RESUMEN
Transmission of bacteria vertically through host tissues ensures offspring acquire symbionts; however, horizontal transmission is an effective strategy for many associations and plays a role in some vertically transmitted symbioses. The bivalve Solemya velum and its gammaproteobacterial chemosynthetic symbionts exhibit evolutionary evidence of both transmission modes, but the dominant strategy on an ecological time scale is unknown. To address this, a specific primer set was developed and validated for the S. velum symbiont using a novel workflow called specific marker design (SMD). Symbionts were quantified in spawned eggs and sediment and seawater samples from S. velum habitats with qPCR. Each egg was estimated to contain 50-100 symbiont genomes. By contrast, symbiont DNA was found at low abundance/occurrence in sediment and seawater, often co-occurring with host mitochondrial DNA, obscuring its origin. To ascertain when eggs become infected, histological sections of S. velum tissues were labelled for symbiont 16S rRNA via in situ hybridization. This revealed symbionts in the ovary walls and mature oocytes, suggesting association in late oogenesis. These data support the hypothesis that S. velum symbionts are vertically transmitted every host generation, thus genetic signatures of horizontal transmission are driven by ecologically infrequent events. This knowledge furthers our understanding of vertical and horizontal mode integration and provides insights across animal-bacterial chemosynthetic symbioses.
Asunto(s)
Bivalvos/microbiología , Gammaproteobacteria/aislamiento & purificación , Simbiosis , Animales , ADN Bacteriano/aislamiento & purificación , Femenino , Gammaproteobacteria/genética , Sedimentos Geológicos/microbiología , Hibridación in Situ , Masculino , Ovario/microbiología , Óvulo/microbiología , ARN Ribosómico 16S , Reacción en Cadena en Tiempo Real de la Polimerasa , Agua de Mar/microbiologíaRESUMEN
The cosmopolitan, bloom-forming diatom, Skeletonema costatum, is a prominent primary producer in coastal oceans, fixing CO2 with ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) that is phylogenetically distinct from terrestrial plant RubisCO. RubisCOs are subdivided into groups based on sequence similarity of their large subunits (IA-ID, II, and III). ID is present in several major oceanic primary producers, including diatoms such as S. costatum, coccolithophores, and some dinoflagellates, and differs substantially in amino acid sequence from the well-studied IB enzymes present in most cyanobacteria and in green algae and plants. Despite this sequence divergence, and differences in isotopic discrimination apparent in other RubisCO enzymes, stable carbon isotope compositions of diatoms and other marine phytoplankton are generally interpreted assuming enzymatic isotopic discrimination similar to spinach RubisCO (IB). To interpret phytoplankton δ(13) C values, S. costatum RubisCO was characterized via sequence analysis, and measurement of its KCO2 and Vmax , and degree of isotopic discrimination. The sequence of this enzyme placed it among other diatom ID RubisCOs. Michaelis-Menten parameters were similar to other ID enzymes (KCO2 = 48.9 ± 2.8 µm; Vmax = 165.1 ± 6.3 nmol min(-1 ) mg(-1) ). However, isotopic discrimination (ε = [(12) k/(13) k - 1] × 1000) was low (18.5; 17.0-19.9, 95% CI) when compared to IA and IB RubisCOs (22-29), though not as low as ID from coccolithophore, Emiliania huxleyi (11.1). Variability in ε-values among RubisCOs from primary producers is likely reflected in δ(13) C values of oceanic biomass. Currently, δ(13) C variability is ascribed to physical or chemical factors (e.g. illumination, nutrient availability) and physiological responses to these factors (e.g. carbon-concentrating mechanisms). Estimating the importance of these factors from δ(13) C measurements requires an accurate ε-value, and a mass-balance model using the ε-value for S. costatum RubisCO is presented. Clearly, appropriate ε-values must be included in interpreting δ(13) C values of environmental samples.
