RESUMEN
While metal immobilization had been increasingly reported with biochar soil amendment (BSA), changes in microbial activity and nitrogen (N) transformation in metal contaminated croplands following biochar addition had been insufficiently addressed. In a field experiment, a Pb/Cd contaminated Inceptisol from North China was amended to topsoil with wheat straw biochar at 0 (CK), 20 (C1) and 40â¯tâ¯ha-1 (C2). The changes within two years following BSA were tested in microbial biomass and respiration, and in abundance of N transforming microbial communities and their activities. Corresponding to the results of decreased soil extractable Cd and Pb, significant reductions in qCO2 were found in rhizosphere and bulk soil only under C2 in the first year. The potential nitrification activity was significantly increased by 20-71%, along with an increase in ammonium (by 7-21%) and nitrate (by 21%-70%) concentration, with BSA compared to CK. Meanwhile, N2O production activity was slightly increased (by up to 20%) but N2O reduction activity greatly enhanced (by up to 84%), with a higher ratio of nosZ/(nirSâ¯+â¯nirK), under C2 in rhizosphere in both wheat seasons. Whereas, such changes were not remarkable in bulk soil. Moreover, microbial communities were less respondent to biochar in the second year following the addition. Therefore, microbial growth and functioning for N transforming and cycling in metal contaminated soils could be largely improved with BSA at 40â¯tâ¯ha-1. Of course, studies are still deserved to mimic the long term changes with biochar in N cycling of the metal contaminated dry croplands.
Asunto(s)
Carbón Orgánico , Metales/metabolismo , Nitrógeno/metabolismo , Rizosfera , Microbiología del Suelo , Contaminantes del Suelo/metabolismo , Biodegradación Ambiental , China , Suelo , TriticumRESUMEN
Biochar has been widely studied for its ability to reduce plant uptake of heavy metals by lowering metal bioavailabilities through adsorption and pH-driven fixation reactions. However, the long-term effect of biochar on heavy metal bioavailabilities in alkaline soils under natural redox condition is rarely studied. Here, we report a study examining the effects of biochar on bioavailability and partitioning of cadmium (Cd) and lead (Pb) among different soil fractions over 3 years in a field study with wheat (Triticum aestivum L.). Plots were established on two similar soils having low and high levels of contamination, both of which were amended in the first year with wheat straw biochar at 0, 20, and 40 t ha-1. Precipitation patterns varied greatly over the study period, with 2014 having record drought, which was followed by 2 years having extreme flooding events. Results showed a significant increase in grain yield and reductions in Cd and Pb concentrations in wheat grain in the biochar-amended soils in 2014. In contrast, bioavailable (exchangeable) heavy metal concentrations and plant uptake of Cd and Pb were significantly higher in the subsequent very wet years in 2015 and 2016, where the effects of biochar were much more variable and had an overall lesser effect on reducing heavy metal uptake. The results suggest that fluctuations in soil pH and redox caused by periodic drought and flood cycles strongly drive metal cycling through mobilization and immobilization of metals associated with different mineral phases. Under these conditions, biochar may have reduced efficacy for reducing heavy metal uptake in wheat.
Asunto(s)
Cadmio/metabolismo , Carbón Orgánico/farmacología , Plomo/metabolismo , Lluvia , Triticum/efectos de los fármacos , Triticum/metabolismo , Biodegradación Ambiental , Disponibilidad Biológica , Cadmio/química , Carbón Orgánico/química , Plomo/química , Suelo/química , Contaminantes del Suelo/química , Contaminantes del Suelo/metabolismo , Contaminantes del Suelo/farmacocinética , Triticum/química , Triticum/crecimiento & desarrolloRESUMEN
Canals are supramolecular complexes observed in the cell wall of Candida maltosa grown in the presence of hexadecane as a sole carbon source. Such structures were not observed in glucose-grown cells. Microscopic observations of cells stained with diaminobenzidine revealed the presence of oxidative enzymes in the canals. 4Î,6Î-diamino-2-phenylindole staining revealed that a substantial part of cellular polyphosphate was present in the cell wall of cells grown on hexadecane in condition of phosphate limitation. The content and chain length of polyphosphates were higher in hexadecane-grown cells than in glucose grown ones. The treatment of cells with yeast polyphosphatase PPX1 resulted in the decrease of the canal size. These data clearly indicated that polyphosphates are constituents of canals; they might play an important role in the canal structure and functioning.
