Gene organization and primary structure of a ribosomal RNA operon from Escherichia coli

Composition and dynamics of the gill microbiota of an invasive Indo-Pacific oyster in the eastern Mediterranean Sea

Gill bacterial communities of Chama pacifica, an Indo-Pacific invasive oyster to the eastern Mediterranean Sea, were compared with those of Chama savignyi, its northern Red Sea congeneric species. Summer and winter bacterial populations were characterized and compared using 16S rDNA clone libraries, and seasonal population dynamics were monitored by automated ribosomal intergenic spacer analysis (ARISA). Clone libraries revealed a specific clade of bacteria, closely related to marine endosymbionts from the Indo-Pacific, found in both ecosystems, of which one taxon was conserved in oysters from both sites. This taxon was dominant in summer libraries and was weakly present in winter ones, where other members of this group were dominant. ARISA results revealed significant seasonal variation in bacterial populations of Mediterranean Sea oysters, as opposed to Red Sea ones that were stable throughout the year. We suggest that this conserved association between bacteria and oyster reflects either a symbiosis between the oyster host and some of its bacteria, a co-invasion of both parties, or both.

Metagenomic analysis of the uterine bacterial microbiota in healthy and metritic postpartum dairy cows

At present, many bacterial species are validly known as etiological agents of dairy cattle metritis, yet the vast uncultured fraction has received no attention so far. The purpose of this study was to use culture-independent methods to describe and compare the uterine bacterial composition in healthy and metritic postpartum Holstein dairy cows. Both group-specific 16S ribosomal DNA PCR-denaturing gradient gel electrophoresis (DGGE) and clone library sequencing of broad-range 16S ribosomal DNA PCR revealed differences in the bacterial communities comparing healthy and metritic cows. Bacterial diversity in healthy and metritic uteri was greater and more complex than described previously by traditional culture methods. Sequences were assigned to 5 major groups (Gammaproteobacteria, Firmicutes, Fusobacteria, Bacteroidetes, and Tenericutes) and to uncultured bacteria. Additionally, DGGE suggested the presence of Actinobacteria. Most clone sequences in the metritic status libraries were affiliated with the phylum Fusobacteria. Many components, especially from other phyla, have not previously been isolated from cases of metritis. In the clone libraries from the healthy status dairy cows, Gammaproteobacteria was the most prominent group and most sequences showed high identity with Mannheimia varigena, Pasteurella hemolytica, and members of the phylum Tenericutes. Our data showed that the uterine bacterial community in postpartum dairy cows differed considerably between healthy and metritic cows and described the occurrence of a previously unrecognized extent of this diversity in the bovine intrauterine microbiota.

Marine isolate Citricoccus sp. KMM 3890 as a source of a cyclic siderophore nocardamine with antitumor activity

A novel actinobacterium, designated KMM 3890 was isolated from a bottom sediment sample collected from the Sakhalin shallow environment. Phylogenetic analysis based on 16S rRNA gene sequences demonstrated strain KMM 3890 affiliation to the genus Citricoccus. In addition to its hemolytic activity, this strain exhibited inhibitory activity against Gram-positive bacteria. It was found that the marine isolate Citricoccus sp. KMM 3890 produced and excreted into the culture medium a large amount of the compound, which was isolated and structurally characterized as known cyclic siderophore nocardamine on the basis of combined spectral analyses. Nocardamine showed inhibitory effects to colony formation of T-47D, SK-Mel-5, SK-Mel-28 and PRMI-7951 tumor cell lines and a weak antimicrobial against Gram-positive bacteria and no revealed cytotoxic activity. This study can be considered as the first report on marine isolate of the genus Citricoccus producing nocardamine with antitumor activity.

Novosphingobium soli sp. nov., isolated from soil

A yellow-pigmented, Gram-negative, rod-shaped, non-spore-forming bacterium, strain CC-TPE-1T, was isolated from oil-contaminated soil near an oil refinery located in Kaohsiung County, Taiwan. 16S rRNA gene sequence analysis of strain CC-TPE-1T showed highest sequence similarity to Novosphingobium naphthalenivorans TUT562T (98.1 %), N. panipatense SM16T (97.9 %) and N. mathurense SM117T (97.6 %) and lower (<97 %) sequence similarity to all other Novosphingobium species. DNA–DNA hybridizations of strain CC-TPE-1T with N. naphthalenivorans DSM 18518T, N. panipatense SM16T and N. mathurense SM117T showed low relatedness of 30 % (reciprocal 35 %), 29.1 % (reciprocal 30.6 %) and 35 % (reciprocal 23.6 %), respectively. The major respiratory quinone was ubiquinone Q-10, the predominant fatty acid was C18 : 1 ω7c (49.9 %) and three 2-hydroxy fatty acids, C14 : 0 2-OH (8.2 %), C15 : 0 2-OH (2.45 %) and C16 : 0 2-OH (1.05 %), were detected. Polar lipids consisted mainly of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, phosphatidyldimethylethanolamine, two sphingoglycolipids, phosphatidylmonomethylethanolamine and several unidentified lipids, and a yellow pigment was also detected. The polyamine pattern contained the single major compound spermidine. Characterization by 16S rRNA gene sequence analysis, physiological parameters, pigment analysis and polyamine, ubiquinone, polar lipid and fatty acid compositions revealed that strain CC-TPE-1T represents a novel species of the genus Novosphingobium, for which we propose the name Novosphingobium soli sp. nov., with the type strain CC-TPE-1T (=DSM 22821T =CCM 7706T =CCUG 58493T).

Diethylene glycol removal by Echinodorus cordifolius (L.): the role of plant-microbe interactions

This work presents the use of the plant Echinodorus cordifolius for remediating diethylene glycol (DEG) contaminated waters. The potential of this plant for treating DEG wastewater in a remediation system was observed. We found that E. cordifolius was able to remove DEG from wastewater, decrease the pH to neutral and remove approximately 95% of the chemical oxygen demand within 12 days. The plants can grow well in DEG wastewater, as indicated by their root and leaf biomass, which was found to be statistically similar to control. Wilting, chlorosis and necrosis were observed in DEG-treated plants, but the relative water content was not significantly different between control and treated plants, suggesting that the plants were able to take up and tolerate DEG present in the wastewater. Plant roots changed to black colour during experimental period. The fluorescence in situ hybridisation and bacterial enrichment confirmed that 4.30 × 10(5) cells/g of sulphate reducing bacteria and 9.30 × 10(8) cells/g of acid-producing bacteria were found associated with the plant roots. Furthermore, volatile fatty acids were found in non-sterile soil treatments, indicating that soil microorganisms are associated with DEG remediation. These results demonstrated that plants and bacteria have the ability to form a relationship to remove the organic contaminant DEG.

