RESUMEN
Socio-economic disparities were associated with disproportionate viral incidence between neighborhoods of New York City (NYC) during the first wave of SARS-CoV-2. We investigated how these disparities affected the co-circulation of SARS-CoV-2 variants during the second wave in NYC. We tested for correlation between the prevalence, in late 2020/early 2021, of Alpha, Iota, Iota with E484K mutation (Iota-E484K), and B.1-like genomes and pre-existing immunity (seropositivity) in NYC neighborhoods. In the context of varying seroprevalence we described socio-economic profiles of neighborhoods and performed migration and lineage persistence analyses using a Bayesian phylogeographical framework. Seropositivity was greater in areas with high poverty and a larger proportion of Black and Hispanic or Latino residents. Seropositivity was positively correlated with the proportion of Iota-E484K and Iota genomes, and negatively correlated with the proportion of Alpha and B.1-like genomes. The proportion of persisting Alpha lineages declined over time in locations with high seroprevalence, whereas the proportion of persisting Iota-E484K lineages remained the same in high seroprevalence areas. During the second wave, the geographic variation of standing immunity, due to disproportionate disease burden during the first wave of SARS-CoV-2 in NYC, allowed for the immune evasive Iota-E484K variant, but not the more transmissible Alpha variant, to circulate in locations with high pre-existing immunity.
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COVID-19 , SARS-CoV-2 , Humanos , Ciudad de Nueva York/epidemiología , SARS-CoV-2/inmunología , SARS-CoV-2/genética , COVID-19/epidemiología , COVID-19/virología , Estudios Seroepidemiológicos , Factores Socioeconómicos , Masculino , Femenino , Adulto , Persona de Mediana Edad , MutaciónRESUMEN
In July 2022, a case of paralytic poliomyelitis resulting from infection with vaccine-derived poliovirus (VDPV) type 2 (VDPV2)§ was confirmed in an unvaccinated adult resident of Rockland County, New York (1). As of August 10, 2022, poliovirus type 2 (PV2)¶ genetically linked to this VDPV2 had been detected in wastewater** in Rockland County and neighboring Orange County (1). This report describes the results of additional poliovirus testing of wastewater samples collected during March 9-October 11, 2022, and tested as of October 20, 2022, from 48 sewersheds (the community area served by a wastewater collection system) serving parts of Rockland County and 12 surrounding counties. Among 1,076 wastewater samples collected, 89 (8.3%) from 10 sewersheds tested positive for PV2. As part of a broad epidemiologic investigation, wastewater testing can provide information about where poliovirus might be circulating in a community in which a paralytic case has been identified; however, the most important public health actions for preventing paralytic poliomyelitis in the United States remain ongoing case detection through national acute flaccid myelitis (AFM) surveillance and improving vaccination coverage in undervaccinated communities. Although most persons in the United States are sufficiently immunized, unvaccinated or undervaccinated persons living or working in Kings, Orange, Queens, Rockland, or Sullivan counties, New York should complete the polio vaccination series as soon as possible.
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Poliomielitis , Vacuna Antipolio Oral , Poliovirus , Adulto , Humanos , New York/epidemiología , Poliomielitis/diagnóstico , Poliomielitis/epidemiología , Poliomielitis/prevención & control , Poliovirus/genética , Vacuna Antipolio Oral/efectos adversos , Estados Unidos , Aguas ResidualesRESUMEN
In May 2019, the New York City Department of Health and Mental Hygiene (NYCDOHMH) detected an unusual cluster of five salmonellosis patients via automated spatiotemporal analysis of notifiable diseases using free SaTScan software (1). Within 1 day of cluster detection, graduate student interviewers determined that three of the patients had eaten prepared food from the same grocery store (establishment A) located inside the cluster area. NYCDOHMH initiated an investigation to identify additional cases, establish the cause, and provide control recommendations. Overall, 15 New York City (NYC) residents with laboratory-diagnosed salmonellosis who reported eating food from establishment A were identified. The most commonly consumed food item was chicken, reported by 10 patients. All 11 clinical isolates available were serotyped as Salmonella Blockley, sequenced, and analyzed by core genome multilocus sequence typing; isolates had a median difference of zero alleles. Environmental assessments revealed food not held at the proper temperature, food not cooled properly, and potential cross-contamination during chicken preparation. Elevated fecal coliform counts were found in two of four ready-to-eat food samples collected from establishment A, and Bacillus cereus was detected in three. The outbreak strain of Salmonella was isolated from one patient's leftover chicken. Establishing automated spatiotemporal cluster detection analyses for salmonellosis and other reportable diseases could aid in the detection of geographically focused, community-acquired outbreaks even before laboratory subtyping results become available.