Asunto(s)
Proteínas Algáceas/metabolismo , Diatomeas/enzimología , Fitoplancton/enzimología , Ribulosa-Bifosfato Carboxilasa/metabolismo , Proteínas Algáceas/genética , Carbono/metabolismo , Isótopos de Carbono/metabolismo , Diatomeas/genética , Cinética , Modelos Biológicos , Datos de Secuencia Molecular , Filogenia , Fitoplancton/genética , Análisis de Secuencia de ProteínaRESUMEN
Chemoautotrophic endosymbionts are the metabolic cornerstone of hydrothermal vent communities, providing invertebrate hosts with nearly all of their nutrition. The Calyptogena magnifica (Bivalvia: Vesicomyidae) symbiont, Candidatus Ruthia magnifica, is the first intracellular sulfur-oxidizing endosymbiont to have its genome sequenced, revealing a suite of metabolic capabilities. The genome encodes major chemoautotrophic pathways as well as pathways for biosynthesis of vitamins, cofactors, and all 20 amino acids required by the clam.
Asunto(s)
Bivalvos/microbiología , Gammaproteobacteria/genética , Genoma Bacteriano , Simbiosis , Animales , Carbono/metabolismo , Crecimiento Quimioautotrófico , Gammaproteobacteria/aislamiento & purificación , Gammaproteobacteria/metabolismo , Gammaproteobacteria/ultraestructura , Datos de Secuencia Molecular , FotosíntesisRESUMEN
A coastal marine sulfide-oxidizing autotrophic bacterium produces hydrophilic filamentous sulfur as a novel metabolic end product. Phylogenetic analysis placed the organism in the genus Arcobacter in the epsilon subdivision of the Proteobacteria. This motile vibrioid organism can be considered difficult to grow, preferring to grow under microaerophilic conditions in flowing systems in which a sulfide-oxygen gradient has been established. Purified cell cultures were maintained by using this approach. Essentially all 4',6-diamidino-2-phenylindole dihydrochloride-stained cells in a flowing reactor system hybridized with Arcobacter-specific probes as well as with a probe specific for the sequence obtained from reactor-grown cells. The proposed provisional name for the coastal isolate is "Candidatus Arcobacter sulfidicus." For cells cultured in a flowing reactor system, the sulfide optimum was higher than and the CO(2) fixation activity was as high as or higher than those reported for other sulfur oxidizers, such as Thiomicrospira spp. Cells associated with filamentous sulfur material demonstrated nitrogen fixation capability. No ribulose 1,5-bisphosphate carboxylase/oxygenase could be detected on the basis of radioisotopic activity or by Western blotting techniques, suggesting an alternative pathway of CO(2) fixation. The process of microbial filamentous sulfur formation has been documented in a number of marine environments where both sulfide and oxygen are available. Filamentous sulfur formation by "Candidatus Arcobacter sulfidicus" or similar strains may be an ecologically important process, contributing significantly to primary production in such environments.
Asunto(s)
Arcobacter/clasificación , Arcobacter/crecimiento & desarrollo , ARN Ribosómico 16S/genética , Agua de Mar/microbiología , Sulfuros/metabolismo , Azufre/metabolismo , Arcobacter/química , Arcobacter/genética , Arcobacter/metabolismo , Dióxido de Carbono/metabolismo , Medios de Cultivo , ADN Ribosómico/análisis , Hibridación Fluorescente in Situ , Microscopía Electrónica , Datos de Secuencia Molecular , Fijación del Nitrógeno , Oxidación-Reducción , Filogenia , Ribulosa-Bifosfato Carboxilasa/metabolismo , Análisis de Secuencia de ADNRESUMEN
Within the endemic invertebrate faunas of hydrothermal vents, five biogeographic provinces are recognized. Invertebrates at two Indian Ocean vent fields (Kairei and Edmond) belong to a sixth province, despite ecological settings and invertebrate-bacterial symbioses similar to those of both western Pacific and Atlantic vents. Most organisms found at these Indian Ocean vent fields have evolutionary affinities with western Pacific vent faunas, but a shrimp that ecologically dominates Indian Ocean vents closely resembles its Mid-Atlantic counterpart. These findings contribute to a global assessment of the biogeography of chemosynthetic faunas and indicate that the Indian Ocean vent community follows asymmetric assembly rules biased toward Pacific evolutionary alliances.