Asunto(s)
Alcanos/farmacología , Candida/efectos de los fármacos , Pared Celular/efectos de los fármacos , 3,3'-Diaminobencidina , Ácido Anhídrido Hidrolasas/química , Candida/química , Candida/metabolismo , Candida/ultraestructura , Pared Celular/química , Pared Celular/metabolismo , Pared Celular/ultraestructura , Medios de Cultivo/química , Medios de Cultivo/farmacología , Diaminas , Glucosa/metabolismo , Glucosa/farmacología , Indoles , Microscopía Electrónica de Transmisión , Polifosfatos/química , Polifosfatos/metabolismo , Coloración y Etiquetado/métodosRESUMEN
BACKGROUND: Limited information is available about the effectiveness of biochar with plant growth-promoting rhizobacteria (PGPR) and compost. A greenhouse study was conducted to evaluate the effect of biochar in combination with compost and PGPR (Pseudomonas fluorescens) for alleviating water deficit stress. Both inoculated and un-inoculated cucumber seeds were sown in soil treated with biochar, compost and biochar + compost. Three water levels - field capacity (D0), 75% field capacity (D1) and 50% field capacity (D2) - were maintained. RESULTS: The results showed that water deficit stress significantly suppressed the growth of cucumber; however, synergistic use of biochar, compost and PGPR mitigated the negative impact of stress. At D2, the synergistic use of biochar, compost and PGPR caused significant increases in shoot length, shoot biomass, root length and root biomass, which were respectively 88, 77, 89 and 74% more than in the un-inoculated control. Significant improvements in chlorophyll and relative water contents as well as reduction in leaf electrolyte leakage demonstrated the effectiveness of this approach. Moreover, the highest population of P. fluorescens was observed where biochar and compost were applied together. CONCLUSION: These results suggest that application of biochar with PGPR and/or compost could be an effective strategy for enhancing plant growth under stress. © 2017 Society of Chemical Industry.
Asunto(s)
Producción de Cultivos/métodos , Cucumis sativus/crecimiento & desarrollo , Pseudomonas fluorescens/fisiología , Suelo/química , Biomasa , Carbón Orgánico/análisis , Carbón Orgánico/metabolismo , Producción de Cultivos/instrumentación , Cucumis sativus/metabolismo , Cucumis sativus/microbiología , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Pseudomonas fluorescens/crecimiento & desarrollo , Microbiología del Suelo , Agua/análisis , Agua/metabolismoRESUMEN
This research was conducted to isolate polycyclic aromatic hydrocarbon-degrading (PAH-degrading) endophytic bacteria and investigate their potential in protecting plants against PAH contamination. Pyrene-degrading endophytic bacteria were isolated from plants grown in PAH-contaminated soil. Among these endophytic bacteria, strain PW7 (Serratia sp.) isolated from Plantago asiatica was selected to investigate the suppression of pyrene accumulation in Triticum aestivum L. In the in vitro tests, strain PW7 degraded 51.2% of the pyrene in the media within 14 days. The optimal biodegradation conditions were pH 7.0, 30 °C, and MS medium supplemented with additional glucose, maltose, sucrose, and peptones. In the in vivo tests, strain PW7 successfully colonized the roots and shoots of inoculated (E+) wheat plants, and its colonization decreased pyrene accumulation and pyrene transportation from roots to shoots. Remarkably, the concentration of pyrene in shoots decreased much more than that in roots, suggesting that strain PW7 has the potential for protecting wheat against pyrene contamination and mitigating the threat of pyrene to human health via food consumption.