Sphaerisporangium krabiense sp. nov., isolated from soil

A Gram-staining-positive, filamentous bacterial strain, designated A-T 0308(T), was isolated from soil of a tropical mangrove forest in Thailand. Strain A-T 0308(T) developed spherical sporangia containing non-motile spores on aerial mycelium. The novel strain contained meso-diaminopimelic acid, N-acetyl-type peptidoglycan and madurose, mannose, ribose, galactose and glucose as whole-cell sugars. The predominant menaquinones were MK-9(H(4)) and MK-9(H(6)); a small amount of MK-9(H(2)) and MK-9 was also detected. Mycolic acids were not detected. The diagnostic phospholipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside and phosphoglycolipid. The predominant cellular fatty acids were iso-C(16:0) and 10-methylated C(17:0). The G+C content of the DNA was 72 mol%. Phenotypic and chemotaxonomic analyses showed that the novel isolate had characteristics typical of members of the genus Sphaerisporangium. 16S rRNA gene sequence analysis also indicated that the strain belongs to the genus Sphaerisporangium and that it represents a clade distinct from other members of the genus with sequence similarities ranging from 96.3 to 97.8% between the novel strain and its closest relatives. Based on the results of phenotypic, chemotaxonomic and phylogenetic studies, strain A-T 0308(T) (=BCC 21702(T) =NBRC 107571(T)) represents a novel species of the genus Sphaerisporangium, for which the name Sphaerisporangium krabiense sp. nov. is proposed.

Sequence variability of the pattern recognition receptor Mermaid mediates specificity of marine nematode symbioses

Selection of a specific microbial partner by the host is an all-important process. It guarantees the persistence of highly specific symbioses throughout host generations. The cuticle of the marine nematode Laxus oneistus is covered by a single phylotype of sulfur-oxidizing bacteria. They are embedded in a layer of host-secreted mucus containing the mannose-binding protein Mermaid. This Ca(2+)-dependent lectin mediates symbiont aggregation and attachment to the nematode. Here, we show that Stilbonema majum-a symbiotic nematode co-occurring with L. oneistus in shallow water sediment-is covered by bacteria phylogenetically distinct to those covering L. oneistus. Mermaid cDNA analysis revealed extensive protein sequence variability in both the nematode species. We expressed three recombinant Mermaid isoforms, which based on the structural predictions display the most different carbohydrate recognition domains (CRDs). We show that the three CRDs (DNT, DDA and GDA types) possess different affinities for L. oneistus and S. majum symbionts. In particular, the GDA type, exclusively expressed by S. majum, displays highest agglutination activity towards its symbionts and lowest towards its L. oneistus symbionts. Moreover, incubation of L. oneistus in the GDA type does not result in complete symbiont detachment, whereas incubation in the other types does. This indicates that the presence of particular Mermaid isoforms on the nematode surface has a role in the attachment of specific symbionts. This is the first report of the functional role of sequence variability in a microbe-associated molecular patterns receptor in a beneficial association.

Composition of bacterial and archaeal communities in freshwater sediments with different contamination levels (Lake Geneva, Switzerland)

The aim of this study was to compare the composition of bacterial and archaeal communities in contaminated sediments (Vidy Bay) with uncontaminated sediments (Ouchy area) of Lake Geneva using 16S rRNA clone libraries. Sediments of both sites were analysed for physicochemical characteristics including porewater composition, organic carbon, and heavy metals. Results show high concentrations of contaminants in sediments from Vidy. Particularly, high contents of fresh organic matter and nutrients led to intense mineralisation, which was dominated by sulphate-reduction and methanogenesis. The bacterial diversity in Vidy sediments was significantly different from the communities in the uncontaminated sediments. Phylogenetic analysis revealed a large proportion of Betaproteobacteria clones in Vidy sediments related to Dechloromonas sp., a group of dechlorinating and contaminant degrading bacteria. Deltaproteobacteria, including clones related to sulphate-reducing bacteria and Fe(III)-reducing bacteria (Geobacter sp.) were also more abundant in the contaminated sediments. The archaeal communities consisted essentially of methanogenic Euryarchaeota, mainly found in the contaminated sediments rich in organic matter. Multiple factor analysis revealed that the microbial community composition and the environmental variables were correlated at the two sites, which suggests that in addition to environmental parameters, pollution may be one of the factors affecting microbial community structure.

Orthogonal gene expression in Escherichia coli

Here, we describe a route orthogonal gene expression which combines orthogonal transcription and translation using library-based selections. We show how orthogonal gene expression can be used to create a minimal orthogonal ribosome and describe how to create orthogonal transcription-translation feed forward loops that introduce tailored information processing delays into gene expression.

Active community profiling via capillary electrophoresis single-strand conformation polymorphism analysis of amplified 16S rRNA and 16S rRNA genes

Here, we report the validation and advancement of a high-throughput method for fingerprinting the active members of a microbial community. This method, termed active community profiling (ACP), provides information about both the composition and the activity of mixed microbial cultures via comparative measurements of amplified 16S rRNA (RNA) and 16S rRNA genes (DNA). Capillary electrophoresis is used to resolve single-strand conformation polymorphisms of polymerase chain reaction (PCR) and reverse transcription PCR (RT-PCR) products, producing electropherograms representative of the community structure. Active members of the community are distinguished by elevated RNA:DNA peak area ratios. Chemostat experiments with defined populations were conducted to validate the ACP approach. Using a pure culture of Escherichia coli, a direct correlation was found between the growth rate and the RNA:DNA peak ratio. In a second validation experiment, a binary culture of E. coli and Pseudomonas putida was subjected to a controlled environmental change consisting of a shift to anaerobic conditions. ACP revealed the expected cessation of growth of P. putida, an obligate aerobe, while the corresponding DNA-only analysis indicated no change in the culture. Finally, ACP was applied to a complex microbial community, and a novel binning approach was demonstrated for integrating the RNA and DNA electropherograms. ACP thus represents a significant advance from traditional DNA-based profiling techniques, which do not distinguish active from inactive or dead cells, and is well suited for high-throughput community analysis.

