Filamentous "Epsilonproteobacteria" dominate microbial mats from sulfidic cave springs

Hydrogen sulfide-rich groundwater discharges from springs into Lower Kane Cave, Wyoming, where microbial mats dominated by filamentous morphotypes are found. The full-cycle rRNA approach, including 16S rRNA gene retrieval and fluorescence in situ hybridization (FISH), was used to identify these filaments. The majority of the obtained 16S rRNA gene clones from the mats were affiliated with the "Epsilonproteobacteria" and formed two distinct clusters, designated LKC group I and LKC group II, within this class. Group I was closely related to uncultured environmental clones from petroleum-contaminated groundwater, sulfidic springs, and sulfidic caves (97 to 99% sequence similarity), while group II formed a novel clade moderately related to deep-sea hydrothermal vent symbionts (90 to 94% sequence similarity). FISH with newly designed probes for both groups specifically stained filamentous bacteria within the mats. FISH-based quantification of the two filament groups in six different microbial mat samples from Lower Kane Cave showed that LKC group II dominated five of the six mat communities. This study further expands our perceptions of the diversity and geographic distribution of "Epsilonproteobacteria" in extreme environments and demonstrates their biogeochemical importance in subterranean ecosystems.     

In situ detection of novel Acidobacteria in microbial mats from a chemolithoautotrophically based cave ecosystem (Lower Kane Cave, WY, USA)

Lower Kane Cave, Wyoming (USA), has hydrogen sulfide-bearing springs that discharge into the cave passage. The springs and cave stream harbour white filamentous microbial mats dominated by Epsilonproteobacteria. Recently, novel 16S rRNA gene sequences from the phylum Acidobacteria, subgroup 7, were found in these cave mats. Although Acidobacteria are ubiquitously distributed in many terrestrial and marine habitats, little is known about their ecophysiology. To investigate this group in Lower Kane Cave in more detail, a full-cycle rRNA approach was applied based on 16S and 23S rRNA gene clone libraries and the application of novel probes for fluorescence in situ hybridization. The 16S and 23S rRNA gene clone libraries yielded seven and six novel acidobacterial operational taxonomic units (OTUs) respectively. The majority of the OTUs were affiliated with subgroups 7 and 8. One OTU was affiliated with subgroup 6, and one OTU could not be assigned to any of the present acidobacterial subgroups. Fluorescence in situ hybridization distinguished two morphologically distinct, rod-shaped cells of the acidobacterial subgroups 7 and 8. Although the ecophysiology of Acidobacteria from Lower Kane Cave will not be fully resolved until cultures are obtained, acidobacterial cells were always associated with the potentially chemolithoautotrophic epsilon- or gammaproteobacterial filaments, suggesting perhaps a lifestyle based on heterotrophy or chemoorganotrophy.     

Drivers of epsilonproteobacterial community composition in sulfidic caves and springs

Epsilonproteobacteria are widely distributed in marine, freshwater, and terrestrial environments, although most well-studied groups are from hydrothermal vents and the human intestinal tract. The environmental variables that control epsilonproteobacterial communities in sulfidic terrestrial environments, however, are poorly understood. Here, the environmental variables that influence epsilonproteobacterial community composition in geographically separated sulfidic caves and springs were determined by coarse and fine-scale approaches: denaturing gradient gel electrophoresis profiling of 23S rRNA PCR amplicons and clone library sequencing of the 16S-ITS-23S rRNA operon. Sequences retrieved from this study were not closely related to cultured representatives, indicating that existing culture collections do not adequately capture the diversity of terrestrial Epsilonproteobacteria. Comparisons of 16S-ITS-23S rRNA operon sequences from four sites revealed that some distant communities (> 8000 km) share closely related populations of Epsilonproteobacteria, while other sites have nearly clonal and phylogenetically distinct populations. Statistical evaluations of sequence data reveal that multiple environmental variables (e.g. temperature, pH, salinity, dissolved oxygen, and bicarbonate concentrations) influence Epsilonproteobacteria community composition. Locations with clonal populations tended to be from higher temperatures and intermediate dissolved oxygen concentrations. rRNA operon sequences outside of the 16S rRNA gene may be critical to recognizing environmental drivers of epsilonproteobacterial community composition.     