Asunto(s)
Fenómenos Fisiológicos Bacterianos , Ecosistema , Sedimentos Geológicos , Invertebrados/fisiología , Animales , Bacterias/clasificación , Bacterias/aislamiento & purificación , Evolución Biológica , Biomasa , Decápodos/clasificación , Decápodos/fisiología , Euryarchaeota/clasificación , Euryarchaeota/aislamiento & purificación , Euryarchaeota/fisiología , Geografía , Sedimentos Geológicos/microbiología , Calor , Invertebrados/clasificación , Invertebrados/microbiología , Datos de Secuencia Molecular , Moluscos/clasificación , Moluscos/fisiología , Océanos y Mares , Agua de Mar , SimbiosisRESUMEN
Methanotrophic bacteria play a major role in the global carbon cycle, degrade xenobiotic pollutants, and have the potential for a variety of biotechnological applications. To facilitate ecological studies of these important organisms, we developed a suite of oligonucleotide probes for quantitative analysis of methanotroph-specific 16S rRNA from environmental samples. Two probes target methanotrophs in the family Methylocystaceae (type II methanotrophs) as a group. No oligonucleotide signatures that distinguish between the two genera in this family, Methylocystis and Methylosinus, were identified. Two other probes target, as a single group, a majority of the known methanotrophs belonging to the family Methylococcaceae (type I/X methanotrophs). The remaining probes target members of individual genera of the Methylococcaceae, including Methylobacter, Methylomonas, Methylomicrobium, Methylococcus, and Methylocaldum. One of the family-level probes also covers all methanotrophic endosymbionts of marine mollusks for which 16S rRNA sequences have been published. The two known species of the newly described genus Methylosarcina gen. nov. are covered by a probe that otherwise targets only members of the closely related genus Methylomicrobium. None of the probes covers strains of the newly proposed genera Methylocella and "Methylothermus," which are polyphyletic with respect to the recognized methanotrophic families. Empirically determined midpoint dissociation temperatures were 49 to 57 degrees C for all probes. In dot blot screening against RNA from positive- and negative-control strains, the probes were specific to their intended targets. The broad coverage and high degree of specificity of this new suite of probes will provide more detailed, quantitative information about the community structure of methanotrophs in environmental samples than was previously available.
Asunto(s)
Alphaproteobacteria/genética , Ecosistema , Microbiología Ambiental , Methylococcaceae/genética , Sondas de Oligonucleótidos/genética , ARN Ribosómico 16S/genética , Alphaproteobacteria/clasificación , Genes de ARNr , Metano/metabolismo , Methylococcaceae/clasificación , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
Toluene uptake by a benthic biofilm community was previously shown to vary seasonally from 0.03 m hr?1 in winter to 0.2 m hr?1 in summer in a solvent-contaminated stream of the Aberjona watershed. We used quantitative PCR to estimate the population dynamics of previously isolated species of toluene-degrading Xanthobacter autotrophicus and Mycobacterium sp. in both toluene-contaminated and uncontaminated reaches of the stream, and to estimate their relative roles in overall biodegradation rate. Quantification using specific 16S rDNA primers forX. autotrophicus and Mycobacterium sp. showed that populations of both species were much larger in the toluene-contaminated than the toluene-free reach, in agreement with earlier culture-based investigations. A relatively brief bloom of X. autotrophicus occurred in the contaminated reach in the summer, while Mycobacterium sp. populations occurred at elevated densities for more than 5 months. Calculations showed that Mycobacterium, previously thought to be less important than Xanthobacter in annual toluene degradation based on single time-point CFU estimates, appears actually more important because of this longer persistence.
