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At least 19 recordsLinked to original sources

PubMed2005

Diversity and vertical distribution of cultured and uncultured Deltaproteobacteria in an intertidal mud flat of the Wadden Sea.

The diversity and distribution of Deltaproteobacteria in an intertidal mud flat of the German Wadden Sea was characterized by molecular biological techniques and cultivation. A 16S rRNA gene library generated with general primers (303 clones) suggested that sulfate-reducing bacteria (SRB) related to Desulfobulbaceae and Desulfosarcina were abundant. Fluorescence in situ hybridization (FISH) with probes targeting these groups was used to characterize their vertical distribution. The combination of FISH with catalysed reporter deposition (CARD-FISH) significantly enhanced the detection of selected subgroups of Deltaproteobacteria, particularly in deeper sediment layers. Up to 11% of all cells were assigned to SRB. Organisms related to Desulfosarcina and Desulfobulbaceae were the dominant SRB in the surface sediments. Two abundant subpopulations of Desulfosarcina-related bacteria were identified by FISH. The SRB community differed between the sampling site and a sandy intertidal flat chosen as a reference. Enrichments and MPN cultures inoculated with surface sediment were monitored by FISH. Nine strains of Deltaproteobacteria were isolated. Four strains were related to Desulfobulbaceae, such as Desulfobacterium catecholicum and Desulfocapsa spp. A subgroup including clone sequences and strains related to D. catecholicum could be detected in situ by a specific FISH probe. The first physiological experiments suggested specific functional roles for the isolates. Two strains utilized environmentally relevant compounds in coastal areas such as catechol and nitrate. One strain related to Desulfocapsa spp. disproportionated thiosulfate and might thus contribute to the sulfur isotope fractionation at the study site. A Fe(III)-reducing strain was obtained that affiliated with the Pelobacter-Desulphuromonas group. This group accounted for up to 6% of total cell numbers and even exceeded SRB numbers in upper sediment layers. These bacteria might substantially contribute to carbon mineralization via dissimilatory reduction of, e.g. Fe(III).

Deltaproteobacteria↗

PubMed2006

Molecular phylogenetic and chemical analyses of the microbial mats in deep-sea cold seep sediments at the northeastern Japan Sea.

Microbial communities inhabiting deep-sea cold seep sediments at the northeastern Japan Sea were characterized by molecular phylogenetic and chemical analyses. White patchy microbial mats were observed along the fault offshore the Hokkaido Island and sediment samples were collected from two stations at the southern foot of the Shiribeshi seamount (M1 site at a depth of 2,961 m on the active fault) and off the Motta Cape site (M2 site at a depth of 3,064 m off the active fault). The phylogenetic and terminal-restriction fragment polymorphism analyses of PCR-amplified 16S rRNA genes revealed that microbial community structures were different between two sampling stations. The members of ANME-2 archaea and diverse bacterial components including sulfate reducers within Deltaproteobacteria were detected from M1 site, indicating the occurrence of biologically mediated anaerobic oxidation of methane, while microbial community at M2 site was predominantly composed of members of Marine Crenarchaeota group I, sulfate reducers of Deltaproteobacteria, and sulfur oxidizers of Epsilonproteobacteria. Chemical analyses of seawater above microbial mats suggested that concentrations of sulfate and methane at M1 site were largely decreased relative to those at M2 site and carbon isotopic composition of methane at M1 site shifted heavier ((13)C-enriched), the results of which are consistent with molecular analyses. These results suggest that the mat microbial communities in deep-sea cold seep sediments at the northeastern Japan Sea are significantly responsible for sulfur and carbon circulations and the geological activity associated with plate movements serves unique microbial habitats in deep-sea environments.

Bacteria↗

PubMed2004

Potential sulfur metabolisms and associated bacteria within anoxic surface sediment from saline meromictic Lake Kaiike (Japan).

