Explore the vast range of titles available.

Archaea , primarily Crenarchaeota , are common in soil; however, the structure of soil archaeal communities and the factors regulating their diversity and abundance remain poorly understood. Here, we used barcoded pyrosequencing to comprehensively survey archaeal and bacterial communities in 146 soils, representing a multitude of soil and ecosystem types from across the globe. Relative archaeal abundance, the percentage of all 16S rRNA gene sequences recovered that were archaeal, averaged 2% across all soils and ranged from 0% to >10% in individual soils. Soil C:N ratio was the only factor consistently correlated with archaeal relative abundances, being higher in soils with lower C:N ratios. Soil archaea communities were dominated by just two phylotypes from a constrained clade within the Crenarchaeota , which together accounted for >70% of all archaeal sequences obtained in the survey. As one of these phylotypes was closely related to a previously identified putative ammonia oxidizer, we sampled from two long-term nitrogen (N) addition experiments to determine if this taxon responds to experimental manipulations of N availability. Contrary to expectations, the abundance of this dominant taxon, as well as archaea overall, tended to decline with increasing N. This trend was coupled with a concurrent increase in known N-oxidizing bacteria, suggesting competitive interactions between these groups.

Anaerobic methanotrophs help regulate Earth's climate and may have been an important part of the microbial ecosystem on the early Earth. The anaerobic oxidation of methane (AOM) is often thought of as a sulfate-dependent process, despite the fact that other electron acceptors are more energetically favorable. Here, we show that microorganisms from marine methane-seep sediment in the Eel River Basin in California are capable of using manganese (birnessite) and iron (ferrihydrite) to oxidize methane, revealing that marine AOM is coupled, either directly or indirectly, to a larger variety of oxidants than previously thought. Large amounts of manganese and iron are provided to oceans from rivers, indicating that manganese- and iron-dependent AOM have the potential to be globally important.

Analyses of archaeal membrane lipids are increasingly being included in ecological studies as a comparatively unbiased complement to gene-based microbiological approaches. For example, crenarchaeol, a glycerol dialkyl glycerol tetraether (GDGT) with a unique cyclohexane moiety, has been postulated as biomarker for ammonia-oxidizing Archaea (AOA). Crenarchaeol has been detected in Nitrosopumilus maritimus and ‘ Candidatus Nitrosocaldus yellowstonii’ representing two of the three lineages within the Crenarchaeota containing described AOA. In this paper we present the membrane GDGT composition of ‘ Candidatus Nitrososphaera gargensis’, a moderately thermophilic AOA, and the only cultivated Group I.1b Crenarchaeon. At a cultivation temperature of 46 °C, GDGTs of this organism consisted primarily of crenarchaeol, its regioisomer, and a novel GDGT. Intriguingly, ‘ Ca . N. gargensis’ is the first cultivated archaeon to synthesize substantial amounts of the crenarchaeol regioisomer, a compound found in large relative abundances in tropical ocean water and some soils, and an important component of the TEX 86 paleothermometer. Intact polar lipid (IPL) analysis revealed that ‘ Ca . N. gargensis’ synthesizes IPLs similar to those reported for the Goup I.1a AOA, Nitrosopumilus maritimus SCMI , in addition to IPLs containing uncharacterized headgroups. Overall, the unique GDGT composition of ‘ Ca . N. gargensis’ extends the known taxonomic distribution of crenarchaeol synthesis to the Group I.1b Crenarchaeota, implicating this clade as a potentially important source of crenarchaeol in soils and moderately high temperature environments. Moreover, this work supports the hypothesis that crenarchaeol is specific to all AOA and highlights specific lipids, which may prove useful as biomarkers for ‘ Ca . N. gargensis’-like AOA.

Mesophilic Crenarchaeota have recently been thought to be significant contributors to nitrogen (N) and carbon (C) cycling. In this study, we examined the vertical distribution of ammonia-oxidizing Crenarchaeota at offshore site in Southern Tyrrhenian Sea. The median value of the crenachaeal cell to amoA gene ratio was close to one suggesting that virtually all deep-sea Crenarchaeota possess the capacity to oxidize ammonia. Crenarchaea-specific genes, nir K and ure C, for nitrite reductase and urease were identified and their affiliation demonstrated the presence of ‘deep-sea’ clades distinct from ‘shallow’ representatives. Measured deep-sea dark CO 2 fixation estimates were comparable to the median value of photosynthetic biomass production calculated for this area of Tyrrhenian Sea, pointing to the significance of this process in the C cycle of aphotic marine ecosystems. To elucidate the pivotal organisms in this process, we targeted known marine crenarchaeal autotrophy-related genes, coding for acetyl-CoA carboxylase ( acc A) and 4-hydroxybutyryl-CoA dehydratase (4- hbd ). As in case of nir K and ure C, these genes are grouped with deep-sea sequences being distantly related to those retrieved from the epipelagic zone. To pair the molecular data with specific functional attributes we performed [ 14 C]HCO 3 incorporation experiments followed by analyses of radiolabeled proteins using shotgun proteomics approach. More than 100 oligopeptides were attributed to 40 marine crenarchaeal-specific proteins that are involved in 10 different metabolic processes, including autotrophy. Obtained results provided a clear proof of chemolithoautotrophic physiology of bathypelagic crenarchaeota and indicated that this numerically predominant group of microorganisms facilitate a hitherto unrecognized sink for inorganic C of a global importance.

