Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 20
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Proc Natl Acad Sci U S A ; 116(45): 22505-22511, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31591189

RESUMO

Glycerol dibiphytanyl glycerol tetraethers (GDGTs) are distinctive archaeal membrane-spanning lipids with up to eight cyclopentane rings and/or one cyclohexane ring. The number of rings added to the GDGT core structure can vary as a function of environmental conditions, such as changes in growth temperature. This physiological response enables cyclic GDGTs preserved in sediments to be employed as proxies for reconstructing past global and regional temperatures and to provide fundamental insights into ancient climate variability. Yet, confidence in GDGT-based paleotemperature proxies is hindered by uncertainty concerning the archaeal communities contributing to GDGT pools in modern environments and ambiguity in the environmental and physiological factors that affect GDGT cyclization in extant archaea. To properly constrain these uncertainties, a comprehensive understanding of GDGT biosynthesis is required. Here, we identify 2 GDGT ring synthases, GrsA and GrsB, essential for GDGT ring formation in Sulfolobus acidocaldarius Both proteins are radical S-adenosylmethionine proteins, indicating that GDGT cyclization occurs through a free radical mechanism. In addition, we demonstrate that GrsA introduces rings specifically at the C-7 position of the core GDGT lipid, while GrsB cyclizes at the C-3 position, suggesting that cyclization patterns are differentially controlled by 2 separate enzymes and potentially influenced by distinct environmental factors. Finally, phylogenetic analyses of the Grs proteins reveal that marine Thaumarchaeota, and not Euryarchaeota, are the dominant source of cyclized GDGTs in open ocean settings, addressing a major source of uncertainty in GDGT-based paleotemperature proxy applications.

2.
Free Radic Biol Med ; 140: 270-278, 2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31071437

RESUMO

Cyclic triterpenoids are a class of lipids that have fascinated chemists, biologist, and geologist alike for many years. These molecules have diverse physiological roles in a variety of bacterial and eukaryotic organisms and a shared evolutionary ancestry that is reflected in the elegant biochemistry required for their synthesis. Cyclic triterpenoids are also quite recalcitrant and are preserved in sedimentary rocks where they are utilized as "molecular fossils" or biomarkers that can physically link microbial taxa and their metabolisms to a specific time or event in Earth's history. However, a proper interpretation of cyclic triterpenoid biosignatures requires a robust understanding of their function in extant organisms and in the evolutionary history of their biosynthetic pathways. Here, I review two potential cyclic triterpenoid evolutionary scenarios and the recent genetic and biochemical studies that are providing experimental evidence to distinguish between these hypotheses. The study of cyclic triterpenoids will continue to provide a wealth of information that can significantly impact the interpretation of lipid biosignatures in the rock record and provides a compelling model of how two natural repositories of evolutionary history available on Earth, the geologic record in sedimentary rocks and the molecular record in living organisms, can be linked.

3.
ISME J ; 13(2): 290-300, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30214028

RESUMO

Differentiating the contributions of photosynthesis and respiration to the global carbon cycle is critical for improving predictive climate models. Carbonic anhydrase (CA) activity in leaves is responsible for the largest biosphere-atmosphere trace gas fluxes of carbonyl sulfide (COS) and the oxygen-18 isotopologue of carbon dioxide (CO18O) that both reflect gross photosynthetic rates. However, CA activity also occurs in soils and will be a source of uncertainty in the use of COS and CO18O as carbon cycle tracers until process-based constraints are improved. In this study, we measured COS and CO18O exchange rates and estimated the corresponding CA activity in soils from a range of biomes and land use types. Soil CA activity was not uniform for COS and CO2, and patterns of divergence were related to microbial community composition and CA gene expression patterns. In some cases, the same microbial taxa and CA classes catalyzed both COS and CO2 reactions in soil, but in other cases the specificity towards the two substrates differed markedly. CA activity for COS was related to fungal taxa and ß-D-CA expression, whereas CA activity for CO2 was related to algal and bacterial taxa and α-CA expression. This study integrates gas exchange measurements, enzyme activity models, and characterization of soil taxonomic and genetic diversity to build connections between CA activity and the soil microbiome. Importantly, our results identify kinetic parameters to represent soil CA activity during application of COS and CO18O as carbon cycle tracers.