Changes in the structure and function of microbial communities in drinking water treatment bioreactors upon addition of phosphorus

Phosphorus was added as a nutrient to bench-scale and pilot-scale biologically active carbon (BAC) reactors operated for perchlorate and nitrate removal from contaminated groundwater. The two bioreactors responded similarly to phosphorus addition in terms of microbial community function (i.e., reactor performance), while drastically different responses in microbial community structure were detected. Improvement in reactor performance with respect to perchlorate and nitrate removal started within a few days after phosphorus addition for both reactors. Microbial community structures were evaluated using molecular techniques targeting 16S rRNA genes. Clone library results showed that the relative abundance of perchlorate-reducing bacteria (PRB) Dechloromonas and Azospira in the bench-scale reactor increased from 15.2% and 0.6% to 54.2% and 11.7% after phosphorus addition, respectively. Real-time quantitative PCR (qPCR) experiments revealed that these increases started within a few days after phosphorus addition. In contrast, after phosphorus addition, the relative abundance of Dechloromonas in the pilot-scale reactor decreased from 7.1 to 0.6%, while Zoogloea increased from 17.9 to 52.0%. The results of this study demonstrated that similar operating conditions for bench-scale and pilot-scale reactors resulted in similar contaminant removal performances, despite dramatically different responses from microbial communities. These findings suggest that it is important to evaluate the microbial community compositions inside bioreactors used for drinking water treatment, as they determine the microbial composition in the effluent and impact downstream treatment requirements for drinking water production. This information could be particularly relevant to drinking water safety, if pathogens or disinfectant-resistant bacteria are detected in the bioreactors.

Characterization of bacterial community structure in a drinking water distribution system during an occurrence of red water

The role of bacteria in the occasional emergence of red water, which has been documented worldwide, has yet to be determined. To better understand the mechanisms that drive occurrences of red water, the bacterial community composition and the relative abundance of several functional bacterial groups in a water distribution system of Beijing during a large-scale red water event were determined using several molecular methods. Individual clone libraries of the 16S rRNA gene were constructed for three red water samples and one sample of normal water. Beta-, Alpha-, and Gammaproteobacteria comprised the major bacterial communities in both red water and normal water samples, in agreement with previous reports. A high percentage of red water clones (25.2 to 57.1%) were affiliated with or closely related to a diverse array of iron-oxidizing bacteria, including the neutrophilic microaerobic genera Gallionella and Sideroxydans, the acidophilic species Acidothiobacillus ferrooxidans, and the anaerobic denitrifying Thermomonas bacteria. The genus Gallionella comprised 18.7 to 28.6% of all clones in the three red water libraries. Quantitative real-time PCR analysis showed that the 16S rRNA gene copy concentration of Gallionella spp. was between (4.1 ± 0.9) × 10⁷ (mean ± standard deviation) and (1.6 ± 0.3) × 10⁸ per liter in red water, accounting for 13.1% ± 2.9% to 17.2% ± 3.6% of the total Bacteria spp. in these samples. By comparison, the percentages of Gallionella spp. in the normal water samples were 0.1% or lower (below the limit of detection), suggesting an important role of Gallionella spp. in the formation of red water.

Novel plasmid-based genetic tools for the study of promoters and terminators in Streptococcus pneumoniae and Enterococcus faecalis

Promoter-probe and terminator-probe plasmid vectors make possible to rapidly examine whether particular sequences function as promoter or terminator signals in various genetic backgrounds and under diverse environmental stimuli. At present, such plasmid-based genetic tools are very scarce in the Gram-positive pathogenic bacteria Streptococcus pneumoniae and Enterococcus faecalis. Hence, we developed novel promoter-probe and terminator-probe vectors based on the Streptococcus agalactiae pMV158 plasmid, which replicates autonomously in numerous Gram-positive bacteria. As reporter gene, a gfp allele encoding a variant of the green fluorescent protein was used. These genetic tools were shown to be suitable to assess the activity of promoters and terminators (both homologous and heterologous) in S. pneumoniae and E. faecalis. In addition, the promoter-probe vector was shown to be a valuable tool for the analysis of regulated promoters in vivo, such as the promoter of the pneumococcal fuculose kinase gene. These new plasmid vectors will be very useful for the experimental verification of predicted promoter and terminator sequences, as well as for the construction of new inducible-expression vectors. Given the promiscuity exhibited by the pMV158 replicon, these vectors could be used in a variety of Gram-positive bacteria.

Molecular analyses of the microbial community composition of an anoxic basin of a municipal wastewater treatment plant reveal a novel lineage of proteobacteria

A culture-independent molecular phylogenetic approach was used to study prokaryotic diversity in an anoxic activated sludge from a municipal wastewater treatment plant. Two 16S rRNA gene libraries were constructed using total genomic DNA and amplified by polymerase chain reaction using primers specific for archaeal or bacterial domains. Phylogenetic analysis of 132 and 249 almost full-length 16S rRNA genes for Archaea and Bacteria, respectively, was done using the ARB software package. Phylogenetic groups affiliated with the Archaea belong to Euryarchaeota (93.8% of the operational taxonomic units [OTUs]) and Crenarchaeota (6.2% of the OTUs). Within the bacterial library, 84.8% of the OTUs represent novel putative phylotypes never described before and affiliated with ten divisions. The Proteobacteria phylum is the most abundant and diversified phylogenetic group representing 60.4% of the OTUs, followed by Bacteroidetes (22.1%) and gram-positives (6.1%). Interestingly, we detected a novel Proteobacteria monophyletic group distinct from the five known subclasses, which we named New Lineage of Proteobacteria (NLP) lineage, and it is composed of eight clones representing 4.6% of the Proteobacteria. A new 16S rRNA-targeted hybridization probe was designed and fluorescent in situ hybridization analyses shows representatives of NLP as cocci-shaped microorganisms. The Chloroflexi, Acidobacterium, and Nitrospira phyla and TM7 candidate division are each represented by ≤3% of clone sequences. A comprehensive set of eight 16S and 23S rRNA-targeted oligonucleotide probes was used to quantify these major groups by dot blot hybridization within 12 samples. The Proteobacteria accounted for 82.5 ± 4.9%, representing the most abundant phyla. The Bacteroidetes and Planctomycetales groups accounted for 4.9 ± 1.3% and 4 ± 1.7%, respectively. Firmicutes and Actinobacteria together accounted for only 1.9 ± 0.5%. The set of probes covers 93.4 ± 14% of the total bacterial population rRNA within the anoxic basin.