The effects of light and of added electron donors and sulfur compounds on sulfur metabolisms in the microbial mat dilutions from the saline meromictic Lake Kaiike were investigated. Sulfide concentrations in the mat dilution without any electron donor gradually increased by approximately 0.6-1 mM in the dark. Additions of lactate, acetate, H(2)/CO(2), propionate and iso-butylate stimulated sulfide production, whereas benzoate did not, indicating the limitation of sulfate reduction by available electron donor concentrations. More sulfide was produced, without a decrease of sulfate, in an elemental sulfur-amended dilution than in a non-amended control. In contrast, the addition of a high concentration of sulfide slowed down sulfide production. After enrichment under various conditions, microbial communities in the dilutions were characterized by a denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene and sequencing. As a result, microorganisms affiliated with mesophilic sulfate-reducing bacteria group within the Deltaproteobacteria and the Epsilonproteobacteria were mainly enriched by the addition of electrons used in this study, suggesting that these microorganisms might play an important role in sulfur metabolisms within the surficial sediment of Lake Kaiike.

DNA, Bacterial↗

PubMed2004

Analysis of microbial diversity in oligotrophic microbial fuel cells using 16S rDNA sequences.

Molecular ecological techniques were applied to analyze the bacterial diversity of two oligotrophic microbial fuel cells (MFCs) enriched using river water or artificial wastewater (AWW) as fuel. Denaturing gradient gel electrophoresis (DGGE) of the PCR amplified 16S rDNA showed that different microbial communities were present in the two MFCs and these were different from the river sediment used to initiate the enrichment. Nearly complete 16S rDNA was amplified and sequenced. Over 80% of the clones were Proteobacteria. Betaproteobacteria were the dominant clones (46.2%) in MFCs fed with river water, and about 64.4% of the clones in MFCs fed with AWW were Alphaproteobacteria. Actinobacteria were found only in the MFC fed with AWW, and Deltaproteobacteria, Acidobacteria, Chloroflexi and Verrucomicrobia in the MFC fed with river water. Many clones were related to uncultured bacteria, some with homology less than 95%, indicating that many novel bacteria were enriched in the oligotrophic MFCs.

Actinobacteria↗

PubMed2005

Characterization of long-chain fatty-acid-degrading syntrophic associations from a biodegraded oil reservoir.

Molecular methods were used to characterize stearate- and heptadecanoate-degrading methanogenic consortia enriched from a low-temperature biodegraded oil field. Stearate- and heptadecanoate-degrading cultures formed acetate. Growth on heptadecanoate was also accompanied by the production of propionate. These fermentation products were transiently accumulated at the beginning of the exponential phase and were further consumed with the concomitant production of methane. Clone libraries of bacterial and archaeal 16S rRNA genes were generated for each stable enrichment. Our 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that the predominant microorganisms in the associations were affiliated with a clone cluster close to the genus Syntrophus in the class "Deltaproteobacteria" and with the methanogenic genera Methanocalculus and Methanosaeta. Confocal scanning laser microscopy showed that the bacterial and archaeal cells formed compact aggregates around the insoluble substrates. No layered structure was observed in the aggregate organization. This study reports the presence of new fatty-acid-degrading syntrophic consortia in oil fields and our results suggest that such associations may have an important ecological role in oil fields under methanogenic conditions.

Acetic Acid↗

PubMed2004

Desulfatibacillum alkenivorans sp. nov., a novel n-alkene-degrading, sulfate-reducing bacterium, and emended description of the genus Desulfatibacillum.