RESUMEN
The diversity of a microbial community covering the surface of a marine nematode was analyzed by performing a 16S ribosomal DNA (rDNA) restriction cutting and sequencing analysis. In two clone libraries constructed by using individual nematodes, 54 and 85 restriction patterns were identified, and only 13 of these patterns were common to both libraries. Sequence analysis indicated that the common patterns belonged to four groups related to sequences of cytophagas, sulfate-reducing bacteria, members of the gamma subclass of the class Proteobacteria, and caulobacters. At least two groups appeared to be permanent members of the community as they were also detected in a 16S rDNA library constructed 3 years previously by using 100 pooled nematode specimens. A surprising outcome was that very dominant filamentous bacteria were apparently not represented in the clone libraries, as quantitative probing showed that none of the common operational taxonomic unit groups displayed the expected overwhelming dominance. Nevertheless, our analysis revealed both an unexpectedly high level of bacterial diversity and heterogeneity in samples representing presumably very similar microenvironments.
Asunto(s)
Bacterias/clasificación , Bacterias/genética , Nematodos/microbiología , Animales , ADN Bacteriano/genética , ADN Ribosómico/genética , Ecosistema , Variación Genética , Biología Marina , Datos de Secuencia Molecular , Filogenia , ARN Ribosómico 16S/genética , Mapeo Restrictivo , Análisis de Secuencia de ADNRESUMEN
Toluene-degrading strains T101 and T102 were isolated from rock surface biomass in a toluene-contaminated freshwater stream. These organisms were present at a density of 5.5 x 10(6) cells/g of rock surface biomass. Both are aerobic, rod-shaped, Gram-negative, non-motile, catalase-positive, oxidase-positive, with yellow pigments, and can grow on benzene. Phylogenetic analyses show that strains T101 and T102 have 16S rDNA sequences identical to Xanthobacter autotrophicus. Fatty acid analyses indicate that they are different strains of the same species Xanthobacter autotrophicus, and that they have high levels of cis-11-octadecenoic acid and cis-9-hexadecenoic acid; 3-hydroxyhexadecanoic acid is the major hydroxy fatty acid present. Strains T101 and T102 had maximal velocities (Vmax) for toluene biodegradation of 3.8 +/- 0.5 and 28.3 +/- 2.2 mumoles toluene/mgprotein-hr, and half-saturation constants (Ks) of 0.8 +/- 0.5 and 11.5 +/- 2.4 microM, respectively. Strain T102 has a higher capacity than strain T101 to degrade toluene, and kinetic calculations suggest that strain T102 may be a major contributor to toluene biodegradation in the stream.
Asunto(s)
Bacterias Aerobias Gramnegativas/clasificación , Tolueno/metabolismo , Contaminantes Químicos del Agua/metabolismo , Biodegradación Ambiental , Biopelículas , ADN Ribosómico/química , Ácidos Grasos/análisis , Bacterias Aerobias Gramnegativas/metabolismo , ARN Ribosómico 16S/genéticaRESUMEN
Bias introduced by the simultaneous amplification of specific genes from complex mixtures of templates remains poorly understood. To explore potential causes and the extent of bias in PCR amplification of 16S ribosomal DNAs (rDNAs), genomic DNAs of two closely and one distantly related bacterial species were mixed and amplified with universal, degenerate primers. Quantification and comparison of template and product ratios showed that there was considerable and reproducible overamplification of specific templates. Variability between replicates also contributed to the observed bias but in a comparatively minor way. Based on these initial observations, template dosage and differences in binding energies of permutations of the degenerate, universal primers were tested as two likely causes of this template-specific bias by using 16S rDNA templates modified by site-directed mutagenesis. When mixtures of mutagenized templates containing AT- and GC-rich priming sites were used, templates containing the GC-rich permutation amplified with higher efficiency, indicating that different primer binding energies may to a large extent be responsible for overamplification. In contrast, gene copy number was found to be an unlikely cause of the observed bias. Similarly, amplification from DNA extracted from a natural community to which different amounts of genomic DNA of a single bacterial species were added did not affect relative product ratios. Bias was reduced considerably by using high template concentrations, by performing fewer cycles, and by mixing replicate reaction preparations.