Asunto(s)
Endófitos/metabolismo , Pirenos/análisis , Serratia/metabolismo , Contaminantes del Suelo/análisis , Triticum/metabolismo , Biodegradación Ambiental , Endófitos/crecimiento & desarrollo , Humanos , Modelos Teóricos , Raíces de Plantas/metabolismo , Raíces de Plantas/microbiología , Pirenos/metabolismo , Serratia/crecimiento & desarrollo , Contaminantes del Suelo/metabolismo , Simbiosis , Triticum/microbiologíaRESUMEN
Microbial diversity of agricultural soils has been well documented, but information on leafy green producing soils is limited. In this study, we investigated microbial diversity and community structures in 32 (16 organic, 16 conventionally managed soils) from California (CA) and Arizona (AZ) using pyrosequencing, and identified factors affecting bacterial composition. Results of detrended correspondence analysis (DCA) and dissimilarity analysis showed that bacterial community structures of conventionally managed soils were similar to that of organically managed soils; while the bacterial community structures in soils from Salinas, California were different (P<0.05) from those in soils from Yuma, Arizona and Imperial Valley, California. Canonical correspondence analysis (CCA) and artificial neural network (ANN) analysis of bacterial community structures and soil variables showed that electrical conductivity (EC), clay content, water-holding capacity (WHC), pH, total nitrogen (TN), and organic carbon (OC) significantly (P<0.05) correlated with microbial communities. CCA based variation partitioning analysis (VPA) showed that soil physical properties (clay, EC, and WHC), soil chemical variables (pH, TN, and OC) and sampling location explained 16.3%, 12.5%, and 50.9%, respectively, of total variations in bacterial community structure, leaving 13% of the total variation unexplained. Our current study showed that bacterial community composition and diversity in major fresh produce growing soils from California and Arizona is a function of soil physiochemical characteristics and geographic distances of sampling sites.
Asunto(s)
Bacterias , Microbiota , Microbiología del Suelo , Suelo/química , Arizona , California , Granjas , Redes Neurales de la ComputaciónRESUMEN
Phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase activity and production of siderophores and indole acetic acid (IAA) are well-known traits of plant growth-promoting rhizobacteria (PGPR). Here we investigated the expression of these traits as affected by salinity for three PGPR strains (Pseudomonas fluorescens, Bacillus megaterium and Variovorax paradoxus) at two salinity levels [2 and 5 % NaCl (w/v)]. Among the three strains, growth of B. megaterium was the least affected by high salinity. However, P. fluorescens was the best strain for maintaining ACC-deaminase activity, siderophore and IAA production under stressed conditions. V. paradoxus was the least tolerant to salts and had minimal growth and low PGPR trait expression under salt stress. Results of experiment examining the impact of bacterial inoculation on cucumber growth at three salinity levels [1 (normal), 7 and 10 dS m(-1)] revealed that P. fluorescens also had good rhizosphere competence and was the most effective for alleviating the negative impacts of salinity on cucumber growth. The results suggest that in addition to screening the PGPR regarding their effect on growth under salinity, PGPR trait expression is also an important aspect that may be useful for selecting the most promising PGPR bacterial strains for improving plant tolerance to salinity stress.
Asunto(s)
Fenómenos Fisiológicos Bacterianos , Cucumis sativus/microbiología , Cucumis sativus/fisiología , Tolerancia a la Sal/fisiología , Microbiología del Suelo , Bacillus megaterium/fisiología , Liasas de Carbono-Carbono , Cucumis sativus/efectos de los fármacos , Cucumis sativus/crecimiento & desarrollo , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos/genética , Ácidos Indolacéticos/metabolismo , Pseudomonas fluorescens/fisiología , Salinidad , Sideróforos/genética , Cloruro de Sodio/farmacologíaRESUMEN
Electron-microscopic examinations have demonstrated local modifications in the cell wall of the yeast Candida maltosa grown on hexadecane. In our earlier studies, these modified sites, observed in other yeasts grown on oil hydrocarbons, were conventionally called 'canals'. The biochemical and cytochemical studies of C. maltosa have revealed a correlation between the formation of 'canals' and decrease in the amount of cell wall polysaccharides, glucan and mannan. The ultrathin sections and surface replicas have shown that the 'canals' are destroyed by pronase, thus indicating that a significant proportion of their content is represented by proteins. This finding was compatible with our earlier data on the localization of oxidative enzymes in 'canals' and possible participation of the 'canals' in the primary oxidation of hydrocarbons. A completely unexpected and intriguing phenomenon has been the appearance of 'canals' in the yeast C. maltosa under starvation conditions. Unlike the yeasts grown on hexadecane, mannan almost disappears in starving cells, while the quantity of glucan first decreases and then is restored to its initial level. The role of 'canals' in starving cells is as yet unclear; it is assumed that they acquire exoenzymes involved in the utilization of products of cell lysis in the starving population. In the future, 'canals' of starving cells will be studied in connection with their possible participation in apoptosis.