Biodiversity and monitoring of colorless filamentous bacteria in sulfide aquatic systems of North Caucasus region

Bacterial mats in sulfide aquatic systems of North Caucasus are basically composed by the species of genera Thiothrix and Sphaerotilus. Additionally, several non-filamentous sulfur-oxidizing bacteria were isolated from the mats and several minor 16S rRNA phylotypes were found in clone libraries from these mats. The minor components were affiliated with Proteobacteria, Chlorobia, Cyanobacteria and Firmicutes. Even in an individual mat population heterogeneity of Thiothrix spp. was revealed by analysis of 16S rRNA gene and RAPD-PCR. Five Thiothrix isolates were described as new species Thiothrix caldifontis sp. nov. and Thiothrix lacustris sp. nov. In the Thiothrix-Sphaerotilus type of bacterial mat the proportion of dominant organisms might be influenced by sulfide concentration in the spring water. The higher sulfide concentration (more than 10 mg/l) in the spring water is more favorable for the development of bacterial mats with dominant Thiothrix organisms than for Thiothrix-Sphaerotilus type of sulfur mat.     

Influence of sulfide and temperature on species composition and community structure of hot spring microbial mats

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80 degrees C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90 degrees C, and a Chloroflexus mat is formed at 65 to 70 degrees C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low-sulfide spring (1 mg liter(-1)) below 70 degrees C, whereas Aquificales were dominant in the high-sulfide spring (12 mg liter(-1)) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.     

Biodiversity and monitoring of colorless filamentous bacteitrtn sulfide aquatic systems of North Caucasus region

Bacterial mats in sulfide aquatic systems of North Caucasus are basically composed by the species of genera Thiothrix and Sphaerotilus. Additionally, several non-filamentous sulfur-oxidizing bacteria were isolated from the mats and several minor 16S rRNA phylotypes were found in clone libraries from these mats. The minor components were affiliated with Proteobacteria, Chlorobia, Cyanobacteria and Firmicutes. Even in an individual mat population heterogeneity of Thiothrix spp. was revealed by analysis of 16S rRNA gene and RAPD-PCR. Five Thiothrix isolates were described as new species Thiothrix caldifontis sp. nov. and Thiothrix lacustris sp. nov. In the Thiothrix-Sphaerotilus type of bacterial mat the proportion of dominant organisms might be influenced by sulfide concentration in the spring water. The higher sulfide concentration (more than 10 mg/1) in the spring water is more favorable for the development of bacterial mats with dominant Thiothrix organisms than for Thiothrix-Sphaerotilus type of sulfur mat.     

Phylogenetic in situ/ex situ analysis of a sulfur mat microbial community from a thermal sulfide stream in the North Caucasus

A phylogenetic in situ/ex situ analysis of a sulfur mat formed by colorless filamentous sulfur bacteria in a thermal sulfide stream (northern spur of the main Caucasian ridge) was carried out. Nine phylotypes were revealed in the mat. Thiothrix sp. and Sphaerotilus sp. were the dominant phylotypes (66.3% and 26.3%, respectively). The 16S rRNA gene nucleotide sequence of Spahaerotilus sp. phylotype from the clone library was identical to the sequences of the seven Sphaerotilus strains isolated from the same source. A very high degree of similarity of Sphaerotilus strains revealed by ERIC-PCR fingerprints indicated little or no population diversity of this species in the mat. Thiothrix phylotype from the clone library and two Thiothrix strains isolated from the same mat sample differed in one to three nucleotides of 16S rRNA genes; this is an indication of this organism's population variability in the mat. 16S rRNA genes of the strains and clones of Thiothrix sp. exhibited the highest similarity (ca. 99%) with Thiothrix unzii; the strains and clones of Sphaerotilus had 99% similarity with the type species Sphaerotilus natans (the only species of this genus) and therefore can be assigned to this species. The minor seven components belong to the phylotypes from the Proteobacteria (3%), as well as the Chlorobia, Cyanobacteria, Clostridia, and Bacteroidetes phylogenetic groups, each of them constituting not more than 1%. Intracellular accumulation of elemental sulfur by Sphaerotilus similar to other filamentous sulfur bacteria was demonstrated for the first time (both in the population of the sulfur spring and in cultures with sulfide). Although mass growth of Sphaerotilus and Thiothrix is typical of bacterial populations of anthropogenic ecosystems (the activated sludge of treatment facilities), stable communities of these bacteria have not been previously found in the sulfur mats or "threads" of natural sulfide springs.     