Asunto(s)
Bacillus subtilis/genética , ADN Ribosómico/genética , Escherichia coli/genética , Reacción en Cadena de la Polimerasa/métodos , ARN Ribosómico 16S/genética , Moldes Genéticos , Vibrio/genética , Secuencia de Bases , Cartilla de ADN , Mutagénesis , Sondas de Oligonucleótidos , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Alineación de Secuencia , Homología de Secuencia de Ácido NucleicoRESUMEN
Two toluene-degrading strains, T103 and T104, were isolated from rock surface biomass in a freshwater stream contaminated with toluene. The strains exhibit different capacities for degradation of toluene and other aromatic compounds and have characteristics of the genus Mycobacterium. Both are aerobic, rod-shaped, gram-positive, nonmotile, and acid-alcohol fast and produce yellow pigments. They have mainly straight-chain saturated and monounsaturated fatty acids with 10 to 20 carbon atoms and large amounts of tuberculostearic acid that are typical of mycobacteria. Fatty acid analyses indicate that T103 and T104 are different mycobacterial strains that are related at the subspecies level. Their identical 16S rDNA sequences are most similar to Mycobacterium aurum and Mycobacterium komossense, and they constitute a new species of fast-growing mycobacteria. Ecological studies reveal that toluene contamination has enriched for toluene-degrading bacteria in the epilithic microbial community. Strains T103 and T104 play only a small role in toluene degradation in the stream, although they are present in the habitat and can degrade toluene. Other microorganisms are consequently implicated in the biodegradation.
Asunto(s)
Mycobacterium/metabolismo , Tolueno/metabolismo , Biodegradación Ambiental , ADN Ribosómico/química , Ácidos Grasos/análisis , Mycobacterium/clasificación , Fenotipo , Filogenia , ARN Ribosómico 16S/genéticaRESUMEN
The bacterial symbiont of the hydrothermal vent tubeworm fixes carbon via the Calvin-Benson cycle and has been shown previously to express a form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO). The gene cbbM, which encodes this enzyme, has been cloned and sequenced. The gene has the highest identity with the cbbM gene from Rhodospirillum rubrum, and analysis of the inferred amino acid sequence reveals that all active-site residues are conserved. This is the first form II RubisCO cloned and sequenced from a chemoautotrophic symbiont and from a deep-sea organism.
Asunto(s)
Bacterias Gramnegativas/genética , Rhodospirillum rubrum/genética , Ribulosa-Bifosfato Carboxilasa/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Clonación Molecular , ADN Bacteriano/análisis , ADN Bacteriano/genética , Biblioteca de Genes , Bacterias Gramnegativas/metabolismo , Datos de Secuencia Molecular , Plásmidos , Poliquetos/microbiología , Ribulosa-Bifosfato Carboxilasa/metabolismo , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Simbiosis/genéticaRESUMEN
A simple method for the quantification of uncultured microorganisms in the environment was developed. In vitro-transcribed 16S rRNA is used as a template for midpoint dissociation temperature (Td) determinations of specific oligonucleotide probes and as a standard in quantitative probing. It replaces the need for total nucleic acids extracted from pure cultures of the organisms to be quantified. A sense RNA of a size almost identical to that of native 16S rRNA can be transcribed from ribosomal DNA clones recovered in studies of the phylogenetic diversity of microbial communities. This in vitro-transcribed rRNA yields dissociation curves typical of oligonucleotides. They parallel curves determined with total nucleic acids but yield slightly higher Td values. Neither unspecific sticking of the probe nor probe washing off the DNA template at low temperatures fully accounted for the discrepancy in probe release from the two templates. This suggests that the native rRNA itself has melting characteristics different from those of its in vitro-transcribed counterpart. However, this difference does not affect the performance of in vitro-transcribed rRNA compared with total nucleic acids as a standard in quantitative hybridizations. No difference was found between the estimates of the relative quantity of a single bacterial species in a mixed community obtained with the two standards, regardless of whether DNA was removed from the samples. This protocol will allow the large-scale quantification of the ecological importance of uncultured microorganisms in natural environments for the first time.