Asunto(s)
Alcanos/metabolismo , Candida/crecimiento & desarrollo , Pared Celular/ultraestructura , Candida/metabolismo , Candida/ultraestructura , Pared Celular/química , Medios de Cultivo , Hidrolasas/metabolismo , Mananos/metabolismo , Microscopía ElectrónicaRESUMEN
Biological treatment of azo dyes commonly requires a combined anaerobic-aerobic process in which initial decolorization is achieved by reductive cleavage of azo bonds on the parent molecule. The present study was conducted to examine the relative importance of co-substrates for driving reductive decolorization of azo dyes by Shewanella sp. strain IFN4 using whole cells and enzyme assays. Results showed that the dye decolorization by strain IFN4 was faster in medium containing 1gL(-1) yeast extract (YE) as compared to nine other co-substrates. Moreover, only YE stimulated azoreductase activity (increased from 1.32 to 4.19U/mg protein). Increasing the level of YE up to 8gL(-)(1) resulted into 81% decolorization of the dye in 1h along with an increase in azoreductase activity up to 6.16U/mg protein. Among the components of YE, only riboflavin stimulated the decolorization process as well as enzyme activity. Moreover, strain IFN4 demonstrated flavin reductase activity, and a significant correlation (r(2)=0.98) between flavin reduction and dye reduction by this strain emphasized the involvement of flavin compounds in the decolorization process. The results of this study show that YE serves both as a source of reducing equivalents and an electron shuttle for catalyzing dye reduction.
Asunto(s)
Compuestos Azo/metabolismo , Colorantes/metabolismo , Mezclas Complejas/metabolismo , Shewanella/metabolismo , Levaduras/química , NADH NADPH Oxidorreductasas/metabolismo , Nitrorreductasas , Oxidación-ReducciónRESUMEN
Azo dyes and their intermediate degradation products are common contaminants of soil and groundwater in developing countries where textile and leather dye products are produced. The toxicity of azo dyes is primarily associated with their molecular structure, substitution groups and reactivity. To avoid contamination of natural resources and to minimize risk to human health, this wastewater requires treatment in an environmentally safe manner. This manuscript critically reviews biological treatment systems and the role of bacterial reductive and oxidative enzymes/processes in the bioremediation of dye-polluted wastewaters. Many studies have shown that a variety of culturable bacteria have efficient enzymatic systems that can carry out complete mineralization of dye chemicals and their metabolites (aromatic compounds) over a wide range of environmental conditions. Complete mineralization of azo dyes generally involves a two-step process requiring initial anaerobic treatment for decolorization, followed by an oxidative process that results in degradation of the toxic intermediates that are formed during the first step. Molecular studies have revealed that the first reductive process can be carried out by two classes of enzymes involving flavin-dependent and flavin-free azoreductases under anaerobic or low oxygen conditions. The second step that is carried out by oxidative enzymes that primarily involves broad specificity peroxidases, laccases and tyrosinases. This review focuses, in particular, on the characterization of these enzymes with respect to their enzyme kinetics and the environmental conditions that are necessary for bioreactor systems to treat azo dyes contained in wastewater.