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Brotes de Enfermedades , Vigilancia en Salud Pública/métodos , Intoxicación Alimentaria por Salmonella/epidemiología , Análisis Espacio-Temporal , Adulto , Automatización , Femenino , Humanos , Masculino , Persona de Mediana Edad , Ciudad de Nueva York/epidemiología , Salmonella/genética , Salmonella/aislamiento & purificación , Intoxicación Alimentaria por Salmonella/diagnóstico , SerogrupoRESUMEN
We characterized a case of neonatal conjunctivitis in New York, USA, caused by Neisseria meningitidis by using whole-genome sequencing. The case was a rare occurrence, and the isolate obtained belonged to an emerging clade (N. meningitidis US nongroupable urethritis) associated with an increase in cases of urethritis since 2015.
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Conjuntivitis/epidemiología , Conjuntivitis/microbiología , Infecciones Meningocócicas/epidemiología , Infecciones Meningocócicas/microbiología , Neisseria meningitidis , Conjuntivitis/historia , Femenino , Genoma Bacteriano , Historia del Siglo XXI , Humanos , Recién Nacido , Masculino , Infecciones Meningocócicas/historia , New York/epidemiología , Filogenia , Polimorfismo de Nucleótido Simple , Uretritis/epidemiología , Uretritis/microbiología , Secuenciación Completa del GenomaAsunto(s)
COVID-19 , SARS-CoV-2 , Humanos , SARS-CoV-2/genética , Ciudad de Nueva York/epidemiología , COVID-19/epidemiologíaRESUMEN
The global mpox epidemic in 2022 was likely caused by transmission of mpox virus (MPXV) through sexual contact networks, with New York City (NYC) experiencing the first and largest outbreak in the United States. By performing a phylogeographic and epidemiological analysis of MPXV, we identify at least 200 introductions of MPXV into NYC and 84 leading to onward transmission. Through a comparative analysis with human immunodeficiency virus (HIV) in NYC, we find that both MPXV and HIV genomic cluster sizes are best fit by scale-free distributions and that people in MPXV clusters are more likely to have previously received an HIV diagnosis (odds ratio=1.58; p =0.012) and be a member of a recently growing HIV transmission cluster, indicating overlapping sexual contact networks. We then model the transmission of MPXV through sexual contact networks and show that highly connected individuals would be disproportionately infected at the start of an epidemic, thereby likely resulting in the exhaustion of the most densely connected parts of the sexual network. This dynamic explains the rapid expansion and decline of the NYC outbreak, as well as the estimated cumulative incidence of less than 2% within high-risk populations. By synthesizing the genomic epidemiology of MPXV and HIV with epidemic modeling, we demonstrate that MPXV transmission dynamics can be understood by general principles of sexually transmitted pathogens.