Assuntos
Dióxido de Carbono/metabolismo , Anidrases Carbônicas/metabolismo , Microbiota , Microbiologia do Solo , Óxidos de Enxofre/metabolismo , Bactérias/enzimologia , Dióxido de Carbono/análise , Fungos/enzimologia , Isótopos de Oxigênio , Fotossíntese , Solo/química , Óxidos de Enxofre/análise
4.
Proc Natl Acad Sci U S A ; 115(51): 12932-12937, 2018 12 18.
Artigo em Inglês | MEDLINE | ID: mdl-30518563

RESUMO

Archaea have many unique physiological features of which the lipid composition of their cellular membranes is the most striking. Archaeal ether-linked isoprenoidal membranes can occur as bilayers or monolayers, possess diverse polar head groups, and a multiplicity of ring structures in the isoprenoidal cores. These lipid structures are proposed to provide protection from the extreme temperature, pH, salinity, and nutrient-starved conditions that many archaea inhabit. However, many questions remain regarding the synthesis and physiological role of some of the more complex archaeal lipids. In this study, we identify a radical S-adenosylmethionine (SAM) protein in Sulfolobus acidocaldarius required for the synthesis of a unique cyclopentyl head group, known as calditol. Calditol-linked glycerol dibiphytanyl glycerol tetraethers (GDGTs) are membrane spanning lipids in which calditol is ether bonded to the glycerol backbone and whose production is restricted to a subset of thermoacidophilic archaea of the Sulfolobales order within the Crenarchaeota phylum. Several studies have focused on the enzymatic mechanism for the synthesis of the calditol moiety, but to date no protein that catalyzes this reaction has been discovered. Phylogenetic analyses of this putative calditol synthase (Cds) reveal the genetic potential for calditol-GDGT synthesis in phyla other than the Crenarchaeota, including the Korarchaeota and Marsarchaeota. In addition, we identify Cds homologs in metagenomes predominantly from acidic ecosystems. Finally, we demonstrate that deletion of calditol synthesis renders S. acidocaldarius sensitive to extremely low pH, indicating that calditol plays a critical role in protecting archaeal cells from acidic stress.


Assuntos
Proteínas Arqueais/fisiologia , Lipídeos de Membrana/química , Estresse Fisiológico , Sulfolobus acidocaldarius/fisiologia , Proteínas Arqueais/química , Proteínas Arqueais/metabolismo , Genoma Arqueal , Concentração de Íons de Hidrogênio , Sulfolobus acidocaldarius/genética , Sulfolobus acidocaldarius/metabolismo
5.
Proc Natl Acad Sci U S A ; 115(23): 5884-5889, 2018 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-29784781

RESUMO

Sterols are essential eukaryotic lipids that are required for a variety of physiological roles. The diagenetic products of sterol lipids, sterane hydrocarbons, are preserved in ancient sedimentary rocks and are utilized as geological biomarkers, indicating the presence of both eukaryotes and oxic environments throughout Earth's history. However, a few bacterial species are also known to produce sterols, bringing into question the significance of bacterial sterol synthesis for our interpretation of sterane biomarkers. Recent studies suggest that bacterial sterol synthesis may be distinct from what is observed in eukaryotes. In particular, phylogenomic analyses of sterol-producing bacteria have failed to identify homologs of several key eukaryotic sterol synthesis enzymes, most notably those required for demethylation at the C-4 position. In this study, we identified two genes of previously unknown function in the aerobic methanotrophic γ-Proteobacterium Methylococcus capsulatus that encode sterol demethylase proteins (Sdm). We show that a Rieske-type oxygenase (SdmA) and an NAD(P)-dependent reductase (SdmB) are responsible for converting 4,4-dimethylsterols to 4α-methylsterols. Identification of intermediate products synthesized during heterologous expression of SdmA-SdmB along with 13C-labeling studies support a sterol C-4 demethylation mechanism distinct from that of eukaryotes. SdmA-SdmB homologs were identified in several other sterol-producing bacterial genomes but not in any eukaryotic genomes, indicating that these proteins are unrelated to the eukaryotic C-4 sterol demethylase enzymes. These findings reveal a separate pathway for sterol synthesis exclusive to bacteria and show that demethylation of sterols evolved at least twice-once in bacteria and once in eukaryotes.


Assuntos
Proteínas de Bactérias/metabolismo , Desmetilação , Methylococcus capsulatus/enzimologia , Methylococcus capsulatus/metabolismo , Esteróis/metabolismo , Animais , Proteínas de Bactérias/genética , Biologia Computacional , Escherichia coli , Células Eucarióticas , Methylococcus capsulatus/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Triterpenos/metabolismo
6.
Proc Natl Acad Sci U S A ; 114(2): 245-250, 2017 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-28028245