Asunto(s)
Compuestos Azo/metabolismo , Proteínas Bacterianas/metabolismo , Colorantes/metabolismo , Oxidorreductasas/metabolismo , Contaminantes Químicos del Agua/metabolismo , Animales , Compuestos Azo/toxicidad , Bacterias/metabolismo , Biodegradación Ambiental , Colorantes/toxicidad , Humanos , Contaminantes Químicos del Agua/toxicidadRESUMEN
Cupriavidus sp. are generally heavy metal tolerant bacteria with the ability to degrade a variety of aromatic hydrocarbon compounds, although the degradation pathways and substrate versatilities remain largely unknown. Here we studied the bacterium Cupriavidus gilardii strain CR3, which was isolated from a natural asphalt deposit, and which was shown to utilize naphthenic acids as a sole carbon source. Genome sequencing of C. gilardii CR3 was carried out to elucidate possible mechanisms for the naphthenic acid biodegradation. The genome of C. gilardii CR3 was composed of two circular chromosomes chr1 and chr2 of respectively 3,539,530 bp and 2,039,213 bp in size. The genome for strain CR3 encoded 4,502 putative protein-coding genes, 59 tRNA genes, and many other non-coding genes. Many genes were associated with xenobiotic biodegradation and metal resistance functions. Pathway prediction for degradation of cyclohexanecarboxylic acid, a representative naphthenic acid, suggested that naphthenic acid undergoes initial ring-cleavage, after which the ring fission products can be degraded via several plausible degradation pathways including a mechanism similar to that used for fatty acid oxidation. The final metabolic products of these pathways are unstable or volatile compounds that were not toxic to CR3. Strain CR3 was also shown to have tolerance to at least 10 heavy metals, which was mainly achieved by self-detoxification through ion efflux, metal-complexation and metal-reduction, and a powerful DNA self-repair mechanism. Our genomic analysis suggests that CR3 is well adapted to survive the harsh environment in natural asphalts containing naphthenic acids and high concentrations of heavy metals.
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Ácidos Carboxílicos/metabolismo , Cupriavidus/genética , Genoma Bacteriano/genética , Metales Pesados/farmacología , Biodegradación Ambiental , Cromosomas Bacterianos/genética , Cupriavidus/efectos de los fármacos , Cupriavidus/metabolismo , Genes Bacterianos , Pruebas de Sensibilidad MicrobianaRESUMEN
In this study, effect of various metal ions and salts on biodecolorization of Reactive black-5, azoreductase activity, and growth of Shewanella sp. strain IFN4 was evaluated. Among the tested metals, Cr²âº, Pb(²âº, Ni²âº, Fe²âº, and Mn²âº did not inhibit the biodecolorization of reactive black-5, azoreductase activity and bacterial growth. Three metals (Cu²âº, Zn²âº, and Co²âº) delayed the decolorization process without completely inhibiting the reaction and also suppressed the bacterial growth. However, no dye decolorization was observed in the presence of Cd²âº (10 mg L⻹). Furthermore, bacterium decolorized the dye at high concentration (15 mg L⻹) of mixed metal ions. Strain IFN4 was also able to decolorize the dye at 50 g NaCl L⻹ and 60 g Na2SO4 L⻹. NaCl was found to be more inhibitory to bacterial growth than Na2SO4and the reverse was observed for azoreductase activity. These findings suggest that strain IFN4 could be used in designing a bioreactor for the treatment of textile effluent.