RESUMEN
Microcosms containing sediment from an aquifer in Cambodia with naturally elevated levels of arsenic in the associated groundwater were used to evaluate the effectiveness of microbially mediated production of iron minerals for in situ As remediation. The microcosms were first incubated without amendments for 28 days, and the release of As and other geogenic chemicals from the sediments into the aqueous phase was monitored. Nitrate or a mixture of sulfate and lactate was then added to stimulate biological Fe(II) oxidation or sulfate reduction, respectively. Without treatment, soluble As concentrations reached 3.9 ± 0.9 µM at the end of the 143-day experiment. However, in the nitrate- and sulfate-plus-lactate-amended microcosms, soluble As levels decreased to 0.01 and 0.41 ± 0.13 µM, respectively, by the end of the experiment. Analyses using a range of biogeochemical and mineralogical tools indicated that sorption onto freshly formed hydrous ferric oxide (HFO) and iron sulfide mineral phases are the likely mechanisms for As removal in the respective treatments. Incorporation of the experimental results into a one-dimensional transport-reaction model suggests that, under conditions representative of the Cambodian aquifer, the in situ precipitation of HFO would be effective in bringing groundwater into compliance with the World Health Organization (WHO) provisional guideline value for As (10 ppb or 0.13 µM), although soluble Mn release accompanying microbial Fe(II) oxidation presents a potential health concern. In contrast, production of biogenic iron sulfide minerals would not remediate the groundwater As concentration below the recommended WHO limit.
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Arsénico/metabolismo , Bacterias/metabolismo , Compuestos Férricos/metabolismo , Compuestos de Hierro/metabolismo , Contaminantes Químicos del Agua/metabolismo , Bacterias/clasificación , Bacterias/genética , Biodegradación Ambiental , Cambodia , Sedimentos Geológicos/química , Sedimentos Geológicos/microbiología , Agua Subterránea/química , Agua Subterránea/microbiología , Modelos Químicos , Datos de Secuencia Molecular , Filogenia , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , ARN Ribosómico 16S/genética , ARN Ribosómico 16S/metabolismoAsunto(s)
Brotes de Enfermedades , Infecciones por Salmonella/epidemiología , Salmonella/aislamiento & purificación , Tortugas/microbiología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Animales , Niño , Preescolar , Humanos , Lactante , Persona de Mediana Edad , Salmonella/genética , Infecciones por Salmonella/transmisión , Estados Unidos/epidemiología , Adulto JovenRESUMEN
ABSTRACT: In 2017 and 2019, five outbreaks of infections from multiple strains of Salmonella linked to the consumption of whole, fresh Maradol papayas were reported in the United States, resulting in 325 ill persons. Traceback, laboratory, and epidemiologic evidence indicated papayas as the likely vehicle for each of these outbreaks and identified the source of papayas. State and U.S. Food and Drug Administration (FDA) laboratories recovered Salmonella from papaya samples from various points of distribution, including at import entry, and conducted serotyping, pulsed-field gel electrophoresis, and phylogenetic analyses of whole genome sequencing data. Federal and state partners led traceback investigations to determine the source of papayas. Four different suppliers of papayas were linked by traceback and laboratory results to five separate outbreaks of Salmonella infections associated with papayas. In 2017, multiple states tested papaya samples collected at retail, and Maryland and Virginia investigators recovered strains of Salmonella associated with one outbreak. FDA collected 183 papaya samples in 2017, and 11 samples yielded 62 isolates of Salmonella. Eleven serotypes of Salmonella were recovered from FDA papaya samples, and nine serotypes were closely related genetically by pulsed-field gel electrophoresis and whole genome sequencing to clinical isolates of four outbreaks, including the outbreak associated with positive state sample results. Four farms in Mexico were identified, and their names were released to the general public, retailers, and foreign authorities. In 2019, FDA collected 119 papaya samples, three of which yielded Salmonella; none yielded the 2019 outbreak strain. Investigators determined that papayas of interest had been sourced from a single farm in Campeche, Mexico, through traceback. This information was used to protect public health through public guidance, recalls, and import alerts and helped FDA collaborate with Mexican regulatory partners to enhance the food safety requirements for papayas imported from Mexico.