An alkene-degrading, sulfate-reducing bacterium, strain PF2803T, was isolated from oil-polluted sediments (Fos Harbour, France). The cells were found to be Gram-negative, non-sporulating, non-motile and to have a slightly curved rod shape. Optimum growth occurred at 1 % (w/v) NaCl, pH 6.8 and 28-30 degrees C. Strain PF2803T oxidized alkenes (from C8 to C23). The G + C content of the genomic DNA was 57.8 mol% (HPLC). On the basis of 16S rRNA gene sequence analyses, strain PF2803T belongs to the family 'Desulfobacteraceae' in the class 'Deltaproteobacteria', with Desulfatibacillum aliphaticivorans as its closest relative (99.6 % identity). Comparative sequence analyses of the dissimilatory sulfite reductase (dsrAB) gene supported the affiliation of strain PF2803T to the genus Desulfatibacillum. DNA-DNA hybridization with its closest taxon demonstrated 48.4 % similarity. On the basis of the results of physiological and genetic analyses, strain PF2803T is identified as a novel species of the genus Desulfatibacillum, for which the name Desulfatibacillum alkenivorans sp. nov. is proposed. The type strain is PF2803T (= DSM 16219T = ATCC BAA-924T).

Alkenes↗

PubMed2006

Desulfuromonas svalbardensis sp. nov. and Desulfuromusa ferrireducens sp. nov., psychrophilic, Fe(III)-reducing bacteria isolated from Arctic sediments, Svalbard.

Two psychrophilic, Gram-negative, rod-shaped, motile bacteria (strains 112T and 102T) that conserved energy from dissimilatory Fe(III) reduction concomitant with acetate oxidation were isolated from permanently cold Arctic marine sediments. Both strains grew at temperatures down to -2 degrees C, with respective temperature optima of 14 degrees C and 14-17 degrees C for strains 112T and 102T. The isolated strains reduced Fe(III) using common fermentation products such as acetate, lactate, propionate, formate or hydrogen as electron donors, and they also grew with fumarate as the sole substrate. As alternatives to Fe(III), they reduced fumarate, S0 and Mn(IV). Based on 16S rRNA gene sequence similarity, strain 112T was most closely related to Desulfuromonas acetoxidans (97.0 %) and Desulfuromonas thiophila NZ27T (95.5 %), and strain 102T to Malonomonas rubra Gra Mal 1T (96.3 %) and Desulfuromusa succinoxidans GylacT (95.9 %) within the Deltaproteobacteria. Strains 112T and 102T therefore represent novel species, for which the names Desulfuromonas svalbardensis sp. nov. (type strain 112T=DSM 16958T=JCM 12927T) and Desulfuromusa ferrireducens sp. nov. (type strain 102T=DSM 16956T=JCM 12926T) are proposed.

Acetic Acid↗

PubMed2006

Desulfoglaeba alkanexedens gen. nov., sp. nov., an n-alkane-degrading, sulfate-reducing bacterium.

Two novel sulfate-reducing bacteria, strains ALDC(T) and Lake, which were able to oxidize n-alkanes, were isolated from a naval oily wastewater-storage facility (VA, USA) and from oilfield production water (OK, USA), respectively. The type strain (ALDC(T)) had a narrow substrate specificity and could grow only with n-alkanes (from C(6) to C(12)), pyruvate, butyrate, hexanoic acid and 4-methyloctanoic acid. Cells of strain ALDC(T) stained Gram-negative and were slightly curved, short rods with oval ends (2.5-3.0x1.0-1.4 microm), often occurring in pairs. Cells tended to form aggregates or large clusters and were non-motile and did not form endospores. Optimum growth occurred between 31 and 37 degrees C and at pH 6.5-7.2. NaCl was not required for growth, but salt concentrations up to 55 g l(-1) could be tolerated. The DNA G+C content was 53.6 mol%. Phylogenetic analysis of the 16S rRNA genes revealed that strains ALDC(T) and Lake were closely related, but not identical (99.9 % similarity). The two strains were not closely related to other known alkane-degrading, sulfate-reducing bacteria or to other genera of the Deltaproteobacteria. Therefore, it is proposed that strain ALDC(T) (=JCM 13588(T)=ATCC BAA-1302(T)) represents the type strain of a novel species and genus, with the name Desulfoglaeba alkanexedens gen. nov., sp. nov.