Asunto(s)
Metales/farmacología , Naftalenosulfonatos/química , Shewanella/metabolismo , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/metabolismo , Biodegradación Ambiental , Relación Dosis-Respuesta a Droga , Metales/administración & dosificación , NADH NADPH Oxidorreductasas/metabolismo , Nitrorreductasas , Shewanella/efectos de los fármacos , Shewanella/enzimología , Factores de TiempoRESUMEN
Biodegradation of polycyclic aromatic hydrocarbons (PAHs) is normally limited by their low solubility and poor bioavailability. Prior research suggests that biosurfactants are synthesized as intermediates during the production of mucilage at the root tip. To date the effects of mucilage on PAH degradation and microbial community response have not been directly examined. To address this question, our research compared 3 cowpea breeding lines (Vigna unguiculata) that differed in mucilage production for their effects on phenanthrene (PHE) degradation in soil. The High Performance Liquid Chromatography results indicated that the highest PHE degradation rate was achieved in soils planted with mucilage producing cowpea line C1, inoculated with Bradyrhizobium, leading to 91.6% PHE disappearance in 5 weeks. In root printing tests, strings treated with mucilage and bacteria produced larger clearing zones than those produced on mucilage treated strings with no bacteria or bacteria inoculated strings. Experiments with 14C-PHE and purified mucilage in soil slurry confirmed that the root mucilage significantly enhanced PHE mineralization (82.7%), which is 12% more than the control treatment without mucilage. The profiles of the PHE degraders generated by Denaturing gradient gel electrophoresis suggested that cowpea C1, producing a high amount of root mucilage, selectively enriched the PHE degrading bacteria population in rhizosphere. These findings indicate that root mucilage may play a significant role in enhancing PHE degradation and suggests that differences in mucilage production may be an important criterion for selection of the best plant species for use in phytoremediation of PAH contaminated soils.
Asunto(s)
Bacterias/efectos de los fármacos , Fabaceae/química , Fenantrenos/química , Exudados de Plantas/farmacología , Raíces de Plantas/química , Bacterias/genética , Biodegradación Ambiental , Fenantrenos/metabolismo , Filogenia , Exudados de Plantas/química , Microbiología del Suelo , Contaminantes del Suelo/química , Contaminantes del Suelo/metabolismoRESUMEN
The aim of this study was to examine the stability of structurally different azo dyes in soil and their impact on the microbial community composition by analyzing phospholipid fatty acid (PLFA) profiles. Sterile and non-sterile soils were amended with three azo dyes, including: Direct Red 81, Reactive Black 5 and Acid Yellow 19 at 160mgkg(-1) soil. The results showed that the azo dyes were quite stable and that large amounts of these dyes ranging from 17.3% to 87.5% were recoverable from the sterile and non-sterile soils after 14 days. The maximum amount of dye was recovered in the case of Direct Red 81. PLFA analysis showed that the azo dyes had a significant effect on microbial community structure. PLFA concentrations representing Gram-negative bacteria in dye-amended soil were substantially less as compared to the PLFA concentration of Gram-positive bacteria. Acid Yellow 19 dye had almost similar effects on the PLFA concentrations representing bacteria and fungi. In contrast, Reactive Black 5 had a greater negative effect on fungal PLFA than that on bacterial PLFA, while the opposite was observed in the case of Direct Red 81. To our knowledge, this is the first study reporting the stability of textile azo dyes in soil and their effects on soil microbial community composition.
Asunto(s)
Compuestos Azo/química , Ácidos Grasos/química , Fosfolípidos/química , Microbiología del Suelo , Contaminantes del Suelo/química , Textiles , Bacterias/química , Bacterias/efectos de los fármacos , Hongos/química , Hongos/efectos de los fármacos , Suelo/químicaRESUMEN
Many legumes have been selected as model plants to degrade organic contaminants with their special associated rhizosphere microbes in soil. However, the function of root nodules during microbe-assisted phytoremediation is not clear. A pot study was conducted to examine phenanthrene (PHE) utilizing bacteria associated with root nodules and the effects of cowpea root nodules on phytoremediation in two different types of soils (freshly contaminated soil and aged contaminated soil). Cowpea nodules in freshly-contaminated soil showed less damage in comparison to the aged-contaminated soil, both morphologically and ultra-structurally by scanning electron microscopy. The study of polycyclic aromatic hydrocarbon (PAH) attenuation conducted by high performance liquid chromatography revealed that more PAH was eliminated from liquid culture around nodulated roots than nodule-free roots. PAH sublimation and denaturation gradient gel electrophoresis were applied to analyze the capability and diversity of PAH degrading bacteria from the following four parts of rhizo-microzone: bulk soil, root surface, nodule surface and nodule inside. The results indicated that the surface and inside of cowpea root nodules were colonized with bacterial consortia that utilized PHE. Our results demonstrated that root nodules not only fixed nitrogen, but also enriched PAH-utilizing microorganisms both inside and outside of the nodules. Legume nodules may have biotechnological values for PAH degradation.