Asunto(s)
Carica , Intoxicación Alimentaria por Salmonella , Brotes de Enfermedades , Humanos , Laboratorios , Filogenia , Salmonella , Intoxicación Alimentaria por Salmonella/epidemiología , Estados Unidos/epidemiologíaRESUMEN
In this study we determined the composition and biogeochemistry of novel, brightly colored, white and orange microbial mats at the surface of a brine seep at the outer rim of the Chefren mud volcano. These mats were interspersed with one another, but their underlying sediment biogeochemistries differed considerably. Microscopy revealed that the white mats were granules composed of elemental S filaments, similar to those produced by the sulfide-oxidizing epsilonproteobacterium "Candidatus Arcobacter sulfidicus." Fluorescence in situ hybridization indicated that microorganisms targeted by a "Ca. Arcobacter sulfidicus"-specific oligonucleotide probe constituted up to 24% of the total the cells within these mats. Several 16S rRNA gene sequences from organisms closely related to "Ca. Arcobacter sulfidicus" were identified. In contrast, the orange mat consisted mostly of bright orange flakes composed of empty Fe(III) (hydr)oxide-coated microbial sheaths, similar to those produced by the neutrophilic Fe(II)-oxidizing betaproteobacterium Leptothrix ochracea. None of the 16S rRNA gene sequences obtained from these samples were closely related to sequences of known neutrophilic aerobic Fe(II)-oxidizing bacteria. The sediments below both types of mats showed relatively high sulfate reduction rates (300 nmol x cm(-3) x day(-1)) partially fueled by the anaerobic oxidation of methane (10 to 20 nmol x cm(-3) x day(-1)). Free sulfide produced below the white mat was depleted by sulfide oxidation within the mat itself. Below the orange mat free Fe(II) reached the surface layer and was depleted in part by microbial Fe(II) oxidation. Both mats and the sediments underneath them hosted very diverse microbial communities and contained mineral precipitates, most likely due to differences in fluid flow patterns.
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Bacterias/clasificación , Bacterias/metabolismo , Biodiversidad , Sedimentos Geológicos/microbiología , Hierro/metabolismo , Azufre/metabolismo , Arcobacter/citología , Arcobacter/genética , Bacterias/genética , Bacterias/aislamiento & purificación , ADN Bacteriano/química , ADN Bacteriano/genética , ADN Ribosómico/química , ADN Ribosómico/genética , Compuestos Férricos/metabolismo , Compuestos Ferrosos/metabolismo , Genes de ARNr , Leptothrix/citología , Datos de Secuencia Molecular , Oxidación-Reducción , Filogenia , ARN Bacteriano/genética , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , Homología de Secuencia de Ácido Nucleico , Sulfuros/metabolismoRESUMEN
Impacts of subsurface biogeochemical processes over time have always been a concern for the long-term performance of zero valent iron (Fe(0))-based permeable reactive barriers (PRBs). To evaluate the biogeochemical impacts, laboratory experiments were performed using flow-through glass columns for 210 days at controlled temperature (20 °C). Two different particle sizes of Fe(0) were used in the columns, and to simulate indigenous microbial activity, extra carbon source was provided in the two columns (biotic columns) and the remaining two columns were kept abiotic using gamma radiations. Heavy metals (Zn, As) were removed efficiently in all the columns, and no exhaustion of treatment capability or clogging was observed during our experimental duration. Newly formed Fe mineral phases and precipitates were characterized using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and micro-XRF techniques in solid phase at the end of the experiment. In addition, 16S rRNA gene extraction was used for microbial community identification in biotic columns. During the incubation, microbial population shifted in favor of Desulfosporosinus species (sulfate-reducing bacteria) from initial dominance of Acidithiobacillus ferrooxidans in sediments. Dominant mineral phases detected in biotic columns were mackinawite (FeS) and sulfate green rust, while in abiotic columns, magnetite/maghemite phases were more prevalent.