Alkanes↗

PubMed2004

Reconstruction of the evolutionary history of the LexA-binding sequence.

In recent years, the recognition sequence of the SOS repressor LexA protein has been identified for several bacterial clades, such as the Gram-positive, green non-sulfur bacteria and Cyanobacteria phyla, or the 'Alphaproteobacteria', 'Deltaproteobacteria' and 'Gammaproteobacteria' classes. Nevertheless, the evolutionary relationship among these sequences and the proteins that recognize them has not been analysed. Fibrobacter succinogenes is an anaerobic Gram-negative bacterium that branched from a common bacterial ancestor immediately before the Proteobacteria phylum. Taking advantage of its intermediate position in the phylogenetic tree, and in an effort to reconstruct the evolutionary history of LexA-binding sequences, the F. succinogenes lexA gene has been isolated and its product purified to identify its DNA recognition motif through electrophoretic mobility assays and footprinting experiments. After comparing the available LexA DNA-binding sequences with the F. succinogenes one, reported here, directed mutagenesis of the F. succinogenes LexA-binding sequence and phylogenetic analyses of LexA proteins have revealed the existence of two independent evolutionary lanes for the LexA recognition motif that emerged from the Gram-positive box: one generating the Cyanobacteria and 'Alphaproteobacteria' LexA-binding sequences, and the other giving rise to the F. succinogenes and Myxococcus xanthus ones, in a transitional step towards the current 'Gammaproteobacteria' LexA box. The contrast between the results reported here and the phylogenetic data available in the literature suggests that, some time after its emergence as a distinct bacterial class, the 'Alphaproteobacteria' lost its vertically received lexA gene, but received later through lateral gene transfer a new lexA gene belonging to either a cyanobacterium or a bacterial species closely related to this phylum. This constitutes the first report based on experimental evidence of lateral gene transfer in the evolution of a gene governing such a complex regulatory network as the bacterial SOS system.

Alphaproteobacteria↗

PubMed2006

Metagenomic analysis of mesopelagic Antarctic plankton reveals a novel deltaproteobacterial group.

Phylogenetic screening of 3200 clones from a metagenomic library of Antarctic mesopelagic picoplankton allowed the identification of two bacterial 16S-rDNA-containing clones belonging to the Deltaproteobacteria, DeepAnt-1F12 and DeepAnt-32C6. These clones were very divergent, forming a monophyletic cluster with the environmental sequence GR-WP33-58 that branched at the base of the myxobacteria. Except for the possession of complete rrn operons without associated tRNA genes, DeepAnt-1F12 and DeepAnt-32C6 were very different in gene content and organization. Gene density was much higher in DeepAnt-32C6, whereas nearly one-third of DeepAnt-1F12 corresponded to intergenic regions. Many of the predicted genes encoded by these metagenomic clones were informational (i.e. involved in replication, transcription, translation and related processes). Despite this, a few putative cases of horizontal gene transfer were detected, including a transposase. DeepAnt-1F12 contained one putative gene encoding a long cysteine-rich protein, probably membrane-bound and Ca2+-binding, with only eukaryotic homologues. DeepAnt-32C6 carried some predicted genes involved in metabolic pathways that suggested this organism may be anaerobic and able to ferment and to degrade complex compounds extracellularly.

Antarctic Regions↗

PubMed2005

Methanogen communities and Bacteria along an ecohydrological gradient in a northern raised bog complex.

Mires forming an ecohydrological gradient from nutrient-rich, groundwater-fed mesotrophic and oligotrophic fens to a nutrient-poor ombrotrophic bog were studied by comparing potential methane (CH(4)) production and methanogenic microbial communities. Methane production was measured from different depths of anoxic peat and methanogen communities were detected by detailed restriction fragment length polymorphism (RFLP) analysis of clone libraries, sequencing and phylogenetic analysis. Potential CH(4) production changed along the ecohydrological gradient with the fens displaying much higher production than the ombrotrophic bog. Methanogen diversity also decreased along the gradient. The two fens had very similar diversity of methanogenic methyl-coenzyme M reductase gene (mcrA), but in the upper layer of the bog the methanogen diversity was strikingly lower, and only one type of mcrA sequence was retrieved. It was related to the Fen cluster, a group of novel methanogenic sequences found earlier in Finnish mires. Bacterial 16S rDNA sequences from the fens fell into at least nine phyla, but only four phyla were retrieved from the bog. The most common bacterial groups were Deltaproteobacteria, Verrucomicrobia and Acidobacteria.