Expression of the nodulation gene nodA in Rhizobium meliloti and localization of the gene product in the cytosol

The nodA gene of Rhizobium meliloti encodes a 21.8-kDa protein, which is conserved in several Rhizobium species. We overproduced the nodA protein as a fusion product with a portion of the lambda cI repressor in Escherichia coli. This fusion protein was purified from inclusion bodies by gel and hydroxyapatite chromatography in the presence of NaDodSO(4). Monospecific polyclonal antibodies against the hybrid protein were used to detect the nodA protein in the cytosol of E. coli and R. meliloti by immunoblotting. In contrast to experiments with antibodies against the R. meliloti nodC membrane protein, the alfalfa-R. meliloti nodulation was not affected by the addition of anti-nodA antibodies to medium and inoculum. This suggests that the nodA protein is located within the cell and is therefore not accessible to antibodies. The expression of the nodA gene is induced in R. meliloti by various compounds present in the exudate of leguminous plants, particularly by the flavone luteolin. We show that the plant hormone trigonelline also has some inducing activity. The nodC protein was further localized in the membrane fraction of R. meliloti. Our experiments demonstrate that the nodC transmembrane protein is not necessary for the uptake of the compounds inducing the synthesis of the nodA protein. The nodA and the nodC proteins were also detected in mature nodules. During nodule development, the nodC protein may be processed to a 34-kDa protein.

A gene coding for tRNA is located near 5' terminus of 16S rRNA gene in Zea mays chloroplast genome

A region of 635 base pairs preceding a gene for 16S rRNA in the Zea mays chloroplast genome has been mapped and its sequence has been determined. Screening for structural elements common to tRNAs reveals a gene coding for tRNA(Val) (GU(U) (C)) positioned 303 base pairs proximal to the 5' end of the 16S rRNA gene. Both the tRNA(Val) and the 16S rRNA are coded in the same DNA strand. The tRNA nucleotide sequence predicted from the DNA sequence meets all structural characteristics common to tRNA primary and secondary structures. In a quantitative comparison with primary structures of the 14 known tRNA(Val) species the chloroplast isoaceptor shows much higher homology with that from prokaryotic than that from eukaryotic species. Regions that Escherichia coli RNA polymerase protects from nuclease attack are observed 25 and 100 base pairs upstream of the tRNA(Val) gene and 105 base pairs upstream of the 16S rRNA gene. Within these regions are short sequences that are very similar to those in the -35 region of E. coli rrn and that may therefore represent all or parts of transcription initiation signals of the respective genes.

Genetic Variation within a Lotic Population of Janthinobacterium lividum

An understanding of the genetic variation within and between populations should allow scientists to address many problems, including those associated with endangered species and the release of genetically modified organisms into the environment. With respect to microorganisms, the release of genetically engineered microorganisms is likely to increase dramatically given the current growth in the bioremediation industry. In this study, genetic variation within a lotic, bacterial population of Janthinobacterium lividum was measured with restriction fragment length polymorphism analysis. Chromosomal DNA from 10 Kettle Creek (Hawk Mountain Sanctuary, Kempton, Pa.) J. lividum isolates was digested with six restriction endonucleases and probed with a 7.5-kb pKK3535 fragment containing the E. coli rrnB rRNA operon. Genetic variation, as measured in terms of nucleotide diversity, was high within the population. The 0.0781 value for genetic variation was especially high given the conservative nature of the genetic probe. The average percent similarity among isolates within the population was 67.25%. Pairwise comparisons of nucleotide diversity values (pi) and similarity coefficients (F) yielded values ranging from 0.0032 to 0.1816 and 0.3363 to 0.9808, respectively. Putative clonemates were not present within the group of isolates; however, all isolates shared 14 fragments across a spectrum of six restriction enzymes. The presence of these common fragments indicates that restriction fragment length polymorphism analysis may provide population- or species-specific diagnostic markers for J. lividum. Data that suggest a plume effect with respect to the downstream movement of J. lividum are also presented. An increase in genetic variation within groups of isolates along the longitudinal gradient of Kettle Creek is also suggested.

Experimental identification and characterization of 97 novel npcRNA candidates in Salmonella enterica serovar Typhi

We experimentally identified and characterized 97 novel, non-protein-coding RNA candidates (npcRNAs) from the human pathogen Salmonella enterica serovar Typhi (hereafter referred to as S. typhi). Three were specific to S. typhi, 22 were restricted to Salmonella species and 33 were differentially expressed during S. typhi growth. We also identified Salmonella Pathogenicity Island-derived npcRNAs that might be involved in regulatory mechanisms of virulence, antibiotic resistance and pathogenic specificity of S. typhi. An in-depth characterization of S. typhi StyR-3 npcRNA showed that it specifically interacts with RamR, the transcriptional repressor of the ramA gene, which is involved in the multidrug resistance (MDR) of Salmonella. StyR-3 interfered with RamR–DNA binding activity and thus potentially plays a role in regulating ramA gene expression, resulting in the MDR phenotype. Our study also revealed a large number of cis-encoded antisense npcRNA candidates, supporting previous observations of global sense–antisense regulatory networks in bacteria. Finally, at least six of the npcRNA candidates interacted with the S. typhi Hfq protein, supporting an important role of Hfq in npcRNA networks. This study points to novel functional npcRNA candidates potentially involved in various regulatory roles including the pathogenicity of S. typhi.

Linkage between bacterial carbon processing and the structure of the active bacterial community at a coastal site in the NW Mediterranean Sea

The temporal dynamics in bulk bacterial parameters and in the richness of the total and active bacterial community, determined from CE-SSCP fingerprints of 16S rRNA genes and 16S rRNA transcripts, respectively, were followed weekly to bimonthly at an oligotrophic coastal site in the NW Mediterranean Sea. Bacterial abundance, bacterial heterotrophic production, and bacterial and community respiration determined over two seasonal cycles displayed large short-term variability and no pronounced temporal pattern was detectable for these parameters. Concentrations in inorganic nutrients, salinity, or concentrations of chlorophyll a could not significantly explain the temporal variability of the bacterial parameters determined. By contrast, bacterial respiration and the bacterial carbon demand were both negatively correlated with the richness of the active bacterial community, while the bacterial parameters determined herein were not related to the richness of the total bacterial community present. Our results indicate that a reduced number of ribotypes is active when rates of bacteria-mediated carbon processes are high. Our approach, based on fingerprints of 16S rRNA transcripts, could represent an interesting tool to investigate the relationship between the structure and function of marine bacteria, in particular, on short temporal and spatial scales.

Development of a 16S rRNA-targeted probe set for Verrucomicrobia and its application for fluorescence in situ hybridization in a humic lake

Members of the highly diverse bacterial phylum Verrucomicrobia are globally distributed in various terrestrial and aquatic habitats. They are key players in soils, but little is known about their role in aquatic systems. Here, we report on the design and evaluation of a 16S rRNA-targeted probe set for the identification of Verrucomicrobia and of clades within this phylum. Subsequently, the probe set was applied to a study concerning the seasonal abundance of Verrucomicrobia in waters of the humic lake Grosse Fuchskuhle (Germany) by catalyzed reporter deposition fluorescence in situ hybridization. The lake hosted diverse Verrucomicrobia clades in all seasons. Either Spartobacteria (up to 19%) or Opitutus spp. (up to 7%) dominated the communities, whereas Prosthecobacter spp. were omnipresent in low numbers (<1%). Verrucomicrobial abundance and community composition varied between the seasons, and between more and less humic basins, but were rather stable in oxic and seasonally anoxic waters.