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Agua Subterránea , Hierro/química , Minerales , Purificación del Agua/métodos , Carbono , Microbiología Ambiental , Compuestos Férricos , Óxido Ferrosoférrico , Compuestos Ferrosos , ARN Ribosómico 16S , Sulfatos/química , Difracción de Rayos XRESUMEN
Studies of the diversity of microorganisms in the environment have been facilitated by use of PCR and reverse transcription PCR (RT-PCR). Inhibition of the PCR by complex sample matrices and low abundance of some target microorganisms require the use of high-sensitivity amplification procedures, involving a large number of cycles or nested PCR methods. Using these methods, we frequently observed contamination of the amplification reagents, including polymerases, by genomic DNA containing nitrogenase (nifH) and rRNA genes. Contaminating genes were sequenced and found to belong to a variety of rRNA clades, but only three major nifH clades. These sequence types included a few nifH sequences reported in previous studies of the environment. Contamination could be reduced by restriction digestion and ultrafiltration of PCR reagents, but efficiency of amplification was also reduced. Our results suggest that studies relying on large numbers of PCR amplification cycles to assess environmental gene diversity should take precautions to assure that clone libraries generated from amplified PCR products are not the result of contaminated PCR reagents.
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Descontaminación/métodos , Contaminación de Equipos/prevención & control , Perfilación de la Expresión Génica/métodos , Variación Genética/genética , Nitrogenasa/genética , Reacción en Cadena de la Polimerasa/instrumentación , Reacción en Cadena de la Polimerasa/métodos , Juego de Reactivos para Diagnóstico , Artefactos , Contaminación de Medicamentos/prevención & control , Nitrogenasa/análisis , Reacción en Cadena de la Polimerasa/normas , Control de Calidad , Reproducibilidad de los Resultados , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Sensibilidad y EspecificidadRESUMEN
Batch microcosms were setup to determine the impact of different sized zero valent iron (Fe(0)) particles on microbial sulfate reduction during the in situ bio-precipitation of metals. The microcosms were constructed with aquifer sediment and groundwater from a low pH (3.1), heavy-metal contaminated aquifer. Nano (nFe(0)), micro (mFe(0)) and granular (gFe(0)) sized Fe(0) particles were added to separate microcosms. Additionally, selected microcosms were also amended with glycerol as a C-source for sulfate-reducing bacteria. In addition to metal removal, Fe(0) in microcosms also raised the pH from 3.1 to 6.5, and decreased the oxidation redox potential from initial values of 249 to -226 mV, providing more favorable conditions for microbial sulfate reduction. mFe(0) and gFe(0) in combination with glycerol were found to enhance microbial sulfate reduction. However, no sulfate reduction occurred in the controls without Fe(0) or in the microcosm amended with nFe(0). A separate dose test confirmed the inhibition for sulfate reduction in presence of nFe(0). Hydrogen produced by Fe(0) was not capable of supporting microbial sulfate reduction as a lone electron donor in this study. Microbial analysis revealed that the addition of Fe(0) and glycerol shifted the microbial community towards Desulfosporosinus sp. from a population initially dominated by low pH and metal-resisting Acidithiobacillus ferrooxidans.
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Acidithiobacillus/metabolismo , Sedimentos Geológicos/microbiología , Agua Subterránea/microbiología , Nanopartículas del Metal/química , Peptococcaceae/metabolismo , Sulfatos/metabolismo , Purificación del Agua/métodos , Acidithiobacillus/genética , Secuencia de Bases , Bélgica , Análisis por Conglomerados , Cartilla de ADN/genética , Hierro/química , Hierro/metabolismo , Datos de Secuencia Molecular , Oxidación-Reducción , Peptococcaceae/genética , Filogenia , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , Difracción de Rayos XRESUMEN
Arsenic contamination of floodplain soils is extensive and additional fresh arsenic inputs to the pedosphere from human activities are ongoing. We investigate the cumulative effects of repetitive soil redox cycles, which occur naturally during flooding and draining, on a calcareous fluvisol, the native microbial community and arsenic mobility following a simulated contamination event. We show through bioreactor experiments, spectroscopic techniques and modelling that repetitive redox cycling can decrease arsenic mobility during reducing conditions by up to 45%. Phylogenetic and functional analyses of the microbial community indicate that iron cycling is a key driver of observed changes to solution chemistry. We discuss probable mechanisms responsible for the arsenic immobilisation observed in-situ. The proposed mechanisms include, decreased heterotrophic iron reduction due to the depletion of labile particulate organic matter (POM), increases to the proportion of co-precipitated vs. aqueous or sorbed arsenic with α-FeOOH/Fe(OH)3 and potential precipitation of amorphous ferric arsenate.