In from the cold The marine Crenarchaeota, members of the bacteria-like Archaea that thrive in the cold, are the dominant bacterioplankton in the world's oceans. They play a major role in global biogeochemical cycles, yet since their discovery over a decade ago their physiology has remained a mystery, largely because it has not been possible to grow them in lab cultures. The isolation of one of these elusive organisms is now reported: it turns out to be a nitrifier, obtaining energy from the oxidation of ammonia to nitrite. Similarity of genes implicated in nitrification between this isolate and as yet uncultured terrestrial Archaea suggests that the capacity for nitrification is widely distributed among non-thermophilic Crenarchaeota in both marine and terrestrial provinces. Based on the metabolism of this isolate, it seems that the marine Crenarchaeota must play an important role in global carbon and nitrogen cycles. For years, microbiologists characterized the Archaea as obligate extremophiles that thrive in environments too harsh for other organisms. The limited physiological diversity among cultivated Archaea suggested that these organisms were metabolically constrained to a few environmental niches. For instance, all Crenarchaeota that are currently cultivated are sulphur-metabolizing thermophiles 1 . However, landmark studies using cultivation-independent methods uncovered vast numbers of Crenarchaeota in cold oxic ocean waters 2 , 3 . Subsequent molecular surveys demonstrated the ubiquity of these low-temperature Crenarchaeota in aquatic and terrestrial environments 4 . The numerical dominance of marine Crenarchaeota—estimated at 10 28 cells in the world's oceans 5 —suggests that they have a major role in global biogeochemical cycles. Indeed, isotopic analyses of marine crenarchaeal lipids suggest that these planktonic Archaea fix inorganic carbon 6 . Here we report the isolation of a marine crenarchaeote that grows chemolithoautotrophically by aerobically oxidizing ammonia to nitrite—the first observation of nitrification in the Archaea. The autotrophic metabolism of this isolate, and its close phylogenetic relationship to environmental marine crenarchaeal sequences, suggests that nitrifying marine Crenarchaeota may be important to global carbon and nitrogen cycles.

Marine Crenarchaeota are the most abundant single group of prokaryotes in the ocean, but their physiology and role in marine biogeochemical cycles are unknown. Recently, a member of this clade was isolated from a sea aquarium and shown to be capable of nitrification, tentatively suggesting that Crenarchaeota may play a role in the oceanic nitrogen cycle. We enriched a crenarchaeote from North Sea water and showed that its abundance, and not that of bacteria, correlates with ammonium oxidation to nitrite. A time series study in the North Sea revealed that the abundance of the gene encoding for the archaeal ammonia monooxygenase alfa subunit (amoA) is correlated with a decline in ammonium concentrations and with the abundance of Crenarchaeota. Remarkably, the archaeal amoA abundance was 1-2 orders of magnitude higher than those of bacterial nitrifiers, which are commonly thought to mediate the oxidation of ammonium to nitrite in marine environments. Analysis of Atlantic waters of the upper 1,000 m, where most of the ammonium regeneration and oxidation takes place, showed that crenarchaeotal amoA copy numbers are also 1-3 orders of magnitude higher than those of bacterial amoA. Our data thus suggest a major role for Archaea in oceanic nitrification.

Active expression of putative ammonia monooxygenase gene subunit A (amoA) of marine group I Crenarchaeota has been detected in the Black Sea water column. It reached its maximum, as quantified by reverse-transcription quantitative PCR, exactly at the nitrate maximum or the nitrification zone modeled in the lower oxic zone. Crenarchaeal amoA expression could explain 74.5% of the nitrite variations in the lower oxic zone. In comparison, amoA expression by γ-proteobacterial ammonia-oxidizing bacteria (AOB) showed two distinct maxima, one in the modeled nitrification zone and one in the suboxic zone. Neither the amoA expression by crenarchaea nor that by β-proteobacterial AOB was significantly elevated in this latter zone. Nitrification in the suboxic zone, most likely microaerobic in nature, was verified by ¹⁵NO[Formula: see text] and ¹⁵N¹⁵N production in ¹⁵NH[Formula: see text] incubations with no measurable oxygen. It provided a direct local source of nitrite for anammox in the suboxic zone. Both ammonia-oxidizing crenarchaea and γ-proteobacterial AOB were important nitrifiers in the Black Sea and were likely coupled to anammox in indirect and direct manners respectively. Each process supplied about half of the nitrite required by anammox, based on ¹⁵N-incubation experiments and modeled calculations. Because anammox is a major nitrogen loss in marine suboxic waters, such nitrification-anammox coupling potentially occurring also in oceanic oxygen minimum zones would act as a short circuit connecting regenerated ammonium to direct nitrogen loss, thus reducing the presumed direct contribution from deep-sea nitrate.