Bacterial and archaeal diversity in two hot spring microbial mats from the geothermal region of Tengchong, China

We investigated the bacterial and archaeal diversity in two hot spring microbial mats from the geothermal region of Tengchong in the Yunnan Province, China, using direct molecular analyses. The Langpu (LP) laminated mat was found by the side of a boiling pool with temperature of 60-65?°C and a pH of 8.5, while the Tengchong (TC) streamer mat consisted of white streamers in a slightly acidic (pH 6.5) hot pool outflow with a temperature of 72?°C. Four 16S rRNA gene clone libraries were constructed and restriction enzyme analysis of the inserts was used to identify unique sequences and clone frequencies. From almost 200 clones screened, 55 unique sequences were retrieved. Phylogenetic analysis showed that the LP mat consisted of a diverse bacterial population [Cyanobacteria, Chloroflexi, Chlorobia, Nitrospirae, 'Deinococcus-Thermus', Proteobacteria (alpha, beta and delta subdivisions), Firmicutes, Bacteroidetes and Actinobacteria], while the archaeal population was dominated by methanogenic Euryarchaeota and Crenarchaeota. In contrast, the TC streamer mat consisted of a bacterial population dominated by Aquificae, while the archaeal population also contained Korarchaeota as well as Crenarchaeota and methanogenic Euryarchaeota. These mats harboured clone sequences affiliated to unidentified lineages, suggesting that they are a potential source for discovering novel bacteria and archaea.     

Novel uncultured Epsilonproteobacteria dominate a filamentous sulphur mat from the 13 degrees N hydrothermal vent field, East Pacific Rise

Rapid growth of microbial sulphur mats have repeatedly been observed during oceanographic cruises to various deep-sea hydrothermal vent sites. The microorganisms involved in the mat formation have not been phylogenetically characterized, although the production of morphologically similar sulphur filaments by a Arcobacter strain coastal marine has been documented. An in situ collector deployed for 5 days at the 13 degrees N deep-sea hydrothermal vent site on the East Pacific Rise (EPR) was rapidly colonized by a filamentous microbial mat. Microscopic and chemical analyses revealed that the mat consisted of a network of microorganisms embedded in a mucous sulphur-rich matrix. Molecular surveys based on 16S rRNA gene and aclB genes placed all the environmental clone sequences within the Epsilonproteobacteria. Although few 16S rRNA gene sequences were affiliated with that of cultured organisms, the majority was related to uncultured representatives of the Arcobacter group (< or = 95% sequence similarity). A probe designed to target all of the identified lineages hybridized with more than 95% of the mat community. Simultaneous hybridizations with the latter probe and a probe specific to Arcobacter spp. confirmed the numerical dominance of Arcobacter-like bacteria. This study provides the first example of the prevalence and ecological significance of free-living Arcobacter at deep-sea hydrothermal vents.     

Bacterial sulfur cycling shapes microbial communities in surface sediments of an ultramafic hydrothermal vent field

The ultramafic-hosted Logatchev hydrothermal field (LHF) is characterized by vent fluids, which are enriched in dissolved hydrogen and methane compared with fluids from basalt-hosted systems. Thick sediment layers in LHF are partly covered by characteristic white mats. In this study, these sediments were investigated in order to determine biogeochemical processes and key organisms relevant for primary production. Temperature profiling at two mat-covered sites showed a conductive heating of the sediments. Elemental sulfur was detected in the overlying mat and metal-sulfides in the upper sediment layer. Microprofiles revealed an intensive hydrogen sulfide flux from deeper sediment layers. Fluorescence in situ hybridization showed that filamentous and vibrioid, Arcobacter-related Epsilonproteobacteria dominated the overlying mats. This is in contrast to sulfidic sediments in basalt-hosted fields where mats of similar appearance are composed of large sulfur-oxidizing Gammaproteobacteria. Epsilonproteobacteria (7-21%) and Deltaproteobacteria (20-21%) were highly abundant in the surface sediment layer. The physiology of the closest cultivated relatives, revealed by comparative 16S rRNA sequence analysis, was characterized by the capability to metabolize sulfur components. High sulfate reduction rates as well as sulfide depleted in (34)S further confirmed the importance of the biogeochemical sulfur cycle. In contrast, methane was found to be of minor relevance for microbial life in mat-covered surface sediments. Our data indicate that in conductively heated surface sediments microbial sulfur cycling is the driving force for bacterial biomass production although ultramafic-hosted systems are characterized by fluids with high levels of dissolved methane and hydrogen.     