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Arsénico/química , Inundaciones , Contaminantes del Suelo/química , Suelo/química , Arsénico/análisis , Reactores Biológicos , Carbonato de Calcio/análisis , Carbonato de Calcio/química , Oxidación-Reducción , Contaminantes del Suelo/análisisRESUMEN
Cold seep ecosystems can support enormous biomasses of free-living and symbiotic chemoautotrophic organisms that get their energy from the oxidation of methane or sulfide. Most of this biomass derives from animals that are associated with bacterial symbionts, which are able to metabolize the chemical resources provided by the seeping fluids. Often these systems also harbor dense accumulations of non-symbiotic megafauna, which can be relevant in exporting chemosynthetically fixed carbon from seeps to the surrounding deep sea. Here we investigated the carbon sources of lithodid crabs (Paralomis sp.) feeding on thiotrophic bacterial mats at an active mud volcano at the Costa Rica subduction zone. To evaluate the dietary carbon source of the crabs, we compared the microbial community in stomach contents with surface sediments covered by microbial mats. The stomach content analyses revealed a dominance of epsilonproteobacterial 16S rRNA gene sequences related to the free-living and epibiotic sulfur oxidiser Sulfurovum sp. We also found Sulfurovum sp. as well as members of the genera Arcobacter and Sulfurimonas in mat-covered surface sediments where Epsilonproteobacteria were highly abundant constituting 10% of total cells. Furthermore, we detected substantial amounts of bacterial fatty acids such as i-C15â¶0 and C17â¶1ω6c with stable carbon isotope compositions as low as -53 in the stomach and muscle tissue. These results indicate that the white microbial mats at Mound 12 are comprised of Epsilonproteobacteria and that microbial mat-derived carbon provides an important contribution to the crab's nutrition. In addition, our lipid analyses also suggest that the crabs feed on other (13)C-depleted organic matter sources, possibly symbiotic megafauna as well as on photosynthetic carbon sources such as sedimentary detritus.
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Carbono/metabolismo , Cadena Alimentaria , Metano/metabolismo , Animales , Anomuros/microbiología , Costa Rica , Ecosistema , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , ARN Ribosómico 16S/genética , ARN Ribosómico 16S/metabolismo , Agua de Mar/microbiologíaRESUMEN
We studied the diversity of Chloroflexus-like bacteria (CLB) in a hypersaline phototrophic microbial mat and assayed their near-infrared (NIR) light-dependent oxygen respiration rates. PCR with primers that were reported to specifically target the 16S rRNA gene from members of the phylum Chloroflexi resulted in the recovery of 49 sequences and 16 phylotypes (sequences of the same phylotype share more than 96% similarity), and 10 of the sequences (four phylotypes) appeared to be related to filamentous anoxygenic phototrophic members of the family Chloroflexaceae. Photopigment analysis revealed the presence of bacteriochlorophyll c (BChlc), BChld, and gamma-carotene, pigments known to be produced by phototrophic CLB. Oxygen microsensor measurements for intact mats revealed a NIR (710 to 770 nm) light-dependent decrease in aerobic respiration, a phenomenon that we also observed in an axenic culture of Chloroflexus aurantiacus. The metabolic ability of phototrophic CLB to switch from anoxygenic photosynthesis under NIR illumination to aerobic respiration under non-NIR illumination was further used to estimate the contribution of these organisms to mat community respiration. Steady-state oxygen profiles under dark conditions and in the presence of visible (VIS) light (400 to 700 nm), NIR light (710 to 770 nm), and VIS light plus NIR light were compared. NIR light illumination led to a substantial increase in the oxygen concentration in the mat. The observed impact on oxygen dynamics shows that CLB play a significant role in the cycling of carbon in this hypersaline microbial mat ecosystem. This study further demonstrates that the method applied, a combination of microsensor techniques and VIS and NIR illumination, allows rapid establishment of the presence and significance of CLB in environmental samples.
