Wide distribution and diversity of members of the bacterial kingdom Acidobacterium in the environment.
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To assess the distribution and diversity of members of the recently identified bacterial kingdom Acidobacterium, members of this kingdom present in 43 environmental samples were surveyed by PCR amplification. A primer designed to amplify rRNA gene sequences (ribosomal DNAs [rDNAs]) from most known members of the kingdom was used to interrogate bulk DNA extracted from the samples. Positive PCR results were obtained with all temperate soil and sediment samples tested, as well as some hot spring samples, indicating that members of this kingdom are very widespread in terrestrial environments. PCR primers specific for four phylogenetic subgroups within the kingdom were used in similar surveys. All four subgroups were detected in most neutral soils and some sediments, while only two of the groups were seen in most low-pH environments. The combined use of these primers allowed identification of a novel lineage within the kingdom in a hot spring environment. Phylogenetic analysis of rDNA sequences from our survey and the literature outlines at least six major subgroups within the kingdom. Taken together, these data suggest that members of the Acidobacterium kingdom are as genetically and metabolically diverse, environmentally widespread and perhaps as ecologically important as the well-known Proteobacteria and gram-positive bacterial kingdoms. (+info)
Physiological and morphological observations on Thiovulum sp.
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Cell suspensions of Thiovulum sp., collected from enrichment cultures, were grown, maintained, and harvested for periods up to 7 months. In open-flow cultures run with aerated seawater, a continuous supply of hydrogen sulfide was provided by diffusion through a semipermeable membrane from either a live culture of Desulfovibrio esturaii, neutralized sodium sulfide, or a N2-H2S gas mixture. Attempts to grow Thiovulum in pure culture failed despite variation in concentrations of dissolved oxygen and hydrogen sulfide in stratified as well as in completely mixed systems. Uptake of 14CO2 and some organic compounds by purified cell suspensions was measured, and values were corrected for the activity of heterotrophic as well as autotrophic contaminants as determined in control experiments. Cell populations exhibited maximum uptake activities during formation of the characteristic veils. Substantial uptake of CO2 in air-saturated seawater was coincident with an optimal concentration of hydrogen sulfide of about 1 mM. Glutamate and a selection of vitamins (B12M biotin, and thiamine) did not significantly affect the uptake of CO2. No substantial uptake of carbon from acetate, glutamate, mannitol, and Casamino Acids was found. Within the range of error indicated, the data are consistent with acceptance of a chemolithotrophic nature of Thiovulum. (+info)
Thiomicrospira kuenenii sp. nov. and Thiomicrospira frisia sp. nov., two mesophilic obligately chemolithoautotrophic sulfur-oxidizing bacteria isolated from an intertidal mud flat.
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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. (+info)
Thiomicrospira chilensis sp. nov., a mesophilic obligately chemolithoautotrophic sulfuroxidizing bacterium isolated from a Thioploca mat.
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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. (+info)
Nitrous oxide production and methane oxidation by different ammonia-oxidizing bacteria.
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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. (+info)
Comparative diversity of ammonia oxidizer 16S rRNA gene sequences in native, tilled, and successional soils.
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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. (+info)
In situ analysis of nitrifying biofilms as determined by in situ hybridization and the use of microelectrodes.
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We investigated the in situ spatial organization of ammonia-oxidizing and nitrite-oxidizing bacteria in domestic wastewater biofilms and autotrophic nitrifying biofilms by using microsensors and fluorescent in situ hybridization (FISH) performed with 16S rRNA-targeted oligonucleotide probes. The combination of these techniques made it possible to relate in situ microbial activity directly to the occurrence of nitrifying bacterial populations. In situ hybridization revealed that bacteria belonging to the genus Nitrosomonas were the numerically dominant ammonia-oxidizing bacteria in both types of biofilms. Bacteria belonging to the genus Nitrobacter were not detected; instead, Nitrospira-like bacteria were the main nitrite-oxidizing bacteria in both types of biofilms. Nitrospira-like cells formed irregularly shaped aggregates consisting of small microcolonies, which clustered around the clusters of ammonia oxidizers. Whereas most of the ammonia-oxidizing bacteria were present throughout the biofilms, the nitrite-oxidizing bacteria were restricted to the active nitrite-oxidizing zones, which were in the inner parts of the biofilms. Microelectrode measurements showed that the active ammonia-oxidizing zone was located in the outer part of a biofilm, whereas the active nitrite-oxidizing zone was located just below the ammonia-oxidizing zone and overlapped the location of nitrite-oxidizing bacteria, as determined by FISH. (+info)
Spatial heterogeneity of bacterial populations along an environmental gradient at a shallow submarine hydrothermal vent near Milos Island (Greece).
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The spatial heterogeneity of bacterial populations at a shallow-water hydrothermal vent in the Aegean Sea close to the island of Milos (Greece) was examined at two different times by using acridine orange staining for total cell counts, cultivation-based techniques, and denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA gene fragments. Concurrent with measurements of geochemical parameters, samples were taken along a transect from the center of the vent to the surrounding area. Most-probable-number (MPN) counts of metabolically defined subpopulations generally constituted a minor fraction of the total cell counts; both counting procedures revealed the highest cell numbers in a transition zone from the strongly hydrothermally influenced sediments to normal sedimentary conditions. Total cell counts ranged from 3.2 x 10(5) cells ml(-1) in the water overlying the sediments to 6.4 x 10(8) cells g (wet weight) of sediment(-1). MPN counts of chemolithoautotrophic sulfur-oxidizing bacteria varied between undetectable and 1.4 x 10(6) cells g(-1). MPN counts for sulfate-reducing bacteria and dissimilatory iron-reducing bacteria ranged from 8 to 1.4 x 10(5) cells g(-1) and from undetectable to 1.4 x 10(6) cells g(-1), respectively. DGGE revealed a trend from a diverse range of bacterial populations which were present in approximately equal abundance in the transition zone to a community dominated by few populations close to the center of the vent. Temperature was found to be an important parameter in determining this trend. However, at one sampling time this trend was not discernible, possibly due to storm-induced disturbance of the upper sediment layers. (+info)