Asunto(s)
Bacterias/crecimiento & desarrollo , Fabaceae/crecimiento & desarrollo , Fabaceae/microbiología , Consorcios Microbianos , Fenantrenos/metabolismo , Nódulos de las Raíces de las Plantas/microbiología , Biodegradación Ambiental , Medios de Cultivo/química , Fabaceae/ultraestructura , Microscopía Electrónica de Rastreo , Microbiología del Suelo , Contaminantes del Suelo/metabolismoRESUMEN
Shiga toxin-producing E. coli O157:H7 and non-O157 have been implicated in many foodborne illnesses caused by the consumption of contaminated fresh produce. However, data on their persistence in soils are limited due to the complexity in datasets generated from different environmental variables and bacterial taxa. There is a continuing need to distinguish the various environmental variables and different bacterial groups to understand the relationships among these factors and the pathogen survival. Using an approach called Topological Data Analysis (TDA); we reconstructed the relationship structure of E. coli O157 and non-O157 survival in 32 soils (16 organic and 16 conventionally managed soils) from California (CA) and Arizona (AZ) with a multi-resolution output. In our study, we took a community approach based on total soil microbiome to study community level survival and examining the network of the community as a whole and the relationship between its topology and biological processes. TDA produces a geometric representation of complex data sets. Network analysis showed that Shiga toxin negative strain E. coli O157:H7 4554 survived significantly longer in comparison to E. coli O157:H7 EDL 933, while the survival time of E. coli O157:NM was comparable to that of E. coli O157:H7 EDL 933 in all of the tested soils. Two non-O157 strains, E. coli O26:H11 and E. coli O103:H2 survived much longer than E. coli O91:H21 and the three strains of E. coli O157. We show that there are complex interactions between E. coli strain survival, microbial community structures, and soil parameters.
Asunto(s)
Escherichia coli O157 , Escherichia coli , Viabilidad Microbiana , Microbiología del Suelo , Arizona , Carga Bacteriana , California , ADN Bacteriano , Escherichia coli/clasificación , Escherichia coli/genética , Escherichia coli O157/clasificación , Escherichia coli O157/genética , Microbiología de Alimentos , Análisis de Secuencia de ADNRESUMEN
Shiga toxin producing Escherichia coli O157 and non-O157 serogroups are known to cause serious diseases in human. However, research on the persistence of E. coli non-O157 serogroups in preharvest environment is limited. In the current study, we compared the survival behavior of E. coli O157 to that of non-O157 E. coli strains in agricultural soils collected from three major fresh produce growing areas of California (CA) and Arizona (AZ). Results showed that the nonpathogenic E. coli O157:H7 4554 survived longer than the pathogenic E. coli O157:H7 EDL933 in Imperial Valley CA and Yuma AZ, but not in soils from the Salinas area. However, E. coli O157:NM was found to persist significantly longer than E. coli O157:H7 EDL933 in all soil tested from the three regions. Furthermore, two non-O157 (E. coli O26:H21 and E. coli O103:H2) survived significantly longer than E. coli O157:H7 EDL933 in all soils tested. Pearson correlation analysis showed that survival of the E. coli strains was affected by different environmental factors. Our data suggest that survival of E. coli O157 and non-O157 may be strain and soil specific, and therefore, care must be taken in data interpretation with respect to survival of this pathogen in different soils.