Effects of temperature and fertilization on total vs. active bacterial communities exposed to crude and diesel oil pollution in NW Mediterranean Sea

The dynamics of total and active microbial communities were studied in seawater microcosms amended with crude or diesel oil at different temperatures (25, 10 and 4 degrees C) in the presence/absence of organic fertilization (Inipol EAP 22). Total and hydrocarbon-degrading microbes were enumerated by fluorescence microscopy and Most Probable Number (MPN) method, respectively. Total (16S rDNA-based) vs. active (16S rRNA) bacterial community structure was monitored by Capillary-Electrophoresis Single Strand Conformation Polymorphism (CE-SSCP) fingerprinting. Hydrocarbons were analyzed after 12 weeks of incubation by gas chromatography-mass spectrometry. Total and hydrocarbon-degrading microbial counts were highly influenced by fertilization while no important differences were observed between temperatures. Higher biodegradation levels were observed in fertilized microcosms. Temperature and fertilization induced changes in structure of total bacterial communities. However, fertilization showed a more important effect on active bacterial structure. The calculation of Simpson's diversity index showed similar trends among temperatures whereas fertilization reduced diversity index of both total and active bacterial communities.

Gallaecimonas pentaromativorans gen. nov., sp. nov., a bacterium carrying 16S rRNA gene heterogeneity and able to degrade high-molecular-mass polycyclic aromatic hydrocarbons

A Gram-negative, rod-shaped, halotolerant bacterium, designated strain CEE_131T, which degraded high-molecular-mass polycyclic aromatic hydrocarbons of four and five rings, was isolated from intertidal sediment of Corcubion Ria in Cee, A Coruña, Spain. Direct sequencing showed ambiguities and suggested heterogeneity. Cloned 16S rRNA gene sequence PCR products yielded five different sequences varying at five positions. Strain CEE_131T showed rather distant relationships to its phylogenetically closest neighbours, including the genera Rheinheimera and Serratia, exhibiting 91 % sequence similarity with Rheinheimera perlucida BA131T and Serratia proteamaculans subsp. quinovora DSM 4597T. The major fatty acids were C16 : 1 ω7c, C16 : 0 and C18 : 1 ω7c. The DNA G+C content was 41.7 mol%. On the basis of these distinct phenotypic and genotypic characteristics, strain CEE_131T is considered to represent a novel species in a new genus in the class Gammaproteobacteria, for which the name Gallaecimonas pentaromativorans gen. nov., sp. nov. is proposed. The type strain is CEE_131T (=DSM 21945T=CECT 7479T).

Effect of temperature stress on structure and function of the methanogenic archaeal community in a rice field soil

The effect of a brief (24 h) temperature shift to 4 degrees C (low-temperature stress) or 50 degrees C (high-temperature stress) was studied in methanogenic slurries of Italian rice field soil incubated at either constant 30 degrees C or 15 degrees C. Low-temperature (low-T) stress showed no effect in either the 30 degrees C or the 15 degrees C incubations. High-temperature (high-T) stress, on the other hand, generally resulted in an increase in the partial pressure of H(2), and the concentrations of acetate and propionate, which accumulated to about 100-200 Pa, 4-6 mM and 0.7-0.9 mM, respectively. The increase in H(2) was transient for 8-15 days. The increases in acetate and propionate were transient for about 20 days only in the 30 degrees C incubations, but persisted in the 15 degrees C incubations until the end of the experiment. The high-T stress did not result in inhibition of CH(4) production in the 30 degrees C incubations, but transiently inhibited the 15 degrees C incubations for about 25-30 days. The archaeal community in the soils was analyzed by terminal restriction fragment length polymorphism of the gene of the SSU rRNA. In the 15 degrees C incubations, the relative gene frequency of members of the Methanosarcinaceae decreased over an incubation period of 54 days, while those of Methanosaetaceae and of methanogenic rice cluster I increased. Temperature stress, high-T stress in particular, tended to reverse this trend. In the 30 degrees C incubations, on the other hand, the relative gene frequency of archaeal members showed the opposite temporal trend or remained constant unlike the 15 degrees C incubations. Again, high-T stress tended to reverse these trends, but the observed effects were much smaller in the 30 degrees C incubations than in the 15 degrees C incubations. In conclusion, a brief high-T stress affected structure and function of the methanogenic archaeal community of rice field soil.

Detection of a novel bacterium associated with spores of the arbuscular mycorrhizal fungus Gigaspora margarita

With PCR-denaturing gradient gel electrophoresis analysis, two bacterial 16S rRNA gene V3 region sequences, 7A and 7B, were detected in association with the crushed spores of the arbuscular mycorrhizal fungus Gigaspora margarita W.N. Becker & I.R. Hall 1976 MAFF520054. DNA sequencing and phylogenetic analysis revealed that 7B was mostly related to the documented cytoplasm endosymbiotic bacterium Candidatus Glomeribacter gigasporarum of G. margarita, but 7A could not be confidently assigned to a known taxon. Further characterization of 7A was conducted by obtaining its almost complete 16S rRNA gene sequence via PCR amplification and sequencing. BLAST search indicates that the 16S rRNA gene sequence did not match any identified species sequences in the GenBank database. Further detection revealed that 7A was also associated with the clean G. margarita MAFF520054 spores that were obtained by the surface-sterilized method or dual culture with Ri T-DNA transformed carrot roots. Many ellipse-shaped or egg-shaped bacterium-like organisms were clustered in layer 3 of the fungal spore wall by transmission electron microscopy observation. Our results indicate that 7A represents a novel bacterial population associated with G. margarita MAFF520054 spores, and its doubtless location (wall or cytoplasm) remains unclear based on the present data.