Nitrification plays an important role in marine biogeochemistry, yet efforts to link this process to the microorganisms that mediate it are surprisingly limited. In particular, ammonia oxidation is the first and rate-limiting step of nitrification, yet ammonia oxidation rates and the abundance of ammonia-oxidizing bacteria (AOB) have rarely been measured in tandem. Ammonia oxidation rates have not been directly quantified in conjunction with ammonia-oxidizing archaea (AOA), although mounting evidence indicates that marine Crenarchaeota are capable of ammonia oxidation, and they are among the most abundant microbial groups in the ocean. Here, we have directly quantified ammonia oxidation rates by 15 N labeling, and AOA and AOB abundances by quantitative PCR analysis of ammonia monooxygenase subunit A ( amoA ) genes, in the Gulf of California. Based on markedly different archaeal amoA sequence types in the upper water column (60 m) and oxygen minimum zone (OMZ; 450 m), novel amoA PCR primers were designed to specifically target and quantify ‘shallow’ (group A) and ‘deep’ (group B) clades. These primers recovered extensive variability with depth. Within the OMZ, AOA were most abundant where nitrification may be coupled to denitrification. In the upper water column, group A tracked variations in nitrogen biogeochemistry with depth and between basins, whereas AOB were present in relatively low numbers or undetectable. Overall, 15 NH 4 + oxidation rates were remarkably well correlated with AOA group A amoA gene copies ( r 2 =0.90, P <0.001), and with 16S rRNA gene copies from marine Crenarchaeota ( r 2 =0.85, P <0.005). These findings represent compelling evidence for an archaeal role in oceanic nitrification.

Key Points The archaeal domain is currently divided into two major phyla, the Euryarchaeota and the Crenarchaeota, based on the RNA component of the small ribosomal subunit (SSU rRNA). During the past few years, uncultivated mesophilic crenarchaeota from marine and terrestrial environments have been identifed using PCR amplification of SSU rRNA. These archaea have been affiliated with Crenarchaeota, because they form a sister group of the hyperthermophilic crenarchaeota in SSU rRNA trees. It was recently recognized that uncultivated mesophilic crenarchaeota include ammonium-oxidizers that might have an important role in the global nitrogen cycle. Recently, the first genome sequence of a mesophilic crenarchaeota, Cenarchaeum symbiosum , was completed. This mesophilic 'crenarchaeon' was included in archaeal phylogenies that are based on the concatenation of ribosomal protein sequences. Whereas C. symbiosum and related mesophilic crenarchaeota form a weakly supported sister group of hyperthermophilic crenarchaeota in a tree that combines SSU and large subunit (LSU) rRNA sequences, they have a robust basal position in a tree that is based on a concatenation of ribosomal proteins. Genome mining shows that C. symbiosum lacks the typical crenarchaeal signatures, and instead has several characteristic euryarchaeal signatures. These data indicate that C. symbiosum (and related mesophilic crenarchaeota) are distinct from hyperthermophilic crenarchaeota. We suggest that these ubiquitous archaea should form a third archaeal phylum and propose to name this new phylum Thaumarchaeota (from the Greek ' thaumas ', meaning wonder). The archaeal domain comprises two phyla, the Euryarchaeota and the Crenarchaeota. Phylogenetic and genomic analyses now show that mesophilic crenarchaeota should not be considered as crenarchaeota. Based on this, the authors advocate the creation of a third archaeal phylum, which they propose to name Thaumarchaeota (from the Greek ' thaumas ', meaning wonder). The archaeal domain is currently divided into two major phyla, the Euryarchaeota and Crenarchaeota. During the past few years, diverse groups of uncultivated mesophilic archaea have been discovered and affiliated with the Crenarchaeota. It was recently recognized that these archaea have a major role in geochemical cycles. Based on the first genome sequence of a crenarchaeote, Cenarchaeum symbiosum , we show that these mesophilic archaea are different from hyperthermophilic Crenarchaeota and branch deeper than was previously assumed. Our results indicate that C. symbiosum and its relatives are not Crenarchaeota, but should be considered as a third archaeal phylum, which we propose to name Thaumarchaeota (from the Greek ' thaumas ', meaning wonder).

For more than 100 years it was believed that bacteria were the only group responsible for the oxidation of ammonia. However, recently, a new strain of archaea bearing a putative ammonia monooxygenase subunit A (amoA) gene and able to oxidize ammonia was isolated from a marine aquarium tank. Ammonia-oxidizing archaea (AOA) were subsequently discovered in many ecosystems of varied characteristics and even found as the predominant causal organisms in some environments. Here, we summarize the current knowledge on the environmental conditions related to the presence of AOA and discuss the possible site-related properties. Considering these data, we deduct the possible niches of AOA based on pH, sulfide and phosphate levels. It is proposed that the AOA might be important actors within the nitrogen cycle in low-nutrient, low-pH, and sulfide-containing environments.