RESUMO

Cyclic triterpenoids are a broad class of polycyclic lipids produced by bacteria and eukaryotes. They are biologically relevant for their roles in cellular physiology, including membrane structure and function, and biochemically relevant for their exquisite enzymatic cyclization mechanism. Cyclic triterpenoids are also geobiologically significant as they are readily preserved in sediments and are used as biomarkers for ancient life throughout Earth's history. Isoarborinol is one such triterpenoid whose only known biological sources are certain angiosperms and whose diagenetic derivatives (arboranes) are often used as indicators of terrestrial input into aquatic environments. However, the occurrence of arborane biomarkers in Permian and Triassic sediments, which predates the accepted origin of angiosperms, suggests that microbial sources of these lipids may also exist. In this study, we identify two isoarborinol-like lipids, eudoraenol and adriaticol, produced by the aerobic marine heterotrophic bacterium Eudoraea adriatica Phylogenetic analysis demonstrates that the E. adriatica eudoraenol synthase is an oxidosqualene cyclase homologous to bacterial lanosterol synthases and distinct from plant triterpenoid synthases. Using an Escherichia coli heterologous sterol expression system, we demonstrate that substitution of four amino acid residues in a bacterial lanosterol synthase enabled synthesis of pentacyclic arborinols in addition to tetracyclic sterols. This variant provides valuable mechanistic insight into triterpenoid synthesis and reveals diagnostic amino acid residues to differentiate between sterol and arborinol synthases in genomic and metagenomic datasets. Our data suggest that there may be additional bacterial arborinol producers in marine and freshwater environments that could expand our understanding of these geologically informative lipids.


Assuntos
Flavobacteriaceae/metabolismo , Transferases Intramoleculares/metabolismo , Triterpenos/metabolismo , Escherichia coli/genética , Flavobacteriaceae/enzimologia , Flavobacteriaceae/genética , Transferases Intramoleculares/genética , Filogenia
7.
Front Microbiol ; 7: 990, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27446030

RESUMO

Sterols are essential components of eukaryotic cells whose biosynthesis and function has been studied extensively. Sterols are also recognized as the diagenetic precursors of steranes preserved in sedimentary rocks where they can function as geological proxies for eukaryotic organisms and/or aerobic metabolisms and environments. However, production of these lipids is not restricted to the eukaryotic domain as a few bacterial species also synthesize sterols. Phylogenomic studies have identified genes encoding homologs of sterol biosynthesis proteins in the genomes of several additional species, indicating that sterol production may be more widespread in the bacterial domain than previously thought. Although the occurrence of sterol synthesis genes in a genome indicates the potential for sterol production, it provides neither conclusive evidence of sterol synthesis nor information about the composition and abundance of basic and modified sterols that are actually being produced. Here, we coupled bioinformatics with lipid analyses to investigate the scope of bacterial sterol production. We identified oxidosqualene cyclase (Osc), which catalyzes the initial cyclization of oxidosqualene to the basic sterol structure, in 34 bacterial genomes from five phyla (Bacteroidetes, Cyanobacteria, Planctomycetes, Proteobacteria, and Verrucomicrobia) and in 176 metagenomes. Our data indicate that bacterial sterol synthesis likely occurs in diverse organisms and environments and also provides evidence that there are as yet uncultured groups of bacterial sterol producers. Phylogenetic analysis of bacterial and eukaryotic Osc sequences confirmed a complex evolutionary history of sterol synthesis in this domain. Finally, we characterized the lipids produced by Osc-containing bacteria and found that we could generally predict the ability to synthesize sterols. However, predicting the final modified sterol based on our current knowledge of sterol synthesis was difficult. Some bacteria produced demethylated and saturated sterol products even though they lacked homologs of the eukaryotic proteins required for these modifications emphasizing that several aspects of bacterial sterol synthesis are still completely unknown.

8.
Proc Natl Acad Sci U S A ; 112(44): 13478-83, 2015 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-26483502

RESUMO

Tetrahymanol is a polycyclic triterpenoid lipid first discovered in the ciliate Tetrahymena pyriformis whose potential diagenetic product, gammacerane, is often used as a biomarker for water column stratification in ancient ecosystems. Bacteria are also a potential source of tetrahymanol, but neither the distribution of this lipid in extant bacteria nor the significance of bacterial tetrahymanol synthesis for interpreting gammacerane biosignatures is known. Here we couple comparative genomics with genetic and lipid analyses to link a protein of unknown function to tetrahymanol synthesis in bacteria. This tetrahymanol synthase (Ths) is found in a variety of bacterial genomes, including aerobic methanotrophs, nitrite-oxidizers, and sulfate-reducers, and in a subset of aquatic and terrestrial metagenomes. Thus, the potential to produce tetrahymanol is more widespread in the bacterial domain than previously thought. However, Ths is not encoded in any eukaryotic genomes, nor is it homologous to eukaryotic squalene-tetrahymanol cyclase, which catalyzes the cyclization of squalene directly to tetrahymanol. Rather, heterologous expression studies suggest that bacteria couple the cyclization of squalene to a hopene molecule by squalene-hopene cyclase with a subsequent Ths-dependent ring expansion to form tetrahymanol. Thus, bacteria and eukaryotes have evolved distinct biochemical mechanisms for producing tetrahymanol.