Planotetraspora kaengkrachanensis sp. nov. and Planotetraspora phitsanulokensis sp. nov., isolated from soil

Two novel bacterial strains were isolated from tropical rain forest soil from Thailand. Strains A-T 0875(T) and A-T 1383(T) stained Gram-positive and were filamentous bacteria that developed cylindrical sporangia containing four oval- to rod-shaped spores at the ends of short sporangiophores on branched aerial mycelium. The cell-wall peptidoglycan contained meso-diaminopimelic acid, glutamic acid and alanine as cell-wall amino acids; whole-cell hydrolysates contained rhamnose, madurose, glucose, galactose and 3-O-methylmannose as whole-cell sugars. The predominant menaquinone was MK-9(H(4)). Mycolic acids were not detected. The diagnostic phospholipid was phosphatidylethanolamine. The predominant cellular fatty acids were iso-C(16 : 0) and 10-methyl-C(17 : 0). For both strains, the G+C content of the genomic DNA was 71 mol%. Phenotypic and chemotaxonomic analyses showed that the characteristics of the two isolates were typical of members of the genus Planotetraspora. Furthermore, 16S rRNA gene sequence analysis also indicated that the strains belonged to the genus Planotetraspora but as representatives of two novel species. Following an evaluation of our phenotypic, chemotaxonomic and genotypic studies, two novel species are proposed, Planotetraspora kaengkrachanensis sp. nov. (type strain A-T 0875(T)=BCC 24832(T)=NBRC 104272(T)) and Planotetraspora phitsanulokensis sp. nov. (type strain A-T 1383(T)=BCC 26045(T)=NBRC 104273(T)).

Atrazine and terbuthylazine mineralization by an Arthrobacter sp. isolated from a sugarcane-cultivated soil in Kenya

A tropical soil from a Kenyan sugarcane-cultivated field showed a very high capability to mineralize (14)C-ring-labeled atrazine. In laboratory experiments this soil mineralized about 90% of the applied atrazine within 98 d. The atrazine-degrading microbial community was enriched in liquid cultures containing atrazine as the sole N source and 100 mgL(-1) glucose as additional C source. From the enrichment culture a bacterial strain was isolated and identified by comparative sequence analysis of the 16S-rDNA as member of the genus Arthrobacter. The enriched mixed culture as well as the isolated strain, designated as Arthrobacter sp. strain GZK-1, could grow on atrazine and terbuthylazine as sole N-sources; Arthrobacter sp. GZK-1 mineralized (14)C-ring-labeled atrazine up to 88% to (14)CO(2) and (14)C-ring-labeled terbuthylazine up to 65% to (14)CO(2) in a liquid culture within 14 d. The enriched microbial consortium as well as the isolated strain could be a potential solution for the remediation of s-triazine polluted agricultural soils.

Distribution and culturability of the uncultivated 'AGG58 cluster' of the Bacteroidetes phylum in aquatic environments

Members of the Bacteroidetes phylum are abundant in aquatic habitats when assessed by fluorescent in situ hybridisation and in some 16S rRNA gene libraries. In this study 16S rRNA gene clone libraries were constructed with bacterial primers that amplify Bacteroidetes sequences well (27F, 1492R) from coastal seawater near Plymouth (UK) during a phytoplankton bloom. Most of the clones (66%, 106/160) affiliated with the Bacteroidetes phylum, and of these 62% (66/106; or 41% 66/160 of the entire library) clustered with marine bacterioplankton clones env.agg58, Arctic97A-17, CF17, CF96 and CF101. This phylogenetic branch of Bacteroidetes was designated the 'AGG58 cluster', and its presence in various aquatic environments was investigated. Two pairs of AGG58-specific 16S rRNA-gene-targeted polymerase chain reaction (PCR) primers were designed and successfully used to detect the cluster in DNA extracts from three UK coastal seawater sites, and from freshwater River Taff epilithon. In addition, 600 putative Bacteroidetes strains were isolated from these sites on relatively high-nutrient agar media. AGG58 cluster specific probes were used to screen the amplified 16S rRNA gene products from the isolates, but no members of the AGG58 cluster were discovered. The least specific probe hybridised with one River Taff water isolate (RW262 NCIMB 13979) which formed a monophyletic group with the genera Crocinitomix, Brumimicrobium and Cryomorpha of the family Cryomorphaceae in the Bacteroidetes phylum. RW262 probably represents the first isolate of a new genus within this family. This study provides new evidence that the uncultivated AGG58 group is abundant, globally distributed, and can be rapidly detected with the new PCR primers described.

Candidatus Monilibacter spp., common bulking filaments in activated sludge, are members of Cluster III Defluviicoccus

Two alphaproteobacterial Neisser negative 'Nostocoida limicola' morphotypes differing slightly in their trichome diameter and filament regularity were dominant populations in the Bendigo, Victoria, Australia activated sludge community removing phosphorus (P). Neither responded to the FISH probes available for any of the other alphaproteobacterial 'N. limicola' morphotypes. Instead both fluoresced with the DF988 FISH probe designed originally to target alphaproteobacterial cluster II Defluviicoccus tetrad forming organisms. A 16S rRNA based clone library from this biomass revealed that the alphaproteobacterial clones grouped closely with Candidatus 'Monilibacter batavus' and Defluviicoccus clones in a cluster separate from the existing cluster I and II Defluviicoccus. When a FISH probe was designed against these, it only hybridized to the thinner and less abundant 'N. limicola' morphotype. Micromanipulation-RT-PCR was used to selectively recover the main 'N. limicola' morphotype and a FISH probe designed against the 16S rRNA clones generated from it showed only this filament fluoresced. From FISH based surveys, both 'N. limicola' variants occurred frequently in phosphorus removal activated sludge systems in Australia treating domestic waste. The data suggest that they represent two new strains of Candidatus 'Monilibacter', which on this evidence are filamentous members of the genus Defluviicoccus, a potential competitor for the polyphosphate accumulating organisms in these communities.

"Candidatus Paraholospora nucleivisitans", an intracellular bacterium in Paramecium sexaurelia shuttles between the cytoplasm and the nucleus of its host

An intracellular bacterium was discovered in two isolates of Paramecium sexaurelia from an aquarium with tropical fish in Münster (Germany) and from a pond in the Wilhelma zoological-botanical garden, Stuttgart (Germany). The bacteria were regularly observed in the cytoplasm of the host, but on some occasions they were found in the macronucleus of the host cell. In these cases, only a few, if any, bacteria were observed remaining in the cytoplasm. The bacterium was not infectious to P. sexaurelia or other species of Paramecium and appeared to be an obligate intracellular bacterium, while bacteria-free host cells were completely viable. The fluorescence in situ hybridisation (FISH) and comparative 16SrDNA sequence analyses showed that the bacterium belonged to a new genus, and was most closely, yet quite distantly, related to Holospora obtusa. In spite of this relationship, the new bacteria differed from Holospora by at least two biological features. Whereas all Holospora species reside exclusively in the nuclei of various species of Paramecium and show a life cycle with a morphologically distinct infectious form, for the new bacterium no infectious form and no life cycle have been observed. For the new bacterium, the name Candidatus Paraholospora nucleivisitans is suggested. The host P. sexaurelia is usually known from tropical and subtropical areas and is not a species typically found in Germany and central Europe. Possibly, it had been taken to Germany with fish or plants from tropical or subtropical waters. Candidatus Paraholospora nucleivisitans may therefore be regarded as an intracellular neobacterium for Germany.

