron acceptor. Chemolithoautotrophic growth was observed with thiosulfate, tetrathionate, sulfur and sulfide. The isolate was not able to grow heterotrophically. Growth of strain Ch-1T was observed between pH 5.3 and 8.5 with an optimum at pH 7.0. The temperature range for growth was between 3.5 and 42 degrees C; the optimal growth temperature was between 32 and 37 degrees C. The mean maximum growth rate on thiosulfate was 0.4 h-1. This is the second Thiomicrospira species described that has a rod-shaped morphology; therefore discrimination between vibrio-shaped Thiomicrospira and rod-shaped Thiobacilli is no longer valid.