Assuntos
Bactérias/genética , Bactérias/metabolismo , Vias Biossintéticas/genética , Triterpenos/metabolismo , Sequência de Aminoácidos , Bactérias/enzimologia , Proteínas de Bactérias/classificação , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Cromatografia Gasosa , Cromatografia Líquida , Desulfovibrio/genética , Desulfovibrio/metabolismo , Cromatografia Gasosa-Espectrometria de Massas , Teste de Complementação Genética , Genoma Bacteriano/genética , Transferases Intramoleculares/genética , Transferases Intramoleculares/metabolismo , Metagenoma/genética , Methylococcaceae/genética , Methylococcaceae/metabolismo , Dados de Sequência Molecular , Estrutura Molecular , Mutação , Filogenia , Homologia de Sequência de Aminoácidos , Triterpenos/química
9.
Microorganisms ; 3(2): 290-309, 2015 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-27682090

RESUMO

The Herman Pit, once a mercury mine, is an impoundment located in an active geothermal area. Its acidic waters are permeated by hundreds of gas seeps. One seep was sampled and found to be composed of mostly CO2 with some CH4 present. The δ(13)CH4 value suggested a complex origin for the methane: i.e., a thermogenic component plus a biological methanogenic portion. The relatively (12)C-enriched CO2 suggested a reworking of the ebullitive methane by methanotrophic bacteria. Therefore, we tested bottom sediments for their ability to consume methane by conducting aerobic incubations of slurried materials. Methane was removed from the headspace of live slurries, and subsequent additions of methane resulted in faster removal rates. This activity could be transferred to an artificial, acidic medium, indicating the presence of acidophilic or acid-tolerant methanotrophs, the latter reinforced by the observation of maximum activity at pH = 4.5 with incubated slurries. A successful extraction of sterol and hopanoid lipids characteristic of methanotrophs was achieved, and their abundances greatly increased with increased sediment methane consumption. DNA extracted from methane-oxidizing enrichment cultures was amplified and sequenced for pmoA genes that aligned with methanotrophic members of the Gammaproteobacteria. An enrichment culture was established that grew in an acidic (pH 4.5) medium via methane oxidation.

10.
Environ Microbiol ; 17(3): 735-50, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24888970

RESUMO

Hopanoids are bacterial surrogates of eukaryotic membrane sterols and among earth's most abundant natural products. Their molecular fossils remain in sediments spanning more than a billion years. However, hopanoid metabolism and function are not fully understood. Burkholderia species are environmental opportunistic pathogens that produce hopanoids and also occupy diverse ecological niches. We investigated hopanoids biosynthesis in Burkholderia cenocepacia by deletion mutagenesis and structural characterization of the hopanoids produced by the mutants. The enzymes encoded by hpnH and hpnG were essential for production of all C35 extended hopanoids, including bacteriohopanetetrol (BHT), BHT glucosamine and BHT cyclitol ether. Deletion of hpnI resulted in BHT production, while ΔhpnJ produced only BHT glucosamine. Thus, HpnI is required for BHT glucosamine production while HpnJ is responsible for its conversion to the cyclitol ether. The ΔhpnH and ΔhpnG mutants could not grow under any stress condition tested, whereas ΔhpnI, ΔhpnJ and ΔhpnK displayed wild-type growth rates when exposed to detergent, but varying levels of sensitivity to low pH and polymyxin B. This study not only elucidates the biosynthetic pathway of hopanoids in B. cenocepacia, but also uncovers a biosynthetic role for the conserved proteins HpnI, HpnJ and HpnK in other hopanoid-producing bacteria.


Assuntos
Burkholderia cenocepacia/metabolismo , Triterpenos/metabolismo , Antibacterianos/farmacologia , Filogenia , Polimixina B/farmacologia , Triterpenos/química
11.
ISME J ; 8(3): 675-684, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24152713

RESUMO

Molecular fossils of 2-methylhopanoids are prominent biomarkers in modern and ancient sediments that have been used as proxies for cyanobacteria and their main metabolism, oxygenic photosynthesis. However, substantial culture and genomic-based evidence now indicates that organisms other than cyanobacteria can make 2-methylhopanoids. Because few data directly address which organisms produce 2-methylhopanoids in the environment, we used metagenomic and clone library methods to determine the environmental diversity of hpnP, the gene encoding the C-2 hopanoid methylase. Here we show that hpnP copies from alphaproteobacteria and as yet uncultured organisms are found in diverse modern environments, including some modern habitats representative of those preserved in the rock record. In contrast, cyanobacterial hpnP genes are rarer and tend to be localized to specific habitats. To move beyond understanding the taxonomic distribution of environmental 2-methylhopanoid producers, we asked whether hpnP presence might track with particular variables. We found hpnP to be significantly correlated with organisms, metabolisms and environments known to support plant-microbe interactions (P-value<10(-6)); in addition, we observed diverse hpnP types in closely packed microbial communities from other environments, including stromatolites, hot springs and hypersaline microbial mats. The common features of these niches indicate that 2-methylhopanoids are enriched in sessile microbial communities inhabiting environments low in oxygen and fixed nitrogen with high osmolarity. Our results support the earlier conclusion that 2-methylhopanoids are not reliable biomarkers for cyanobacteria or any other taxonomic group, and raise the new hypothesis that, instead, they are indicators of a specific environmental niche.