Reduced susceptibility to amoxicillin of oral streptococci following amoxicillin exposure

As antibiotic pressure often triggers bacterial resistance, the use of short-duration therapies is increasingly recommended. The objective of the present study was to evaluate both the clinical efficiency and the impact on oral streptococci of a 3 day versus a 7 day amoxicillin therapy for odontogenic infection requiring tooth extraction. On day 0, patients were randomly assigned to a 3 day or 7 day amoxicillin treatment. The tooth was extracted on day 2 and the post-operative follow-up was carried out on day 9. Oral flora was collected on days 0, 9 and 30, and the susceptibility of the streptococci to amoxicillin was determined. The results showed that treatment with amoxicillin for 3 or 7 days had a similar clinical efficiency, and also induced similar selection of oral streptococci with reduced susceptibility to amoxicillin, suggesting that the selection of strains with reduced susceptibility to amoxicillin is a rapid phenomenon, appearing even with short-duration therapies.

16S rRNA gene sequence-based analysis of clostridia related to conversion of germfree mice to the normal state

AIMS

To determine phylogenetic groups of clostridia inhabiting the mouse intestine that are essential for normalization of germfree (GF) mice.

METHODS AND RESULTS

Using both the culture method and cloning, clostridia inhabiting the mouse intestine were isolated, and phylogenetic analysis based on 16S rRNA gene sequences was carried out. As a result, the isolates were found to have novel sequences, and no isolate was determined to be identical to previously known identified clostridia. Although the taxonomy of mouse intestinal clostridia was complex, many of them belonged to Clostridium clusters XIVa and IV in conventional (CV) and limited flora mice and ex-germfree mice administered chloroform-treated CV mouse faeces. The clostridia that belonged to cluster XIVa were most often present and showed the highest diversity.

CONCLUSIONS

Clostridia belonging clusters XIVa and IV are dominant in the mouse intestine as in other gut ecosystems. The novel groups in these clusters are essential for normalization of GF mice.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study can be applied in the strict control of mouse intestinal microbiota and will provide important information for normalization of GF mice and also for research on microbiology of the mouse intestine.

Synthesis of orthogonal transcription-translation networks

Orthogonal, parallel and independent, systems are one key foundation for synthetic biology. The synthesis of orthogonal systems that are uncoupled from evolutionary constraints, and selectively abstracted from cellular regulation, is an emerging approach to making biology more amenable to engineering. Here, we combine orthogonal transcription by T7 RNA polymerase and translation by orthogonal ribosomes (O-ribosomes), creating an orthogonal gene expression pathway in Escherichia coli. We design and implement compact, orthogonal gene expression networks. In particular we focus on creating transcription-translation feed-forward loops (FFLs). The transcription-translation FFLs reported cannot be created by using the cells' gene expression machinery and introduce information-processing delays on the order of hours into gene expression. We refactor the rRNA operon, uncoupling the synthesis of the orthogonal 16S rRNA for the O-ribosome from the synthesis and processing of the rest of the rRNA operon, thereby defining a minimal module that can be added to the cell for O-ribosome production. The minimal O-ribosome permits the rational alteration of the delay in an orthogonal gene expression FFL. Overall this work demonstrates that system-level dynamic properties are amenable to rational manipulation and design in orthogonal systems. In the future this system may be further evolved and tuned to provide a spectrum of tailored dynamics in gene expression and investigate the effects of delays in cellular decision-making processes.

Assessment of the microbial diversity at the surface of Livarot cheese using culture-dependent and independent approaches

The microbial diversity of the surface of a commercial red-smear cheese, Livarot cheese, sold on the retail market was studied using culture-dependent and independent approaches. Forty yeasts and 40 bacteria from the cheese surface were collected, dereplicated using single-strand conformation polymorphism (SSCP) analysis and identified using rRNA gene sequencing for the culture-dependent approach. The culture-independent approach involved cloning and sequencing of the 16S rRNA gene and SSCP analysis from total DNA extracted from the cheese. The most dominant bacteria were Microbacterium gubbeenense, Leucobacter komagatae and Gram-negative bacteria from the Gamma-Proteobacteria class. Fluorescence in situ hybridization (FISH) analysis was also used to study the cheese microbial diversity with class-level and specific rRNA-targeted probes for bacteria and yeasts, respectively. FISH analysis confirmed that Gamma-Proteobacteria were important microorganisms in this cheese. Four specific FISH probes targeting the dominant yeasts present in the cheese, Candida catenulata, Candida intermedia, Geotrichum spp. and Yarrowia lipolytica, were also designed and evaluated. These probes allowed the detection of these yeasts directly in cheese. The use of the rRNA gene-based approach combined with FISH analysis was useful to investigate the diversity of a surface microbial consortium from cheese.

Optimization of three FISH procedures for in situ detection of anaerobic ammonium oxidizing bacteria in biological wastewater treatment

Fluorescence in situ hybridization (FISH) using fluorochrome-labeled DNA oligonucleotide probes has been successfully applied for in situ detection of anaerobic ammonium oxidizing (anammox) bacteria. However, application of the standard FISH protocols to visualize anammox bacteria in biofilms from a laboratory-scale wastewater reactor produced only weak signals. Increased signal intensity was achieved either by modifying the standard FISH protocol, using peptide nucleic acid probes (PNA FISH), or applying horse radish peroxidase- (HRP-) labeled probes and subsequent catalyzed reporter deposition (CARD-FISH). A comparative analysis using anammox biofilm samples and suspended anammox biomass from different laboratory wastewater bioreactors revealed that the modified standard FISH protocol and the PNA FISH probes produced equally strong fluorescence signals on suspended biomass, but only weak signals were obtained with the biofilm samples. The probe signal intensities in the biofilm samples could be enhanced by enzymatic pre-treatment of fixed cells, and by increasing the hybridization time of the PNA FISH protocol. CARD-FISH always produced up to four-fold stronger fluorescent signals but unspecific fluorescence signals, likely caused by endogenous peroxidases as reported in several previous studies, compromised the results. Interference of the development of fluorescence intensity with endogenous peroxidases was also observed in cells of aerobic ammonium oxidizers like Nitrosomonas europea, and sulfate-reducers like Desulfobacter postgatei. Interestingly, no interference was observed with other peroxidase-positive microorganisms, suggesting that CARD-FISH is not only compromised by the mere presence of peroxidases. Pre-treatment of cells to inactivate peroxidase with HCl or autoclavation/pasteurization failed to inactive peroxidases, but H(2)O(2) significantly reduced endogenous peroxidase activity. However, for optimal inactivation, different H(2)O(2) concentrations and incubation time may be needed, depending on nature of sample and should therefore always be individually determined for each study.