Biogeochemical cycling and microbial diversity in the thrombolitic microbialites of Highborne Cay,Bahamas

Thrombolites are unlaminated carbonate build‐ups that are formed via the metabolic activities of complex microbial mat communities. The thrombolitic mats of Highborne Cay, Bahamas develop in close proximity (1–2 m) to accreting laminated stromatolites, providing an ideal opportunity for biogeochemical and molecular comparisons of these two distinctive microbialite ecosystems. In this study, we provide the first comprehensive characterization of the biogeochemical activities and microbial diversity of the Highborne Cay thrombolitic mats. Morphological and molecular analyses reveal two dominant mat types associated with the thrombolite deposits, both of which are dominated by bacteria from the taxa Cyanobacteria and Alphaproteobacteria. Diel cycling of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were measured in all thrombolitic mat types. DO production varied between thrombolitic types and one morphotype, referred to in this study as ‘button mats’, produced the highest levels among all mat types, including the adjacent stromatolites. Characterization of thrombolite bacterial communities revealed a high bacterial diversity, roughly equivalent to that of the nearby stromatolites, and a low eukaryotic diversity. Extensive phylogenetic overlap between thrombolitic and stromatolitic microbial communities was observed, although thrombolite‐specific cyanobacterial populations were detected. In particular, the button mats were dominated by a calcified, filamentous cyanobacterium identified via morphology and 16S rRNA gene sequencing as Dichothrix sp. The distinctive microbial communities and chemical cycling patterns within the thrombolitic mats provide novel insight into the biogeochemical processes related to the lithifying mats in this system, and provide data relevant to understanding microbially induced carbonate biomineralization.     

Biogeochemistry of an Iron-Rich Hypersaline Microbial Mat (Camargue, France)

In situ microsensor measurements were combined with biogeochemical methods to determine oxygen, sulfur, and carbon cycling in microbial mats growing in a solar saltern (Salin-de-Giraud, France). Sulfate reduction rates closely followed the daily temperature changes and were highest during the day at 25°C and lowest during the night at 11°C, most probably fueled by direct substrate interactions between cyanobacteria and sulfate-reducing bacteria. Sulfate reduction was the major mineralization process during the night and the contribution of aerobic respiration to nighttime DIC production decreased. This decrease of aerobic respiration led to an increasing contribution of sulfide (and iron) oxidation to nighttime O₂ consumption. A peak of elemental sulfur in a layer of high sulfate reduction at low sulfide concentration underneath the oxic zone indicated anoxygenic photosynthesis and/or sulfide oxidation by iron, which strongly contributed to sulfide consumption. We found a significant internal carbon cycling in the mat, and sulfate reduction directly supplied DIC for photosynthesis. The mats were characterized by a high iron content of 56 mol Fe cm^–3, and iron cycling strongly controlled the sulfur cycle in the mat. This included sulfide precipitation resulting in high FeS contents with depth, and reactions of iron oxides with sulfide, especially after sunset, leading to a pronounced gap between oxygen and sulfide gradients and an unusual persistence of a pH peak in the uppermost mat layer until midnight.     

Influence of Sulfide and Temperature on Species Composition and Community Structure of Hot Spring Microbial Mats

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80°C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90°C, and a Chloroflexus mat is formed at 65 to 70°C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low-sulfide spring (1 mg liter⁻¹) below 70°C, whereas Aquificales were dominant in the high-sulfide spring (12 mg liter⁻¹) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.     

Biodiversity of the microbial mat of the Garga hot spring

Background

Microbial mats are a good model system for ecological and evolutionary analysis of microbial communities. There are more than 20 alkaline hot springs on the banks of the Barguzin river inflows. Water temperature reaches 75 °C and pH is usually 8.0–9.0. The formation of microbial mats is observed in all hot springs. Microbial communities of hot springs of the Baikal rift zone are poorly studied. Garga is the biggest hot spring in this area.

Results

In this study, we investigated bacterial and archaeal diversity of the Garga hot spring (Baikal rift zone, Russia) using 16S rRNA metagenomic sequencing. We studied two types of microbial communities: (i) small white biofilms on rocks in the points with the highest temperature (75 °C) and (ii) continuous thick phototrophic microbial mats observed at temperatures below 70 °C. Archaea (mainly Crenarchaeota; 19.8% of the total sequences) were detected only in the small biofilms. The high abundance of Archaea in the sample from hot springs of the Baikal rift zone supplemented our knowledge of the distribution of Archaea. Most archaeal sequences had low similarity to known Archaea. In the microbial mats, primary products were formed by cyanobacteria of the genus Leptolyngbya. Heterotrophic microorganisms were mostly represented by Actinobacteria and Proteobacteria in all studied samples of the microbial mats. Planctomycetes, Chloroflexi, and Chlorobi were abundant in the middle layer of the microbial mats, while heterotrophic microorganisms represented mostly by Firmicutes (Clostridia, strict anaerobes) dominated in the bottom part. Besides prokaryotes, we detect some species of Algae with help of detection their chloroplasts 16 s rRNA.