Assuntos
Bactérias/metabolismo , Sedimentos Geológicos/microbiologia , Plantas/metabolismo , Compostos Policíclicos/metabolismo , Bactérias/classificação , Bactérias/genética , Cianobactérias/genética , Cianobactérias/metabolismo , Ecossistema , Fósseis , Biblioteca Gênica , Metagenômica , Fotossíntese
12.
Org Geochem ; 56: 120-130, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24496464

RESUMO

Hopanoids are triterpenoids produced mainly by bacteria, are ubiquitous in the environment, and have many important applications as biological markers. A wide variety of related hopanoid structures exists, many of which are polyfunctionalized. These modifications render the hopanoids too involatile for conventional gas chromatography (GC) separation, so require either laborious oxidative cleavage of the functional groups or specialized high temperature (HT) columns. Here we describe the systematic evaluation and optimization of a HT-GC method for the analysis of polyfunctionalized hopanoids and their methylated homologs. Total lipid extracts are derivatized with acetic anhydride and no further treatment or workup is required. We show that acid or base hydrolysis to remove di- and triacylglycerides leads to degradation of several BHP structures. DB-XLB type columns can elute hopanoids up to bacteriohopane-tetrol at 350 °C, with baseline separation of all 2-methyl/desmethyl homologs. DB-5HT type columns can additionally elute bacteriohopaneaminotriol and bacteriohopaneaminotetrol, but do not fully separate 2-methyl/desmethyl homologs. The method gave 2- to 7-fold higher recovery of hopanoids than oxidative cleavage and can provide accurate quantification of all analytes including 2-methyl hopanoids. By comparing data from mass spectra with those from a flame ionization detector, we show that the mass spectromet (MS) response factors for different hopanoids using either total ion counts or m/z 191 vary substantially. Similarly, 2-methyl ratios estimated from selected-ion data are lower than those from FID by 10-30% for most hopanoids, but higher by ca. 10% for bacteriohopanetetrol. Mass spectra for a broad suite of hopanoids, including 2-methyl homologs, from Rhodopseudomonas palustris are presented, together with the tentative assignment of several new hopanoid degradation products.

13.
Proc Natl Acad Sci U S A ; 109(32): 12905-10, 2012 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-22826256

RESUMO

Hopanoids methylated at the C-3 position are a subset of bacterial triterpenoids that are readily preserved in modern and ancient sediments and in petroleum. The production of 3-methylhopanoids by extant aerobic methanotrophs and their common occurrence in modern and fossil methane seep communities, in conjunction with carbon isotope analysis, has led to their use as biomarker proxies for aerobic methanotrophy. In addition, these lipids are also produced by aerobic acetic acid bacteria and, lacking carbon isotope analysis, are more generally used as indicators for aerobiosis in ancient ecosystems. However, recent genetic studies have brought into question our current understanding of the taxonomic diversity of methylhopanoid-producing bacteria and have highlighted that a proper interpretation of methylhopanes in the rock record requires a deeper understanding of their cellular function. In this study, we identified and deleted a gene, hpnR, required for methylation of hopanoids at the C-3 position in the obligate methanotroph Methylococcus capsulatus strain Bath. Bioinformatics analysis revealed that the taxonomic distribution of HpnR extends beyond methanotrophic and acetic acid bacteria. Phenotypic analysis of the M. capsulatus hpnR deletion mutant demonstrated a potential physiological role for 3-methylhopanoids; they appear to be required for the maintenance of intracytoplasmic membranes and cell survival in late stationary phase. Therefore, 3-methylhopanoids may prove more useful as proxies for specific environmental conditions encountered during stationary phase rather than a particular bacterial group.