Asunto(s)
Bacterias/aislamiento & purificación , ADN Ribosómico/análisis , Microbiología Ambiental , ARN Ribosómico 16S/genética , Transcripción GenéticaRESUMEN
The bacterial endosymbionts of two species of the bivalve genus Solemya from the Pacific Ocean, Solemya terraeregina and Solemya pusilla, were characterized. Prokaryotic cells resembling gram-negative bacteria were observed in the gills of both host species by transmission electron microscopy. The ultrastructure of the symbiosis in both host species is remarkably similar to that of all previously described Solemya spp. By using sequence data from 16S rRNA, the identity and evolutionary origins of the S. terraeregina and S. pusilla symbionts were also determined. Direct sequencing of PCR-amplified products from host gill DNA with primers specific for Bacteria 16S rRNA genes gave a single, unambiguous sequence for each of the two symbiont species. In situ hybridization with symbiont-specific oligonucleotide probes confirmed that these gene sequences belong to the bacteria residing in the hosts gills. Phylogenetic analyses of the 16S rRNA gene sequences by both distance and parsimony methods identify the S. terraeregina and S. pusilla symbionts as members of the gamma subdivision of the Proteobacteria. In contrast to symbionts of other bivalve families, which appear to be monophyletic, the S. terraeregina and S. pusilla symbionts share a more recent common ancestry with bacteria associating endosymbiotically with bivalves of the superfamily Lucinacea than with other Solemya symbionts (host species S. velum, S. occidentalis, and S. reidi). Overall, the 16S rRNA gene sequence data suggest that the symbionts of Solemya hosts represent at least two distinct bacterial lineages within the gamma-Proteobacteria. While it is increasingly clear that all extant species of Solemya live in symbiosis with specific bacteria, the associations appear to have multiple evolutionary origins.
Asunto(s)
Bacterias/genética , Bivalvos/microbiología , Genes Bacterianos , ARN Bacteriano/genética , ARN Ribosómico 16S/genética , Simbiosis , Animales , Bacterias/clasificación , Bacterias/aislamiento & purificación , Secuencia de Bases , Bivalvos/ultraestructura , Sondas de ADN/genética , Hibridación in Situ , Microscopía Electrónica , Datos de Secuencia Molecular , FilogeniaRESUMEN
Adults of the bivalve species Solemya velum live in symbiosis with chemoautotrophic bacteria in specialized gill bacteriocytes. The bacteria play an essential nutritional role in the mature association, fixing CO2 via the Calvin cycle with energy obtained through the oxidation of reduced sulfur compounds. To understand how the continuity of this partnership is maintained between host generations, we investigated the mode of symbiont transfer in S. velum. A diagnostic assay using the polymerase chain reaction and primers specific for the S. velum symbiont ribulose-1,5-bisphosphate carboxylase (RubisCO) gene consistently detected bacterial sequence in female gonad tissue, suggesting the presence of symbiont cells in host ovaries and a vertical mode of symbiont transmission from mother to offspring. Furthermore, intracellular bacteria were present in the developing gills of juveniles that had not yet hatched from the gelatinous capsule in which larval development occurs (11 days after fertilization). By 64 days postfertilization, the typical adult gill ultrastructure of alternating bacteriocytes and symbiont-free-intercalary cells was apparent. Knowledge about the mode of symbiont transfer in S. velum allows further study into the dynamics of host-symbiont interactions in chemoautotrophic associations.
Asunto(s)
Moluscos/microbiología , Simbiosis , Animales , Secuencia de Bases , Cartilla de ADN , ADN Bacteriano/análisis , Femenino , Branquias/microbiología , Branquias/ultraestructura , Datos de Secuencia Molecular , Ovario/microbiología , Reacción en Cadena de la Polimerasa , Ribulosa-Bifosfato Carboxilasa/genéticaRESUMEN
The phylogeny of Thiothrix ramosa based on 16S rRNA sequences was determined. This species is the first species in this genus that has been shown to be capable of autotrophic growth with reduced sulfur compounds as sole energy sources. T. ramosa forms a monophyletic clade with Thiothrix nivea, as determined by distance, parsimony, and maximum-likelihood methods. Both of these species clearly belong to the gamma subdivision of the Proteobacteria, where they are loosely associated with other sulfur-oxidizing chemoautotrophic organisms.