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Biodiversidad , Chloroflexus/genética , Consumo de Oxígeno/fisiología , Filogenia , Pigmentos Biológicos/análisis , Agua de Mar/microbiología , Proteínas Bacterianas/análisis , Bacterioclorofilas/análisis , Secuencia de Bases , Carotenoides/análisis , Chloroflexus/fisiología , Cartilla de ADN/genética , Datos de Secuencia Molecular , Fotosíntesis/fisiología , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , EspañaRESUMEN
In many environments, biological nitrogen fixation can alleviate nitrogen limitation. The high rates of N(2) fixation often observed in cyanobacterial mats suggest that N(2) fixation may be an important source of N. In this study, organisms expressing nifH were identified in a Lyngbya sp.- and two Microcoleus chthonoplastes-dominated cyanobacterial mats. The pattern of nitrogenase activity was determined for the Lyngbya sp. mat and a Microcoleus chthonoplastes mat sampled directly in Guerrero Negro, Mexico. Their maximum rates were 23 and 15 micro mol of C(2)H(4) m(-2) h(-1), respectively. The second Microcoleus mat, which was maintained in a greenhouse facility, had a maximum rate of 40 micro mol of C(2)H(4) m(-2) h(-1). The overall diel pattern of nitrogenase activity in the three mats was similar, with the highest rates of activity occurring during the dark period. Analysis of nifH transcripts by reverse transcription-PCR revealed that several different organisms were expressing nifH during the dark period. nifH phylotypes recovered from these mats were similar to sequences from the unicellular cyanobacterial genera Halothece, Myxosarcina, and Synechocystis, the filamentous cyanobacterial genera Plectonema and Phormidium, and several bacterial nifH groups. The results of this study indicate that several different organisms, some of which were not previously known to fix nitrogen, are likely to be responsible for the observed dark-period nitrogenase activity in these cyanobacterial mats.
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Cianobacterias/metabolismo , Fijación del Nitrógeno , Secuencia de Bases , Cianobacterias/clasificación , Cianobacterias/genética , Cianobacterias/aislamiento & purificación , ADN Bacteriano/genética , ADN Bacteriano/metabolismo , Expresión Génica , Genes Bacterianos , México , Oxidorreductasas/genética , Filogenia , Microbiología del AguaRESUMEN
The nitrogenase activity and phylogenetic diversity of nitrogen fixing microorganisms in several different cyanobacterial mat types from Guerrero Negro, Baja California, Mexico were investigated by acetylene reduction assay, and by amplification and sequencing of the nitrogenase nifH gene. Acetylene reduction assays performed on a Lyngbya sp. and two Microcoleus chthonoplastes dominated microbial mats showed a typical diel pattern of nitrogenase activity in these mats. The highest rates of activity were found at night, with 40 and 37 micromol C(2)H(4) m(-2) h(-1) measured in the Microcoleus mats, and 9 micromol C(2)H(4) m(-2) h(-1) in the Lyngbya mat. Nitrogenase sequences were obtained that clustered with sequences from cyanobacteria, gamma-Proteobacteria, and cluster 3 of nifH. In addition, novel and divergent sequences were also recovered. The composition of nifH sequence types recovered differed between the Lyngbya and Microcoleus mats. Interestingly, nifH sequences belonging to filamentous cyanobacteria were absent in most mat samples even though both mats were dominated by filamentous cyanobacteria. nifH sequences clustering with those of unicellular cyanobacteria were found, some of which were virtually identical to the nifH sequence from Halothece sp. MPI96P605, which had previously been isolated from the mat. In manipulation experiments, the Lyngbya and Microcoleus mats were allowed to re-colonize a cleared surface. In these developing mats, nifH sequences not previously observed in the mats were discovered. Our results showed that organisms capable of N(2) fixation were present in N(2) fixing mats, that the composition of the N(2) fixing communities differs between mats, and that filamentous cyanobacterial diazotrophs may not have a large role in the early stages of mat development.