Bacteria↗

PubMed2006

Identification and cultivation of anaerobic, syntrophic long-chain fatty acid-degrading microbes from mesophilic and thermophilic methanogenic sludges.

We investigated long-chain fatty acid (LCFA)-degrading anaerobic microbes by enrichment, isolation, and RNA-based stable isotope probing (SIP). Primary enrichment cultures were made with each of four LCFA substrates (palmitate, stearate, oleate, or linoleate, as the sole energy source) at 55 degrees C or 37 degrees C with two sources of anaerobic granular sludge as the inoculum. After several transfers, we obtained seven stable enrichment cultures in which LCFAs were converted to methane. The bacterial populations in these cultures were then subjected to 16S rRNA gene-based cloning, in situ hybridization, and RNA-SIP. In five of seven enrichment cultures, the predominant bacteria were affiliated with the family Syntrophomonadaceae. The other two enrichment cultures contained different bacterial populations in which the majority of members belonged to the phylum Firmicutes and the class Deltaproteobacteria. After several attempts to isolate these dominant bacteria, strain MPA, belonging to the family Syntrophomonadaceae, and strain TOL, affiliated with the phylum Firmicutes, were successfully isolated. Strain MPA converts palmitate to acetate and methane in syntrophic association with Methanospirillum hungatei. Even though strain TOL assimilated [(13)C]palmitate in the original enrichment culture, strain TOL has not shown the ability to degrade LCFAs after isolation. These results suggest that microbes involved in the degradation of LCFAs under methanogenic conditions might not belong only to the family Syntrophomonadaceae, as most anaerobic LCFA-degrading microbes do, but may also be found in phylogenetically diverse bacterial groups.

Bacteria, Anaerobic↗

PubMed2006

Sulfide oxidation coupled to arsenate reduction by a diverse microbial community in a soda lake.

We characterized the arsenate-reducing, sulfide-oxidizing population of Mono Lake, California, by analyzing the distribution and diversity of rrnA, cbbL, and dissimilatory arsenate reductase (arrA) genes in environmental DNA, arsenate-plus sulfide-amended lake water, mixed cultures, and isolates. The arsenate-reducing community was diverse. An organism represented by an rrnA sequence previously retrieved from Mono Lake and affiliated with the Desulfobulbaceae (Deltaproteobacteria) appears to be an important member of the arsenate-reducing, sulfide-oxidizing community. Sulfide oxidation coupled with arsenate reduction appears to proceed via a two-electron transfer, resulting in the production of arsenite and an intermediate S compound that is subsequently disproportionated. A realgar-like As/S mineral was formed in some experiments.

Arsenates↗

PubMedDate not supplied

[The new facultatively chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium Desulfovermiculus halophilus gen. nov., sp. nov., isolated from an oil field].

The new mesophilic, chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium strain 11-6 could grow at a NaCl concentration in the medium of 30-230 g/l, with an optimum at 80-100 g/l. Cells were vibrios motile at the early stages of growth. Lactate, pyruvate, malate, fumarate, succinate, propionate, butyrate, crotonate, ethanol, alanine, formate, and H2 + CO2 were used in sulfate reduction. Butyrate was degraded completely, without acetate accumulation. In butyrate-grown cells, a high activity of CO dehydrogenase was detected. Additional growth factors were not required. Autotrophic growth occurred, in the presence of sulfate, on H2 + CO2 or formate without other electron donors. Fermentation of pyruvate and fumarate was possible in the absence of sulfate. Apart from sulfate, sulfite, thiosulfate, and elemental sulfur were able to serve as electron acceptors. The optimal growth temperature was 37 degrees C; the optimum pH was 7.2. Desulfoviridin was not detected. Menaquinone MK-7 was present. The DNA G+C content was 55.2 mol %. Phylogenetically, the bacterium represented a separate branch within the cluster formed by representatives of the family Desulfohalobiaceae in the subclass Deltaproteobacteria. The bacterium was assigned to a new genus and species, Desulfovermiculus halophilus gen. nov., sp. nov. The type strain is 11-6T (= VKM B-2364), isolated from the highly mineralized formation water of an oil field.

Carboxylic Acids↗

PubMed2006

Comparison of bacterial communities in New England Sphagnum bogs using terminal restriction fragment length polymorphism (T-RFLP).

Wetlands are major sources of carbon dioxide, methane, and other greenhouse gases released during microbial degradation. Despite the fact that decomposition is mainly driven by bacteria and fungi, little is known about the taxonomic diversity of bacterial communities in wetlands, particularly Sphagnum bogs. To explore bacterial community composition, 24 bogs in Vermont and Massachusetts were censused for bacterial diversity at the surface (oxic) and 1 m (anoxic) regions. Bacterial diversity was characterized by a terminal restriction fragment length (T-RFLP) fingerprinting technique and a cloning strategy that targeted the 16S rRNA gene. T-RFLP analysis revealed a high level of diversity, and a canonical correspondence analysis demonstrated marked similarity among bogs, but consistent differences between surface and subsurface assemblages. 16S rDNA sequences derived from one of the sites showed high numbers of clones belonging to the Deltaproteobacteria group. Several other phyla were represented, as well as two Candidate Division-level taxonomic groups. These data suggest that bog microbial communities are complex, possibly stratified, and similar among multiple sites.

Bacteria↗

PubMed2025

South African Myxococcota: an untapped resource for microbial ecolo gy and biotechnology.

An extraordinary multicellular life cycle, ecological versatility, and prolific production of bioactive secondary metabolites characterise the phylum Myxococcota. While research has predominantly focused on Myxococcota in Asia, Europe, and North America, their potential occurrence in Sub-Saharan Africa remains largely unexplored. To date, only one study has isolated Myxococcota in South Africa, with additional findings limited to incidental detection through metagenomic studies. Considering South Africa's ecological diversity, its biomes may represent promising but under-examined environments for systematic bioprospecting aimed at discovering novel Myxococcota with ecological or biotechnological potential. The recent reclassification of Myxococcota from the former Deltaproteobacteria has provided a more coherent taxonomic framework to guide future ecological and systematic studies. This review presents an overview of the taxonomic revision and explores the potential occurrence of Myxococcota in South African biomes. It covers the challenges associated with conventional culture-based isolation methods and highlights potential genome- and metagenome-based approaches, including the use of metagenome-assembled genomes (MAGs) to identify cryptic biosynthetic gene clusters (BGCs), while acknowledging current limitations. Considering the increasing resistance to chemical fungicides in South African agriculture, this review further explores the potential of Myxococcota-derived secondary metabolites as candidate bioprotective alternatives. By identifying current research gaps, it aims to support future efforts towards systematic bioprospecting to investigate the ecological and biotechnological potential of Myxococcota in South Africa. KEY POINTS: • South African biomes may harbour novel Myxococcota with biosynthetic potential. • Genome mining could reveal cryptic biosynthetic gene clusters (BGCs). • Myxococcota metabolites may help control resistant fungal phytopathogens.

South Africa↗

PubMed2006

Desulfomicrobium thermophilum sp. nov., a novel thermophilic sulphate-reducing bacterium isolated from a terrestrial hot spring in Colombia.

A moderately thermophilic, sulphate-reducing bacterium, designated strain P6-2(T), was isolated from a terrestrial hot spring located at a height of 2,500 m in the Andean region, Colombia (5 degrees 43'69''N, 73 degrees 6'10''W). Cells of strain P6-2(T) were rod-shaped, stained Gram-negative and were motile by means of a single polar flagellum. The strain grew lithotrophically with H(2) as the electron donor and organotrophically on lactate, pyruvate, ethanol, malate, fumarate, n-propanol and succinate in the presence of sulphate as the terminal electron acceptor. Fumarate and pyruvate was fermented. Strain P6-2(T) grew optimally at 55 degrees C (range 37-60 degrees C), pH 6.6 (range 5.8-8.8) in the presence of 0.5% NaCl (range 0-4.5%) with lactate and sulphate and produced acetate, CO(2) and H(2)S as the major end-products. Sulphate, sulphite and thiosulphate could be used as electron acceptors but not elemental sulphur or nitrate. The G + C content of the genomic DNA was 58.7 mol%. The 16S rRNA sequence analysis indicated that strain P6-2(T) was a member of the class Deltaproteobacteria, domain Bacteria with Desulfomicrobium baculatum being the closest relative (similarity value of 94%). Phylogeny of genes encoding alpha- and beta-subunits of the dissimilatory sulphite reductase (dsrAB genes) supported its affiliation to members of the genus Desulfomicrobium. On the basis of this evidence, we propose to assign strain P6-2(T) as new species of the genus Desulfomicrobium, D. thermophilum sp. nov., with strain P6-2(T) as the type strain (= DSM 16697(T) = CCUG 49732(T)).

1-Propanol↗

PubMed2004

Bacterial diversity and ecosystem function of filamentous microbial mats from aphotic (cave) sulfidic springs dominated by chemolithoautotrophic "Epsilonproteobacteria".

Filamentous microbial mats from three aphotic sulfidic springs in Lower Kane Cave, Wyoming, were assessed with regard to bacterial diversity, community structure, and ecosystem function using a 16S rDNA-based phylogenetic approach combined with elemental content and stable carbon isotope ratio analyses. The most prevalent mat morphotype consisted of white filament bundles, with low C:N ratios (3.5-5.4) and high sulfur content (16.1-51.2%). White filament bundles and two other mat morphotypes had organic carbon isotope values (mean delta13C=-34.7 per thousand, 1sigma=3.6) consistent with chemolithoautotrophic carbon fixation from a dissolved inorganic carbon reservoir (cave water, mean delta13C=-7.4 per thousand for two springs, n=8). Bacterial diversity was low overall in the clone libraries, and the most abundant taxonomic group was affiliated with the "Epsilonproteobacteria" (68%), with other bacterial sequences affiliated with Gammaproteobacteria (12.2%), Betaproteobacteria (11.7%), Deltaproteobacteria (0.8%), and the Acidobacterium (5.6%) and Bacteriodetes/Chlorobi (1.7%) divisions. Six distinct epsilonproteobacterial taxonomic groups were identified from the microbial mats. Epsilonproteobacterial and bacterial group abundances and community structure shifted from the spring orifices downstream, corresponding to changes in dissolved sulfide and oxygen concentrations and metabolic requirements of certain bacterial groups. Most of the clone sequences for epsilonproteobacterial groups were retrieved from areas with high sulfide and low oxygen concentrations, whereas Thiothrix spp. and Thiobacillus spp. had higher retrieved clone abundances where conditions of low sulfide and high oxygen concentrations were measured. Genetic and metabolic diversity among the "Epsilonproteobacteria" maximizes overall cave ecosystem function, and these organisms play a significant role in providing chemolithoautotrophic energy to the otherwise nutrient-poor cave habitat. Our results demonstrate that sulfur cycling supports subsurface ecosystems through chemolithoautotrophy and expand the evolutionary and ecological views of "Epsilonproteobacteria" in terrestrial habitats.

Biodiversity↗