Asunto(s)
Filogenia , ARN Ribosómico 16S/genética , Thiotrichaceae/clasificación , Secuencia de Bases , ADN Bacteriano , ADN Ribosómico/genética , Datos de Secuencia Molecular , Thiotrichaceae/genéticaRESUMEN
The coexistence of two phylogenetically distinct symbiont species within a single cell, a condition not previously known in any metazoan, is demonstrated in the gills of a Mid-Atlantic Ridge hydrothermal vent mussel (family Mytilidae). Large and small symbiont morphotypes within the gill bacteriocytes are shown to be separate bacterial species by molecular phylogenetic analysis and fluorescent in situ hybridization. The two symbiont species are affiliated with thioautotrophic and methanotrophic symbionts previously found in monospecific associations with closely related mytilids from deep-sea hydrothermal vents and hydrocarbon seeps.
Asunto(s)
Bivalvos/microbiología , Bacterias Gramnegativas/clasificación , ARN Ribosómico 16S/genética , Simbiosis , Animales , Secuencia de Bases , Branquias/microbiología , Branquias/ultraestructura , Bacterias Gramnegativas/genética , Bacterias Gramnegativas/ultraestructura , Bacterias Gramnegativas Quimiolitotróficas/clasificación , Bacterias Gramnegativas Quimiolitotróficas/genética , Bacterias Gramnegativas Quimiolitotróficas/ultraestructura , Hibridación Fluorescente in Situ , Biología Marina , Metano/metabolismo , Methylococcaceae/clasificación , Methylococcaceae/genética , Methylococcaceae/ultraestructura , Datos de Secuencia Molecular , Filogenia , Azufre/metabolismoRESUMEN
Microbial community structure in natural environments has remained largely unexplored yet is generally considered to be complex. It is shown here that in a Mid-Atlantic Ridge hydrothermal vent habitat, where food webs depend on prokaryotic primary production, the surface microbial community consists largely of only one bacterial phylogenetic type (phylotype) as indicated by the dominance of a single 16S rRNA sequence. The main part of its population occurs as an ectosymbiont on the dominant animals, the shrimp Rimicaris exoculata, where it grows as a monoculture within the carapace and on the extremities. However, the same bacteria are also the major microbial component of the free-living substrate community. Phylogenetically, this type forms a distinct branch within the epsilon-Proteobacteria. This is different from all previously studied chemoautotrophic endo- and ectosymbioses from hydrothermal vents and other sulfidic habitats in which all the bacterial members cluster within the gamma-Proteobacteria.
Asunto(s)
Bacterias/genética , Bacterias/aislamiento & purificación , Microbiología del Agua , Animales , Bacterias/clasificación , Secuencia de Bases , Sondas de ADN/genética , ADN Bacteriano/genética , Decápodos/microbiología , Ecosistema , Calor , Datos de Secuencia Molecular , Filogenia , ARN Bacteriano/genética , ARN Ribosómico 16S/genética , SimbiosisRESUMEN
The phylogenetic relationships of chemoautotrophic endosymbionts in the gutless marine oligochaete Inanidrilus leukodermatus to chemoautotrophic ecto- and endosymbionts from other host phyla and to free-living bacteria were determined by comparative 16S rRNA sequence analysis. Fluorescent in situ hybridization confirmed that the 16S rRNA sequence obtained from these worms originated from the symbionts. The symbiont sequence is unique to I. leukodermatus. In phylogenetic trees inferred by both distance and parsimony methods, the oligochaete symbiont is peripherally associated with one of two clusters of chemoautotrophic symbionts that belong to the gamma subdivision of the Proteobacteria. The endosymbionts of this oligochaete form a monophyletic group with chemoautotrophic ectosymbionts of a marine nematode. The oligochaete and nematode symbionts are very closely related, although their hosts belong to separate, unrelated animal phyla. Thus, cospeciation between the nematode and oligochaete hosts and their symbionts could not have occurred. Instead, the similar geographic locations and habitats of the hosts may have influenced the establishment of these symbioses.