The persistence of bifidobacteria populations in a river measured by molecular and culture techniques

AIMS

To determine relative to faecal coliforms (FC) and sulfite-reducing clostridia (SRC), the environmental persistence of natural populations of Bifidobacterium spp. enumerated by culturing and quantitative polymerase chain reaction (q-PCR).

METHODS AND RESULTS

Dialysis tubing containing river supplemented with overnight cultures of Bifidobacterium adolescentis (BA) and Bifidobacterium dentium (BD) or urban wastewater were suspended in a river for up to 10 days. At intervals, the contents of each dialysis tube were assayed using q-PCR assays for BA and BD, and selective culture media for FC, SRC, total bifidobacteria (TB), sorbitol-fermenting bifidobacteria (SFB) and cultivable BA. Mean summer T(90) values were 251 h for SRC, 92 h for FC, 48 h for BA and BD by q-PCR, and 9 h for TB.

CONCLUSIONS

Bifidobacterium spp. was the population with the lowest persistence, showing seasonal differences in T(90) when measured by culture techniques or by q-PCR. This difference in relative persistence is because of a longer persistence of molecular targets than cultivable cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The persistence of a viable bifidobacteria cells is shorter, but the longest persistence of molecular targets. This factor could be used for origin the faecal pollution in water for the development of microbial source tracking (MST).

Culturable microbes in shallow groundwater underlying ornithogenic soil of Cape Hallett, Antarctica

The objective of this study was to investigate the culturable psychrotolerant microbial community in groundwater from Seabee Hook, Antarctica. Shallow groundwater can be present in coastal regions at higher latitudes during the Antarctic summer. Perched groundwater atop ice-cemented permafrost occurs on Seabee Hook, Cape Hallett, at depths from 5 to 80 cm below the soil surface. Compared with terrestrial water from other sites in Antarctica, the groundwater was high in salt and nutrients, reflecting proximity to the sea and ornithogenic soil. Microbial communities in groundwater samples from Seabee Hook exhibited aerobic metabolism of 14C-acetate at 5 degrees C. Numbers of culturable aerobic heterotrophs in the samples ranged from <10 to ca. 1 x 106 colony-forming units.mL-1, and similar numbers of microaerophiles and nitrate reducers were detected. In contrast, numbers of nitrifiers, sulfate reducers, and iron reducers were up to 1000-fold lower. All cultures were incubated at 5 degrees C. Aerobic heterotrophic bacteria isolated from the groundwater were assigned to Actinobacteria, Proteobacteria, or Bacteroidetes. The isolates were most similar to cultured bacteria from Antarctic soil or sediment and were cold, salt, and alkaline pH tolerant, indicating they are adapted to in situ conditions.

Arcicella rosea sp. nov., isolated from tap water

Strain TW5(T), a motile, Gram-negative bacterium that produced pale-pink colonies, was isolated from tap water on R2A agar at 20 degrees C. 16S rRNA gene sequence studies showed that the strain clustered with Arcicella aquatica (99.0 % sequence similarity to the type strain). The main polyamine present was spermidine, the quinone system comprised menaquinone MK-7 and the polar lipid profile consisted of a mixture of aminophospholipids, aminolipids, glycolipids and uncharacterized polar lipids. The fatty acid profile was slightly different from that reported for A. aquatica. The results of DNA-DNA hybridizations and physiological and biochemical tests clearly allowed both genotypic and phenotypic differentiation of the isolate from A. aquatica. On the basis of these results, it is proposed that the strain should be classified within a novel species of the genus Arcicella. The name proposed for this taxon is Arcicella rosea sp. nov.; the type strain is TW5(T) (=CCUG 55942(T) =CCM 7523(T)).

Molecular characterization of the symbionts associated with marine nematodes of the genus Robbea

Marine nematodes that carry sulfur-oxidizing bacteria on their cuticle (Stilbonematinae, Desmodoridae) migrate between oxidized and reduced sand layers thereby supplying their symbionts with oxygen and sulfide. These symbionts, in turn, constitute the worms' major food source. Due to the accessibility, abundance and relative simplicity of this association, stilbonematids may be useful to understand symbiosis establishment. Nevertheless, only the symbiont of Laxus oneistus has been found to constitute one single phylotype within the Gammaproteobacteria. Here, we characterized the symbionts of three yet undescribed nematodes that were morphologically identified as members of the genus Robbea. They were collected at the island of Corsica, the Cayman Islands and the Belize Barrier Reef. The surface of these worms is covered by a single layer of morphologically undistinguishable bacteria. 18S rDNA-based phylogenetic analysis showed that all three species belong to the Stilbonematinae, although they do not form a distinct cluster within that subfamily. 16S rDNA-based analysis of the symbionts placed them interspersed in the cluster comprising the sulfur-oxidizing symbionts of L. oneistus and of marine gutless oligochaetes. Finally, the presence and phylogeny of the aprA gene indicated that the symbionts of all three nematodes can use reduced sulfur compounds as an energy source.

Exploring the diversity of the bifidobacterial population in the human intestinal tract

Although the health-promoting roles of bifidobacteria are widely accepted, the diversity of bifidobacteria among the human intestinal microbiota is still poorly understood. We performed a census of bifidobacterial populations from human intestinal mucosal and fecal samples by plating them on selective medium, coupled with molecular analysis of selected rRNA gene sequences (16S rRNA gene and internally transcribed spacer [ITS] 16S-23S spacer sequences) of isolated colonies. A total of 900 isolates were collected, of which 704 were shown to belong to bifidobacteria. Analyses showed that the culturable bifidobacterial population from intestinal and fecal samples include six main phylogenetic taxa, i.e., Bifidobacterium longum, Bifidobacterium pseudocatenulatum, Bifidobacterium adolescentis, Bifidobacterium pseudolongum, Bifidobacterium breve, and Bifidobacterium bifidum, and two species mostly detected in fecal samples, i.e., Bifidobacterium dentium and Bifidobacterium animalis subp. lactis. Analysis of bifidobacterial distribution based on age of the subject revealed that certain identified bifidobacterial species were exclusively present in the adult human gut microbiota whereas others were found to be widely distributed. We encountered significant intersubject variability and composition differences between fecal and mucosa-adherent bifidobacterial communities. In contrast, a modest diversification of bifidobacterial populations was noticed between different intestinal regions within the same individual (intrasubject variability). Notably, a small number of bifidobacterial isolates were shown to display a wide ecological distribution, thus suggesting that they possess a broad colonization capacity.