Assuntos
Genes Bacterianos/genética , Methylococcus capsulatus/genética , Methylococcus capsulatus/metabolismo , Triterpenos Pentacíclicos/biossíntese , Filogenia , Sequência de Bases , Clonagem Molecular , Biologia Computacional , Primers do DNA/genética , Escherichia coli , Deleção de Genes , Teste de Complementação Genética , Funções Verossimilhança , Espectrometria de Massas , Metilação , Methylococcus capsulatus/ultraestrutura , Microscopia Eletrônica de Transmissão , Modelos Genéticos , Dados de Sequência Molecular , Estrutura Molecular , Triterpenos Pentacíclicos/química , Alinhamento de Sequência , Análise de Sequência de DNA
14.
J Bacteriol ; 194(5): 1158-68, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22210764

RESUMO

"Candidatus Chloracidobacterium thermophilum" is a recently discovered chlorophototroph from the bacterial phylum Acidobacteria, which synthesizes bacteriochlorophyll (BChl) c and chlorosomes like members of the green sulfur bacteria (GSB) and the green filamentous anoxygenic phototrophs (FAPs). The pigments (BChl c homologs and carotenoids), quinones, lipids, and hopanoids of cells and chlorosomes of this new chlorophototroph were characterized in this study. "Ca. Chloracidobacterium thermophilum" methylates its antenna BChls at the C-8(2) and C-12(1) positions like GSB, but these BChls were esterified with a variety of isoprenoid and straight-chain alkyl alcohols as in FAPs. Unlike the chlorosomes of other green bacteria, "Ca. Chloracidobacterium thermophilum" chlorosomes contained two major xanthophyll carotenoids, echinenone and canthaxanthin. These carotenoids may confer enhanced protection against reactive oxygen species and could represent a specific adaptation to the highly oxic natural environment in which "Ca. Chloracidobacterium thermophilum" occurs. Dihydrogenated menaquinone-8 [menaquinone-8(H(2))], which probably acts as a quencher of energy transfer under oxic conditions, was an abundant component of both cells and chlorosomes of "Ca. Chloracidobacterium thermophilum." The betaine lipid diacylglycerylhydroxymethyl-N,N,N-trimethyl-ß-alanine, esterified with 13-methyl-tetradecanoic (isopentadecanoic) acid, was a prominent polar lipid in the membranes of both "Ca. Chloracidobacterium thermophilum" cells and chlorosomes. This lipid may represent a specific adaptive response to chronic phosphorus limitation in the mats. Finally, three hopanoids, diploptene, bacteriohopanetetrol, and bacteriohopanetetrol cyclitol ether, which may help to stabilize membranes during diel shifts in pH and other physicochemical conditions in the mats, were detected in the membranes of "Ca. Chloracidobacterium thermophilum."


Assuntos
Acidobacteria/química , Bacterioclorofilas/análise , Carotenoides/análise , Lipídeos/análise , Triterpenos Pentacíclicos/análise , Quinonas/análise
15.
Proc Natl Acad Sci U S A ; 107(19): 8537-42, 2010 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-20421508

RESUMO

The rise of atmospheric oxygen has driven environmental change and biological evolution throughout much of Earth's history and was enabled by the evolution of oxygenic photosynthesis in the cyanobacteria. Dating this metabolic innovation using inorganic proxies from sedimentary rocks has been difficult and one important approach has been to study the distributions of fossil lipids, such as steranes and 2-methylhopanes, as biomarkers for this process. 2-methylhopanes arise from degradation of 2-methylbacteriohopanepolyols (2-MeBHPs), lipids thought to be synthesized primarily by cyanobacteria. The discovery that 2-MeBHPs are produced by an anoxygenic phototroph, however, challenged both their taxonomic link with cyanobacteria and their functional link with oxygenic photosynthesis. Here, we identify a radical SAM methylase encoded by the hpnP gene that is required for methylation at the C-2 position in hopanoids. This gene is found in several, but not all, cyanobacteria and also in alpha -proteobacteria and acidobacteria. Thus, one cannot extrapolate from the presence of 2-methylhopanes alone, in modern environments or ancient sedimentary rocks, to a particular taxonomic group or metabolism. To understand the origin of this gene, we reconstructed the evolutionary history of HpnP. HpnP proteins from cyanobacteria, Methylobacterium species, and other alpha-proteobacteria form distinct phylogenetic clusters, but the branching order of these clades could not be confidently resolved. Hence,it is unclear whether HpnP, and 2-methylhopanoids, originated first in the cyanobacteria. In summary, existing evidence does not support the use of 2-methylhopanes as biomarkers for oxygenic photosynthesis.