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Escherichia coli/crecimiento & desarrollo , Microbiología del Suelo , Agricultura , Arizona , Escherichia coli/clasificación , Escherichia coli O157/crecimiento & desarrollo , SueloRESUMEN
Bacterial communities associated with tree canopies have been shown to be specific to their plant hosts, suggesting that plant species-specific traits may drive the selection of microbial species that comprise their microbiomes. To further examine the degree to which the plant taxa drive the assemblage of bacterial communities in specific plant microenvironments, we evaluated bacterial community structures associated with the phyllosphere, dermosphere, and rhizosphere of seven tree species representing three orders, four families and four genera of plants from a pristine Dense Ombrophilous Atlantic forest in Brazil, using a combination of PCR-DGGE of 16S rRNA genes and clone library sequencing. Results indicated that each plant species selected for distinct bacterial communities in the phyllosphere, dermosphere, and rhizosphere, and that the bacterial community structures are significantly related to the plant taxa, at the species, family, and order levels. Further characterization of the bacterial communities of the phyllosphere and dermosphere of the tree species showed that they were inhabited predominantly by species of Gammaproteobacteria, mostly related to Pseudomonas. In contrast, the rhizosphere bacterial communities showed greater species richness and evenness, and higher frequencies of Alphaproteobacteria and Acidobacteria Gp1. With individual tree species each selecting for their specific microbiomes, these findings greatly increase our estimates of the bacterial species richness in tropical forests and provoke questions concerning the ecological functions of the microbial communities that exist on different plant parts.
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Bacterias/clasificación , Filogenia , Rizosfera , Microbiología del Suelo , Árboles/microbiología , Bacterias/genética , Brasil , ADN Bacteriano/genética , Bosques , Datos de Secuencia Molecular , Corteza de la Planta/microbiología , Hojas de la Planta/microbiología , Raíces de Plantas/genética , ARN Ribosómico 16S/genética , Especificidad de la EspecieRESUMEN
Shiga toxin-producing Escherichia coli O157:H7 has been implicated in many foodborne illnesses. In this study, survival of E. coli O157:H7 in 32 soils from California (CA) and Arizona (AZ) was investigated. Our goal was to correlate the survival time of E. coli O157:H7 in soils with 16S rRNA pyrosequencing based bacterial community composition. Kohonen self-organizing map of survival and associated soil chemical, physical and biological variables using artificial neural network analysis showed that survival of E. coli O157:H7 in soils was negatively correlated with salinity (EC), but positively correlated with total nitrogen (TN) and water soluble organic carbon (WSOC). Bacterial diversity as determined by the Shannon diversity index had no significant (P = 0.635) effect on ttd, but individual bacterial phyla had different effects. The survival of E. coli O157:H7 was positively correlated with the abundances of Actinobacteria (P < 0.001) and Acidobacteria (P < 0.05), and negatively correlated with those of Proteobacteria and Bacteroidetes (P < 0.05). Our data showed that specific groups of bacteria correlate with the persistence of E. coli O157:H7 in soils thus opening new ways to study the influence of certain bacterial phyla on persistence of this pathogen and other related pathogens in complex environments.
Asunto(s)
Fenómenos Fisiológicos Bacterianos , Escherichia coli O157/fisiología , Interacciones Microbianas , Microbiología del Suelo , Arizona , Bacterias/clasificación , Bacterias/genética , Biodiversidad , California , ADN Bacteriano/análisis , Escherichia coli O157/genética , Viabilidad Microbiana , Redes Neurales de la Computación , Salinidad , Análisis de Secuencia de ADN , Suelo/químicaRESUMEN
Phytate-mineralizing rhizobacteria (PMR) perform an essential function for the mineralization of organic phosphorus but little is known about their ecology in soils and rhizosphere. In this study, PCR-based methods were developed for detection and quantification of the Bacillus ß-propeller phytase (BPP) gene. Experiments were conducted to monitor the presence and persistence of a phytate-mineralizing strain, Bacillus sp. MQH19, after inoculation of soil microcosms and within the rhizosphere. The occurrence of the BPP gene in natural pasture soils from Chilean Andisols was also examined. The results showed that the Bacillus BPP gene was readily detected in sterile and nonsterile microcosms, and that the quantitative PCR (qPCR) methods could be used to monitor changes in the abundance of the BPP gene over time. Our results also show that the addition of phytate to nonsterile soils induced the expression of the BPP gene in the rhizosphere of ryegrass and the BPP gene was detected in all pasture soils sampled. This study shows that phytate addition soils induced changes in the abundance and expression of Bacillus BPP to genes in the rhizosphere and demonstrates that Bacillus BPP gene is cosmopolitan in pasture soils from Chilean Andisols.