Conclusions

High abundance of Archaea in samples from hot springs of the Baikal rift zone supplemented our knowledge of the distribution of Archaea. Most archaeal sequences had low similarity to known Archaea. Metagenomic analysis of microbial communities of the microbial mat of Garga hot spring showed that the three studied points sampled at 70 °C, 55 °C, and 45 °C had similar species composition. Cyanobacteria of the genus Leptolyngbya dominated in the upper layer of the microbial mat. Chloroflexi and Chlorobi were less abundant and were mostly observed in the middle part of the microbial mat. We detected domains of heterotrophic organisms in high abundance (Proteobacteria, Firmicutes, Verrucomicrobia, Planctomicetes, Bacteroidetes, Actinobacteria, Thermi), according to metabolic properties of known relatives, which can form complete cycles of carbon, sulphur, and nitrogen in the microbial mat. The studied microbial mats evolved in early stages of biosphere formation. They can live autonomously, providing full cycles of substances and preventing live activity products poisoning.

     

Phylogenetic in situ/ex situ analysis of a sulfur mat microbial community from a thermal sulfide spring in the north Caucasus

A phylogenetic in situ/ex situ analysis of a sulfur mat formed by colorless filamentous sulfur bacteria in a thermal sulfide spring (northern spur of the main Caucasian ridge) was carried out. Nine phylotypes were revealed in the mat. Thiothrix sp. and Sphaerotilus sp. were the dominant phylotypes (66.3% and 26.3%, respectively). The 16S rRNA gene nucleotide sequence of Sphaerotilus sp. phylotype from the clone library was identical to the sequences of the seven Sphaerotilus strains isolated from the same source. A very high degree of similarity of Sphaerotilus strains revealed by ERIC-PCR fingerprints indicated little or no population diversity of this species in the mat. Thiothrix phylotype from the clone library and two Thiothrix strains isolated from the same mat sample differed in one to three nucleotides of 16S rRNA genes; this is an indication of this organism’s population variability in the mat. 16S rRNA genes of the strains and clones of Thiothrix sp. exhibited the highest similarity (ca. 99%) with Thiothrix unzii; the strains and clones of Sphaerotilus had 99% similarity with the type species Sphaerotilus natans (the only species of this genus) and therefore can be assigned to this species. The minor seven components belong to the phylotypes from the Proteobacteria (3%), as well as the Chlorobia, Cyanobacteria, Clostridia, and Bacteroidetes phylogenetic groups, each of them constituting not more than 1%. Intracellular accumulation of elemental sulfur by Sphaerotilus similar to other filamentous sulfur bacteria was demonstrated for the first time (both in the population of the sulfur spring and in cultures with sulfide). Although mass growth of Sphaerotilus and Thiothrix is typical of bacterial populations of anthropogenic ecosystems (the activated sludge of treatment facilities), stable communities of these bacteria have not been previously found in the sulfur mats or “threads” of natural sulfide springs.     

Archaeal and bacterial diversity in hot springs on the Tibetan Plateau, China

The diversity of archaea and bacteria was investigated in ten hot springs (elevation >4600 m above sea level) in Central and Central-Eastern Tibet using 16S rRNA gene phylogenetic analysis. The temperature and pH of these hot springs were 26-81°C and close to neutral, respectively. A total of 959 (415 and 544 for bacteria and archaea, respectively) clone sequences were obtained. Phylogenetic analysis showed that bacteria were more diverse than archaea and that these clone sequences were classified into 82 bacterial and 41 archaeal operational taxonomic units (OTUs), respectively. The retrieved bacterial clones were mainly affiliated with four known groups (i.e., Firmicutes, Proteobacteria, Cyanobacteria, Chloroflexi), which were similar to those in other neutral-pH hot springs at low elevations. In contrast, most of the archaeal clones from the Tibetan hot springs were affiliated with Thaumarchaeota, a newly proposed archaeal phylum. The dominance of Thaumarchaeota in the archaeal community of the Tibetan hot springs appears to be unique, although the exact reasons are not yet known. Statistical analysis showed that diversity indices of both archaea and bacteria were not statistically correlated with temperature, which is consistent with previous studies.     

Community structure of free-floating filamentous cyanobacterial mats from the Wonder Lake geothermal springs in the Philippines

Cyanobacterial mats were characterized from pools of 45-60 degrees C in near-neutral pH, low-sulphide geothermal springs in the Philippines. Mat structure did not vary with temperature. All mats possessed highly ordered layers of airspaces at both the macroscopic and microscopic level, and these appear to be an adaptation to a free-floating growth habit. Upper mat layers supported biomass with elevated carotenoid:chlorophyll a ratios and an as yet uncharacterized waxy layer on the dorsal surface. Microscopic examination revealed mats comprised a single Fischerella morphotype, with abundant heterocysts throughout mats at all temperatures. Molecular analysis of mat community structure only partly matched morphological identification. All samples supported greater 16S rDNA-defined diversity than morphology suggested, with a progressive loss in the number of genotypes with increasing temperature. Fischerella-like sequences were recovered from mats occurring at all temperatures, but some mats also yielded Oscillatoria-like sequences, although corresponding phenotypes were not observed. Phylogenetic analysis revealed that Fischerella-like sequences were most closely affiliated with Fischerella major and the Oscillatoria-like sequences with Oscillatoria amphigranulata.     

Anoxygenic microbial mats of hot springs: thermophilic Chlorobium sp.

Abstract Non-laminated, green to yellow-green microbial mats, with Chlorobium sp. as the only phototroph, occurred from 55 to about 40°C in hot springs in and near Rotorua, New Zealand. The pH ranged from 4.3 to 6.2 and sulfide from 0.2 to 1.8 mM. This Chlorobium sp. is unique in its ability to form populations at temperatures as high as 55°C. Spectroradiometric measurements with a fiber-optic microprobe in the intact Chlorobium mass showed great opacity with less than 0.1% of the incident radiation (at photosynthetically usable wavelengths) available at 0.7 mm depth within the mat, although the concentrated Chlorium population sometimes extended to 3 mm depth. Sulfide-dependent, anoxygenic photosynthesis was demonstrated by [¹⁴C]bicarbonate assimilation in mat suspensions and in intact mats by a sulfide-specific microelectrode. No oxygen evolution occurred and no O₂ was present within the mat. A light-enhanced uptake of [¹⁴C]acetate also occurred in cell suspensions. This rate was not enhanced by sulfide.     

An integrated study reveals diverse methanogens, Thaumarchaeota, and yet-uncultivated archaeal lineages in Armenian hot springs

Culture-independent and enrichment techniques, with an emphasis on members of the Archaea, were used to determine the composition and structure of microbial communities inhabiting microbial mats in the source pools of two geothermal springs near the towns of Arzakan and Jermuk in Armenia. Amplification of small-subunit rRNA genes using “universal” primers followed by pyrosequencing (pyrotags) revealed highly diverse microbial communities in both springs, with >99 % of pyrosequences corresponding to members of the domain Bacteria. The spring in Arzakan was colonized by a photosynthetic mat dominated by Cyanobacteria, in addition to Proteobacteria, Bacteroidetes, Chloroflexi, Spirochaeta and a diversity of other Bacteria. The spring in Jermuk was colonized by phylotypes related to sulfur, iron, and hydrogen chemolithotrophs in the Betaproteobacteria and Epsilonproteobacteria, along with a diversity of other Bacteria. Analysis of near full-length small subunit rRNA genes amplified using Archaea-specific primers showed that both springs are inhabited by a diversity of methanogens, including Methanomicrobiales and Methanosarcinales and relatives of Methanomassiliicoccus luminyensis, close relatives of the ammonia-oxidizing archaeon (AOA) “Candidatus Nitrososphaera gargensis”, and the yet-uncultivated Miscellaneous Crenarchaeotal Group and Deep Hydrothermal Vent Crenarchaeota group 1. Methanogenic enrichments confirmed the predicted physiological diversity, revealing methylotrophic, acetoclastic, and hydrogenotrophic methanogenesis at 45 and 55 °C, but not 65 °C. This is one of only a few studies combining cultivation-independent and -dependent approaches to study archaea in moderate-temperature (37–73 °C) terrestrial geothermal environments and suggests important roles for methanogenic archaea and AOA in the carbon and nitrogen biogeochemical cycles in these environments.