Assuntos
Sedimentos Geológicos/química , Metiltransferases/metabolismo , Rodopseudomonas/enzimologia , Triterpenos/análise , Triterpenos/metabolismo , Acetilação , Cromatografia Gasosa-Espectrometria de Massas , Transferases Intramoleculares/metabolismo , Família Multigênica/genética , Filogenia , Rodopseudomonas/genética , Triterpenos/química
16.
J Bacteriol ; 191(19): 6145-56, 2009 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19592593

RESUMO

Sedimentary hopanes are pentacyclic triterpenoids that serve as biomarker proxies for bacteria and certain bacterial metabolisms, such as oxygenic photosynthesis and aerobic methanotrophy. Their parent molecules, the bacteriohopanepolyols (BHPs), have been hypothesized to be the bacterial equivalent of sterols. However, the actual function of BHPs in bacterial cells is poorly understood. Here, we report the physiological study of a mutant in Rhodopseudomonas palustris TIE-1 that is unable to produce any hopanoids. The deletion of the gene encoding the squalene-hopene cyclase protein (Shc), which cyclizes squalene to the basic hopene structure, resulted in a strain that no longer produced any polycyclic triterpenoids. This strain was able to grow chemoheterotrophically, photoheterotrophically, and photoautotrophically, demonstrating that hopanoids are not required for growth under normal conditions. A severe growth defect, as well as significant morphological damage, was observed when cells were grown under acidic and alkaline conditions. Although minimal changes in shc transcript expression were observed under certain conditions of pH shock, the total amount of hopanoid production was unaffected; however, the abundance of methylated hopanoids significantly increased. This suggests that hopanoids may play an indirect role in pH homeostasis, with certain hopanoid derivatives being of particular importance.


Assuntos
Membrana Celular/metabolismo , Rodopseudomonas/metabolismo , Triterpenos/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/fisiologia , Cromatografia Gasosa-Espectrometria de Massas , Concentração de Íons de Hidrogênio , Transferases Intramoleculares/genética , Transferases Intramoleculares/fisiologia , Microscopia Eletrônica de Transmissão , Estrutura Molecular , Mutação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Rodopseudomonas/genética , Rodopseudomonas/crescimento & desenvolvimento , Rodopseudomonas/ultraestrutura , Triterpenos/química
17.
Curr Biol ; 19(14): R567-74, 2009 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-19640495

RESUMO

The rise of atmospheric O(2) was a milestone in the history of life. Although O(2) itself is not a climate-active gas, its appearance would have removed a methane greenhouse present on the early Earth and potentially led to dramatic cooling. Moreover, by fundamentally altering the biogeochemical cycles of C, N, S and Fe, its rise first in the atmosphere and later in the oceans would also have had important indirect effects on Earth's climate. Here, we summarize major lines of evidence from the geological literature that pertain to when and how O(2) first appeared in significant amounts in the atmosphere. On the early Earth, atmospheric O(2) would initially have been very low, probably <10(-5) of the present atmospheric level. Around 2.45 billion years ago, atmospheric O(2) rose suddenly in what is now termed the Great Oxidation Event. While the rise of oxygen has been the subject of considerable attention by Earth scientists, several important aspects of this problem remain unresolved. Our goal in this review is to provide a short summary of the current state of the field, and make the case that future progress towards solving the riddle of oxygen will benefit greatly from the involvement of molecular biologists.


Assuntos
Atmosfera/química , Efeito Estufa , Oxigênio/análise , Oxigênio/história , Fotossíntese/fisiologia , Carbono/química , Fenômenos Geológicos , História Antiga , Metais/química , Oxirredução , Enxofre/química
18.
J Bacteriol ; 190(6): 1928-36, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-18178739

RESUMO

A series of Methanosarcina barkeri mutants lacking the genes encoding the enzymes involved in the C1 oxidation/reduction pathway were constructed. Mutants lacking the methyl-tetrahydromethanopterin (H4MPT):coenzyme M (CoM) methyltransferase-encoding operon (delta mtr), the methylene-H4MPT reductase-encoding gene (delta mer), the methylene-H4MPT dehydrogenase-encoding gene (delta mtd), and the formyl-methanofuran:H4MPT formyl-transferase-encoding gene (delta ftr) all failed to grow using either methanol or H2/CO2 as a growth substrate, indicating that there is an absolute requirement for the C1 oxidation/reduction pathway for hydrogenotrophic and methylotrophic methanogenesis. The mutants also failed to grow on acetate, and we suggest that this was due to an inability to generate the reducing equivalents needed for biosynthetic reactions. Despite their lack of growth on methanol, the delta mtr and delta mer mutants were capable of producing methane from this substrate, whereas the delta mtd and delta ftr mutants were not. Thus, there is an Mtr/Mer bypass pathway that allows oxidation of methanol to the level of methylene-H4MPT in M. barkeri. The data further suggested that formaldehyde may be an intermediate in this bypass; however, no methanol dehydrogenase activity was found in delta mtr cell extracts, nor was there an obligate role for the formaldehyde-activating enzyme (Fae), which has been shown to catalyze the condensation of formaldehyde and H4MPT in vitro. Both the delta mer and delta mtr mutants were able to grow on a combination of methanol plus acetate, but they did so by metabolic pathways that are clearly distinct from each other and from previously characterized methanogenic pathways.


Assuntos
Proteínas Arqueais/genética , Methanosarcina barkeri/genética , Mutação , Pterinas/metabolismo , Acetatos/metabolismo , Oxirredutases do Álcool/genética , Oxirredutases do Álcool/metabolismo , Proteínas Arqueais/metabolismo , Dióxido de Carbono/metabolismo , Formaldeído/metabolismo , Hidrogênio/metabolismo , Metano/metabolismo , Metanol/metabolismo , Methanosarcina barkeri/enzimologia , Methanosarcina barkeri/metabolismo , Modelos Biológicos , Mutagênese , Óperon/genética , Oxirredução
19.
J Virol ; 81(3): 1451-60, 2007 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-17108044

RESUMO

Tumor necrosis factor (TNF) is a multifunctional cytokine that has a role in induction and regulation of host innate and adaptive immune responses. The importance of TNF antiviral mechanisms is reflected by the diverse strategies adopted by different viruses, particularly members of the herpesvirus family, to block TNF responses. TNF binds and signals through two receptors, Tnfrsf1a (TNF receptor 1 [TNFR1], or p55) and Tnfrsf1b (TNFR2, or p75). We report here that herpes simplex virus 1 (HSV-1) infection of TNF-/- mice on the resistant C57BL/6 genetic background results in significantly increased susceptibility (P < 0.0001, log rank test) to fatal HSV encephalitis (HSE) and prolonged persistence of elevated levels of virus in neural tissues. In contrast, although virus titers in neural tissues of p55-/- N13 mice were elevated to levels comparable to what was found for the TNF-/- mice, the p55-/- N13 mice were as resistant as control C57BL/6 mice (P > 0.05). The incidence of fatal HSE was significantly increased by in vivo neutralization of TNF using soluble TNFR1 (sTNFR1) or depletion of macrophages in C57BL/6 mice (P = 0.0038 and P = 0.0071, respectively). Strikingly, in vivo neutralization of TNF in HSV-1-infected p55-/- p75-/- mice by use of three independent approaches (treatment with soluble p55 receptor, anti-TNF monoclonal antibody, or in vivo small interfering RNA against TNF) resulted in significantly increased mortality rates (P = 0.005), comparable in magnitude to those for C57BL/6 mice treated with sTNFR1 (P = 0.0018). Overall, these results indicate that while TNF is required for resistance to fatal HSE, both p55 and p75 receptors are dispensable. Precisely how TNF mediates protection against HSV-1 mortality in p55-/- p75-/- mice remains to be determined.


Assuntos
Antivirais/farmacologia , Encefalite por Herpes Simples/imunologia , Receptores do Fator de Necrose Tumoral/fisiologia , Transdução de Sinais/fisiologia , Simplexvirus/efeitos dos fármacos , Fator de Necrose Tumoral alfa/metabolismo , Animais , Encefalite por Herpes Simples/virologia , Camundongos , Camundongos Endogâmicos C57BL , Receptores do Fator de Necrose Tumoral/genética , Simplexvirus/genética , Simplexvirus/patogenicidade
20.
Proc Natl Acad Sci U S A ; 102(30): 10664-9, 2005 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-16024727

RESUMO

In the methanogenic archaeon Methanosarcina barkeri Fusaro, the N5-methyl-tetrahydrosarcinapterin (CH3-H4SPT):coenzyme M (CoM) methyltransferase, encoded by the mtr operon, catalyzes the energy-conserving (sodium-pumping) methyl transfer from CH3-H4SPT to CoM during growth on H2/CO2 or acetate. However, in the disproportionation of C-1 compounds, such as methanol, to methane and carbon dioxide, it catalyzes the reverse, endergonic transfer from methyl-CoM to H4SPT, which is driven by sodium uptake. It has been proposed that a bypass for this energy-consuming reaction may occur via a direct methyl transfer from methanol to H4SPT. To test this, an mtr deletion mutant was constructed and characterized in M. barkeri Fusaro. The mutant is unable to grow on methanol, acetate or H2/CO2, but can grow on methanol with H2/CO2 and, surprisingly, methanol with acetate. 13C labeling experiments show that growth on acetate with methanol involves a previously unknown methanogenic pathway, in which oxidation of acetate to a mixture of CO2 and formic acid is coupled to methanol reduction. Interestingly, although the mutant is unable to grow on methanol alone, it remains capable of producing methane from this substrate. Thus, the proposed Mtr bypass does exist, but is unable to support growth of the organism.


Assuntos
Metano/biossíntese , Metanol/metabolismo , Methanosarcina barkeri/crescimento & desenvolvimento , Methanosarcina barkeri/metabolismo , Metiltransferases/metabolismo , Isótopos de Carbono , Técnicas de Transferência de Genes , Methanosarcina barkeri/genética , Metiltransferases/genética , Óperon/genética , Acetato de Sódio
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA